molecules Article Construction of Zn(II) Linear Trinuclear Secondary Building Units from A Coordination Polymer Based on α-Acetamidocinnamic Acid and 4-Phenylpyridine Daniel Ejarque 1 , Teresa Calvet 2 , Mercè Font-Bardia 3 and Josefina Pons 1, * 1 Departament de Química, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain; daniel.ejarque@uab.cat 2 Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain; mtcalvet@ub.edu 3 Unitat de Difracció de Raig-X, Centres Científics i Tecnològics de la Universitat de Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís, 1-3, 08028 Barcelona, Spain; mercef@ccit.ub.edu * Correspondence: josefina.pons@uab.es; Tel.: +34-935-812-895 Academic Editor: Constantina Papatriantafyllopoulou   Received: 15 July 2020; Accepted: 8 August 2020; Published: 9 August 2020 Abstract: The synthesis and characterization of one coordination polymer and two trinuclear complexes are presented. The coordination polymer [Zn2 (µ-O,O’-ACA)2 (ACA)2 (4-Phpy)2 ]n (1) has been obtained by the reaction between Zn(OAc)2 ·2H2 O, α-acetamidocinnamic acid (HACA), and 4-phenylpyridine (4-Phpy) using EtOH as solvent. Its recrystallization in CH3 CN or EtOH yields two trinuclear complexes, both having pinwheel arrays with formulas [Zn3 (µ-ACA)6 (4-Phpy)2 ]·4CH3 CN (2·4CH3 CN) and [Zn3 (µ-ACA)6 (EtOH)2 ]·4EtOH (3·4EtOH), respectively. These trinuclear species, unavoidably lose their solvent co-crystallized molecules at RT yielding the complexes [Zn3 (µ-ACA)6 (4-Phpy)2 ] (2) and [Zn3 (µ-ACA)6 (EtOH)2 ] (3). In addition, compound 2 has also been obtained reacting Zn(OAc)2 ·2H2 O, HACA, and 4-Phpy in a 1:2:2 ratio using CH3 CN as solvent. Compounds 1–3 have been characterized by analytical and spectroscopic techniques. Furthermore, single crystals suitable for X-ray diffraction method for compounds 1, 2·4CH3 CN, and 3·4EtOH were obtained and their supramolecular interactions have been studied and discussed, showing 2D supramolecular planes for the trinuclear complexes and a 3D supramolecular network for the coordination polymer. Finally, the supramolecular interactions of 2·4CH3 CN and 3·4EtOH have been compared using Hirshfeld surface analysis and electrostatic potential calculations. Keywords: Zn(II); α-acetamidocinnamic acid; coordination polymer; trinuclear complexes; secondary building unit; X-ray crystal structures; hirshfeld surface analysis; electrostatic surface potential 1. Introduction The synthesis of coordination polymers (CPs) and discrete polynuclear coordination complexes has become a promising research area during the last decades. The polynuclear nature of these entities, being used as secondary building units (SBUs), serve as rigid, directional, and stable building blocks. Besides, their combination with organic polytopic linkers by coordination bonds build up metal-organic frameworks (MOFs) with a broad variety of applications in catalysis [1], separation [2], gas storage [3], magnetism [4], sensing [5], and so on [6–8]. Moreover, their simple synthetic methodology and ability to easily join metal atoms compared with primary (mononuclear metal center) or tertiary (metal-organic polyhedron) building units have established their study as one of the main topics in MOFs research [9–11]. Aside from coordination bonds, supramolecular interactions (H-bonds, C-H···π, π···π interactions) are also a determining factor which influence in the final structural array Molecules 2020, 25, 3615; doi:10.3390/molecules25163615 www.mdpi.com/journal/molecules Molecules 2020, 25, 3615 2 of 23 of the crystalline materials through its cooperative effect [12,13]. These weak interactions are also important in the final properties of the designed materials owing to their possibility to interact with host molecules displaying interesting applications [14,15]. Among all the SBUs, those containing carboxylate ligands are of special interest for their capability to display a great variety of coordination modes, forming di-, tri-, or tetranuclear metal carboxylates [16,17]. In addition, the presence of different functional groups in these units promote the formation of patterns of supramolecular interactions known as supramolecular synthons, which also contribute to the stabilization of the crystal packing through intermolecular interactions [12]. It is noteworthy to mention that all these structural features are influenced by many factors which dictate the final structural scaffold, such as the ionic counterions, the metal/linker ratio, the temperature, or the solvent polarity [17]. Particularly, carboxylate trinuclear compounds based on pinwheel motifs with formula [M3 (CO2 )6 (L)n ] (n = 2 or 4), where the coordination number of the lateral positions could be four or five depending on the metal center, have been used as SBUs for the synthesis of MOFs showing potential catalytic [18], magnetic [19], and fluorescent [20] properties. Furthermore, the fact that a high number of these types of arrays contain labile solvent molecules on their lateral positions, makes them appropriate for the exchange of either their lateral positions or their carboxylate moieties by polytopic linkers, conserving the pinwheel array and forming 2D or 3D materials [16,21,22]. Several complexes presenting this type of structure have been reported using a large variety of metal centers [19,21–28], being the zinc containing linear trinuclear complexes one of the most employed [20,29–34]. Zinc carboxylate complexes have been extensively used due to the great variety of coordination numbers of their carboxylate ligands (from two to eight, with four, five and six being most common) and arrangements [35,36]. Moreover, presenting a d10 configuration, Zn(II) atoms contribute to eliminate the ligand field effect and favor the generation of diverse geometries as well as the reorganization of the ligands into highly ordered arrays, owing to its zero crystal field stabilization energy. All these characteristics together with their luminescent [37,38] and biological applications [39,40], make their use interesting as metal centers. Recently, our group has been studying the reactivity of cinnamic acid derivative ligands towards Cu(II) [41], Zn(II), and Cd(II) [42] metal nodes. Specifically, the α-acetamidocinnamic acid (HACA), which incorporates an additional acetamide group in the cinnamic acid structure, has been examined in combination with the d10 metal ions Zn(II) and Cd(II) yielding isostructural monomeric complexes ([M(ACA)2 (H2 O)2 ], M = Zn(II) or Cd(II)), whose reactivity in presence of the 4-phenylpyridine ligand show a different behavior between Zn(II) and Cd(II), yielding a monomeric [Zn(4-Phpy)2 (ACA)2 (H2 O)2 ]·3H2 O and a dimeric [Cd(4-Phpy)2 (µ-ACA)(ACA)]2 ·2EtOH complexes. To the best of our knowledge, the use of ACA as a ligand for the synthesis of coordination complexes has not been previously studied before this recent publication [42]. Despite that, its use for the asymmetric hydrogenation of its double bond has been tested in a few publications [43–47] as well as their potential use as a precursor in the formation of L-phenylalanine amino acid [48,49]. As a continuation of our previous study, in this contribution we have assayed the reaction between Zn(OAc)2 ·2H2 O, HACA, and 4-Phpy using EtOH as solvent, yielding the CP [Zn2 (µ-O,O’-ACA)2 (ACA)2 (4-Phpy)2 ]n (1), which by recrystallization in CH3 CN or EtOH forms the trinuclear complexes with pinwheel arrays [Zn3 (µ-ACA)6 (4-Phpy)2 ]·4CH3 CN (2·4CH3 CN) and [Zn3 (µ-ACA)6 (EtOH)2 ]·4EtOH (3·4EtOH), respectively. These trinuclear species unavoidably lose their solvent co-crystallized molecules at room temperature (RT) yielding the complexes [Zn3 (µ-ACA)6 (4-Phpy)2 ] (2) and [Zn3 (µ-ACA)6 (EtOH)2 ] (3). Moreover, compound 2 was also obtained by an alternative method through the reaction between Zn(OAc)2 ·2H2 O, HACA, and 4-Phpy using CH3 CN as solvent at RT (Scheme 1). Molecules 2020, 25, 3615 3 of 23 Molecules 2020, 25, x FOR PEER REVIEW 3 of 24 Outlineofofthe Scheme1.1.Outline Scheme thesynthetic synthetic schemes schemes forfor compounds compounds 1–3.1–3. 2. Results and Discussion 2. Results and Discussion 2.1. Synthesis and Characterization 2.1. Synthesis and Characterization Compound 1 was prepared via combination of Zn(OAc)2 ·2H2 O, HACA, and 4-Phpy in a 1:2:2 molar Compound 1 was prepared via combination of Zn(OAc)2·2H2O, HACA, and 4-Phpy in a 1:2:2 ratio using EtOH as solvent at room temperature (RT). When compound 1 was recrystallized in CH3 CN molar ratio using EtOH as solvent at room temperature (RT). When compound 1 was recrystallized or EtOH, the trinuclear species 2·4CH3 CN or 3·4EtOH were obtained. The corresponding co-crystallized in CH3CN or EtOH, the trinuclear species 2·4CH3CN or 3·4EtOH were obtained. The corresponding solvent molecules co-crystallized weremolecules solvent unavoidably werelost during thelost unavoidably work-up duringofthe thework-up powdersofatthe RT,powders resulting at in RT,2 and Furthermore, 3.resulting compound 2 was also obtained by the reaction in 2 and 3. Furthermore, compound 2 was also obtained by the reaction between Zn(OAc) 2 ·2H 2 O, betweenHACA, and 4-Phpy Zn(OAc) in a 1:2:2 molar ratio using CH3 CN molar 2·2H2O, HACA, and 4-Phpy in a 1:2:2 as solvent ratioatusing RT (seeCHExperimental Section, Method 3CN as solvent at RT (see B). By contrast,Section, Experimental in our Method previousB).paper [42], theincomplexes By contrast, our previous[Zn(4-Phpy) paper [42], 2 (ACA) 2 (H2 O)2 ]·3H the complexes 2 O and [Zn(4- [Cd(4-Phpy) (µ-ACA)(ACA)] Phpy)2(ACA)22(H2O)2]·3H2O and 2 ·2EtOH [Cd(4-Phpy)2(µ-ACA)(ACA)]2·2EtOH were obtained from2 the2 O)2 ] were obtained from the reaction between [M(ACA) (H (M = Zn(II) reaction or Cd(II)) between [M(ACA)and 24-Phpy (H2O)2] (M ligand in aor1:4 = Zn(II) ratio and Cd(II)) for the Zn(II) 4-Phpy complex, ligand in a 1:4and ratioafor 1:2the ratio for the Zn(II) Cd(II) complex,complex, and a 1:2using EtOH ratio asCd(II) for the solvent at RT. using EtOH as solvent at RT. complex, Compounds 1–3 Compounds 1–3 were were characterized characterized by by elemental analysis, FTIR-ATR, 11H, 13 elemental analysis, 13C{ 1 H},and C{1H}, andDEPT- DEPT-135 135 NMR NMR spectroscopies spectroscopies and crystal and single single X-ray crystaldiffraction X-ray diffraction method. method. Moreover,Moreover, HR-ESI-MS HR-ESI-MS spectrometry spectrometry was carried out was forcarried 1 usingout CH for 3 1 CN using and CH EtOH 3CNas and EtOH solvents. as The solvents. crystal The crystal structures structures 2·4CH 3 CN and 2·4CH CN and 3·4EtOH were also compared using Hirshfeld Surface Analysis 3·4EtOH were also compared using Hirshfeld Surface Analysis and electrostatic potential calculations. 3 and electrostatic potential calculations. The elemental analysis of compounds 1–3 agrees with the proposed formula without co-crystallized The elemental The solvent molecules. analysis of compounds positive ionization mass 1–3 agrees spectra with (ESIthe proposed + -MS) of 1 wereformula without recorded in CHco- CN 3 crystallized and EtOH using solvent themolecules. The positive conditions. same experimental ionization mass In spectra (ESI -MS)compound both solvents, + of 1 were recorded 1 was brokenin CH3CN and EtOH using the same experimental conditions. In both solvents, compound 1 was broken resulting in the same monomeric fragment with m/z 495.0505 (100%) attributable to [Zn(ACA)2 + Na]+ resulting in the same monomeric fragment with m/z 495.0505 (100%) attributable to [Zn(ACA)2 + Na]+ (Figure S1a,b). Moreover, in the CH3 CN spectrum two additional fragments were observed, one with (SI: Figure S1a and S1b). Moreover, in the CH3CN spectrum two additional fragments were observed, m/z 650.1235 (100%) corresponding to [Zn(ACA)2 (4-Phpy) + Na]+ and +the other with m/z 967.1127 one with m/z 650.1235 (100%) corresponding to [Zn(ACA)2(4-Phpy) + Na] and the other with m/z (89%) assigned to [Zn2 (ACA)4 + Na]+ (Figure S1c,d). The FTIR-ATR spectra of 1–3 displayed the 967.1127 (89%) assigned to [Zn2(ACA)4 + Na] (SI: Figure S1c and + S1d). The FTIR-ATR spectra of 1–3 characteristic carboxylate bands in the range 1583–1563 cm−1 for νas−1(COO), displayed the characteristic carboxylate bands in the range 1583–1563 cm and between 1392 and for νas(COO), and between 1379 cm −1 for ν (COO). The difference between these bands [∆ = ν (COO) - ν (COO)] is 204 (1), 183 s 1392 and 1379 cm for νs(COO). The difference between these bands [Δ = νas(COO) −1 as s - νs(COO)] is 204 (2) and 171 (3) cm −1 , suggesting monodentate (1) and bridged (2 and 3) coordination modes of the (1), 183 (2) and 171 (3) cm−1, suggesting monodentate (1) and bridged (2 and 3) coordination modes carboxylate moieties [50,51] (Figures S2–S4). Moreover, some specific groups of the ACA ligands such Molecules 2020, 25, 3615 4 of 23 as the amine unit (ν(N-H)), the alkene moieties (ν(C-H)alk ) or the carbonyl group (ν(C=O)), as well as the bands attributable to the aromatic groups ν(C-H)ar , ν(C=C/C=N), δ(C-H)ip , and δ(C-H)oop are also identified [52]. Furthermore, the presence of coordinated EtOH molecules in 3 allows further identification of some bands between 3308 and 3275 cm−1 assignable to ν(O-H). The 1 H and 13 C{1 H} NMR spectra of complexes 1–3 have been recorded in dmso-d6 solutions showing a displacement with respect to the free ligands. In the 1 H NMR, the signals attributable to the amine unit of the ACA ligand appeared between 9.30 and 9.19 ppm, followed by the aromatic protons of the 4-Phpy ligand, which are only observed in compounds 1 and 2 between 8.77 and 7.53 ppm owing to the absence of 4-Phpy in compound 3. It is noteworthy that the change in the order of the o-H and the m-H atoms of the pyridyl ring from the 4-Phpy ligands between 1 and 2, appearing at 7.91 and 7.86 for 1 and at 7.76 and 7.82 ppm for 2. In addition, the o-H of the ACA ligand appears between 7.55 and 7.51 for 1–3, and it is overlapped with some of the aromatic protons of the 4-Phpy previously mentioned in 1 and 2, displaying a multiplet signal for those spectra. Furthermore, the remaining aromatic protons from the ACA ligand are shown between 7.36 and 7.27 ppm, being remarkable another change in the order of appearance in compound 1 respect to the trinuclear complexes 2 and 3. In compound 1, the alkene proton appears first at 7.30 ppm, followed by the p-H of the ACA at 7.27 ppm. By contrast, in compounds 2 and 3 the order of appearance is changed, appearing the p-H of the ACA at 7.29 ppm and the alkene protons at 7.25 (2) and 7.24 (3) ppm. The signals of the methyl protons from the ACA ligands are also observed between 1.99 and 1.95 ppm (Figures S5–S7). Furthermore, in compound 3, apart from the signals of the ACA ligand, those corresponding to the coordinated EtOH molecules are also observed displaying three signals at 4.39, 3.45 and 1.05 corresponding to the hydroxyl moiety, the CH2 and CH3 groups, respectively. In the 13 C{1 H} NMR spectra of compounds 1–3 the carbon atoms from the carbonyl groups appear between 170.8 and 170.6 ppm, followed by the carboxylate carbon atoms, which appear at 168.5 ppm for the three complexes. The two carbons from the alkene groups appear separately, being at 128.3 and 128.2 ppm the not protonated and at 135.1 ppm the protonated one. Then, the aromatic protons from the ACA ligand appear between 130.0 and 128.4 ppm, which required DEPT-135 experiments in order to distinguish between the o-C and the quaternary carbon of the aromatic ring (Figures S8–S10). The last atoms of the ACA ligand correspond to the methyl carbon atoms, which appear at 23.1 ppm. The signals corresponding to the 4-Phpy ligand in 1 and 2 start at 150.0 ppm (o-C from the pyridyl ring), followed by the p-C of the same ring (149.1–148.8 ppm) and the quaternary carbon atom from the phenyl ring (136.6–136.4 ppm). The next signals from the 4-Phpy are shown at 129.4 ppm, where the m-C and p-C from the phenyl ring appear together. Finally, the o-C from the phenyl (127.2 ppm) and the m-C from the pyridyl (122.1–121.9 ppm) appear as the last signals from the 4-Phpy ligand. In addition, in compound 3, the signals corresponding to the coordinated EtOH molecules appeared at 56.1 and 18.6 ppm, corresponding to the CH2 and CH3 carbon atoms, respectively. 2.2. Crystal and Extended Structure of 1 Compound 1 crystallizes in the monoclinic P21 /c space group. It consists of a Zn(II) polymeric chain expanded along the a axis through two crystallographically different Zn(II) metal centers with slightly different bond lengths and bond angles. Both metal centers present a [ZnNO3 ] core exhibiting O-Zn-O bond angles between 101.6(1)◦ and 129.1(1)◦ , and O-Zn-N between 89.4(1)◦ and 139.1(2)◦ (Table 1; Figure 1a). The distortion on the tetrahedral or square planar geometry can be determined by the τ4 parameter [53], where the values range between 1.00 for a perfect tetrahedral geometry, to 0.00 for a perfect square planar geometry. In compound 1, the two different Zn(II) metal centers present values of the τ4 parameter of 0.81 (Zn1) and 0.80 (Zn2), indicating similar distorted tetrahedral geometries. Molecules 2020, 25, x FOR PEER REVIEW 5 of 24 Molecules 2020, 25, 3615 5 of 23 Table 1. Selected bond lengths (Å), bond angles (°), and intermolecular interactions (Å) of compound 1. Table 1. Selected bond lengths (Å), bond angles (◦ ), and intermolecular interactions (Å) of compound 1. Bond Lengths (Å) Bond Lengths (Å) Zn(1)-O(1) 1.949(4) Zn(2)-O(7) 1.979(3) Zn(1)-O(1) Zn(1)-O(4) 1.949(4) 1.977(3) Zn(2)-O(7) Zn(2)-O(10)#1 1.979(3) 2.005(5) Zn(1)-O(4) 1.977(3) Zn(2)-O(10)#1 2.005(5) Zn(1)-O(12) Zn(1)-O(12) 2.008(3) 2.008(3) Zn(2)-O(6) Zn(2)-O(6) 2.010(3) 2.010(3) Zn(1)-N(2) Zn(1)-N(2) 2.072(4) 2.072(4) Zn(2)-O(6) Zn(2)-O(6) 2.054(4) 2.054(4) Bond Angles(◦(°) Bond Angles ) O(1)-Zn(1)-O(4) 129.1(1) O(7)-Zn(2)-O(10)#1 106.6(2) O(1)-Zn(1)-O(4) 129.1(1) O(7)-Zn(2)-O(10)#1 106.6(2) O(1)-Zn(1)-O(12) O(1)-Zn(1)-O(12) 101.9(1) 101.9(1) O(7)-Zn(2)-O(6) O(7)-Zn(2)-O(6) 101.6(1) 101.6(1) O(4)-Zn(1)-O(12) O(4)-Zn(1)-O(12) 116.7(1) 116.7(1) O(10)#1-Zn(2)-O(6) O(10)#1-Zn(2)-O(6) 103.8(1) 103.8(1) O(1)-Zn(1)-N(2) O(1)-Zn(1)-N(2) 116.0(2) 116.0(2) O(7)-Zn(2)-N(7) O(7)-Zn(2)-N(7) 108.2(2) 108.2(2) O(4)-Zn(1)-N(2) O(4)-Zn(1)-N(2) 97.1(1) 97.1(1) O(10)#1-Zn(2)-N(7) O(10)#1-Zn(2)-N(7) 139.1(2) 139.1(2) O(12)-Zn(1)-N(2) 89.4(1) O(6)-Zn(2)-N(7) 89.6(1) O(12)-Zn(1)-N(2) 89.4(1) O(6)-Zn(2)-N(7) 89.6(1) Intermolecular Interactions Intermolecular Interactions(Å)(Å) D-H···A D-H···A D-H D-H (Å)(Å) H···A (Å) H···A (Å) D···A D···A (Å) >D-H···A (◦ ) >D-H···A (°) N(1)-H(1)···O(2) N(1)-H(1)···O(2) 0.86 0.86 2.02 2.02 2.870(5) 2.870(5) 173 173 N(4)-H(4)···O(8) 0.86 2.09 2.899(6) 157 N(4)-H(4)···O(8) 0.86 2.09 2.899(6) 157 C(46)-H(46A)···O(9) 0.96 2.53 3.429(7) 155 C(46)-H(46A)···O(9) C(46)-H(46C)···O(8) 0.96 0.96 2.53 2.49 3.429(7) 3.204(8) 131 155 C(46)-H(46C)···O(8) C(31)-H(31)···Cg(4) 0.96 0.93 2.49 2.67 3.204(8) 3.516(5) 151 131 C(31)-H(31)···Cg(4) C(40)-H(40)···Cg(4) 0.93 0.93 2.67 2.79 3.516(5) 3.571(5) 142 151 C(64)-H(64)···Cg(1) C(40)-H(40)···Cg(4) 0.93 0.93 2.97 2.79 3.693(8) 3.571(5) 135 142 #1: x + 1,y,z; Cg(1) = C(29) C(30) C(64)-H(64)···Cg(1) 2.97 C(34); Cg(2) =3.693(8) 0.93C(31) C(32) C(33) 135 N(7) C(19) C(47) C(48) C(49) #1: x + C(50); Cg(3) ==C(29) 1,y,z; Cg(1) C(60)C(30) C(61)C(31) C(62)C(32) C(63)C(33) C(64) C(34); Cg(4) ==N(7) C(65); Cg(2) C(51)C(19) C(52)C(47) C(53)C(48) C(54)C(49) C(55)C(50); C(56)Cg(3) = C(60) C(61) C(62) C(63) C(64) C(65); Cg(4) = C(51) C(52) C(53) C(54) C(55) C(56) Figure Figure 1. (a) General 1. (a). Generalview viewof ofthe the polymeric polymericchain chainof of11along the aa axis. alongthe axis. In In detail detail view view of (b) core of (b) core atoms atoms of the polymeric chain. (c) N-H···O, C-H···O, and π·· π intramolecular interactions. (d) of the polymeric chain. (c) N-H···O, C-H···O, and π·· π intramolecular interactions. (d) N-H···O and N-H···O and C- C-H···π intramolecularinteractions. H···π intramolecular interactions.TheThephenyl, phenyl,pyridyl, pyridyl,andandother otheratoms atoms which which do do not not participate participate in in any intramolecular interaction have been omitted for clarity in the detailed any intramolecular interaction have been omitted for clarity in the detailed views. views. Molecules 2020, 25, 3615 6 of 23 The CP 1 is composed of dimeric units with their metal centers presenting the same coordination sphere, which contains two ACA and one 4-Phpy ligands each one. The ACA ligands display two types of coordination modes: monodentate via carboxylate group or bridge via carboxylate and carbonyl groups. Despite the two different roles of the ACA ligands in this compound, their carboxylate groups exhibit always a monodentate coordination mode (Figure 1b). The Zn-O bond lengths are between 1.949(4) and 2.010(3) Å with no significant differences between the carboxylate and the carbonyl Zn-O bond lengths. In addition, the Zn-N bond lengths are slightly longer than the Zn-O bonds, with values of 2.054(4) and 2.072(4) Å. These values are similar to other Zn(II) compounds with Zn-O coordination through carbonyl groups [54–56] or carboxylate ligands which display monodentate coordination modes in combination with pyridine derivative ligands [57,58]. The intramolecular interactions of 1 are promoted by the bridging and monodentate ACA ligands. The bridging ligands act as hydrogen bond donors via NH and m-H moieties displaying three different interactions, two of them with oxygen atoms of carbonyl units (N-H···O), and one with an uncoordinated oxygen atom from a carboxylate group (C-H···O). Moreover, the bridging ACA ligands display a π···π interaction between its aromatic ring and the pyridyl ring of the 4-Phpy (Figure 1c). By contrast, the monodentate ACA ligands act as hydrogen bond donors by C-H···π interactions through their methyl groups with the phenyl unit of a bridging ACA ligand (Figure 1d; Table S1). Compound 1 expands its structure along the c direction through two groups of interactions in which only the monodentate ACA ligands participate. The former is composed of one strong H-bond between the amine unit and the uncoordinated oxygen atom from the carboxylate group (Figure 2a). The latter is formed of three moderate interactions [59], one H-bond between the same groups as the previous H-bond (N-H···OCOO ), and two C-H···O interactions, which assemble two methyl protons with one oxygen atom from a carbonyl and one from a monodentate carboxylate group of the same nearby polymeric chain (Figure 2b). These interactions expand the structure of 1 along the c direction, forming 2D layers through the ac plane in combination with the expansion of the polymeric chains (Figure 2c). Furthermore, there are three C-H···π interactions, which expand the structure through the bc plane. In two of them the aromatic ring from a 4-Phpy connect two different polymeric chains throughout the c direction by a m-H and a o-H atoms of a bridged and a monodentate ACA ligands. In addition, the aromatic ring of the m-H atom participates in another C-H···π interaction with a bridged ACA ligand, expanding the structure through the b direction together with the intramolecular C-H···π interaction previously described (Table 1; Figure 3; Table S1). All this set of interactions expands the structure forming a 3D network. Molecules 2020, Molecules 25, x3615 2020, 25, FOR PEER REVIEW 77 of of 24 23 Figure 2. In detail view of: (a) N-H···O interactions. (b) N-H···O and C-H···O interactions through the Figure 2. Inchains. polymeric detail view of: (a) N-H···O (c) General interactions. view of the 2D layers(b) N-H···O formed and C-H···O interactions by intermolecular through interactions along the the polymeric chains. (c) General view of the 2D layers formed by intermolecular interactions ac plane in 1. The phenyl, pyridyl and other atoms which do not participate in any of the mentionedalong the ac plane in 1.have interactions The been phenyl, pyridyl omitted forand other atoms which do not participate in any of the mentioned clarity. interactions have been omitted for clarity. Furthermore, there are three C-H···π interactions, which expand the structure through the bc plane. In two of them the aromatic ring from a 4-Phpy connect two different polymeric chains throughout the c direction by a m-H and a o-H atoms of a bridged and a monodentate ACA ligands. In addition, the aromatic ring of the m-H atom participates in another C-H···π interaction with a bridged ACA ligand, expanding the structure through the b direction together with the Molecules 2020, 25, x FOR PEER REVIEW 8 of 24 Molecules 2020, 25, 3615 8 of 23 intramolecular C-H···π interaction previously described (Table 1; Figure 3; SI: Table S1). All this set of interactions expands the structure forming a 3D network. Figure 3. (a) General view of the supramolecular bc plane. (b) In-detail view of the former C-H···π Figure 3. (a) General view of the supramolecular bc plane. (b) In-detail view of the former C-H···π interactions in 1. The phenyl, pyridyl and other atoms which do not participate in any of the mentioned interactions in 1. The phenyl, pyridyl and other atoms which do not participate in any of the interactions have been omitted for clarity. mentioned interactions have been omitted for clarity. 2.3. Crystal Structures 2·4CH3 CN and 3·4EtOH 2.3. Crystal Structures 2·4CH3CN and 3·4EtOH Compound 2·4CH3 CN crystallizes in the monoclinic P21 /c space group. On the other hand, compoundCompound 3·4EtOH2·4CH 3CN crystallizes in the monoclinic P21/c space group. On the other hand, crystallizes in the monoclinic P21 space group. Both compounds form linear compound 3·4EtOH crystallizes in the monoclinic P21 space group. Both compounds form linear trinuclear arrays presenting two different types of Zn(II) ions, one central and two terminal metal trinuclear arrays presenting two different types of Zn(II) ions, one central and two terminal metal atoms, but in 2·4CH3 CN the terminal metal atoms are equal while in 3·4EtOH they present slightly atoms, but in 2·4CH3CN the terminal metal atoms are equal while in 3·4EtOH they present slightly different bond lengths and angles. The central metal atoms for both compounds exhibited a [ZnO6 ] different bond lengths and angles. The central metal atoms for both compounds exhibited a [ZnO6] core formed by six carboxylate groups from six ACA ligands connected to the terminal metal atoms core formed by six carboxylate groups from six ACA ligands connected to the terminal metal atoms through six bridged coordination modes. The terminal metal atoms in 2·4CH3 CN present a [ZnO3 N] through six bridged coordination modes. The terminal metal atoms in 2·4CH3CN present a [ZnO3N] core corecomposed composedby bythree three ACA ACA ligands with bridged ligands with bridgedcoordination coordinationmodes modes and and a 4-Phpy a 4-Phpy ligand ligand which which completes completesthethe coordination sphere(Figure coordination sphere (Figure 4a). 4a). Differently, Differently, in 3·4EtOH in 3·4EtOH the bridged the bridged ACA ligands ACA ligands are are maintained but the 4-Phpy ligand is exchanged by an EtOH molecule, maintained but the 4-Phpy ligand is exchanged by an EtOH molecule, displaying a [ZnO displaying a [ZnO 4 ] core 4] core (Figure (Figure4b). 4b).In Inaddition, addition, 2·4CH 2·4CH33CNCN presents presentstwo twopairs pairsofofco-crystallized co-crystallizedCHCH 3 CN 3CN molecules molecules while while 3·4EtOHpresents 3·4EtOH presentsfour fourdifferent different co-crystallized EtOHmolecules. co-crystallized EtOH molecules. The distinction on the geometry of the hexacoordinated Zn(II) center between octahedral and trigonal prismatic is evaluated through the average twist angle (ata), but it must be noted that this value does not give information on the distortion of the geometry [60,61]. While higher ata around 60◦ belongs from octahedral geometry, the lower values close to 0◦ pertain to a trigonal prism geometry. Compound 2·4CH3 CN exhibits an ata value of 60.00◦ (torsion angles: 60.32◦ , 57.80◦ , 61.88◦ ) and compound 3·4EtOH presents an ata of 59.82◦ (torsion angles: 59.10◦ ; 58.88◦ , 61.49◦ ), both indicating an octahedral geometry with Zn-O bond lengths between 2.0861(15) and 2.1644(15) Å (2·4CH3 CN) and between 2.150(3) and 2.172(3) Å (3·4EtOH), and bond angles ranging from 89.61(6) to 93.10(6)◦ in 2·4CH3 CN and between 87.06(9) to 92.96(9)◦ for 3·4EtOH, indicating a slightly distortion on the geometry in both central metal atoms (Tables 2 and 3). Moreover, the four-coordinated centers present Zn-O bond lengths between 1.9254(15) and 1.9673(15) Å, a Zn-N bond length of 2.0358(17) Å and bond angles ranging between 99.97(7)◦ and 119.84(7)◦ in 2·4CH3 CN. Conversely, in compound 3·4EtOH, the Zn-O bond lengths are between 1.934(2) and 1.985(2) Å and the bond angles range between 92.69(10)◦ and 123.27(10)◦ . The distortion of the four-coordinated geometry is evaluated using the τ4 parameter, presenting a value of 0.87 for 2·4CH3 CN and 0.87 and 0.86 for Zn2 and Zn3 respectively, in 3·4EtOH. These values indicate a tetrahedral geometry with a slight distortion in all the four-coordinated metal atoms. Furthermore, Molecules 2020, 25, 3615 9 of 23 in both compounds the values of bond lengths and angles are in accordance with similar structures consisting of linear trinuclear arrays bridged by carboxylate ligands with nitrogen atoms from pyridine Molecules 2020, 25, x FOR PEER REVIEW 9 of 24 derivative ligands [32,34], or oxygen atoms from solvent molecules, in the lateral positions [31,33,34]. Figure 4. Molecular structure of complex: (a) 2·4CH3 CN and (b) 3·4EtOH. (c) N-H···O intramolecular Figure 4. Molecular interactions structure of the ACA ofin ligands complex: (a) 2·4CH 2·4CH3 CN 3CN and (b) 3·4EtOH. (c) N-H···O intramolecular and 3·4EtOH with labels assigned for complex 3·4EtOH. interactions of the ACA ligands in 2·4CH 3CN and 3·4EtOH with labels assigned for complex 3·4EtOH. The phenyl and other atoms which do not participate in any of the mentioned interactions have been The phenyl omitted and other atoms which do not participate in any of the mentioned interactions have been for clarity. omitted for clarity. Table 2. Selected bond lengths (Å), bond angles (◦ ), and intermolecular interactions (Å) of compound 2·4CH The 3 CN. distinction on the geometry of the hexacoordinated Zn(II) center between octahedral and trigonal prismatic is evaluated through the average twist angle (ata), but it must be noted that this Bond Lengths (Å) value does not give information on the distortion of the geometry [60,61]. While higher ata around Zn(1)-O(1) 2.1028(15) Zn(2)-O(2) 1.9465(14) 60° belongs from octahedral geometry, the lower values close to 0° pertain to a trigonal prism Zn(1)-O(4) 2.1644(15) Zn(2)-O(8) 1.9673(15) geometry.Zn(1)-O(7) Compound 2·4CH3CN exhibits an ata value of 60.00° (torsion 2.0861(15) Zn(2)-O(5) angles: 60.32°, 57.80°, 61.88°) 1.9254(15) and compoundZn(2)-N(4)3·4EtOH presents an2.0358(17)ata of 59.82° (torsion angles: 59.10°; 58.88°, 61.49°), both indicating an octahedral geometry with Zn-O Bond bond Angleslengths (◦ ) between 2.0861(15) and 2.1644(15) Å (2·4CH3CN) and between 2.150(3) and 2.172(3) Å (3·4EtOH), and bond angles ranging from 89.61(6) O(1)-Zn(1)-O(4) 90.39(6) O(1)-Zn(1)-O(4)#1 89.61(6) to 93.10(6)° in 2·4CH3CN and between O(7)-Zn(1)-O(1) 87.06(9) to 92.96(9)° 90.00(6) for 3·4EtOH, indicating O(7)-Zn(1)-O(4) 93.10(6)a slightly distortion on the geometry O(7)#1-Zn(1)-O(4) in both central metal 86.90(6) atoms (Tables 2 and 3). O(1)#1-Zn(1)-O(1) 180.00(7) O(4)-Zn(1)-O(4)#1 Moreover, 180.00(4)present Zn-O bond the four-coordinated centers O(7)#1-Zn(1)-O(7) lengths between 180.01.9254(15) and O(2)-Zn(2)-N(4) 1.9673(15) 101.22(7) Å and bond O(5)-Zn(2)-N(4) Å, a Zn-N bond length of 2.0358(17) angles ranging between 103.85(7) 99.97(7)° and O(8)-Zn(2)-N(4) 99.97(7) O(5)-Zn(2)-O(2) 119.84(7) 119.84(7)° in 2·4CH3CN. Conversely, in compound 3·4EtOH, the Zn-O bond lengths are between O(2)-Zn(2)-O(8) 117.26(7) O(5)-Zn(2)-O(8) 110.86(7) 1.934(2) and 1.985(2) Å and the bond angles range between ◦ 92.69(10)° and 123.27(10)°. The distortion Twist Angles ( ) of the four-coordinated geometry is evaluated using the τ4 parameter, presenting a value of 0.87 for 2·4CHO(1)-Cg(1)-Cg(1)#1-O(4) 60.32 O(4)-Cg(1)-Cg(1)#1-O(7) 57.80 3CN and 0.87 and 0.86 for Zn2 and Zn3 respectively, in 3·4EtOH. These values indicate a O(7)-Cg(1)-Cg(1)#1-O(1) 61.88 tetrahedral geometry with a slight distortion in all the four-coordinated metal atoms. Furthermore, in both compounds the values of bond Intermolecular lengths and Interactions angles are(Å)in accordance with similar structures consisting D-H···A of linear trinuclear D-H arrays (Å) bridged by carboxylate H···A (Å) ligands D···A >D-H···A (Å) with nitrogen (◦ ) from atoms C(44)-H(44)···N(1W) pyridine derivative ligands [32,34], 0.95or oxygen atoms 2.60 from solvent3.496(4) 157 positions molecules, in the lateral C(4W)-H(4W)A···O(9) [31,33,34]. 0.98 2.30 3.279(3) 177 C(4W)-H(4W)C···O(3) 0.98 2.46 3.428(4) 172 Finally, both trinuclear structures C(22)-H(22A)···Cg(2) 0.98 display six moderate intramolecular 2.69 3.553(3) N-H···O148 interactions between the amine and C(27)-H(27)···Cg(3) the carbonyl 0.95 units of the amide 2.88 moieties from 3.608(3) the different bridged 134 ACA ligands, Cg(3)···Cg(4) connecting all the carboxylic 3.8858(14)ligands between them and supporting the disposition of the ligands #1: -x + 1,-y + 1,-z + 1; Cg(1) = In in the molecular array. 2·4CH O(1) 3CN, Cg(2) O(4) O(7); there=are three C(26) different C(27) C(28) C(29)values C(30)for these C(31); interactions. Cg(3) = C(4) Differently, in 3·4EtOH, the structure C(5) C(6) shows C(7) C(8) C(9); six=different Cg(4) N(4) C(34) values C(35) for C(36)the N-H···O C(37) C(38) interactions (Figure 4c; SI: Tables S2 and S3). Molecules 2020, 25, 3615 10 of 23 Table 3. Selected bond lengths (Å), bond angles (◦ ), and intermolecular interactions (Å) of compound 3·4EtOH. Bond Lengths (Å) Zn(1)-O(1) 2.172(3) Zn(1)-O(4) 2.173(3) Zn(1)-O(7) 2.159(3) Zn(1)-O(10) 2.172(3) Zn(1)-O(13) 2.150(3) Zn(1)-O(16) 2.161(3) Zn(2)-O(2) 1.952(2) Zn(2)-O(5) 1.967(2) Zn(2)-O(8) 1.934(2) Zn(2)-O(19) 1.985(2) Zn(3)-O(11) 1.9617(18) Zn(3)-O(14) 1.940(2) Zn(3)-O(17) 1.948(2) Zn(3)-O(20) 1.985(2) Bond Angles (◦ ) O(1)-Zn(1)-O(4) 87.06(9) O(7)-Zn(1)-O(1) 89.52(9) O(7)-Zn(1)-O(4) 90.31(9) O(7)-Zn(1)-O(10) 90.45(9) O(7)-Zn(1)-O(16) 89.71(9) O(10)-Zn(1)-O(4) 92.96(9) O(13)-Zn(1)-O(1) 89.69(9) O(13)-Zn(1)-O(4) 89.75(9) O(13)-Zn(1)-O(10) 90.35(9) O(13)-Zn(1)-O(16) 90.23(9) O(16)-Zn(1)-O(1) 92.74(9) O(16)-Zn(1)-O(10) 87.23(8) O(1)-Zn(1)-O(10) 179.96(11) O(13)-Zn(1)-O(7) 179.20(10) O(16)-Zn(1)-O(4) 179.80 (11) O(2)-Zn(2)-O(5) 114.81(10) O(2)-Zn(2)-O(19) 99.26(11) O(5)-Zn(2)-O(19) 105.43(11) O(8)-Zn(2)-O(2) 122.91(10) O(8)-Zn(2)-O(5) 115.08(9) O(8)-Zn(2)-O(19) 92.69(10) O(11)-Zn(3)-O(20) 99.53(10) O(14)-Zn(3)-O(11) 123.27(10) O(14)-Zn(3)-O(17) 113.34(10) O(14)-Zn(3)-O(20) 97.72(10) O(17)-Zn(3)-O(11) 115.20(9) O(17)-Zn(3)-O(20) 107.00(10) Twist Angles (◦ ) O(1)-Cg(1)-Cg(2)-O(13) 59.10 O(7)-Cg(1)-Cg(2)-O(16) 58.88 O(4)-Cg(1)-Cg(2)-O(10) 61.49 Intermolecular Interactions (Å) D-H···A D-H (Å) H···A (Å) D···A (Å) >D-H···A (◦ ) O(19)-H(19)O···O(3W) 0.845(19) 1.861(19) 2.536(4) 135.8(17) O(20)-H(20)O···O(2W) 0.83(2) 1.76(2) 2.585(4) 174(4) O(3W)-H(3WO)···O(4W) 0.84 1.91 2.669(4) 149 O(2W)-H(2WO)···O(1W) 0.84 2.01 2.683(3) 136 O(4W)-H(4WO)···O(6) 0.84 1.85 2.685(4) 175 O(1W)-H(1WO)···O(18) 0.84 1.88 2.712(4) 172 C(31)-H(31)···O(4W) 0.95 2.54 3.481(5) 172 C(53)-H(53)···O(1W) 0.95 2.52 3.460(5) 172 C(4W)-H(4WA)···O(20) 0.98 2.61 3.418(7) 140 C(4W)-H(4WB)···O(2) 0.98 2.63 3.502(6) 148 C(7W)-H(7WB)···Cg(3) 0.99 2.97 3.954(7) 172 C(20)-H(20)···Cg(4) 0.95 2.88 3.674(4) 142 C(60)-H(60)···Cg(5) 0.95 2.90 3.705(4) 143 C(69)-H(69B)···Cg(4) 0.99 2.69 3.611(4) 155 C(67)-H(67A)···Cg(5) 0.99 2.85 3.703(4) 145 Cg(1) = O(1) O(4) O(7); Cg(2) = O(10) O(13) O(16); Cg(3) = C(15) C(16) C(17) C(18) C(19) C(20); Cg(4) = C(4) C(5) C(6) C(7) C(8) C(9); Cg(5) = C(37) C(38) C(39) C(40) C(41) C(42) Finally, both trinuclear structures display six moderate intramolecular N-H···O interactions between the amine and the carbonyl units of the amide moieties from the different bridged ACA ligands, connecting all the carboxylic ligands between them and supporting the disposition of the ligands in the molecular array. In 2·4CH3 CN, there are three different values for these interactions. Differently, in 3·4EtOH, the structure shows six different values for the N-H···O interactions (Figure 4c; Tables S2 and S3). Molecules 2020, 25, 3615 11 of 23 2.4. Extended Structures of 2·4CH3 CN and 3·4EtOH The intermolecular interactions of 2·4CH3 CN are mainly through C-H···π associations between the ACA ligands and C-H···O/C-H···N interactions between the ACA ligands and the two co-crystallized CH3 CN molecules, which present different behaviors. One co-crystallized CH3 CN molecule exhibits a moderate C-H···N interaction without propagation of the structure. Otherwise, the second CH3 CN molecule interacts through two protons of its -CH3 moiety with two carbonyl oxygen atoms from nearby trinuclear units, forming two strong C-H···O interactions which expand the structure through the c axis (Figure 5a). Molecules 2020, 25, x FOR PEER REVIEW 12 of 24 Figure 5. (a) In detail view of the C-H···N and C-H···O interactions of 2·4CH3 CN between the two types Figure 5. (a) In detail view of the C-H···N and C-H···O interactions of 2·4CH3CN between the two of co-crystallized acetonitrile molecules (highlighted in green and purple) and the trinuclear units types of co-crystallized acetonitrile molecules (highlighted in green and purple) and the trinuclear which expand the structure along the c axis. (b) In detail view of the C-H···π and π··· π interactions units which expand the structure along the c axis. (b) In detail view of the C-H···π and π··· π which contribute to the formation of the bc plane. (c) General view of the resulting plane along the bc interactions which contribute to the formation of the bc plane. (c) General view of the resulting plane axes due to the C-H···O and the planar interactions. The phenyl, pyridyl, and other atoms which do not along the bc axes due to the C-H···O and the planar interactions. The phenyl, pyridyl, and other atoms participate in any of the mentioned interactions have been omitted for clarity. which do not participate in any of the mentioned interactions have been omitted for clarity. Furthermore, three ACA ligands of three different trinuclear units show two C-H···π interactions. In theFurthermore, first interaction,threethe ACA H-donor ligands of three is a -CH different trinuclear units show two C-H···π 3 moiety from a first trinuclear unit, which interacts interactions. with an aromaticIn the ringfirst frominteraction, a nearby theACA H-donor is a -CH5b, ligand (Figure 3 moiety from a first trinuclear unit, which pink centroid). The second interaction associates the o-H atom of the previous aromatic ACA ring with(Figure interacts with an aromatic ring from a nearby ACA ligand a phenyl5b, pink ring fromcentroid). The second a neighboring ACA ligand (Figure 5b, blue centroid). In addition, the same phenyl ring which displays the second C-H···πa interaction associates the o-H atom of the previous aromatic ACA ring with a phenyl ring from neighboring interaction ACA also liganda(Figure promotes 5b, bluewith π···π stacking centroid). In addition, a pyridyl ring fromthe same phenyl a 4-Phpy ring trinuclear of the first which displays unit the second C-H···π interaction also promotes a π···π stacking with a pyridyl (Figure 5b, blue and yellow centroids). This set of interactions together with the C-H···O ring from a 4-Phpy of the interactions first trinuclear previously unit (Figure mentioned, expand5b, theblue and yellow structure throughcentroids). This the bc axes, set of ainteractions forming 2D plane (Tabletogether with5c). 2; Figure the C-H···O On theinteractions other hand, previously in 3·4EtOH, mentioned, expand theand the co-crystallized structure through coordinated the bc EtOH axes, forming molecules as wella as 2D plane (Table 2; Figure 5c). two of the ACA aromatic rings from the trinuclear units are involved in most of the interactions. On the other hand, in 3·4EtOH, the co-crystallized and coordinated EtOH molecules as well as The co-crystallized EtOH molecules connect each trinuclear unit to two neighboring ones through two of the ACA two slightly aromatic different rings patterns offrom the trinuclear intermolecular units are involved interactions, while thein most of C-H···π the interactions. interactions The join each co-crystallized EtOH molecules trinuclear unit to another four. connect each trinuclear unit to two neighboring ones through two slightly different patterns of intermolecular interactions, while the C-H···π interactions join each trinuclear unit to another four. Both patterns of the co-crystallized EtOH molecules start with an H-bond between the hydroxyl groups of a coordinated and a co-crystallized EtOH molecules, with the difference that this H-bond presents a moderate strength for one co-crystallized EtOH molecule (Figure 6a, dark blue EtOH molecule), while for the other present a strong strength (Figure 6a, dark green EtOH molecule). Molecules 2020, 25, 3615 12 of 23 Both patterns of the co-crystallized EtOH molecules start with an H-bond between the hydroxyl groups of a coordinated and a co-crystallized EtOH molecules, with the difference that this H-bond presents a moderate strength for one co-crystallized EtOH molecule (Figure 6a, dark blue EtOH molecule), while for the other present a strong strength (Figure 6a, dark green EtOH molecule). Moreover, each of these co-crystallized EtOH molecules are held together with another co-crystallized EtOH molecule via a moderate H-bond between their hydroxyl groups. The patterns are completed by a strong H-bond between the hydroxyl groups of the second co-crystallized EtOH molecules and the oxygen atoms from carbonyl groups of neighboring trinuclear units. These interactions are also supported by a strong C-H···O interaction between the o-H of ACA ligands from the central trinuclear Molecules unit and the 2020, 25, x FOR PEER hydroxyl REVIEW groups 13 of 24 from these second co-crystallized EtOH molecules, which also connect the trinuclear units directly through the second co-crystallized EtOH molecules (Table 3; Figure 6a, molecules, which also connect the trinuclear units directly through the second co-crystallized EtOH light green and purple EtOH molecules). molecules (Table 3; Figure 6a, light green and purple EtOH molecules). Figure 6. (a) In detail view of the H-bonds, C-H···O and planar interactions of complex 3·4EtOH. Figure 6. (a) In detail view of the H-bonds, C-H···O and planar interactions of complex 3·4EtOH. (b) (b) General view of the supramolecular 2D plane formed along the bc axes. The different types of General view of the supramolecular 2D plane formed along the bc axes. The different types of co- co-crystallized EtOH molecules have been highlighted in different colors and the phenyl, pyridyl, and crystallized EtOH molecules have been highlighted in different colors and the phenyl, pyridyl, and other atoms which do not participate in any of the mentioned interactions have been omitted for clarity. other atoms which do not participate in any of the mentioned interactions have been omitted for clarity. Moreover, two of the co-crystallized EtOH molecules exhibit other weak interactions with the same trinuclear units connected by the previously mentioned interactions. The first interacts with a Moreover, two of the co-crystallized EtOH molecules exhibit other weak interactions with the hydroxyl group from a coordinated EtOH molecule through a moderate C-H···O interaction with its same trinuclear units connected by the previously mentioned interactions. The first interacts with a methyl moiety, which also display another moderate C-H···O interaction with an oxygen atom from a hydroxyl group from a coordinated EtOH molecule through a moderate C-H···O interaction with its carbonyl group of a second trinuclear unit (Figure 6a, dark green EtOH molecule). The second shows a methyl moiety, which also display another moderate C-H···O interaction with an oxygen atom from C-H···π interaction between a proton from its -CH2 group with an aromatic ring from an ACA ligand a carbonyl group of a second trinuclear unit (Figure 6a, dark green EtOH molecule). The second (Figure 6a, purple and red centroids). shows a C-H···π interaction between a proton from its -CH2 group with an aromatic ring from an ACAFinally, ligandtwo ACA 6a, (Figure ligands purplefrom andeach redtrinuclear centroids).unit displays four C-H···π interactions. Two of them are formed between Finally, two ACAo-H atoms ligandsfromfromtwo different each nearby trinuclear unit trinuclear unitsC-H···π displays four with two different aromatic interactions. Two of rings from ACA ligands of the same central trinuclear unit. The remaining them are formed between O-H atoms from two different nearby trinuclear units with two two C-H···π interactions different associate aromatictwo hydrogen rings from ACAatoms from two ligands -CH of the 2 moieties same centraloftrinuclear coordinated EtOH unit. The molecules remainingfrom two different C-H···π trinuclear units with the same aromatic rings as the previous planar interactions interactions associate two hydrogen atoms from two -CH2 moieties of coordinated EtOH molecules (Figure 6a, brown and yellow centroids). All this set of interactions expands the structure of 3·4EtOH from different trinuclear units with the same aromatic rings as the previous planar interactions along the bc axes, forming (Figurea6a, 2Dbrown plane and (Figure 6b).centroids). All this set of interactions expands the structure of 3·4EtOH yellow along the bc axes, forming a 2D plane (Figure 6b). 2.5. Hirshfeld Surface Analysis Hirshfeld surface analysis of complexes 2·4CH3CN and 3·4EtOH have been performed with CrystalExplorer17.5 [62]. All the surfaces have been calculated at an isovalue of 0.5 e·au−3. In addition, the disorder present in a co-crystallized EtOH molecule of 3·4EtOH has been identified, and the fractional occupancy has been corrected to 1 in the .cif file. Moreover, the Electrostatic Surface Potential (ESP) of 2·4CH3CN and 3·4EtOH have been calculated by Density Functional Theory (DFT) Molecules 2020, 25, x FOR PEER REVIEW 14 of 24 Molecules 2020, 25, 3615 13 of 23 their identification while the fingerprint plot outlines the distances between the atoms involved in these contacts. Furthermore, the ESP calculations allow the identification of electropositive (blue) and electronegative 2.5. Hirshfeld Surface(red) regions, whose complementarity supports the presence of supramolecular Analysis interactions [64]. Hirshfeld The mainsurface analysis associations of complexes of 2·4CH 2·4CH3 CN 3CN and 3·4EtOH areand 3·4EtOHinhave highlighted been performed the Hirshfeld surface with views CrystalExplorer17.5 [62]. All the surfaces have been calculated at an isovalue of 0.5 e·au −3 . In addition, mapped with dnorm in Figures 7 and 8. Additional Hirshfeld surface mappings, ESP representations the anddisorder present in 2D fingerprint a co-crystallized plots EtOH molecule of the co-crystallized of 3·4EtOHofhas solvent molecules been 2·4CH identified, and the 3CN and 3·4EtOH are fractional occupancy has been corrected illustrated in the SI: Figures S11 and S12. to 1 in the .cif file. Moreover, the Electrostatic Surface Potential (ESP) of 2·4CH 3 In the dnorm CN and 3·4EtOH have been calculated by Density Functional representations of the two trinuclear complexes, the different intermolecular Theory (DFT) at the H- B3LYP/6-31 G(d,p) level using TONTO [63]. Both ESP surfaces have been represented bonds, C-H···O/N and planar interactions can be identified as red regions supporting the interactions over the range −0.03 au (red), previously through in described zero the(white), to 0.03 au corresponding (blue). Unfortunately, structural sections (Figures the Hirshfeld 7a and 8a).Surface The 2DAnalysis of fingerprint the CP 1 as well as their ESP calculations could not be performed owing to its plot of 3·4EtOH shows the presence of prominent O···H/H···O contacts represented as sharp spikes in polymeric array. the Hirshfeld surfaces, de + di ≈ 1.6–1.8 in combination Å range. Differently, with 2D fingerprint in complex 2·4CH3plots, CN theseare regions a powerful seem graphical asymmetrictool and to evaluate supramolecular interactions present in crystal structures. The surface show more discrete spikes (Figures 7b and 8b). The reason of this asymmetric fingerprint plot is the mapping facilitates their identification different while the fingerprint type of interactions plot outlines of the co-crystallized the distances acetonitrile between molecules with the theatoms involved trinuclear unitsinof these contacts. Furthermore, the ESP calculations allow the identification 2·4CH3CN. Whereas one type of co-crystallized acetonitrile molecules act as H-bond acceptor of electropositive (blue) and electronegative (red) regions, whose complementarity supports the presence through its nitrogen atom (C-H···N interaction), the other acetonitrile molecule interact with the of supramolecular interactions [64]. atoms of the trinuclear units through two types of C-H···O interactions, displaying carbonyl oxygen The main intermolecular associations interactionsofwith 2·4CH 3 CN and different 3·4EtOH are H-acceptors highlighted where in the unit the trinuclear Hirshfeld act assurface H-bondviewsdonor mapped with d for the C-H···Nnorm in Figures 7 and 8. Additional Hirshfeld surface mappings, and H-bond acceptor for the C-H···O interactions. These interactions present different ESP representations and 2D fingerprint distances (de + di ≈ plots 2.4–2.6of Åtheforco-crystallized the H···N contacts solventandmolecules of 2·4CH de + di ≈ 2.1–2.3 Å for3 CNtheand 3·4EtOH O···H) areis and this illustrated in the Figures S11 and S12. illustrated in the 2D fingerprint plot with asymmetric spikes. Figure 7. (a) Hirshfeld surface dnorm representations, (b) 2D fingerprint plot highlighting the Figure 7. (a) Hirshfeld surface dnorm representations, (b) 2D fingerprint plot highlighting the intermolecular interactions, and (c) graphical summary of the percentage of each contact involved in intermolecular interactions, and (c) graphical summary of the percentage of each contact involved in the Hirshfeld surface of 2·4CH3 CN. the Hirshfeld surface of 2·4CH3CN. Molecules 2020, 25, 3615 14 of 23 Molecules 2020, 25, x FOR PEER REVIEW 15 of 24 Figure 8. 8.(a)(a)Hirshfeld Figure Hirshfeldsurface surfacednorm dnormrepresentations, representations,(b) (b)2D2Dfingerprint fingerprintplot highlighting plot highlightingthethe intermolecular intermolecular interactions, and interactions, (c)(c) and graphical summary graphical summary of of thethe percentage percentageof each contact of each involved contact in in involved thethe Hirshfeld surface of 3·4EtOH. Hirshfeld surface of 3·4EtOH. In Moreover, the dnorm representations if we compare of the thetwo trinuclear summary ofcomplexes, contacts of thethe different intermolecular two trinuclear H-bonds, complexes, the C-H···O/N and planar interactions can be identified as red regions supporting the H···O/O···H contacts present a 12.3% of the surface associated in 3·4EtOH, which means a 4.4% of interactions previously described differencein respect the corresponding to 2·4CH3CN, structural with a 7.9% sections of the (Figures 7a and (Figures surface implied 8a). The7c2D fingerprint and plot of 8c). This difference 3·4EtOH shows the presence of prominent O···H/H···O contacts represented could be justified owing to the higher number of H···O/O···H contacts observed in 3·4EtOH as sharp spikes in the(eight de + dinteractions) i ≈ 1.6–1.8 Åin range. Differently, comparison with in complex 2·4CH 2·4CH3 CN these regions 3CN (four interactions), as wellseem as theasymmetric shorter H···Aanddistances show more discrete spikes (Figures 7b and 8b). The reason of this asymmetric fingerprint observed in the 2D fingerprint plot of 3·4EtOH respect to the plot of 2·4CH3CN. Furthermore, the plot is the different type of interactions presence of H···Nof the co-crystallized contacts in 2·4CH3CN acetonitrile also standsmolecules out, withwith the of a 6.0% trinuclear unitsimplied, the surface of 2·4CH 3 CN.in while Whereas 3·4EtOH onethere typeisofnotco-crystallized implied surface acetonitrile molecules in the H···N act (Table contacts as H-bond 4). acceptor through its nitrogen atom (C-H···N interaction), the other acetonitrile molecule interact with the carbonyl oxygen atoms of the trinuclear Tableunits through two 4. Comparison of the types of C-H···O interactions supramolecular interactions,of displaying compounds intermolecular interactions 2·4CH3CN and 3·4EtOH. with different H-acceptors where the trinuclear unit act as H-bond donor for the C-H···N and H-bond Complex D-H···A Number of Interactions % Hirshfeld Surface Implied acceptor for the C-H···O interactions. These interactions present different distances (de + di ≈ 2.4–2.6 Å C-H···N for the H···N contacts and de + di ≈ 2.1–2.3 Å for the O···H) solvent 2 and this is illustrated in the 6.02D fingerprint plot with asymmetric C-H···OC=O spikes. 4 7.9 2·4CH 3CN C-H···π 4 Moreover, if we compare the summary of contacts of the two trinuclear complexes, the H···O/O···H 28.1 contacts present a 12.3% of π ··· theπ surface associated in 43·4EtOH, which means a 4.4% 2.9 of difference O-H···O solvent 2 respect to 2·4CH3 CN, with a 7.9% of the surface implied (Figures 7c and 8c). This difference could be justified owing to the higherOC=O···H-O solvent number 2 of H···O/O···H contacts observed in 3·4EtOH (eight interactions) in comparison with C-H···O 2·4CH CN solvent (four interactions), as 2 as the shorter H···A distances well 12.3 observed in 3·4EtOH 3 C-H solvent···OCOO 1 the 2D fingerprint plot of 3·4EtOH respect to the plot of 2·4CH3 CN. Furthermore, the presence of H···N contacts in 2·4CH3C-H also ···O CN solvent out, with a 6.0% of the1surface implied, while in 3·4EtOH there is not coordinated EtOH stands C-H··· π implied surface in the H···N contacts (Table 4). 5 20.4 The planar interactions present in the two trinuclear compounds have been confirmed using curvedness mapping of the involved regions in these interactions. In addition, ESP surfaces have been used to check the charge complementarity between the parts which participate in these Molecules 2020, 25, 3615 15 of 23 Table 4. Comparison of the supramolecular interactions of compounds 2·4CH3 CN and 3·4EtOH. Complex D-H···A Number of Interactions % Hirshfeld Surface Implied C-H···Nsolvent 2 6.0 C-H···OC=O 4 7.9 2·4CH3 CN C-H···π 4 28.1 π ··· π 4 2.9 O-H···Osolvent 2 OC=O ···H-Osolvent 2 C-H···Osolvent 2 12.3 3·4EtOH C-Hsolvent ···OCOO 1 C-Hsolvent ···Ocoordinated EtOH 1 C-H··· π 5 20.4 The planar interactions present in the two trinuclear compounds have been confirmed using curvedness mapping of the involved regions in these interactions. In addition, ESP surfaces have been used to check the charge complementarity between the parts which participate in these associations (Figures S13 and S14). The general fingerprint plots of Figures 7b and 8b also display a “wings” shape indicating the presence of C-H···π interactions [65], which in combination with the summary of contacts of each compound show a difference in the percentage of the surface involved in the dnorm Hirshfeld surface of 2·4CH3 CN compared with 3·4EtOH. Compound 2·4CH3 CN presents a percentage of C···H/H···C contacts with a 28.1% of the surface implied (four interactions), which is a 7.7% of difference compared with 3·4EtOH (five interactions). This difference could be explained owing to the presence of the 4-Phpy ligand in 2·4CH3 CN, which apart from participating in planar interactions, also perform C···H and H···C weak contacts, which cannot be considered as planar interactions but increase the percentage of the surface implied in the Hirshfeld mappings and could have some influence in the crystal packing through cooperative effects (Table 4). Differently, in 3·4EtOH, the exchange of the 4-Phpy molecules by coordinated EtOH molecules displays a decrease of the C···H/H···C contacts, even though the number of C-H···π interactions (five interactions) is higher in 3·4EtOH than in 2·4CH3 CN (Table 4). Moreover, the ESP surfaces of 2·4CH3 CN and 3·4EtOH show the charge complementarity between electronegative charged aromatic rings from the ACA ligands and electropositive charged hydrogen atoms from the ACA and 4-Phpy aromatic rings and the CH3 moieties, involved in all the planar interactions of the two compounds. Additionally, the π···π interactions present in 2·4CH3 CN are also observed in the summary of contacts involved in the dnorm representation and, although their identification in the general 2D fingerprint plots is difficult to distinguish, the ESP surface show well the charge complementarity between the electronegative charged ACA rings and the electropositive 4-Phpy rings. Moreover, the summary of contacts shows a higher percentage of the surface implied in 2·4CH3 CN (2.9%) compared with 3·4EtOH (1.7%) for the C···C contacts, which is probably done to the presence of π···π interactions in 2·4CH3 CN. It is noteworthy that in the three structures the ACA aromatic rings are placed avoiding the planar stacking between them and favoring the formation of C-H···π interactions, while the π···π interactions are formed between aromatic rings of ACA (electron donors) and 4-Phpy (electron acceptors) in 1 (intramolecular interaction) and 2·4CH3 CN (intermolecular interaction). The ESP surfaces reveal that the lack of charge complementarity between ACA rings could be the factor which promotes the formation of C-H···π interactions, whereas the π···π stackings are formed by mixed ACA and 4-Phpy rings, whose charge complementarity has been observed by the ESP surfaces (Figure 9). This effect has also been observed in recently synthesized Zn(II) complexes containing ACA and 4-Phpy ligands by our group [42]. The reason of the electronegative charge in the ACA aromatic ring could be the combination of their double bond and the acetamide moiety, which by resonance effect, confers to the aromatic ring an electronegative charge, while for the 4-Phpy the nitrogen atom, which is more promotes the formation of C-H···π interactions, whereas the π···π stackings are formed by mixed ACA and 4-Phpy rings, whose charge complementarity has been observed by the ESP surfaces (Figure 9). This effect has also been observed in recently synthesized Zn(II) complexes containing ACA and 4-Phpy ligands by our group [42]. The reason of the electronegative charge in the ACA Molecules 2020, aromatic ring25,could 3615 be the combination of their double bond and the acetamide moiety, which 16 ofby 23 resonance effect, confers to the aromatic ring an electronegative charge, while for the 4-Phpy the nitrogen atom, which is more electronegative than the rest of the carbon atoms of the rings, pull up electronegative than the rest of the carbon atoms of the rings, pull up the charge from the pyridyl and, the charge from the pyridyl and, to a lesser extent, from phenyl ring, providing an electropositive to a lesser extent, from phenyl ring, providing an electropositive charge to these rings. charge to these rings. Figure 9. Electrostatic Surface Potential (ESP) surfaces highlighting the electropositive (blue) and Figure 9. Electrostatic Surface Potential (ESP) surfaces highlighting the electropositive (blue) and electronegative (red) regions over the range ±0.03 au for complexes: (a) 2·4CH CN and (b) 3·4EtOH. electronegative (red) regions over the range ±0.03 au for complexes: (a) 2·4CH33CN and (b) 3·4EtOH. 3. Conclusions In this paper, we present the reaction of Zn(OAc)2 ·2H2 O in combination with HACA and 4-Phpy in EtOH as solvent, yielding the 1D CP 1 with tetrahedral geometry, which extends its structure through a carboxylate-carbonyl bridge of their ACA ligands. Its recrystallization in CH3 CN and EtOH yields two trinuclear complexes with pinwheel arrays and formula [Zn3 (µ-ACA)6 (L)2 ] (L= 4-Phpy (2), EtOH (3)). Moreover, compound 2 has been obtained by an alternative method reacting Zn(OAc)2 ·2H2 O, HACA, and 4-Phpy in a 1:2:2 ratio using CH3 CN as solvent at RT. These trinuclear complexes contain two types of Zn(II) metal centers, one with octahedral (central) and the other two with tetrahedral geometries. The crystal structure of the three compounds have been elucidated, and their molecular and supramolecular interactions have been discussed obtaining 2D arrays for the two trinuclear complexes and a 3D network for the CP 1. Furthermore, Hirshfeld surface analysis has been used to analyze and compare the supramolecular interactions of the trinuclear complexes. The Hirshfeld surfaces as well as the ESP mappings allow us the identification of different type of supramolecular interactions supporting the information obtained by the structural study. Interestingly, the ESP calculations show that the aromatic rings of the 4-Phpy act as electron acceptors and the ACA aromatic rings act as electron donors and thus, favoring the formation of π···π interactions between 4-Phpy and ACA aromatic rings (1 and 2·4CH3 CN). Otherwise, the lack of charge complementarity between ACA aromatic rings lead to the formation of C-H···π interactions between nearby ACA ligands in the three structural arrays. Finally, the co-crystallized solvent molecules in structures 2·4CH3 CN and 3·4EtOH also have an important contribution in the crystal packing, connecting the trinuclear arrays by different types of interactions, which have also been identified. 4. Experimental Section 4.1. Materials and Methods Zinc(II) acetate dihydrate (Zn(OAc)2 ·2H2 O), α-acetamidocinnamic acid (HACA), 4-phenylpyridine (4-Phpy), ethanol (EtOH), and acetonitrile (CH3 CN) as solvents, were purchased from Sigma-Aldrich (Darmstadt, Germany). Deuterated dimethylsulfoxide (dmso-d6 ) was used for the NMR experiments and was purchased from Eurisotop (Saint-Aubin, France). All of them were used without further purification. All the reactions and manipulations were carried out in air at room temperature (RT). Elemental analyses (C, H, and N) were carried on a Thermo Scientific (Waltham, MA, USA) Flash 2000 CHNS Analyzer. HR-ESI-MS measurements were recorded after dissolving the corresponding solid of CP 1 in CH3 CN and EtOH in a MicroTOF-Q (Bruker Daltonics GmbH, Bremen, Germany) instrument equipped with an electrospray ionization source (ESI) in positive mode. Na+ ions come Molecules 2020, 25, 3615 17 of 23 from the EtOH solvent which contains < 50 ppb. Conditions were those used in routine experiments. The nebulizer pressure was 1.5 bar, the desolvation temperature was 180 ◦ C, dry gas at 6 L min−1 , the capillary counter-electrode voltage was 5 kV, and the quadrupole ion energy, 5.0 eV. FTIR-ATR spectra were recorded on a Perkin Elmer (Waltham, MA, USA) spectrometer, equipped with an attenuated total reflectance (ATR) accessory model MKII Golden Gate with a diamond window in the range 4000–500 cm−1 . 1 H, 13 C{1 H}, and DEPT-135 NMR spectra were recorded on an NMR-FT Bruker 360 and 400 (Karlsruhe, Germany) MHz spectrometers in dmso-d6 solution at RT. All chemical shifts (δ) are given in ppm relative to tetramethylsilane (TMS) as internal standard. 4.2. Synthesis of [Zn2 (µ-O,O’-ACA)2 (ACA)2 (4-Phpy)2 ]n (1) An EtOH solution (20 mL) of Zn(OAc)2 ·2H2 O (152 mg, 0.692 mmol) was added dropwise to a solution of HACA (283 mg, 1.38 mmol) and 4-Phpy (215 mg, 1.39 mmol) in EtOH (10 mL) as solvent. The resulting solution was stirred for 18 h at RT until a white solid precipitated. The white precipitate was washed with 10 mL of cold EtOH, filtered and dried under vacuum. Suitable colorless crystals were obtained by keeping the mother liquors on the fridge for 5 days. Yield: 382 mg (88%) (based on Zn). Elemental analysis calc.(%) for C66 H58 Zn2 N6 O12 (1257.98): C 63.01, H 4.65, N 6.68; found: C 63.10, H 4.49, N 6.67. HR-MS (ESI+ , CH3 CN): m/z (%) = 495.0505 (100%) (calc. for [Zn(ACA)2 + Na]+ = 495.0505); 650.1235 (100%) (calc. for [Zn(ACA)2 (4-Phpy) + Na]+ = 650.1240); 967.1127 (89%) (calc. for [Zn2 (ACA)4 + Na]+ = 967.1118). HR-MS (ESI+, EtOH): m/z (%) = 495.0505 (100%) (calc. for [Zn(ACA)2 + Na]+ = 495.0505). FTIR-ATR (wavenumber, cm−1 ): 3217(w) [ν(N-H)], 3161(w) [ν(N-H)], 3054(m) [ν(C-H)ar ], 2985(w) [ν(C-H)alk ], 2859(w) [ν(C-H)al ], 1672(w) [ν(C=O)], 1651(w), 1583(s) [νas (COO)], 1551(sh) [ν(C=C/C=N)], 1509(m), 1489(m), 1446(w), 1422(w), 1379(s) [νs (COO)], 1346(s) [δ(C=C/C=N)], 1311(m), 1279(m), 1226(w), 1210(w), 1184(w), 1158(w), 1141(w), 1126(w), 1072(w) [δip (C-H)], 1046(w), 1030(w), 1012(w), 1002(m) [δip (C-H)], 971(w), 931(w), 838(w), 794(w), 765(s) [δoop (C-H)], 733(m), 688(s) [δoop (C-H)], 622(m), 591(m). 1 H NMR (360 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 9.30 [2H, s, NHACA ], 8.77 [2H, d. 3 J = 5.8 Hz, o-Hpy ,4-Phpy ], 7.91 [2H, d, 3 J = 5.8 Hz, m-Hpy ,4-Phpy ], 7.86 [2H, d, 3 J = 7.6 Hz, o-Hph ,4-Phpy ], 7.55 [7H, m, o-HACA + m-Hph ,4-Phpy + p-Hph ,4-Phpy ], 7.36 [4H, t, 3 J = 7.5 Hz, m-HACA ], 7.30 [2H, s, NH-C-CHACA ], 7.27 [2H, d, 3 J = 7.5 Hz, p-HACA ], 1.99 [6H, s, CO-CH3 ,ACA ]. 13 C{1 H} NMR (400 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 170.8 [NH-COACA ], 168.5 [CO2 ,ACA ], 150.0 [o-Cpy ,4-Phpy ], 149.1 [Ph-Cpy ,4-Phpy ], 136.4 [Py-Cph ,4-Phpy ], 135.1 [O2 C-CACA ], 130.0 [o-CACA ], 129.8 [HN-C-CH-CACA ], 129.4 [m-Cph ,4-Phpy + p-Cph ,4-Phpy ], 129.1 [p-CACA ], 128.4 [m-CACA ], 128.2 [NH-C-CHACA ], 127.2 [o-Cph ,4-Phpy ], 122.1 [m-Cpy ,4-Phpy ], 23.1 [CO-CH3 ,ACA ]. DEPT-135 NMR (360 MHz; dmso-d6 ; Me4 Si, 298 K): δ = 149.9 [o-Cpy ,4-Phpy ], 130.0 [o-CACA ], 129.4 [m-Cph ,4-Phpy + p-Cph ,4-Phpy ], 129.1 [p-CACA ], 128.4 [m-CACA ], 128.2 [O2 C-C-CACA ], 127.2 [o-Cph ,4-Phpy ], 122.1 [m-Cpy ,4-Phpy ], 23.1 [CO-CH3 ,ACA ]. 4.3. Synthesis of [Zn3 (µ-ACA)6 (4-Phpy)2 ] (2) Method A. A small amount of 1 (56.5 mg, 0.0449 mmol) was dissolved in CH3 CN (50 mL) using a water bath at 60 ◦ C. The solution was heated and stirred for 4 h until 1 is dissolved. The clear solution was stirred for 3 h at RT and then was kept on the fridge for 14 h. The solution was evaporated under vacuum until a white crystalline powder precipitated. The powder was washed with 10 mL of cold CH3 CN, filtered and dried under vacuum. Suitable colorless crystals of [Zn3 (µ-ACA)6 (4-Phpy)2 ]·4CH3 CN (2·4CH3 CN) were obtained by recrystallization of 1 in CH3 CN and slow evaporation of the solution at RT for 8 days. Yield: 37.8 mg (77%) (based on Zn). Method B. A hot CH3 CN solution (30 mL, 60 ◦ C) of Zn(OAc)2 ·2H2 O (150 mg, 0.683 mmol) was added dropwise to a solution of HACA (280 mg, 1.36 mmol) and 4-Phpy (217 mg, 1.40 mmol) in CH3 CN (20 mL) as solvent at RT. After two minutes, a white solid precipitated (2) and the dispersion was stirred for 18 h. The white precipitate was washed with 10 mL of cold CH3 CN, filtered and dried under vacuum. Suitable colorless crystals of [Zn3 (µ-ACA)6 (4-Phpy)2 ]·4CH3 CN (2·4CH3 CN) were obtained by recrystallization of 2 in CH3 CN and slow evaporation of the solution at RT for 6 days. Yield: 298 mg (76%) (based on Zn). Molecules 2020, 25, 3615 18 of 23 Elemental analysis calc.(%) for C88 H78 Zn3 N8 O18 (1731.77): C 61.03, H 4.54, N 6.47; found: C 60.77, H 4.46, N 6.32. FTIR-ATR (wavenumber, cm−1 ): 3386(w), 3236(m) [ν(N-H)], 3054–3021(br) [ν(C-H)ar ], 2980–2929(br) [ν(C-H)alk + ν(C-H)al ], 1678(m) [ν(C=O)], 1653(sh), 1616(w), 1573(s) [νas (COO)], 1536(m) [ν(C=C/C=N)], 1505(m), 1488(m), 1446(w), 1390(s) [νs (COO)], 1366(s), 1347(s) [δ(C=C/C=N)], 1270(m), 1258(sh), 1228(w), 1212(m), 1182(w), 1157(w), 1122(w), 1075(w) [δip (C-H)], 1030(w) [δip (C-H)], 1013(w) [δip (C-H)], 959(w), 925(w), 897(w), 838(w), 791(m), 760(s) [δoop (C-H)], 746(sh), 688(s) [δoop (C-H)], 624(m), 616(sh), 590(s), 579(s), 561(m). 1 H NMR (400 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 9.19 [6H, s, NHACA ], 8.66 [4H, d. 3 J = 6.2 Hz, o-Hpy ,4-Phpy ], 7.82 [4H, d, 3 J = 7.3 Hz, o-Hph ,4-Phpy ], 7.76 [4H, d, 3 J = 6.2 Hz, m-Hpy ,4-Phpy ], 7.53 [18H, m, o-HACA + m-Hph ,4-Phpy + p-Hph ,4-Phpy ], 7.35 [12H, t, 3 J = 7.7 Hz, m-HACA ], 7.29 [6H, d, 3 J = 7.3 Hz, p-HACA ], 7.25 [6H, s, NH-C-CHACA ], 1.96 [18H, s, CO-CH3 ,ACA ]. 13 C{1 H} NMR (360 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 170.7 [NH-COACA ], 168.5 [CO2 ,ACA ], 150.0 [o-Cpy ,4-Phpy ], 148.8 [Ph-Cpy ,4-Phpy ], 136.6 [Py-Cph ,4-Phpy ], 135.1 [O2 C-CACA ], 129.9 [o-CACA ], 129.7 [HN-C-CH-CACA ], 129.4 [m-Cph ,4-Phpy + p-Cph ,4-Phpy ], 129.1 [p-CACA ], 128.4 [m-CACA ], 128.2 [NH-C-CHACA ], 127.2 [o-Cph ,4-Phpy ], 121.9 [m-Cpy ,4-Phpy ], 23.1 [CO-CH3 ,ACA ]. DEPT-135 NMR (360 MHz; dmso-d6 ; Me4 Si, 298 K): δ = 150.0 [o-Cpy ,4-Phpy ], 129.9 [o-CACA ], 129.4 [m-Cph ,4-Phpy + p-Cph ,4-Phpy ], 129.1 [p-CACA ], 128.4 [m-CACA ], 128.2 [O2 C-C-CACA ], 127.2 [o-Cph ,4-Phpy ], 122.0 [m-Cpy ,4-Phpy ], 23.1 [CO-CH3 ,ACA ]. 4.4. Synthesis of [Zn3 (µ-ACA)6 (EtOH)2 ] (3) A small amount of 1 (57.1 mg, 0.0454 mmol) was dissolved in EtOH (40 mL). The solution was stirred for 2 h until 1 is dissolved. The clear solution was stirred for 17 h at RT and then evaporated under vacuum and kept on the fridge for 3 days. After this time, a small amount of a white crystalline powder (3) was obtained. The powder was washed with 10 mL of cold EtOH, filtered and dried under vacuum. Suitable colorless crystals of [Zn3 (µ-ACA)6 (EtOH)2 ]·4EtOH (3·4EtOH) were obtained by recrystallization of 1 and slow evaporation of the solution at RT for 2 days. Yield: 18.9 mg (46%) (based on Zn). Elemental analysis calc.(%) for C70 H72 Zn3 N6 O20 (1513.52): C 55.55, H 4.79, N 5.55; found: C 55.37, H 4.64, N 5.42. FTIR-ATR (wavenumber, cm−1 ): 3308–3275(w) [ν(O-H)EtOH], 3227(w) [ν(N-H)], 3166(w), 3055–3026(w) [ν(C-H)ar ], 2976–2881(w) [ν(C-H)alk + ν(C-H)al ], 1674(w), 1652(w) [ν(C=O)], 1585(sh), 1563(s) [νas (COO)], 1539(s) [ν(C=C/C=N)], 1516(sh), 1492(m), 1446(m), 1392(s) [νs (COO)], 1345(s) [δ(C=C/C=N)], 1274(m), 1212(w), 1183(w), 1119(w), 1091(w), 1080(w), 1047(m) [δip (C-H)], 1013(w) [δip (C-H)], 962(w) [δip (C-H)], 926(w), 878(w), 846(w), 790(m), 764(m) [δoop (C-H)], 744(m) [δoop (C-H)], 689(s) [δoop (C-H)], 591(s), 580(sh). 1 H NMR (360 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 9.20 [6H, s, NHACA ], 7.51 [12H, d, 3 J = 6.9 Hz, o-HACA ], 7.35 [12H, t, 3 J = 7.1 Hz, m-HACA ], 7.29 [6H, d, 3 J = 6.8 Hz, p-HACA ], 7.24 [6H, s, NH-C-CHACA ], 4.39 [2H, t, 3 J = 4.9 Hz, OH,EtOH ], 3.45 [4H, m, CH2 ,EtOH ], 1.95 [18H, s, CO-CH3 ,ACA ], 1.05 [6H, t, 3 J = 7.0 Hz, CH3 ,EtOH ]. 13 C{1 H} NMR (360 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 170.6 [NH-COACA ], 168.5 [CO2 ,ACA ], 135.1 [O2 C-CACA ], 129.7 [HN-C-CH-CACA ], 129.4 [o-CACA ], 129.2 [p-CACA ], 128.4 [m-CACA ], 128.3 [NH-C-CHACA ], 56.1 [CH2 ,EtOH ], 23.1 [CO-CH3 ,ACA ], 18.6 [CH3 ,EtOH ]. DEPT-135 NMR (360 MHz; dmso-d6 ; Me4 Si; 298 K): δ = 129.4 [o-CACA ], 129.2 [p-CACA ], 128.4 [m-CACA ], 128.3 [NH-C-CHACA ], 56.1 [CH2 ,EtOH ], 23.1 [CO-CH3 ,ACA ], 18.6 [CH3 ,EtOH ]. 5. X-ray Crystallographic Data For compounds 1, 2·4CH3 CN, and 3·4EtOH, a colorless prism-like specimens were used for the X-ray crystallographic analysis. The X-ray intensity data were measured on a D8 Venture system equipped with a multilayer monochromate and a Mo microfocus (λ = 0.71073 Å). For 1, 2·4CH3 CN, and 3·4EtOH, the frames were integrated with the Bruker SAINT Software package using a narrow-frame algorithm. All hydrogen atoms were refined using a riding model (AFIX) with an isotropic temperature factor equal to 1.2, the equivalent temperature factor of the atom to which are linked and thus, the bond lengths of X-H were fixed. The structures were solved and refined using SHELX (version 2018/3) [66]. For 1, the integration of the data using a monoclinic unit cell yielded a total of 80,518 reflections to a maxim θ angle of 30.70◦ (0.70 Å), of which 18,035 were independent Molecules 2020, 25, 3615 19 of 23 (average redundancy 4.465, completeness = 98.4%), Rint = 20.23%, Rsig = 19.69%) and 8129 (45.07%) were greater than 2σ(F2 ). The calculated minimum and maximum transmission coefficients (based on crystal size) are 0.6289 and 0.7461. For 2·4CH3 CN, the integration of the data using a monoclinic unit cell yielded a total of 141282 reflections to a maxim θ angle of 30.55◦ (0.70 Å), of which 13913 were independent (average redundancy 10.155, completeness = 99.8%), Rint = 6.04%, Rsig = 3.35%) and 10988 (78.98%) were greater than 2σ(F2 ). The calculated minimum and maximum transmission coefficients (based on crystal size) are 0.6411 and 0.7461. For 3·4EtOH, the integration of the data using a monoclinic unit cell yielded a total of 25525 reflections to a maxim θ angle of 30.97◦ (0.69 Å), of which 25,525 were independent (average redundancy 1.000, completeness = 99.7%), Rint = 4.21%, Rsig = 5.58%) and 20515 (80.37%) were greater than 2σ(F2 ). The calculated minimum and maximum transmission coefficients (based on crystal size) are 0.6349 and 0.7461. For 1, 2·4CH3 CN and 3·4EtOH, the final cell constants and volume are based upon the refinement of the XYZ-centroids of reflections above 2θ σ(I). Data were corrected for absorption effects using the Multi-Scan method (SADABS). Crystal data and relevant details of structure refinement for compounds 1, 2·4CH3 CN and 3·4EtOH, are reported in Table 5. CCDC 2016324 (1), 2016325 (2·4CH3 CN), and 2016323 (3·4EtOH) contain the Supplementary Information of this paper. Molecular graphics were generated using Mercury 4.3.1 software [67,68] with POV-Ray Package [69]. Color codes for all molecular graphics: dark blue (Zn), red (O), light blue (N), dark gray (C), and white (H). Table 5. Crystal data and structure refinement for 1, 2·4CH3 CN, and 3·4EtOH. 1 2·4CH3 CN 3·4EtOH Empirical Formula C66 H58 N6 O12 Zn2 C96 H90 N12 O18 Zn3 C78 H96 N6 O24 Zn3 Formula weight 1257.92 1895.90 1697.71 T (K) 293(2) 100(2) 100(2) Wavelength (Å) 0.71073 0.71073 0.71073 System, space group Monoclinic, P21 /c Monoclinic, P21 /c Monoclinic, P21 Unit cell dimensions a (Å) 10.1338(8) 15.7748(10) 13.2110(4) b (Å) 24.469(2) 23.7227(15) 24.9706(9) c (Å) 25.598(2) 13.1019(8) 13.3721(4) β (◦ ) 111.681(4) 112.111(2) 113.6880(10) V (Å3 ) 5898.3(8) 4542.4(5) 4039.6(2) Z 4 2 2 Dcalc (mg/m3 ) 1.417 1.386 1.396 µ (mm−1 ) 0.883 0.861 0.962 F (000) 2608 1968 1776 Crystal size (mm−3 ) 0.141×0.052×0.032 0.150×0.368×0.398 0.142×0.252×0.505 −11 <= h <= 14, −34 <= −21 <= h <= 22, −33 <= −19 <= h <= 19, −36 <= hkl ranges k <= 34, −36 <= l <= 36 k <= 33, −18 <= l <= 17 k <= 36, −19 <= l <= 19 2θ range (◦ ) 2.176 to 30.705 2.211 to 30.554 2.452 to 30.972 Reflections collected/ 80518/18035/ 0.2023 141282/13913/ 0.0604 25525/25525/ 0.0421 unique/[Rint ] Completeness to θ (%) 98.4 99.8 99.7 Absorption correction Semi-empirical Semi-empirical Semi-empirical Max. and min. 0.7461 and 0.6289 0.7461 and 0.6411 0.7461 and 0.6349 transmission Molecules 2020, 25, 3615 20 of 23 Table 5. Cont. Full-matrix least-square Full-matrix least-square Full-matrix least-square Refinement method on F2 on F2 on F2 Data/Restrains/Parameters 18035/0/780 13913/0/588 25525/17/1016 Goodness-on-fit on F2 1.038 1.043 1.032 R1 = 0.0756 R1 = 0.0442 R1 = 0.0348 Final R indices [I > 2σ(I)] wR2 = 0.1335 wR2 = 0.1155 wR2 = 0.0823 R1 = 0.2135 R1 = 0.0639 R1 = 0.0473 R indices (all data) wR2 = 0.1958 wR2 = 0.1259 wR2 = 0.0885 Extinction coefficient n/a n/a n/a Largest Diff. peak and 0.986 and −1.239 0.538 and −2.492 0.726 and −1.656 hole (e. Å−3 ) Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/25/16/3615/s1, Tables S1–S3. Intramolecular interactions of compounds 1, 2·4CH3 CN, and 3·4EtOH, Figure S1. HR-ESI-MS spectra of compound 1; Figures S2–S4. FTIR-ATR spectra of compounds 1–3; Figures S5–S7. 1H NMR spectra of compounds 1–3; Figures S8–S10. 13C{1 H} NMR and DEPT-135 spectra of compounds 1–3; Figures S11 and S12. Hirshfeld surface dnorm and ESP representations of the co-crystallized solvent molecules in 2·4CH3 CN and 3·4EtOH. Figures S13 and S14. Hirshfeld surface curvedness mappings with their corresponding ESP representations of 2·4CH3 CN and 3·4EtOH; Figures S15–S17. Thermal ellipsoid plots of 1, 2·4CH3 CN, and 3·4EtOH. Complete information about the crystal structure and molecular geometry is available in. cif format as Supporting Information. Author Contributions: Conceptualization, J.P.; methodology, D.E.; software, D.E.; validation, J.P. and T.C.; formal analysis, D.E. and M.F.-B; investigation, D.E.; resources, J.P. and T.C.; data curation, D.E. and M.F.-B.; writing—original draft preparation, D.E.; writing—review and editing, J.P. and T.C.; visualization, D.E.; supervision, J.P.; project administration, J.P.; funding acquisition, J.P. All authors have read and agreed to the published version of the manuscript. Funding: This work was financed by the CB615921 project, the CB616406 project from “Fundació La Caixa” and the 2017SGR1687 project from the Generalitat de Catalunya. D.E. acknowledges the PIF pre-doctoral fellowship from the Universitat Autònoma de Barcelona. Conflicts of Interest: The authors declare no conflict of interest. References 1. Farrusseng, D.; Aguado, S.; Pinel, C. Metal-organic frameworks: Opportunities for catalysis. Angew. Chem. Int. Ed. 2009, 48, 7502–7513. [CrossRef] 2. Adil, K.; Belmabkhout, Y.; Pillai, R.S.; Cadiau, A.; Bhatt, P.M.; Assen, A.H.; Maurin, G.; Eddaoudi, M. Gas/vapour separation using ultra-microporous metal-organic frameworks: Insights into the structure/separation relationship. Chem. Soc. Rev. 2017, 46, 3402–3430. [CrossRef] 3. He, Y.; Zhou, W.; Qian, G.; Chen, B. Methane storage in metal-organic frameworks. Chem. Soc. Rev. 2014, 43, 5657–5678. [CrossRef] 4. Mínguez Espallargas, G.; Coronado, E. Magnetic functionalities in MOFs: From the framework to the pore. Chem. Soc. Rev. 2018, 47, 533–557. [CrossRef] 5. Zhang, M.; Feng, G.; Song, Z.; Zhou, Y.-P.; Chao, H.-Y.; Yuan, D.; Tan, T.T.Y.; Guo, Z.; Hu, Z.; Tang, B.Z.; et al. Two-dimensional metal-organic framework with wide channels and responsive turn-on fluorescence for the chemical sensing of volatile organic compounds. J. Am. Chem. Soc. 2014, 136, 7241–7244. [CrossRef] 6. Hendon, C.H.; Rieth, A.J.; Korzyński, M.D.; Dincǎ, M. Grand challenges and future opportunities for metal-organic frameworks. Acs Cent. Sci. 2017, 3, 554–563. [CrossRef] [PubMed] 7. Ricco, R.; Pfeiffer, C.; Sumida, K.; Sumby, C.J.; Falcaro, P.; Furukawa, S.; Champness, N.R.; Doonan, C.J. Emerging applications of metal-organic frameworks. Cryst. Eng. Comm. 2016, 18, 6532–6542. [CrossRef] 8. Lian, X.; Fang, Y.; Joseph, E.; Wang, Q.; Li, J.; Banerjee, S.; Lollar, C.; Wang, X.; Zhou, H.C. Enzyme-MOF (metal-organic framework) composites. Chem. Soc. Rev. 2017, 46, 3386–3401. [CrossRef] [PubMed] Molecules 2020, 25, 3615 21 of 23 9. Ha, J.; Lee, J.H.; Moon, H.R. Alterations to secondary building units of metal-organic frameworks for the development of new functions. Inorg. Chem. Front. 2020, 7, 12–27. [CrossRef] 10. Kalmutzki, M.J.; Hanikel, N.; Yaghi, O.M. Secondary building units as the turning point in the development of the reticular chemistry of MOFs. Sci. Adv. 2018, 4, 1–16. [CrossRef] [PubMed] 11. Tranchemontagne, D.J.; Mendoza-Cortés, J.L.; O’Keeffe, M.; Yaghi, O.M. Secondary building units, nets and bonding in the chemistry of metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1257–1283. [CrossRef] [PubMed] 12. Desiraju, G.R. Supramolecular synthons in crystal engineering-a new organic synthesis. Angew. Chem. Int. Ed. 1995, 34, 2311–2327. [CrossRef] 13. Blake, A.J.; Champness, N.R.; Hubberstey, P.; Li, W.S.; Withersby, M.A.; Schröder, M. Inorganic crystal engineering using self-assembly of tailored building-blocks. Coord. Chem. Rev. 1999, 183, 117–138. [CrossRef] 14. Wittmann, T.; Tschense, C.B.L.; Zappe, L.; Koschnick, C.; Siegel, R.; Stäglich, R.; Lotsch, B.V.; Senker, J. Selective host-guest interactions in metal-organic frameworks via multiple hydrogen bond donor-acceptor recognition sites. J. Mater. Chem. A 2019, 7, 10379–10388. [CrossRef] 15. Liu, J.; Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C.Y. Applications of metal-organic frameworks in heterogeneous supramolecular catalysis. Chem. Soc. Rev. 2014, 43, 6011–6061. [CrossRef] 16. Eddaoudi, M.; Moler, D.B.; Li, H.; Chen, B.; Reineke, T.M.; O’Keeffe, M.; Yaghi, O.M. Modular chemistry: Secondary building units as a basis for the design of highly porous and robust metal-organic carboxylate frameworks. Acc. Chem. Res. 2001, 34, 319–330. [CrossRef] 17. Rigamonti, L.; Carlino, S.; Halibi, Y.; Demartin, F.; Castellano, C.; Ponti, A.; Pievo, R.; Pasini, A. Copper 1D coordination polymers and dimers: Role of the carboxylate and the ammonium cation, crystal structures and magnetic studies. Polyhedron 2013, 53, 157–165. [CrossRef] 18. Lippard, S.J. Oxo-bridged polyiron centers in biology and chemistry. Angew. Chem. Int. Ed. Engl. 1988, 27, 344–361. [CrossRef] 19. Reisner, E.; Telser, J.; Lippard, S.J. A planar carboxylate-rich tetrairon(II) complex and its conversion to linear triiron(II) and paddlewheel diiron(II) complexes. Inorg. Chem. 2007, 46, 10754–10770. [CrossRef] 20. Wang, X.-W.; Chen, F.-P.; Chen, L.; Chen, J.-Z.; Jiang, W.-J.; Cai, T.-J.; Deng, Q. Crystal structures and fluorescent properties of two linear trinuclear zinc(II) complexes. J. Mol. Struct. 2007, 842, 75–80. [CrossRef] 21. Kim, Y.; Jung, D.-Y. Structure evolution and coordination modes of metal-carboxylate frameworks with robust linear trinuclear complexes as building units. Cryst. Eng. Comm. 2012, 14, 4567–4569. [CrossRef] 22. Davies, R.P.; Less, R.J.; Lickiss, P.D.; White, A.J.P. Framework materials assembled from magnesium carboxylate building units. Dalton Trans. 2007, 2528–2535. [CrossRef] 23. Rardin, R.L.; Bino, A.; Poganiuch, P.; Tolman, W.B.; Liu, S.; Lippard, S.J. Synthesis and characterization of the linear trinuclear complexes [M3 II (O2 CCH3 )6 (biphme)2 ], M = Mn, Fe. Angew. Chem Int. Ed. Engl. 1990, 29, 812–814. [CrossRef] 24. Ménage, S.; Vitols, S.E.; Bergerat, P.; Codjovi, E.; Kahn, O.; Girerd, J.J.; Guillot, M.; Solans, X.; Calvet, T. Structure of the linear trinuclear complex MnII 3 (CH3 CO2 )6 (bpy)2 . determination of the J electron-exchange parameter through magnetic susceptibility and high-field magnetization measurements. Inorg. Chem. 1991, 30, 2666–2671. [CrossRef] 25. Clegg, W.; Little, I.R.; Straughan, B.P. Zinc carboxylate complexes: Structural characterization of the mixed-metal linear trinuclear complexes MZn2 (crot)6 (base)2 (M = Mn, Co, Ni, Zn, Cd, Mg, Ca, Sr; crot- = crotonate(l-); base = quinoline, 6-methylquinoline). Inorg. Chem. 1988, 27, 1916–1923. [CrossRef] 26. Chen, Y.; Wang, X.W.; Hu, B.; Chen, F.-P.; Chen, J.-Z.; Chen, L. Synthesis, characterization and crystal structure of a new linear trinuclear manganese(II) complex, [Mn3 (PhCH=CHCO2 )6 (BPY)2 ]·H2 O (BPY=2,2-bipyridine). J. Coord. Chem. 2007, 60, 2401–2408. [CrossRef] 27. Wang, X.-W.; Chen, Y.; Chen, J.-Z.; Liu, J.-H.; Han, L. Structure and stability of a linear trinuclear cobalt(II) complex: Co3 (PhCH=CHCO2 )6 (bpy)2 . Z. Nat.. 2008, 63b, 129–133. [CrossRef] 28. Vasile Scăeteanu, G.; Chifiriuc, M.C.; Bleotu, C.; Kamerzan, C.; Mărutescu, L.; Daniliuc, C.G.; Maxim, C.; Calu, L.; Olar, R.; Badea, M. Synthesis, structural characterization, antimicrobial activity, and in vitro biocompatibility of new unsaturated carboxylate complexes with 2,20 -bipyridine. Molecules 2018, 23, 157. [CrossRef] Molecules 2020, 25, 3615 22 of 23 29. Konidaris, K.F.; Kaplanis, M.; Raptopoulou, C.P.; Perlepes, S.P.; Manessi-Zoupa, E.; Katsoulakou, E. Dinuclear versus trinuclear complex formation in zinc(II) benzoate/pyridyl oxime chemistry depending on the position of the oxime group. Polyhedron 2009, 28, 3243–3250. [CrossRef] 30. Clegg, W.; Little, I.R.; Straughan, B.P. Zinc carboxylate complexes: structural characterisation of some binuclear and linear trinuclear complexes. J. Chem. Soc. Dalton Trans. 1986, 6, 1283–1288. [CrossRef] 31. Tarushi, A.; Totta, X.; Raptopoulou, C.P.; Psycharis, V.; Psomas, G.; Kessissoglou, D.P. Structural features of mono- and tri-nuclear Zn(II) complexes with a non-steroidal anti-inflammatory drug as ligand. Dalton Trans. 2012, 41, 7082–7091. [CrossRef] [PubMed] 32. Zeleňák, V.; Sabo, M.; Massa, W.; Llewellyn, P. Preparation, characterisation and crystal structure of two zinc(II) benzoate complexes with pyridine-based ligands nicotinamide and methyl-3-pyridylcarbamate. Inorg. Chim. Acta 2004, 357, 2049–2059. [CrossRef] 33. Smolková, R.; Zeleňák, V.; Gyepes, R.; Sabolová, D.; Imrichová, N.; Hudecová, D.; Smolko, L. Synthesis, characterization, DNA binding, topoisomerase I inhibition and antimicrobial activity of four novel zinc(II) fenamates. Polyhedron 2018, 141, 230–238. [CrossRef] 34. Smolková, R.; Zeleňák, V.; Smolko, L.; Sabolová, D.; Kuchár, J.; Gyepes, R. Novel Zn(II) complexes with non-steroidal anti-inflammatory ligand, flufenamic acid: Characterization, topoisomerase I inhibition activity, DNA and HSA binding studies. J. Inorg. Biochem. 2017, 177, 143–158. [CrossRef] 35. Melnik, M.; Györyová, K.; Skorsepa, J.; Holloway, C.E. Zinc(II) compounds: Classification and analysis of crystallographic and structural data. J. Coord. Chem. 1995, 35, 179–279. [CrossRef] 36. Song, W.; Cui, X.-Z.; Wang, X.-G.; Liang, L.; Yang, E.-C.; Zhao, X.-J. Structural diversity of Zn(II)/Cd(II) coordination polymers constructed from mixed ligand systems of conformationally flexible azo functionalized bis-imidazolate and dicarboxylates. Polyhedron 2017, 127, 266–277. [CrossRef] 37. Zhang, D.; Xue, Z.-Z.; Pan, J.; Li, J.-H.; Wang, G.-M. Dual ligand strategy for constructing a series of d10 coordination polymers: syntheses, structures, photoluminescence, and sensing properties. Cryst. Growth Des. 2018, 18, 1882–1890. [CrossRef] 38. Qi, Y.-J.; Wang, Y.-J.; Li, X.-X.; Zhao, D.; Sun, Y.-Q.; Zheng, S.-T. Two d10 metal-organic frameworks as low-temperature luminescent molecular thermometers. Cryst. Growth Des. 2018, 18, 7383–7390. [CrossRef] 39. Chen, Y.; Huang, P.; Chen, H.; Wang, S.; Wang, H.; Guo, J.; Zhang, X.; Zhang, S.; Yan, J.; Xia, J.; et al. Assessment of the biocompatibility and biological effects of biodegradable pure Zinc material in the colorectum. Acs Biomater. Sci. Eng. 2018, 4, 4095–4103. [CrossRef] 40. Tian, X.; Hussain, S.; de Pace, C.; Ruiz-Pérez, L.; Battaglia, G. ZnII complexes for bioimaging and correlated applications. Chem. Asian J. 2019, 14, 509–526. [CrossRef] 41. Soldevila-Sanmartín, J.; Calvet, T.; Font-Bardia, M.; Domingo, C.; Ayllón, J.A.; Pons, J. Modulating: P-hydroxycinnamate behavior as a ditopic linker or photoacid in copper(II) complexes with an auxiliary pyridine ligand. Dalton Trans. 2018, 47, 6479–6493. [CrossRef] [PubMed] 42. Ejarque, D.; Sánchez-Férez, F.; Calvet, T.; Font-Bardia, M.; Pons, J. Exploring the reactivity of α-Acetamidocinnamic acid and 4-Phenylpyridine with Zn(II) and Cd(II). Inorg. Chim. Acta 2020, 509, 119695. [CrossRef] 43. Rivera, V.M.; Ruelas-Leyva, J.P.; Fuentes, G.A. Pd and Ru complexes bearing axially chiral ligands for the asymmetric hydrogenation of C=C and C=O double bonds. Catal. Today 2013, 213, 109–114. [CrossRef] 44. Bhaduri, S.; Lahiri, G.K.; Munshi, P. Hydrogenation of α-acetamidocinnamic acid with polystyrene-supported rhodium catalysts. J. Organomet. Chem. 2000, 606, 151–155. [CrossRef] 45. Madarász, J.; Nánási, B.; Kovács, J.; Balogh, S.; Farkas, G.; Bakos, J. Immobilized phosphine–phosphite rhodium complexes: Highly active and enantioselective catalysts for asymmetric hydrogenation under continuous flow conditions. Mon. Chem. 2018, 149, 19–25. [CrossRef] 46. Inoue, M.; Ohta, K.; Ishizuka, N.; Enomoto, S. Asymmetric hydrogenation of α-Acetamidocinnamic acid with chiral Rhodium complexes of DIOP and BPPM on charcoal. Chem. Pharm. Bull. 1983, 31, 3371–3376. [CrossRef] 47. Gheorghiu, C.C.; Machado, B.F.; Salinas-Martínez De Lecea, C.; Gouygou, M.; Román-Martínez, M.C.; Serp, P. Chiral rhodium complexes covalently anchored on carbon nanotubes for enantioselective hydrogenation. Dalton Trans. 2014, 43, 7455–7463. [CrossRef] 48. Nakamichi, K.; Nabe, K.; Yamada, S.; Tosa, T.; Chibata, I. L-Phenylalanine formation from acetamidocinnamic acid by newly isolated bacteria. Appl. Microbiol. Biotechnol. 1984, 19, 100–105. [CrossRef] Molecules 2020, 25, 3615 23 of 23 49. Nishida, Y.; Nakamichi, K.; Nabe, K.; Tosa, T. Continuous production of L-phenylalanine from acetamidocinnamic acid using co-immobilized cells of Corynebacterium sp. and Paracoccus denitrificans. Appl. Biochem. Biotechnol. 1987, 9, 479–483. [CrossRef] 50. Deacon, G.B.; Phillips, R.J. Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination. Coord. Chem. Rev. 1980, 33, 227–250. [CrossRef] 51. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds: Part A: Theory and Applications in Inorganic Chemistry, 6th ed.; Wiley Interscience: Hoboken, NJ, USA, 2000. 52. Williams, D.H.; Fleming, I. Spectroscopic Methods in Organic Chemistry, 5th ed.; McGrawHill: London, UK, 1995. 53. Yang, L.; Powell, D.R.; Houser, R.P. Structural variation in copper(I) complexes with pyridylmethylamide ligands: Structural analysis with a new four-coordinate geometry index, τ4 . Dalton Trans. 2007, 955–964. [CrossRef] [PubMed] 54. Rivas, J.C.M.; Salvagni, E.; Parsons, S. Investigating the effect of hydrogen bonding environments in amide cleavage reactions at zinc(II) complexes with intramolecular amide oxygen co-ordination. Dalton Trans. 2004, 4185–4192. [CrossRef] [PubMed] 55. Girma, K.B.; Lorenz, V.; Blaurock, S.; Edelmann, F.T. Coordination chemistry of acrylamide. 5. Crystal structures of complexes of metal(II) perchlorates and tetrafluoroborates with acrylamide. Z. Anorg. Allg. Chem. 2006, 632, 1874–1878. [CrossRef] 56. Pal Chaudhuri, U.; Whiteaker, L.R.; Mondal, A.; Klein, E.L.; Powell, D.R.; Houser, R.P. Substituted pyridylmethylamide ligands and their zinc complexes. Inorg. Chim. Acta 2007, 360, 3610–3618. [CrossRef] 57. Zeleňák, V.; Císařová, I.; Llewellyn, P. Diversity of carboxylate coordination in two novel zinc(II) cinnamate complexes. Inorg. Chem. Commun. 2007, 10, 27–32. [CrossRef] 58. Chakraborty, G.; Mandal, S.K. Neutral luminescent metal-organic frameworks: Structural diversification, photophysical properties, and sensing applications. Inorg. Chem. 2017, 56, 14556–14566. [CrossRef] 59. Steiner, T. The hydrogen bond in the solid state. Angew. Chem. Int. Ed. 2002, 41, 48–76. [CrossRef] 60. Morse, P.M.; Girolami, G.S. Are d0 ML6 complexes always octahedral? The X-ray structure of trigonal-prismatic [Li(tmed)]2 [ZrMe6 ]. J. Am. Chem. Soc. 1989, 111, 4114–4116. [CrossRef] 61. Friese, J.C.; Krol, A.; Puke, C.; Kirschbaum, K.; Giolando, D.M. Trigonal prismatic vs octahedral coordination geometry: Syntheses and structural characterization of hexakis(arylthiolato) zirconate complexes. Inorg. Chem. 2000, 39, 1496–1500. [CrossRef] 62. Wolff, S.K.; Grimwood, D.J.; McKinnon, J.J.; Jayatilaka, D.; Spackman, M.A. CrystalExplorer17.5; University of Western, Australia: Crawley, Australia, 2017. 63. Jayatilaka, D.; Grimwood, D.J. Tonto: A fortran based object-oriented system for quantum chemistry and crystallography. Comput. Sci.-Iccs 2003, 4, 142–151. 64. Spackman, M.A.; McKinnon, J.J.; Jayatilaka, D. Electrostatic potentials mapped on Hirshfeld surfaces provide direct insight into intermolecular interactions in crystals. CrystEngComm 2008, 10, 377–388. [CrossRef] 65. Spackman, M.A.; McKinnon, J.J. Fingerprinting intermolecular interactions in molecular crystals. CrystEngComm 2002, 4, 378–392. [CrossRef] 66. Sheldrick, G.M. A short history of SHELX. Acta Cryst. 2008, A64, 112–122. [CrossRef] [PubMed] 67. Macrae, C.F.; Edgington, P.R.; McCabe, P.; Pidcock, E.; Shields, G.P.; Taylor, R.; Towler, M.; van de Streek, J. Mercury: Visualization and analysis of crystal structures. J. Appl. Cryst. 2006, 39, 453–457. [CrossRef] 68. Macrae, C.F.; Bruno, I.J.; Chisholm, J.A.; Edgington, P.R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P.A. Mercury CSD 2.0 — new features for the visualization and investigation of crystal structures. J. Appl. Cryst. 2008, 41, 466–470. [CrossRef] 69. Persistence of Vision Pty. Ltd. Persistence of Vision (TM) Raytracer; Persistence of Vision Pty. Ltd.: Williamstown, Australia, 2004. Sample Availability: Samples of the compounds are available from the authors. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).