Journal of Molecular Structure 1284 (2023) 135419
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Variable behaviour of a flexible bispyrazole ligand: A Co(II) polymer
and a unique Cu(II) penta-coordinated dimer
Joan Soldevila-Sanmartín a, Teresa Calvet b, Mercè Font-Bardia c,
Duane Choquesillo-Lazarte d, Josefina Pons a,∗
a
Departament de Química, Universitat Autònoma de Barcelona, 08913 Bellaterra, Barcelona, Spain
b
Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain
c
Unitat de Difracció de Raigs-X, Centres Científics i Tecnològics de la Universitat de Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís, 1-3, 08028
Barcelona, Spain
d
Laboratorio de Estudios Cristalógraficos, IACT (CSIC-Universidad de Granada), Avda. de las Palmeras 4, Armilla, 18100 Granada, Spain
a r t i c l e i n f o a b s t r a c t
Article history: Hoping to highlight the flexibility of a bispyrazole ligand possessing an ether chain including a weak
Received 31 January 2023 spot (1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxabutyl]benzene (L)), its reactivity against coordinatively
Revised 20 March 2023
flexible metal centres has been assayed. Thus Co(II) and Cu(II) coordination complexes of L have been
Accepted 23 March 2023
synthesized and fully characterized by analytical and spectroscopical methods. Their X-ray crystal struc-
Available online 24 March 2023
ture elucidation has allowed to ascertain that while the Co(II) compound {[Co(L)Cl2 ]·1/2H2 O}n (1) pos-
Keywords: sesses a polymeric structure, much like its Zn(II), Cd(II) and Hg(II) analogues, the Cu(II) compound
Co(II) complexes [Cu2 LCl4 ] (2) displays a completely unexpected dimeric architecture. The previously unreported coordi-
Cu(II) complexes nation mode of the ligand in the Cu(II) compound causes dramatical changes in the morphology of the
N,O-hybrid ligands resulting complexes. Their crystal structures are discussed in deep, and the causes behind their differing
Pyrazole ligands architectures are examined through comparison with bibliographical references.
© 2023 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1. Introduction ondary building units for the development of extended frameworks
[15,16]. Over the last two decades, our group has been working
The understanding of the structure-properties relationship in on the synthesis of such ligands, specializing on those contain-
coordination compounds has grown at an astonishing rate during ing pyrazoles as the main functional group. As such, a wide ar-
the last decades [1–3]. As such, the development of materials pos- ray of polypyrazole ligands bearing amino [17–23], diamino [24–
sessing tailored properties through network-based approaches is 27], thioether [28–32], dithioether [33–37], thiolate [38], sulfone
one of the most researched topics today [1,3–5]. However, the need [39,40] and sulfoxide [39] chains have been synthesized, and their
to develop smarter materials, capable of fulfilling a multi-purpose reactivity against several metal centres studied. Amongst those
role, has led to the realization that these demands could be better mentioned flexible chains, in the last years, those containing alco-
accomplished by ligands capable of adopting different conforma- hol and ether groups have been intensively studied in our group,
tions, and even changing between them as a response to an exter- designing and synthesizing a family of bispyrazole ether ligands
nal stimulus, rather than rigid ones [6–9]. [41,42] and testing their reactivity against different metal centres
Amongst them, ligands containing N-heterocyclic donors linked such as Pd(II), Pt(II), Zn(II), Cd(II) and Hg(II) [43–45], resulting in
by flexible chains can adopt surprising conformations owing to the obtaining of various coordination compounds bearing a wide
the free rotation around the chain, resulting in the formation of variety of coordination environments and architectural motifs.
coordination compounds bearing unusual architectural motifs or In this sense, we have compared the coordination be-
fascinating properties [10–14]. In particular, those with a metala- haviour of two positional isomers of a bispyrazole ether
cyclic or polymeric architecture stand out, as they can act as sec- ligand (Scheme 1): (1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)−2-
oxabutyl]benzene (ortho-isomer) and 1,4-bis([4-(3,5-dimethyl-1H-
pyrazol-1-yl)−2-oxabutyl]benzene (para-isomer), against d10 metal
∗
Corresponding author.
centers [46], demonstrating that the different orientation of the
E-mail address: josefina.pons@uab.cat (J. Pons). substituting arms caused a marked preference for the dimeric
https://doi.org/10.1016/j.molstruc.2023.135419
0022-2860/© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
a 1:1 metal to ligand ratio. For 1, the resulting solution was kept
under reflux conditions for 48 h. After that period, the solution
was concentrated to a half of its volume and left to evaporate, re-
sulting in the obtaining of a blue precipitate. For 2, upon then ad-
dition of the metal to the ligand solution, a green precipitate ap-
peared immediately. Suitable crystals were obtained by layering a
CH2 Cl2 solution with hexane which was kept in the fridge for one
month for 1, or by recrystallization in EtOH for one month for 2.
Their single crystal X-ray structure revealed that compound 1 is
a coordination polymer, {[Co(L)Cl2 ]·1/2H2 O}n , while 2 is a dimeric
compound, [Cu2 (L)Cl4 ] (Scheme 2).
Scheme 1. Ortho- (left) and para- (right) isomers of a bispyrazole ether ligand. The All compounds were characterized by analytical and spectro-
ligand used in this work is highlighted in blue and labelled. scopic techniques. Spectroscopic details of the characterization of
all compounds are found in the Exp. Sect. and Supporting Infor-
mation (S.I.). Recorded powder patterns agree with the elucidated
metalacyclic architecture for the para- isomer, while compounds crystal structures (S.I: Figures S1, S2). Elemental analyses (EA) of
bearing the ortho- isomer showed lineal polymeric motifs. More- all compounds agree with the proposed formulae.
over, it was also observed that while the para- isomer showed a The FTIR-ATR spectra of the two compounds in the range of
NN’- bridging coordination mode regardless of the metal, the ortho- 40 0 0–50 0 cm−1 confirms the coordination of the ligand to the
isomer displayed different coordination modes on different metals, metal centre (S.I. Figures S3, S4). The most characteristic bands
such as NN’-bridging for Zn(II) and NON’-chelating and bridging for of the IR spectra are those corresponding to [ν (C = C/C = N)ar ]
Cd(II) and Hg(II) [46]. (1555–1552 cm−1 ), [δ (C = C/C = N)ar ] (1440 cm−1 ), [δ (C–H)ip ]
On this basis, we decided to delve further in the behaviour (1103–1058 cm−1 ) and [δ (C–H)oop ] (840–744 cm−1 ) [50,51]. These
of the ortho- isomer (1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)−2- signals are attributable to the pyrazole and phenyl rings present
oxabutyl]benzene (L)). Our previous studies of the behaviour of L in the ligand. Moreover, for compound 1, the region between 3600
against first-row metal cations only included Zn(II) [46]. However, and 3100 cm−1 hosts a broad band attributable to [ν (O–H)] from
owing to its electronic configuration, the range of available coor- H2 O molecules.
dination geometries is limited, showing a marked preference for The UV–Vis spectra have been recorded in CH2 Cl2 for 1 and
dimeric metallacyclic architectures. Thus, it was decided to expand EtOH for 2 (≈ 1·10−3 M) (S.I: Figures S5, S6). For 1, the recorded
the study to coordinatively flexible first-row transition metals. Our spectrum shows one band in the visible region at 651 nm with
prior studies similar N,O-hybrid pyrazole ligands showed that the a shoulder at 587 nm. These can be attributed to 4 A2 →4 T2 tran-
use of Cu(II) metal centres afforded a plethora of new arrange- sitions for Co(II) atoms in a distorted tetrahedral geometry [52–
ments, ranging from mononuclear to tetrameric and even poly- 54], which agrees with its elucidated crystal structure. For 2, the
meric complexes [47–49] therefore, providing not only variable co- recorded spectrum shows two bands at 678 and a shoulder at
ordination geometries but also gives access to variable nuclearity. 867 nm. For square pyramidal Cu(II) compounds, their recorded
Thus, we hoped that their availability of a wide array of coordi- UV–Vis spectra may occasionally show a low energy shoulder (ʎ
nation geometries would allow to highlight the ligand’s flexibil- > 800 nm) associated to a main broad band between 550 and
ity, resulting in the formation of compounds with previously un- 700 nm [54,55]. Thus, the signal at 678 nm can be attributed to a
reported architectures for L. Moreover, the behaviour of this family 2 E →2 T
g 2g transition in a square pyramidal Cu(II) metal centre [56],
of compounds against Co(II) has not been reported. Therefore, we which is in agreement with its elucidated crystal structure. All ɛ
first employed Cu(II) to expand our knowledge on this family of values (49–361 M−1 cm−1 ) are consistent with Laporte-forbidden
N,O-hybrid bispyrazole ligands further explored their coordination transitions [56].
chemistry with Co(II). Thus, the reactivity of L against MCl2 ·x(H2 O)
salt (M = Co(II), x = 6; M = Cu(II), x = 0) was assayed, resulting
2.2. Crystal and extended structure of 1
in compounds {[Co(L)Cl2 ]·1/2H2 O}n (1) and [Cu2 (L)Cl4 ] (2).
Compound 1 crystallizes in the monoclinic crystal system hav-
2. Results and discussion ing a C2/c space group, showing a polymeric structure. In it, L
acts as a bidentate NN’-bridged ligand, with an anti-conformation
2.1. Synthesis and general characterization (Fig. 1). As stated before, this compound is isostructural with
its Zn(II) analogue {[Zn(L)Cl2 ]·1/2H2 O}n previously reported by
For the synthesis of these complexes, an ethanolic solution our group [46] and shares the polymeric chain motif with
of the corresponding MCl2 ·x(H2 O) salt (M = Co(II), x = 6 (1); {[Cd(L)Cl2 ]·1/2EtOH}n and {[Hg(L)Cl2 ]·1/2EtOH}n [46].
M = Cu(II), x = 0 (2)) is added dropwise to an ethanolic solution of Its tetrahedral (τ 4 = 0.89) [57] [CoN2 Cl2 ] core comprises two
1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)−2-oxabutyl]benzene (L) in chlorine atoms and two nitrogen atoms provided by two differ-
Scheme 2. Synthetic reactions carried out in this work. Compounds are shown with their numbering scheme. Occluded solvent molecules have been removed for clarity.
2
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
Fig. 1. 1D coordination polymer 1, showing relevant atoms (a). In detail, the coordination environment around the Co(II) node (b). Solvent molecules (H2 O) and hydrogen
atoms have been excluded for clarity.
Table 1
Selected bond lengths (Å), angles (°) and intermolecular interactions of 1.
Bond lengths (Å)
Co(1)-N(1) 2.0410(16) Co(1)-Cl(1) 2.2710(6)
Co(1)-N(3)#1 2.0406(17) Co(1)-Cl(2) 2.2388(6)
Co(1)···Co(1)#1 12.490(9)
Bond angles (°)
Cl(1)-Co(1)-Cl(2) 106.79(2) N(3)#1-Co(1)-Cl(2) 105.53(5)
N(3)#1-Co(1)-Cl(1) 117.54(5) N(1)-Co(1)-Cl(2) 116.91(5)
N(1)-Co(1)-Cl(1) 106.73(5) N(1)-Co(1)-N(3)#1 103.86(7)
Intermolecular interactions
D-H···A (Å) D-H (Å) H-D···A (Å) >D–H···A (°)
O3A-H3A···Cl2 2.572(5) 0.983 3.531(5) 161.41(6)
#1: x, y + 1, z + 1/2
ent L. A search in the CCDC database [58] reveals the existence between encapsulated water molecules is 13.536(2) Å. They occupy
of fifty-one reported structures with the same core. The vast ma- non-connected cavities, which account for 1.8% of unit cell volume
jority (78.40%) are monomers, while reports of similar compounds (86.91 Å3 ), calculated defining a prove radius of 1.2 Å (Figure S7).
bearing polypyrazole bridging ligands are much scarce, with only Relevant intermolecular interactions are summarized on Table 1.
a handful of dimers (19.64%) [14,59–61] and one polymer (1.96%)
[62] being reported. 2.3. Crystal and extended structure of 2
In 1, adjacent Co(II) centres are connected by L via a
NN’-bidentate bridging mode in an anti-conformation, result- Compound 2 crystallizes in the orthorhombic system, having a
ing in the formation of an infinite 1D helical chain along Cmc21 space group, showing a dimeric structure (Fig. 3). In it, L
the c axis (Fig. 1). The distance between repeating units is displays a new coordination behaviour, and a rather unusual one.
23.768(4) Å, while adjacent Co(II) atoms lie at 12.490(9) Å. Moreover, it does not feature a polymeric motif, but a dimeric one.
This distance is larger than those found in related bispyrazole The L ligand chelates via one nitrogen and one oxygen of each side
polymer {[Co(Me2 bpz)Cl2 ]·1/2H2 O}n (Me2 bpz = 1,1 -dimethyl-4,4 - to a Cu(II) atom, resulting in a NOO’N’-chelated and bridged coor-
bispyrazole) (9.734(2) Å) [62]. The dihedral angle between the dination mode in a syn-conformation.
mean planes of the pyrazole rings in the centrosymmetric L is In this dimer, Cu(II) atoms adopt a [CuNOCl3 ] core in a slightly
68.71(3)°, showing its twisting around the benzene rings. However, distorted square pyramidal geometry (τ 5 = 0.11) [63]. The basal
alternating pyrazolyl rings, which belong to different L, are almost plane comprises the two bridging chlorine atoms linking two Cu(II)
parallel (dihedral angles between mean planes of pyrazolyl rings atoms in the same plane, a terminal chlorine atom and one nitro-
being 14.5(3)°). Relevant bond lengths and angles for 1 are sum- gen atom of the L ligand. Finally, the coordination sphere is com-
marized in Table 1. All values agree with other Co(II) tetrahedral pleted by an oxygen belonging to L occupying the apical position,
compounds possessing pyrazole and chloride ligands [14,59–62]. which lies at a longer distance due to Jahn-Teller effect [64].
The extended structure of this compound is dominated by the A search in the CCDC database [58] reveals a total of thirty-one
presence of occluded H2 O molecules. They bind together a left- crystal structures bearing a chlorine-bridged dimeric [CuNOCl3 ]
handed and a right-handed chain, forming an interesting double core, but for the immense majority (twenty-nine crystal struc-
supramolecular chain parallel to the crystallographic c axis, thanks tures, 93.5%) the apical position is occupied by the bridging chlo-
to a symmetrical double O–H···Cl2 interaction (Fig. 2). The distance rine atoms, and only in one case (3.2%) by the oxygen atom [65].
3
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
Fig. 2. Supramolecular castellated double chain for polymer 1, view along a (a) and b (b) axis. Occluded H2 O molecules have been highlighted in the ball and stick mode.
Fig. 3. Compound 2, showing all its non-hydrogen atoms and their numbering scheme (a). In detail, the coordination environment around the Co(II) node (b). Hydrogen
atoms have been excluded for clarity. Supramolecular chain, view along b axis (c).
Moreover, of all structures with similar core, none of them bears The supramolecular structure of 2 is dominated by interac-
a tetradentate ligand. Due to the spatial constraints induced by tion between the terminal chlorine atoms and hydrogen atoms
the coordination of oxygen atoms. Compound 2 has a peculiar of the alkylic chain. These interactions result in the formation of
throne shape. In it, the phenyl ring acts as the backrest of the supramolecular chains along the c axis (Fig. 3, Table 2). These
throne, being almost perpendicular (85.7(3)°) to the plane con- chains form a dense network parallel threads arranged in a zig-zag
taining the Cu(II) and bridging chlorine atoms. The alkylic chain pattern.
and the pyrazole groups, which resemble the armrests, bind to
the Cu(II) atoms in a syn-syn mode, defining planes which inter- 2.4. Structural discussion
sect at an angle of 70.9(3)° between themselves and at 72.7(3)°
with the plane containing the Cu(II) and bridging chlorine atoms. When considering our previously published results of the reac-
Relevant bond lengths and angles for 2 have been summarized tivity of L against MCl2 (M = Zn(II), Cd(II) and Hg(II)) [46], these
in Table 2. All values agree with related chlorine-bridged dimer new results are rather intriguing. While the architectural motif in
[Cu2 (tetraisopropylpyridine-2,6-dicarboxamide)2 Cl4 ] [65]. 1 is similar to those previously reported, compound 2, possessing
4
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
Table 2
Selected bond lengths (Å), angles (°) and intermolecular interactions for 2.
Bond lengths (Å)
Cu(1)-N(2) 1.977(8) Cu(1)-Cl(1) 2.321(2)
Cu(1)-O(1) 2.340(6) Cu(1)-Cl(2) 2.292(3)
Cu(1)···Cu(1) 3.348(3) Cu(1)-Cl(3) 2.292(3)
Bond angles (°)
N(1)-Cu(1)-Cl(3) 93.1(3) N(1)-Cu(1)-O(1) 90.0(3)
N(1)-Cu(1)-Cl(2) 172.4(3) Cl(3)-Cu(1)-O(1) 94.28(18)
Cl(3)-Cu(1)-Cl(2) 92.27(11) Cl(2)-Cu(1)-O(1) 94.9(2)
N(1)-Cu(1)-Cl(1) 89.5(3) Cl(1)-Cu(1)-O(1) 99.93(19)
Cl(3)-Cu(1)-Cl(1) 165.56(12) Cu(1)-Cl(1)-Cu(1)#1 92.32(14)
Cl(2)-Cu(1)-Cl(1) 83.98(11) Cu(1)#1-Cl(2)-Cu(1) 93.81(14)
Cl(3)-Cu(1)-Cl(2) 92.27(11) N(1)-Cu(1)-O(1) 90.0(3)
Intermolecular interactions
D-H···A (Å) D-H (Å) H-D···A (Å) >D–H···A (°)
C5-H28···Cl3 2.548(3) 1.089 3.635(3) 176.84(11)
C5-H6···Cl3 2.548(3) 1.089 3.635(3) 176.84(11)
#1: -x, y, z
Fig. 4. Most common structural motifs for compounds possessing a [Co(NPyr )2 Cl2 ] core.
Table 3
Summary of architectural motifs found for CCDC database searches for compounds possessing [Co(NPz )2 Cl2 ] and [Co(NPyr )2 Cl2 ] cores.
Structural motif Number (percentage of total) Examples (CSD REFcode)
[Co(NPz )2 Cl2 ] Monomeric 3 (100%) HEXTEJ [67]
HOJHIY [68]
HOJHOE [68]
[Co(NPyr )2 Cl2 ] Monomeric 61 (80.3%) ARUFUP [69]
DILDUY [70]
Polymeric 5 (6.6%) XADBAG [71] DUKWEN [72]
Dimeric Metallacycle 5 (6.6%) ASOKOI [73]
FILCUA [74]
Trimeric Metallacycle 2 (2.7%) JASZEL [75]
Other 3 (4.0%) GAQSID [76]
OFAYEZ [77]
Cu(II) as metal centre soundly deviates from the expected results, tures found in the CCDC database [58], the compound possesses a
as its architectural motif has not previously been reported for this monomeric metalacyclic or dimeric motif (Fig. 4).
family of ligands. Thus, we decided to perform a structural study, Owing to the scarcity of data (only three reported structures
hoping that it could shed some light on the unusual coordination with a [CoNPz Cl2 ] core was found in the CCDC database [58]), a
behaviour of L towards Cu(II), when compared to the rest of re- similar search was performed for compounds bearing a tetrahe-
ported compounds bearing Zn(II), Cd(II), Hg(II) [46] and Co(II). dral [Co(NPyr )2 Cl2 ] core containing the most ubiquitous aromatic
As stated before, in compound 1, L shares the same coordi- N-donor, pyridine. Once again, it was found that the overwhelm-
nation behaviour than in its Zn(II), Cd(II) and Hg(II) compounds, ing majority (80.3%, Table 3) of compounds possess the monomeric
which are all isostructural coordination polymers of general for- metalacyclic motif (Fig. 4), while dimeric/trimeric metalacyclic and
mulae {[M(L)Cl2 ]·1/2X}n (M = Zn(II), X = H2 O; M = Cd(II), Hg(II), polymeric motifs are much scarcer (9.4% and 6.6%, respectively,
X = EtOH) [46], and thus possess the polymeric motif (Fig. 4). Table 3).
However, it is the first time that this motif is reported for com- For compound 2, a search in the CCDC database [58] for simi-
pounds bearing a [Co(NPz )2 Cl2 ] core, as in the only similar struc- lar pyrazole compounds possessing a [CuNPz OCl3 ] core surprisingly
5
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
Table 4
Summary of architectural motifs found for CCDC database searches for compounds possessing a [Cu(NPyr )OCl3 ]
core.
Structural motif Number (percentage of total) Examples (CSD REFcode)
[Cu(NPyr )OCl3 ] Penta-coordinated dimeric 12 (85.7%) QUCREO [78] OMOLAF [79]
Tetrameric 1 (7.1%) TOGLAC [80]
Polymeric 1 (7.1%) TOGLEG01 [81]
Fig. 5. Most common structural motifs for compounds possessing a [Cu(NPyr )OCl3 ] core.
retrieves no data, and thus, a search for compounds possessing a 4. Experimental section
[CuNPyr OCl3 ] core, using the more ubiquitous pyridine ligand in-
stead of a pyrazole ligand, was performed, retrieving fourteen re- 4.1. Materials and general details
ported structures (Table 4). Most of them (twelve, 85.7%, Table 4)
are penta-coordinated Cu(II) dimers, with two bridging chlorine Cobalt(II) chloride hexahydrate (CoCl2 ·6H2 O), copper(II) chlo-
atoms and a third terminal chlorine, much like compound 2. All of ride (CuCl2 ), ethanol (EtOH), methanol (MeOH) and diethyl ether
them bear two hybrid N,O-donor ligands, while compound 2 would (Et2 O) were purchased from Sigma Aldrich and used without fur-
be the first member of this family of compounds to bear only ther purification. Reactions and manipulation were carried out in
one ligand. The rest of the reported structures bear a tetrameric air at room temperature (r.t.) or reflux conditions. The ligand (L)
(one, 7.1%) or a polymeric (1, 7.1%) architectural motif (Table 4, was synthesized according to the procedure reported in the liter-
Fig. 5). In any case, for the majority of compound bearing this ature [41,43]. Powder X-ray patterns (PXRD) were measured with
kind of core, the penta-coordinated dimeric motif is the most com- a Siemens D50 0 0 apparatus (with 40 kW and 45 mA using Cu kα
mon one. These data suggests that this motif is highly favoured for radiation with ʎ = 1.5406 Å). Patterns were recorded from 2θ = 5°
Cu(II) metal centres in combination with similar ligands. The en- to 40° with a step scan of 0.02° counting for 1 s at each step. El-
ergy stabilization deriving from the ligand’s chelate effect and the emental analyses (EA) (C, H, N) were carried out on a Thermo Sci-
formation of the dimeric core may overcome the steric hindrance entific Flash 20 0 0 CHNS Analyses. FTIR-ATR spectra were recorded
caused by the ortho-substituted arms of the ligand [66], resulting on a Tensor 27 (Bruker) spectrometer, equipped with an attenuated
in the obtaining of the penta-coordinated dimeric motif instead of total reflectance (ATR) accessory model MKII Golden Gate with dia-
the polymeric one. mond window in the range 40 0 0–60 0 cm−1 . The electronic spectra
in MeOH (≈ 1·10−3 M) were run on a JASCO V-780 UV–Visible/NIR
3. Conclusions Spectrophotometer with a quartz cell having a path length of 1 cm
in the range of 50 0–110 0 nm at r.t.
Two new metal complexes {[Co(L)Cl2 ]·1/2H2 O}n (1) and
[Cu2 (L)Cl4 ] (2) containing a flexible bispyrazole ether ligand have 4.2. Synthesis of compound {[Co(L)Cl2 ]·1/2H2 O}n (1)
been synthesized and fully characterized. Detailed examination of
their crystal structures revealed that while compound 1 keeps a An absolute EtOH (20 mL) solution of CoCl2 ·6H2 O (3.18 mmol,
polymeric architecture, compound 2 displayed a completely dif- 0.754 g) was added dropwise to a solution of L (3.18 mmol, 1.22 g)
ferent behaviour, having a penta-coordinated dimeric architecture. in absolute EtOH (20 mL). The resulting solution was stirred under
This behaviour was rather surprising, as the ligand is expected to reflux conditions for 48 h. During this time, the solution shifted
adopt an anti-conformation (leading to a polymeric architecture) from a deep violet colour to a light blue. After that period, the
owing to the steric hindrance caused by the ortho-substitution of solution was concentrated up to 10 ml and left to evaporate until
the ligand, instead of the syn-conformation adopted in 2. Moreover, a blue precipitate appeared. The resulting precipitate was filtered
the resulting structure is rather unique, with the ligand adopt- off, washed with 5 mL of cold Et2 O and dried under vacuum.
ing a peculiar chair conformation. A thorough search in the CCDC Suitable crystals for X-ray diffraction were obtained by layering
database [55] reveals that for the majority (85.7%) of similar Cu(II) a CH2 Cl2 solution of the blue precipitate with hexane and leaving
compounds, the penta-coordinated dimeric motif is prevalent, sug- it in the fridge at 4 °C for one month.
gesting that it possesses enough stability to overcome the steric Yield: 41.8% (0.407 g) Elem Anal. Calc. for C44 H62 Cl4 N8 O5 Co2
hindrance caused by the ortho- substitution of the ligands, which (1042.67): C, 50.68, H 5.99, H 10.75. Found: C 50.75, H 5.78,
favours the polymeric architecture for other metal centres such N 10.43. FTIR-ATR (wavenumber, cm−1 ): 3370(br) [ν (O–H)],
as Co(II), Zn(II), Cd(II) and Hg(II). Finally, this works highlights 3135(w)−3078(w) [ν (C–H)ar ], 2963(w)−2869(w) [ν (C–H)al ],
the flexibility of L, which can adopt several different coordination 1552(s) [ν (C = C/C = N)]ar , 1466(m), 1440(m) [δ (C = C/C = N)]ar ,
modes and act as a polytopic ligand through four different coordi- 1420(m), 1371(m), 1352(s), 1311(w), 1263(w), 1218(m), 1186(m),
native sites. 1124(m), 1100(s), 1094(s) [δ (C–H)ip + ν (C–O-C)], 1066(s), 1048(s),
6
J. Soldevila-Sanmartín, T. Calvet, M. Font-Bardia et al. Journal of Molecular Structure 1284 (2023) 135419
876(w), 813(w), 790(s) [δ (C–H)oop ], 760(vs) [δ (C–H)oop ], 637(w), a selected wavelength of 0.72932. An MD2M-Maatel diffractome-
524(w). UV–Vis (MeOH, 1.06·10−3 M) ʎmax (ɛ(M−1 cm−1 )) = 587 nm ter fitted with a Dectris Pilatus 6 M detector was employed. The
(sh, 231), 651 nm (360). samples were kept at 100 K with an Oxford Cryosystems 700 se-
ries Cryostream. Data was processed with APEX3 suite [83]. The
4.3. Synthesis of compound [Cu2 (L)Cl4 ] (2) structure was solved by Intrinsic Phasing using the ShelXT program
[84], which revealed the position of all non-hydrogen atoms. These
An absolute EtOH (20 mL) solution of CuCl2 (3.18 mmol, atoms were refined on F2 by a full-matrix least- squares procedure
0.428 g) was added dropwise to a solution of L (3.18 mmol, 1.22 g) using anisotropic displacement parameter [85]. All hydrogen atoms
in absolute EtOH (20 mL). A green precipitate appeared almost im- were in difference Fourier maps and included as fixed contribu-
mediately. The resulting solution was stirred at r.t. until no more tions riding on attached atoms with isotropic thermal displace-
precipitate appeared. After that period, the resulting green precip- ment parameters 1.2 or 1.5 times those of the respective atom. The
itate was filtered off, washed with 5 mL of cold Et2 O and dried OLEX2 software was used as a graphical interface [86].
under vacuum. For compound 2, a green prism-like specimen was used for
Suitable crystals for X-ray diffraction were obtained via recrys- the X-ray crystallographic analysis. The X-ray intensity data was
tallization of the green precipitate in EtOH for one month at r.t. measured on a D8 Venture system equipped with a multilayer
Yield: 71.6% (0.749 g). Elem. Anal. Calc. for C22 H36 Cl4 N4 O2 Cu2 monochromator and a Mo microfocus (λ = 0.71073 Å). The frames
(657.40): C 40.19, H 5.52, N 8.52. Found: C 40.30, H 5.47, N were integrated with the Bruker SAINT software package using
8.35. FTIR-ATR (wavenumber, cm−1 ): 3132(w)−3089(w) [ν (C–H)ar ], a narrow-frame algorithm. Data was corrected for absorption ef-
2939(w)−2872(w) [ν (C–H)al ], 1555(s) [ν (C = C/C = N)]ar , 1472(m), fects using the multi-Scan method (SADABS) [87]. The structure
1440(m) [δ (C = C/C = N)]ar , 1396(m), 1357(w), 1315(s), 1254(m), was solved and refined using the Bruker SHELXTL Software Pack-
1228(w), 1215(w), 1188(w), 1143(w), 1103(s) [ν (C–O-C], 1058(s) age [84,85]
[δ (C–H)ip ], 1014(s), 993(s), 840(s) [δ (C–H)oop ], 818(m), 785(s) Crystal data and relevant details of structure refinement are re-
[δ (C–H)oop ], 744(s) [δ (C–H)oop ], 635(m), 624(m). UV–Vis (MeOH, ported in Table 5. Molecular graphics were generated with Mercury
1.25·10−3 M) ʎmax (ɛ(M−1 cm−1 )) = 678 nm (75), 867 nm (sh, 49). 4.1.3 [88,89] with POV-Ray package [90]. Colour codes for molecu-
lar graphics: grey (C), white (H), green (Cl), red (O), light blue (N),
dark blue (Co), orange (Cu).
4.4. X-ray crystallography
Appendix A. Supplementary Data
For compound 1 data was collected at BL13 (XALOC) [82] at
the ALBA synchrotron with an undulator source and channel-cut FTIR-ATR spectra, additional figures and UV–Vis spectra are
Si(111) monochromator and Kirkpatrick-Baez focusing mirrors with available as Supporting Information. CCDC 2236407 and 2236667
Table 5
Crystallographic data for compounds 1 and 2.
1 2
Empirical Formula C44 H62 Cl4 Co2 N8 O5 C22 H36 Cl4 Cu2 N4 O2
Formula weight 1042.67 657.43
T (K) 100(2) 293(2)
Wavelength (Å) 0.7293 0.71073
System, space group Monoclinic, C2/c Orthorhombic, Cmc21
Unit cell dimensions
a (Å) 29.9778(10) 21.873(16)
b (Å) 8.0411(3) 7.781(4)
c (Å) 23.7682(8) 15.377(7)
α (°) 90 90
β (°) 122.0530(10) 90
ϒ (°) 90 90
V (Å3 ) 4856.0(3) 2617(3)
Z 4 4
Dcalc (mg/m3 ) 1.426 1.669
μ (mm−1 ) 1.017 2.062
F (000) 2176 1352
Crystal size (mm−3 ) 0.12 × 0.10 × 0.10 0.068 × 0.062 × 0.043
hkl ranges −35≤h ≤ 35, −28≤h ≤ 28,
−9 ≤ k ≤ 9, −10≤k ≤ 10,
−28≤l ≤ 28 −19≤l ≤ 19
θ range (°) 1.841 to 25.722 2.649 to 27.572
Reflections collected/unique 33,398 / 4269 / [Rint ] = 0.0520 15,100 / 3080 / [Rint ] = 0.2017
/[Rint ]
Completeness to θ (%) 99.4 99.9
Absorption correction Semi-empirical Semi-empirical
Max. and min. transmission 0.0298 and 0.0098 0.7454 and 0.5078
Refinement method Full-matrix least-square on /F/2 Full-matrix least-square on /F/2
Data/Restrains/Parameters 4269 / 0 / 289 3080 / 1 / 159
Goodness-on-fit on /F/2 1.039 1.029
Final R indices [I>2σ (I)] R1= 0.0379 R1= 0.0607
wR2= 0.1115 wR2= 0.0997
R indices (all data) R1= 0.0382 R1= 0.1282
wR2= 0.1118 wR2= 0.1196
Extinction coefficient n/a n/a
Largest diff. peak and hole (e.Å−3 ) 0.568 and −0.457 0.805 and −0.679
7
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The authors declare that they have no known competing finan- [13] A. Beheshti, A. Lalegani, G. Bruno, H. Amiri Rudbari, Investigating the effect of
flexible ligands on the crystal engineering of the iron(II) coordination com-
cial interests or personal relationships that could have appeared to pounds, J. Mol. Struct. 1051 (2013) 244–249, doi:10.1016/j.molstruc.2013.08.
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S.A. Stoian, A. Ozarowski, Dinuclear metallacycles with single M–X–M bridges
CRediT authorship contribution statement
(X = Cl –, Br – ; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): strong anti-
ferromagnetic superexchange interactions, Inorg. Chem. 56 (2017) 2884–2901,
Joan Soldevila-Sanmartín: Investigation, Visualization, Writing doi:10.1021/acs.inorgchem.6b02933.
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