This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. http://pubs.acs.org/journal/acsodf Article New Highly Charged Iron(III) Metal−Organic Cube Stabilized by a Bulky Amine Carlos Cruz, Andreś Igor Vega Carvallo, Evgenia Spodine, Albert Escuer, Jose ́ F. Marco, Nieves Meneń dez, Diego Venegas-Yazigi, and Veroń ica Paredes-García* Cite This: ACS Omega 2020, 5, 22238−22247 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: In this work, we report a new octanuclear cluster based on FeIII and the ligand 1H-imidazole-4,5-dicarboxylic acid, [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O (1), with a metal core containing eight FeIII connected by only one type of organic ligand. A peak at 573 m/z in the mass spectra of the compound suggests the adduct species {[Fe8(IDC)12]+8H}4−. By X- ray photoelectron spectroscopy, the oxidation state of the iron cation was confirmed to be 3+, also identifying the presence of a quaternary nitrogen species, which act as a countercation of the anionic metal core [Fe8(IDC)12]12−. Mössbauer spectra recorded at different temperatures show an isomer shift and quadrupole splitting parameters that confirm the existence of only FeIII-HS in the structure of 1. X-ray analysis reveals that compound 1 crystallizes in the orthorhombic system space group Ibam, confirming a molecular cluster structure with an almost regular cube as geometry, with the FeIII atoms located at the corners of the cube and connected by μ-1κ2N,O:2κ2N′,O‴-IDC3− bridges. Additionally, the magnetic measurements reveal a weak antiferromagnetic coupling in the Fe8III coordination cluster (J = −3.8 cm−1). To the best of our knowledge, 1 is the first member of the family of cubes assembled with 1H- imidazole-4,5-dicarboxylic acid and FeIII cation, exhibiting high pH stability over a broad pH range, making it an ideal candidate for the design of supramolecular structures and metal−organic frameworks. 1. INTRODUCTION in the literature exhibit the magnetocaloric effect at low One of the fascinating fields in coordination chemistry is the temperatures due to the large spin, small anisotropy, and high research in polynuclear molecular compounds, also called density of low-lying excited states.12 Research in coordination coordination clusters. This type of compound corresponds to clusters based on FeIII is interesting in molecular magnetism not molecular entities formed by multiple metal cation arrange- only by its rich coordination chemistry but also because this spin ments, connected by organic or inorganic ligands.1 The carrier can present spin values ranging from 5/2 to 1/2, molecular structure and properties of the coordination cluster depending on the coordination environment. These features are intrinsically related to the nature of the chosen metal center make these types of compounds attractive for applications like and the interaction between them through the bridging spin switches and magnetic refrigerants.13−16 From a structural viewpoint, the literature reports several FeIII ligands.2−4 Then, coordination clusters presenting cations with coordination clusters with a wide variety of nuclearities, unpaired electrons are attractive in the field of molecular topologies, and geometries, such as [Fe 6 (O 2 )O 2 - magnetism.5−8 The slow relaxation of the magnetization (O2CPh)12(H2O)2] reported by McCusker et al.17 and reported for the disc-shaped Mn 1 2 I I / I I I compound, {[Fe8(O)2(OH)12(tacn)6]Br7(H2O)}Br·8H2O reported by [Mn12O12(O2CR)16(H2O)4] (R = methyl, phenyl), is a product Wieghardt et al.18 (O2CPh− = benzoate; tacn = 1,4,7- of the high-spin state and magnetic anisotropy of the triazacyclononane). Both compounds present planar moieties paramagnetic centers.9,10 Furthermore, two Cr10III wheels as central cores, constructed by oxides/peroxides anions in the bridged by acetate and alkoxide ligands, case of Fe6 and oxides/hydroxides anions in Fe8. Using [Cr10(O2CMe)10(OR)20], show a different magnetic behavior phosphonic acids, Konar et al. obtained [Fe9(μ3-O)4(O3PPh- depending on the alkoxide ligand present in the wheel. The authors report that the methoxide ligand favors a ferromagnetic behavior, while the ethoxide ligand favors an antiferromagnetic Received: May 22, 2020 behavior.11 Additionally, two mixed-valence coordination Accepted: July 7, 2020 clusters [Mn12IIIMn7IIO8(HL)12(N3)3(MeO)5.5(MeOH)3.5- Published: August 14, 2020 (H 2 O) 1 . 5 (OH) 0 . 5 ](OAc)·10H 2 O and [Na 2 Mn 1 1 I I I - Mn 4 II O 8 (HL) 10 (OAc) 2 (H 2 O) 2 (OCH 3 ) 1.5 (N 3 ) 2.5 ](OAc)· 10H2O·2MeOH (H3L = 2,6-(hydroxymethyl)phenol), reported © 2020 American Chemical Society https://dx.doi.org/10.1021/acsomega.0c02420 22238 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article (Me)2)3(O2CCMe3)13] and [Fe12(μ2-O)4(μ3- 2.2.3. Thermogravimetric Analysis. Thermogravimetric O)4(O2CCHPh2)14(4-tbuPhPO3H)6] (O3PPh(Me)22− = 3,5- (TG) analysis was performed on a Mettler Toledo TGA/DSC dimethylphenyl phosphonate; O 2 CCMe 3 − = pivalate; STAR system. The samples were introduced in an alumina O 2 CCHPh 2 − = diphenylacetate; 4- t buPhPO 3 H − = holder and heated under a nitrogen atmosphere from room p-tbutylphenyl phosphonate), with Fe9 and Fe12 central cores, temperature to 900 °C at a heating rate of 5 °C/min. showing an icosahedral and a double butterfly structure, 2.2.4. Single-Crystal X-ray Diffraction. A single crystal of 1 respectively. 19 Kang et al. reported the mixed-valence was directly selected from the reaction beaker and glued on the Fe18 III Fe24 II coordination cluster [{Fe(Tp)(CN) 3 }24{Fe- tip of a capillary glass using epoxy resin. Scans on the Bruker (H 2 O) 2 } 6 {Fe(dpp)(H 2 O)} 12 (CF 3 SO 3 ) 6 ]·18H 2 O (Tp = APEXII diffractometer confirmed enough crystal quality to hydrotris(pyrazolyl)borate; dpp = 1,3-di(4-pyridyl)propane).20 perform full recording using X-ray radiation of Mo Kα (λ = The Fe18IIIFe24II cluster has a number large enough of metal 0.71073 Å). The data were reduced by SAINT,27 and empirical centers to be considered as a nanocage.20 absorption corrections were applied using SADABS.28 The From the experimental viewpoint, several polynuclear FeIII structure was solved with the ShelXT29 structure solution compounds found in the literature were synthesized using two program using direct methods and refined with the ShelXL30 or more ligands, giving rise in many cases to complex refinement package with least-squares minimization. Additional structures.21−23 In this article, we report a novel Fe8 III data concerning the crystallographic and the refinement octanuclear cube-type coordination cluster parameters are detailed in the Supporting Information. Top- [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O (1) obtained using osPro 5.0 software31 was used for structure drawing. During the 1H-imidazole-4,5-dicarboxylic acid (H3IDC) as a unique ligand. structure completion process by difference Fourier synthesis, it The structure and composition of the octanuclear cluster were was clear that there was a high amount of space left by the Fe8 obtained by single-crystal X-ray diffraction, X-ray photoelectron cubes of the complex within the cell, having an ill-defined spectroscopy (XPS), and other complementary techniques. electron density. Although the triethylammonium and water Furthermore, the characterization of 1 was complemented with molecules were identified preliminarily at this point, refinement Mössbauer spectroscopy, electronic paramagnetic resonance, by any model we tried was unsuccessful. Efforts to measure at and magnetic susceptibility measurements. low temperatures failed since crystals crack. Synthetic modifications were also tried to change triethylammonium by 2. EXPERIMENTAL SECTION an alkaline metal or other ammonium such as tetramethylam- 2.1. Synthesis of [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O monium or tetraethylammonium without any good results. (1). Caution: The reaction involves the mixture of a moderate Since efforts to model the disorder of the solvating molecules by amount of triethylamine (Et3N) and glacial acetic acid using a meaningful scheme failed, a well-documented method (CH3COOH). Fuming vapors are released, so care must be for the modeling of unresolved electron density, PLATON- taken in this procedure. SQUEEZE, was used.32,33 Alert B is present in the check cif file. To a suspension of Fe(acac)3 (0.5 mmol) and H3IDC (1 CHEMS01 Type_1 is due to the use of the “[Fe8C60H12 N24O48 mmol) in a mixture of 10 mL of water and N,N′- + solvent]” expression to remark that the reported formula dimethylformamide (DMF) (1:1 H2O/DMF), 5 mL of Et3N Fe8C60H12N24O48 lacks a specific amount of solvent and was added with constant stirring. After a few minutes, the countercations molecules because of the use of SQUEEZE. suspension disappears, and the resulting dissolution changes the PLAT084 and PLAT230 can be assigned to the unresolved initial orange color to a deep red color. After 10 min of stirring, 5 effects such as the disorder in chemical species. Despite this, mL of glacial CH3COOH was added, giving a deep reddish- most of the structural determination alerts are related to cation/ brown solution, which was left undisturbed for a few weeks, solvent disorder, thus allowing one to consider that the giving yellow prismatic crystals of 1 (Figure S1). MW = 4475.86 geometry for the Fe8 cluster is reliable. Therefore, based on g/mol. Yield: 50% based on iron(III) salt. Anal. Calc. for: the complementary analyses, 12 triethylammonium (Et3NH+) C162H300N46O71Fe8 (1): C, 43.47%; H, 6.77%; N, 14.40%; Fe, as counterions, 10 N,N′-dimethylformamide, and 13 water 9.98%. Found: C, 43.35%; H, 6.71%; N, 14.36%; Fe, 9.98%. crystallization molecules per Fe8 cube unit were included in the 2.2. Physical Measurements. 2.2.1. Elemental Analysis. final formula (C162H300N46O71Fe8). The quantitative content of C, H, and N was obtained on a 2.2.5. X-ray Photoelectron Spectroscopy. XPS data were Thermos CHNS flash 2000 elemental analyzer using solid recorded using a PHOIBOS-150 hemispherical electron crystalline samples of 1. The quantitative content of Fe was analyzer (Specs) under a pressure lower than 2 × 10−9 mbar determined using atomic absorption spectroscopy. Three using Al Kα radiation. The X-ray gun was operated at a power of samples of 1 from different batches were measured in triplicate. 100 W to minimize radiation-induced damage to the sample. All Solid crystalline samples of 1 were digested in a 0.5% HNO3 the spectra were recorded at a constant pass energy of 30 eV. solution, and the iron concentration was measured with a Perkin The binding energy scale was referenced to the main C 1s Elmer PinAAcle 900F atomic absorption spectrophotometer contribution due to aliphatic carbon, which was set at 284.6 eV. equipped with an acetylene burner using a flux of acetylene:air of All spectra were computer-fitted to a sum of pseudo-Voigt 2.51:10 L min−1 as an oxidant mixture. An Fe lamp of 248.33 nm profiles using Shirley background subtraction. wavelength was used with standard solutions in a linear range of 2.2.6. Mössbauer Spectroscopy. The Mössbauer spectra of 0.1−3,0 mgFe L−1. finely ground crystals of 1 were recorded between 295 and 4.2 K. 2.2.2. Mass Spectrometry. Mass spectra were measured in a The measurements were recorded using two 57Co(Rh) γ-ray Linear Ion Trap LTQ-XL Thermo Scientific spectrometer and sources mounted on both ends of an electromagnetic transducer were analyzed with the software MMass 5.5.0.24−26 The analysis operated in the triangular mode. One of the sources was used for was carried out in a DMF:H2O solution of 1 (pH ≈ 6.0) in energy calibration with α-Fe (6 μm) foil. The spectra were negative ion mode, scanning in a range of m/z of 150−1500 analyzed by a nonlinear fit using the NORMOS program,34 and (Table S2 shows the peak list of the mass spectrum). the energy calibration was made using α-Fe (6 μm) foil. Variable 22239 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article temperatures were obtained with an Oxford Spectromag 4000 M {[Fe8(IDC)12]+8H}4−. Other adducts species with lower cryostat connected to an ITC-503 Oxford Instruments temper- intensities were also identified at 1147, 764, and 458 m/z, ature controller. To avoid saturation effects and optimize the which correlate with {[Fe8(IDC)12]+10H}2−, signal-to-noise ratio, the sample thickness was 10 mg of natural {[Fe8(IDC)12]+9H}3−, and {[Fe8(IDC)12]+7H}5−, respec- Fe cm−2. tively. This result corroborates that the anionic species 2.2.7. Electronic Paramagnetic Resonance. EPR spectra [Fe8(IDC)12]12− is the correct representation for the Fe8 were collected on a Bruker EMX-1572 spectrometer working at cluster.37,38 9.39 GHz (X-band) using polycrystalline samples of 1 at 298 K. 3.2. X-ray Single-Crystal Structural Characterization. 2.2.8. Magnetic Measurements. Magnetic measurements X-ray single-crystal analysis reveals that 1 corresponds to a were carried out using a Quantum Design Dynacool Physical discreet octanuclear cluster forming a cubic polyhedron, which Properties Measurement System (PPMS) equipped with a crystallizes in the highly symmetric Ibam orthorhombic system vibrating sample magnetometer (VSM). The dc data were (Table 1). Each corner of the cube is occupied by one FeIII collected under externally applied fields of 1 kOe in the 1.8−300 K temperature range. Also, magnetization measurements at the Table 1. Crystallographic Refinement Data for 1 variable field were performed at 1.8, 3, 5, and 8 K from 0 to 90 empirical formula C162H300N46O71Fe8a kOe. The magnetic signal from the sample holder was negligible formula weight (g mol−1) 4475.86a to affect our data accuracy and was not considered. Diamagnetic temperature (K) 293(2) corrections (estimated from Pascal constants) were consid- crystal system orthorhombic ered.35 The simulation of the temperature-dependent magnetic space group Ibam susceptibility data was performed by exact diagonalization of the a (Å) 18.051(8) spin Hamiltonian employing the PHI software.36 b (Å) 29.079(13) c (Å) 33.766(15) 3. RESULTS AND DISCUSSION α (°) 90 3.1. Synthesis. Concerning the synthesis of 1, the organic β (°) 90 ligand H3IDC can be considered as a polyprotic acid. Depending γ (°) 90 on the pH of the media, this ligand can be present in the final volume (Å3) 17,724(13) product with different protonation degrees (Scheme 1). Z 4 ρcalc (g/cm3) 0.856 Scheme 1. pKa Values of the Organic Ligand H3IDC μ (mm−1) 0.692 F(000) 4528.0 crystal size (mm3) 0.986 × 0.363 × 0.274 radiation Mo Kα (λ = 0.71073) 2θ range for data collection (°) 5.954−52 index ranges −22 ≤ h ≤ 22, −35 ≤ k ≤ 35, −41 ≤ l ≤ 41 The initial suspension of H3IDC in an H2O/DMF mixture reflections collected 67,448 gave a pH near 3, indicating that the full protonated H3IDC independent reflections 8864 [Rint = 0.0848, Rsigma = 0.0601] should be the predominant species in this media. When data/restraints/parameters 8864/0/320 triethylamine (Et3N; 36 mmol) was added, the pH increased goodness-of-fit on F2 1.297 to 11, causing a displacement of the equilibrium to the more final R indices [I ≥ 2σ (I)] R1 = 0.1537, wR2 = 0.3714 reactive ionic species HIDC2−/IDC3−, which are now able to final R indices [all data] R1 = 0.2003, wR2 = 0.4078 coordinate the FeIII centers. Then, at the end of the reaction, the largest diff. peak/hole (e Å−3) 2.08/−1.05 acidification with glacial acetic acid (87 mmol) decreased the a The empirical formula and molecular weight given in the table pH of the solution to 4. Regarding the pH fluctuation in the consider the counterions and solvate molecules determined by all the reaction and the different protonation degrees of the H3IDC analysis techniques used in the experimental section. ligand (IDC3−/HIDC2−/H2IDC−), it is possible to infer that the assembly of iron(III) with the organic species should generate multiple possibilities for the final formula of Fe8III cluster. Thus, center (Figure 1a), being the edges organic ligands. Continuous an anionic [Fe8(IDC)12]12−, neutral [Fe8(HIDC)12], or cationic shape measurement (CShM) was used to evaluate the distortion [Fe8(H2IDC)12]12+ species could be considered as a product. of the cube. The iron moiety was compared with an ideal cube Considering that the species of the ligand are dependent on the using the SHAPE software,39 obtaining a CShM value of 0.004 pH, it is reasonable to infer that IDC3− anion should be the and confirming an almost perfect cubic arrangement of the predominant species at pH = 11 (pKa3 = 11.8), being also able to coordination cluster (Table S3). This cube is obtained by the coordinate the Fe III cations to give the Fe 8 cluster asymmetric unit containing two crystallographically independ- [Fe8(IDC)12]12−. Later, the pH decreases to 4, causing the ent iron centers and three full deprotonated IDC3− ligands. quantitative protonation of Et3N (pKa = 10.8) needed to induce Fe(1) and Fe(2) present the same coordination environment, the crystallization of the anionic cluster, [Fe8(IDC)12]12−. The FeN3O3, produced by the coordination of three κN,O-IDC3− fact that the Fe8 cluster was assembled under a basic medium molecules, which also form three independent FeNCCO chelate and crystallized under a acidic medium can be taken as evidence rings (Figure 1b). The geometry of each FeN3O3 moiety was about the chemical stability of [Fe8(IDC)12]12− over a broad pH also compared with an ideal octahedron using the SHAPE. range. CShM values of 1.13 and 1.00 were obtained for Fe(1) and Figure S2 shows the mass spectrum of 1 obtained by the linear Fe(2), respectively, confirming that the geometry of both ion trap in the range of 150−1500 m/z. The base peak at 573 m/ cations is well described as octahedron (Tables S4 and S5). On z c o r re l a t e s v e r y w el l w it h t h e ad d u c t sp e c i e s the other hand, as depicted in Figure 1c, the IDC3− anion is 22240 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article state (HS), having an FeN3O3 environment formed by κ2N,O′- HDCB2−/κ2N,O′-MeDCBI2− and κ4O,N,N′,O′-3,5-tBu2salpn, being the cations bridged by μ-1κ2N,O:2κ2N′,O‴-imidazole ligand as in 1 and presenting Fe−N = 2.126(3)−2.107(1) and Fe−O = 1.883(2)Å−2.223 Å bond distances.40 Also, in other imidazoles FeIII-HS compounds, the average Fe−N is 2.091 Å .41 All these data permitted us to infer that the Fe(1) and Fe(2) cations present in 1 can be assigned as FeIII-HS. Therefore, the iron cluster previously determined from structural X-ray measurements can be represented as [Fe8(IDC)12]12−. Literature reports different analogous M8-HnIDCn−3 com- pounds based on other transition metal cations (2−18), which are summarized in Table 2. For example, Liu et al. obtained under solvothermal conditions an anionic NiII cluster, [Ni8(HIDC)12]8− (2). This Ni8II cube is surrounded by a large number of solvent molecules and protonated 4,4′-trimethyle- Figure 1. (a) Molecular structure of 1 and view of the packing through nedipiperidine as countercations.42 Likewise, by a solvothermal the c axis. (b) Coordination environment of FeIII centers in 1 and (c) μ- reaction, Xu et al. reported the synthesis of another 0D NiII- 1κ2N,O:2κ2N′,O‴ bis-chelating bridge mode of IDC3−. neutral cubic cluster [(Ni8(H2IDC)8(HIDC)4)]·8(C2H5OH)· 18(H2O) (3), in which the H3IDC ligand is found both as di- acting as the μ-1κ2N,O:2κ2N′,O‴-IDC3− bis-chelating bridge, and monoprotonated species and also surrounded by solvate leading to an intercation distance of Fe(1)···Fe(2) = 6.3754(3) molecules.43 Meanwhile, Cheng et al. reported the synthesis at Å (Figure 1c). Additionally, each [Fe(IDC)3] moiety is chiral, room temperature of another anionic cluster without solvate being the handedness of Fe(1) Λ and Fe(2) Δ. Because of the molecules [Me4N]20[Co8(IDC)12] (4),44 but unfortunately, the Λ−Δ alternating arrangement, a centrosymmetric compound is crystalline structure was not reported in the publication. obtained. In compound 1, the Fe−N and Fe−O bond distances Moreover, extended networks obtained from the M8 anionic are in the range of 2.028(7)−2.093(7) Å and 1.985(6)− cluster and stabilized by the incorporation of a second metal 2.003(7) Å for Fe(1) and in the range of 2.069(7)−2.098 (7) Å cation have also been reported (5−10). In these cases, the and 1.979(7)−2.005(7) for Fe(2). Usually, in coordination imidazole ligand is present in the full deprotonated form compounds, the bond distance can be associated with the (IDC3−), giving a cluster with a highly negative charge. For oxidation and spin state of the cation. For example, Angaridis et compounds 6−10, the anionic cluster is stabilized by the linkage al. reported two molecular systems [Fe(3,5- tBu2salpn)- of alkaline cations to the carboxylate groups belonging to the (MeDCBI)Fe(3,5-tBu2-salpn)] and {[Fe- imidazole ligand.45 Besides, Cheng et al. reported a mixed- (3,5-tBu2salpn)]2(HDCBI)} (3,5-tBu2salpn = dianion of 1,3- valence CoII/CoIII cubic cluster forming a 1D heterometallic bis-[(di-tert-butylsalicylidene)amino]propane); H2MeDCBI = coordination polymer [Ni(cyclam)] 4 [Ni(cyclam)- 4,5-dicarboxy-1-methyl-1H-imidazole; H3DCBI = 4,5-dicarbox- (H2O)2]2{[Ni(cyclam)][Co8(IDC)12]}·41H2O (5). This ex- yimidazole).40 Both compounds are based on FeIII in a high-spin tended compound is assembled by the [Co6IICo2III(IDC)12]14− Table 2. Summary of M8 Cubes Reported in the Literature formula of the compound synthesis type dimension charge of the cluster H3IDC species ref [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O (1) R.T.e 0D −12 IDC3− this work Ni8(HIDC)12(H2TMDP)4(DMF)4(EtOH)4 (H2O)6a (2) solvothermal 0D −8 HIDC2− 42 [(Ni8(H2IDC)8(HIDC)4)]·8(C2H5OH)·18(H2O) (3) solvothermal 0D 0 H2IDC−/HIDC2− 43 [Me4N]20[Co8(IDC)12]b (4) R.T. 0D −20 IDC3− 44 [Ni(cyclam)]4[Ni(cyclam)(H2O)2]2 (5) R.T. 1D −14 IDC3− 44 {[Ni(cyclam)][Co8(IDC)12]}·41H2Oc K20[Ni8IDC12]·74(H2O) (6) R.T. 3D −20 IDC3− 43 K20[Ni8IDC12]·50(H2O) (7) R.T. 3D −20 IDC3− 43 K20[Ni8IDC12]·29(H2O) (8) R.T. 3D −20 IDC3− 43 {[Li11(Ni8IDC12)(H2O)12]Li9(H2O)20} (9) solvothermal 3D −20 IDC3− 45 {[Na20(Ni8IDC12)(H2O)28](H2O)13 (CH3OH)2} (10) solvothermal 3D −20 IDC3− 45 Zn12(guanidinium)8(IDC)8(HIDC)4·(DMF)8(H2O)3 (11) solvothermal 3D −16 HIDC2−/IDC3− 46 Cd8Na8(HIDC)8(IDC)4(H2Pip)2·(EtOH)5(H2O)37d (12) solvothermal 3D −12 HIDC2−/IDC3− 46 Zn8K8(HIDC)12(DMF)5(H2O)16 (13) solvothermal 3D −8 HIDC2− 46 Cd8K8(HIDC)12(DMF)5(H2O)16 (14) solvothermal 3D −8 HIDC2− 46 Co8K8(HIDC)12(DMF)5(H2O)16 (15) solvothermal 3D −8 HIDC2− 46 Mn8K8(HIDC)12(DMF)5(H2O)16 (16) solvothermal 3D −8 HIDC2− 46 [Cr4In4(HIDC)12]·H2O (17) solvothermal 0D 0 HIDC2− 47 [Cr7.28In0.72(HIDC)12]·H2O (18) solvothermal 0D 0 HIDC2− 47 a H2TMDP2+ = 4,4′-trimethylenedipiperidinium. bMe4N+ = tetramethylammonium, crystalline structure not reported. ccyclam = 1,4,8,11- tetraazacyclotetradecane. dH2Pip2+ = piperazinium. eR.T. = room temperature. 22241 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article Figure 2. (a) High-resolution Fe 2p, N 1s, C 1s, and O 1s XPS spectra. (b) Fe 2p spectra recorded after different exposure times to the X-ray beam of the XPS spectrometer: (a) 7 min, (b) 42 min, (c) 107 min, (d) 172 min, (e) 237 min, (f) 302 min, (g) 367 min, (h) 432 min, (i) 497 min, and (j) 562 min. Note the progressive transformation of the initial FeIII-HS species in an FeII-HS species. (c) N 1s spectra recorded after different exposure times to the X-ray beam of the XPS spectrometer: (a) 12 min, (b) 77 min, (c) 142 min, (d) 205 min, (e) 270 min, (f) 367 min, (g) 432 min, (h) 497 min, (i) 562 min, and (j) 592 min. Note how the intensity of the initial triethylammonium (Et3NH+) species decreases with increasing X-ray irradiation times. cluster, which is coordinated by the carboxylate group to the hindrance to avoid the assembly between the iron clusters, [Ni(cyclam)]2+ complexes.44 thus producing a molecular crystal packing for 1, as was also On the other hand, Alkordi et al. reported six 3D networks reported for the Ni8II analogous system with 4,4′-trimethylene- built from M8II anionic cubes (11−16).46 dipiperidinium.42 Accordingly, XPS, TG, and FTIR were Zn12(guanidinium)8(IDC)8(HIDC)4·(DMF)8(H2O)3 11 and performed to complement the structural characterization. Cd8Na8(HIDC)8(IDC)4(H2Pip)2(EtOH)5(H2O)37 12 contain 3.3. XPS. To gather more information about the chemical HIDC2− and IDC3− species as ligands. In the case of 11, the composition of 1, Fe 2p, N 1s, C 1s, and O 1s high-resolution negative charge is balanced by both guanidinium and zinc XPS spectra were also collected (Figure 2a). The Fe 2p spectrum cations, being the zinc cations also coordinating the carboxylates consists of an asymmetric spin-orbit doublet with binding groups belonging to the anionic cubes originating in this form energies of the Fe 2p3/2 and Fe 2p1/2 core levels of 711.5 and the 3D structure. For 12, sodium and a protonated amine 725.2 eV, respectively, and a small shake-up satellite at 717.8 eV. (piperazinium) are also balancing the charge of the cubic cluster. The shape of the spectrum, the binding energies of its different The authors also report a series of compounds components, and the presence of the small satellite are all M8K8(HIDC)12(DMF)5(H2O)16 (M = ZnII, CdII, CoII, and characteristic of iron in 3+ oxidation state and high-spin MnII) (13−16), containing only the HIDC3− species as a ligand, configuration,48,49 confirming the observation in the structural but in these cases, only alkaline cations are stabilizing the characterization. The N 1s spectrum was best-fitted to two [M8(HIDC)12]8− cluster in the 3D networks. The two last contributions. The major one, located at a binding energy of examples (17 and 18) were reported by Zhai et al.47 and 398.7 eV, can be ascribed to an amine-type or aromatic-type N− correspond to In I I I -Cr I I I heterometallic 0D cubes H bond belonging to the imidazole ring of the organic [Cr4In4(HIDC)12]·H2O and [Cr7.28In0.72(HIDC)12]·H2O, ligand.50,51 The higher binding energy component at 401.1 eV being neutral species and only including the HIDC2− in the is characteristic of a quaternary nitrogen species,50,51 which must structure. belong to the triethylammonium (Et3NH+) present in the In our case, although the molecular structure of the Fe8III core intercluster space of 1 and acting as a countercation. A fit was well identified by X-ray single-crystal analysis due to the size considering also the contribution to the N 1s spectrum of a of the cluster and the high symmetry of the cell, part of the ternary amine was not successful, discarding the presence of electronic density surrounding the cluster remained invisible for trimethylamine in the final product. The C 1s spectrum contains this technique, as has also been reported in an analogous cobalt three different carbon species at 284.6, 285.8, and 288.4 eV, octanuclear cluster.44 However, according to the examples which can be associated with C−C or C−H bonds; C−N, C−O, mentioned above, the full deprotonated IDC3− species generates CN, or C ≡ N bonds; and OCO bonds, respectively.50,51 M8 cubes with the highest negative charge, which is stabilized by The O 1s spectrum contains three contributions. The main one other metal cations or bulky protonated amines. Then, 12 at 531.4 eV can be associated with CO bonds in OCO counterions must be present in the compound to neutralize the groups, while the second one at 533.0 eV may correspond to C− negative charge of the resulting [Fe8(IDC)12]12− cluster. Since O bonds in OCO groups.50,51 The minor component at no additional iron centers were found in the intercluster space, 535.0 eV might be ascribed to a small oxygen satellite. only the triethylammonium cation should be acting as a All the identified bonds are part of the IDC3− anionic ligand counterion. This counterion also provides enough steric present in the cluster [Fe8(IDC)12]12−. Nevertheless, from a 22242 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article Figure 3. (a) Plots of χm vs T and χm−1 vs T for 1. (b) Images of magnetic pathways for the Fe8 moiety in 1 and the binuclear Fe2 simplified model. chemical viewpoint, the presence of a quaternary nitrogen degradation of quaternary nitrogen species (deprotonation) species corroborates that triethylammonium (Et3NH+) is the has also been reported for some organic compounds.50 The countercation of the anionic iron cluster, which is also consistent results are relevant because they stress the need of being with the reaction condition used to obtain 1. Therefore, the extremely careful when recording XPS data for this type of molecular structure of the iron cluster is deduced to be compound. Otherwise, erroneous conclusions can be drawn [Et3NH]12[Fe8(IDC)12]. from the recorded data. An important fact that was found during the development of 3.4. FTIR and Thermogravimetric Measurements. this work is that the sample is very sensitive to the irradiation by Figure S3a,b shows the infrared spectra of 1, compared with the X-rays of the XPS spectrometer and that it undergoes those of trimethylamine in acidic media and N,N-dimethylfor- important chemical changes after relatively short irradiation mamide. A clear match of the first two spectra between 3000 and times. To minimize the occurrence of these changes, we used a 2400 cm−1 can be observed, in agreement with the presence of low power in the X-ray gun (100 W against the more usual 300 the cationic Et3NH+ species in 1 (Figure S3a). Also, the strong W) and slightly higher pass energy (30 eV vs the usual 20 eV) to absorption at 1680 cm−1 (observed in the spectrum of 1) is record the data. Using a constant pass energy of 30 eV instead of exactly in the same position of the CO vibration associated 20 eV allows recording the spectra with a larger number of with DMF molecules (Figure S3b), indicating that this molecule counts in a given time without compromising too much the must also be present in the final formula. Additionally, energy resolution. So, for the Fe 2p spectrum shown in Figure thermogravimetric analysis was performed under a nitrogen 2b, we used only one scan (less than 5 min of irradiation) since atmosphere (Figure S4) to characterize the presence of solvent increasing the number of scans can lead to chemical change- molecules and thermal stability of 1. The cluster is stable until s.Figure 2b collects the Fe 2p spectra recorded after several 250 °C, showing two weight losses of 5.2% (30−90 °C) and increasing irradiation times. It is evident that, even after short 16.1% (190−250 °C) associated with solvate molecules. irradiation times (see spectra (b) and (c) in Figure 2b), the lines Considering that both H2O and DMF were used as a solvent of the Fe 2p spectrum shift to lower binding energies and a in the synthesis of 1 and as it has been reported for other strong shake-up satellite starts developing at around 714 eV. compounds,52 it is reasonable to assign the first loss to the These results clearly indicate that the initial FeIII-HS is release of 13 water molecules (5.2%) and the second one to 10 progressively reduced to an FeII-HS species upon X-ray DMF molecules (16.3%). At higher temperatures, a third weight irradiation. In fact, the spectra recorded at intermediate loss of 30.2% (250−360 °C) is observed. Literature data show irradiation times contain both FeII-HS/FeIII-HS contributions. that triethylammonium salts (triethylammonium bis-7,7,8,8- After long irradiation times (Figure 2b), the Fe 2p spectrum only tetracyanoquinodimethane) have a thermal decomposition shows the presence of FeII-HS species.49 Important changes are process between 195 and 220 °C.53 Additionally, the inorganic also observed in the N 1s spectra 2c. In this case, a decrease in cluster ([(HTEA)(TEA)0.75]2[PSb2IIIMo5VMo7VIO40]) shows a the intensity of the protonated Et3NH+ species is observed upon continuous weight loss (14.6%) between 44 and 573 °C, which X-ray irradiation. However, and contrary to the iron case, the is attributed by the authors to the release of tryethylamine.54 quaternary nitrogen species appears to be more resilient, as it is Therefore, the loss of 30.2% can be associated to the release of still present after long irradiation times. The mechanisms giving 12 trimethylamine (27.4%) belonging to 12 Et3NH+ acting as place to chemical changes under X-ray irradiation in XPS are counterions.55 Considering the solvate molecules, the final complex and have been commented in detail elsewhere.51 In formula of 1 is [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O, which particular, in the case of the reduction of metal cations in oxides, correlates very well with the elemental analysis given in the interionic Auger decay processes appear to play an important experimental section (section 2.1.1). With these results in mind, role.50 Among all the chemical changes reported, the Mössbauer spectroscopy, electronic paramagnetic resonance, 22243 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article and magnetic susceptibility measurements were also performed to characterize the properties of [Et3NH]12[Fe8(IDC)12]· 10DMF·13H2O. 3.5. EPR and Magnetic Measurements. The X-band EPR spectrum at room temperature of a polycrystalline sample of 1 shows a broad signal characteristic of an FeIII-HS ion with S = 5/ 2,56,57 with a line width of 376 G and a resonant field of 3330 G giving a value of g = 2.016 (Figure S5a). Magnetic measurements of 1 as a function of temperature were performed using a polycrystalline sample in the range of 1.8−300 K at 1 kOe. The temperature dependence of the magnetization is shown in Figure 3a as χm vs T and χm−1 vs T plots. The χm vs T plot shows an increase in the χm value as the temperature is lowered, leading to a maximum of 0.3 emu mol−1 at 50 K. From this temperature, a constant decrease is observed, leading to a non-zero value of 0.2 emu mol−1 at 1.8 K. On the other hand, the χm−1 vs T plot gives C and θ values of 44.6 emu mol−1 and −73.2 K, Figure 4. Fitting of χmT vs T at 1 kOe and using a simplified binuclear respectively. Furthermore, a 35.5 emu K mol−1 value is obtained model. at room temperature (4.44 emu K mol−1 per FeIII center) from the χmT vs T plot (Figure S5b), close to the expected for eight magnetic coupling constant of J = −3.8 cm−1 was obtained, with non-interacting FeIII-HS centers, 35.56 emu K mol−1 consider- an agreement factor of R = 8.5 × 10−3 (R = Σ(χmTobs) − ing SFe = 5/2 and g = 2.016. Lowering the temperature, the χmT (χmTexp)2/Σ(χmTobs)2). The use of a free g value gave a better fit product constantly decreases as the temperature reaches 100 K. (Figure S5c), obtaining J and g values of −5.28 cm−1 and 2.178, Below this temperature, a more pronounced decrease is respectively. In both cases, the negative sign and a similar observed, reaching a minimum value of 0.3 emu K mol−1 at magnitude of the magnetic exchange coupling confirm the 1.8 K. Clearly, the susceptibility data shows that an antiferromagnetic nature of the superexchange interaction of antiferromagnetic behavior is the predominant phenomenon FeIII-HS cations through μ-1κ2N,O:2κ2N′,O‴ bridges. However, of the Fe8III coordination cluster. Field-dependent magnet- the use of a g value of 2.016, obtained from EPR measurements, ization measurements were performed at 1.8, 3, 5, and 8 K and seems to be more adequate and in agreement with the structural represented as Nβ vs H and Nβ vs HT−1 plots (Figure S6). The features of the FeIII-HS cations. The magnitude and sign of the curves Nβ vs H show a lack of saturation at the studied coupling constants also are in agreement with the antiferro- conditions, leading to a maximum near to 4 μB at 90 kOe, very far magnetic interactions observed by Angaridis et al.40 between than the value expected for eight FeIII cations in high spin (40 FeIII-HS/FeIII-HS mediated by μ-1κ2N,O:2κ2N′,O‴ bridges with μB). For an antiferromagnetic system with a spin state of S = 0 at J = −4.8(2) cm−1. The interaction between FeIII-HS/FeIII-HS low temperatures, the observed magnetization only can belong can be rationalized considering the five magnetic orbitals from non-zero spin states that are close to the ground state. associated with FeIII-HS in an octahedral environment (two eg Then, the absence of saturation and the small values obtained for and three t2g). Thus, the interaction through the IDC3− ligand the magnetization corroborate that antiferromagnetic inter- generates a greater possibility of overlapping between the five actions predominate in the Fe8III coordination cluster at low orbitals of each FeIII-HS center.58 The fact that the binuclear temperatures. model presents a rather moderate fit of the magnetic behavior As Figure 3 shows, 12 equivalent μ-1κ2N,O:2κ2N′,O‴ can be explained on the base of the crude simplification of the magnetic pathways can be established (the edges of the cube) octanuclear structure of 1. An analogous Ni8II cluster was between the eight FeIII-HS in the octanuclear molecular reported by Liu et al.,42 (H2TMDP)4(DMF)4(EtOH)4- structure of 1, leading to the following spin Hamiltonian: (H2O)6[Ni8(HImDC)12] (DMF = N,N′-dimethylformamide, EtOH = ethanol, and H2TMDP = 4,4′-trimethylenedipiper- Ĥ 8 = −JSFe1SFe2 − JSFe2 SFe3 − JSFe3 SFe4 − JSFe4 SFe1 idinium), having the same cubic structure of 1 and the same μ- − JSFe5 SFe6 − JSFe6 SFe7 − JSFe7 SFe8 − JSFe5 SFe8 1κ2N,O:2κ2N′,O‴ connectivity between the metal cations. This compound also presents an antiferromagnetic behavior, with an − JSFe1SFe5 − JSFe2 SFe6 − JSFe3 SFe7 − JSFe4 SFe8 identical χm vs T tendency compared with 1. Although no exchange coupling values were given for this Ni8 cluster, this No analytical model has been developed for such a complex example suggests that the bulk magnetic properties of such cubic system. For this reason, the use of a simplified model was systems are related not only with the particular magnetic necessary. Considering the symmetry of the cluster, the cubic interactions of the metal cations through μ-1κ2N,O:2κ2N′,O‴ system can be simplified to a binuclear system that consists in but also with the spin topology arrangement within the whole two FeIII-HS cations, connected by a single μ-1κ2N,O:2κ2N′,O‴ cluster structure. In any case, more experimental and theoretical bridge (Figure 3b), leading to the following spin Hamiltonian: analyses should be performed to clarify the magnetic behavior of Ĥ 2 = −JSFe1SFe2 compound 1, perhaps studying the orbitals involved in each magnetic exchange pathway and the role of the topology of the A fit of the experimental susceptibility data by matrix cluster in the bulk magnetic properties. diagonalization using the Ĥ 2 spin Hamiltonian using the 3.6. Mössbauer Spectroscopy. The temperature evolution PHI36 software was performed between 300 and 1.8 K, of the Mössbauer spectra of 1 at 295, 77, and 4.2 K is shown in considering SFei = 5/2 and maintaining the g factor fixed to Figure 5. In the studied temperature range, each spectrum the experimental value obtained by EPR, g = 2.016 (Figure 4). A consists of a doublet, corroborating that Fe(1) and Fe(2) 22244 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article identify that a reduction process centered on the metal cation is produced under experimental conditions of the XPS technique. In fact, the recorded data have to be carefully analyzed to obtain the correct information on the oxidation state of the metal cation in this type of compound. Additionally, Mössbauer spectroscopy corroborated the spin and oxidation state of the iron center within the cluster, leaving no doubt that only FeIII-HS ions are present in the structure of 1. The performed magnetic measurements revealed that weak antiferromagnetic coupling is dominant in the whole temperature range. Although the literature reports the existence of MnII, NiII, CoII/III, ZnII, and CrIII-InIII negative or neutral cubic analogous systems forming 0D, 1D, or 3D compounds with either H2IDC−/HIDC2−/ IDC3− anionic species, compound 1 is the first member of this family based on FeIII. Despite the challenges presented for the characterization of 1, the present work collects a complete chemical and physical description of a new FeIII-HS coordina- tion cluster with a novel cubic structure. ■ ASSOCIATED CONTENT * Supporting Information sı The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c02420. Image of the yellow prismatic crystals of 1 (Figure S1); mass spectra (Figure S2); FTIR spectra (Figure S3); TG Figure 5. Mössbauer spectra of 1 at different temperatures. in the N2 atmosphere (Figure S4); EPR spectra, χmT vs T plot at 1 kOe; best-fit curve at 1 kOe (Figure S5); Nβ vs H present the same coordination environment. Furthermore, the and Nβ vs HT−1 plot (Figure S6); complete crystal data Mössbauer parameters at room temperature, isomer shift (δ = and structure (Table S1); peak list of mass spectra (Table 0.336(1) mm s−1) and quadrupole splitting (ΔEQ = 0.369(4) S2); and results of CShM calculation (Tables S3−5) mm s−1), are characteristics of FeIII-HS. As the temperature (PDF) decreases, the isomer shift increases, δ = 0.447(1) mm s−1 at 4.2 Crystal data and structure refinement for 1 (CIF) K, according to the second-order Doppler shift; nevertheless, the quadrupole splitting is nearly independent of the temperature (ΔEQ = 0.352(2) mm s−1 at 4.2 K), as expected for FeIII-HS ions for which the quadrupolar interaction is due only to the lattice ■ AUTHOR INFORMATION Corresponding Author contribution. In the same way, the presence of only a doublet Verónica Paredes-García − Facultad de Ciencias Exactas, even at 4.2 K would be indicative of the absence of magnetic ́ Departamento de Ciencias Quimicas, Universidad Andres Bello, order or that the relaxation time is shorter than the lifetime of the 8370146 Santiago, Chile; CEDENNA, 8380494 Santiago, nuclear excited state.59 For the antiferromagnetic FeIII-HS Chile; orcid.org/0000-0002-7537-7430; Phone: +56-2- coupled system, a sextet should be observed in the Mössbauer 26615756; Email: vparedes@unab.cl spectrum, below the critical temperature (50 K). Nevertheless, the spectra recorded at room temperature, 77 K, and 4 K are Authors almost the same, consisting of a sharp doublet instead of a sextet. Carlos Cruz − Facultad de Ciencias Exactas, Departamento de This behavior indicates that the relaxation time of compound 1 ́ Ciencias Quimicas, Universidad Andres Bello, 8370146 Santiago, is shorter than the lifetime of the nuclear excited state Chile; CEDENNA, 8380494 Santiago, Chile (experimental measurement time, 10−7 s).51 Such kind of Andrés Igor Vega Carvallo − Facultad de Ciencias Exactas, paramagnetic fast spin relaxation has also been reported for ́ Departamento de Ciencias Quimicas, Universidad Andres Bello, other polynuclear FeIII-HS coupled systems.60,61 8370146 Santiago, Chile; CEDENNA, 8380494 Santiago, Chile; orcid.org/0000-0001-6501-4161 4. CONCLUSIONS Evgenia Spodine − CEDENNA, 8380494 Santiago, Chile; A new iron octanuclear coordination cluster 1 was successfully ́ Facultad de Ciencias Quimicas y Farmacéuticas, Departamento synthesized under an acid−base reaction using a single ligand, ́ de Quimica ́ Inorgánica y Analitica, Universidad de Chile, 1H-imidazole-4,5-dicarboxylic acid (H3IDC). The cluster 8380492 Santiago, Chile [Fe8(IDC)12]12− is formed in basic media and crystallized in Albert Escuer − Departament de Quimica ́ Inorgànica, Universitat acid media, proving the chemical stability of the anionic Fe8 de Barcelona, 08028 Barcelona, Spain; orcid.org/0000- cluster in a wide pH range. On the other hand, XPS is a very 0002-6274-6866 powerful technique that permitted to identify the existence of José F. Marco − Instituto de Quimica ́ ́ Rocasolano, 28013 Fisica triethylammonium cations as a charge compensator that balance Madrid, Spain the charge of the anionic cluster, and to corroborate the Nieves Menéndez − Departamento de Quimica ́ ́ Aplicada, Fisica chemical identity of the cluster [Fe8(IDC)12]12− determined by Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 single-crystal X-ray diffraction. Moreover, it was possible to Madrid, Spain 22245 https://dx.doi.org/10.1021/acsomega.0c02420 ACS Omega 2020, 5, 22238−22247 ACS Omega http://pubs.acs.org/journal/acsodf Article Diego Venegas-Yazigi − CEDENNA, 8380494 Santiago, Chile; (11) McInnes, E. J. L.; Anson, C.; Powell, A. K.; Thomson, A. J.; ́ Facultad de Quimica y Biologia,́ Departamento de Quimica ́ de los Poussereau, S.; Sessoli, R. Solvothermal Synthesis of [Cr10(μ- Materiales, Universidad de Santiago de Chile, 9170022 Santiago, O2CMe)10(μ-OR)20] ‘Chromic Wheels’ with Antiferromagnetic (R = Chile; orcid.org/0000-0001-7816-2841 Et) and Ferromagnetic (R = Me) Cr(III)···Cr(III) Interactions. Chem. Commun. 2001, 10, 89−90. Complete contact information is available at: (12) Liu, J.-L.; Leng, J.-D.; Lin, Z.; Tong, M.-L. Ferromagnetic https://pubs.acs.org/10.1021/acsomega.0c02420 Homometallic Mn19 Cluster and Heterometallic Na2Mn15 Cluster with Large Spin State as Magnetic Refrigerants. Chem. − Asian J. 2011, 6, Notes 1007−1010. The authors declare no competing financial interest. (13) Goura, J.; Chandrasekhar, V. Molecular Metal Phosphonates. Accession code CCDC 1810846 contains the supplementary Chem. Rev. 2015, 115, 6854−6965. crystallographic data for this publication. These data can be (14) Kitashima, R.; Imatomi, S.; Yamada, M.; Matsumoto, N.; Maeda, obtained free of charge via www.ccdc.cam.ac.uk/data_request/ Y. Gradual Two-step Spin Crossover Behavior of Binuclear Iron(III) cif, or by emailing data_request@ccdc.cam.ac.uk, or by Complex Bridged by trans-1,2-Bis(4-pyridyl)ethylene. Chem. Lett. 2005, 34, 1388−1389. contacting The Cambridge Crystallographic Data Centre, 12 (15) Sheikh, J. A.; Jena, H. S.; Clearfield, A.; Konar, S. Phosphonate Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. ■ Based High Nuclearity Magnetic Cages. Acc. Chem. Res. 2016, 49, 1093−1103. ACKNOWLEDGMENTS (16) Evangelisti, M.; Candini, A.; Ghirri, A.; Affronte, M.; Piligkos, S.; The authors acknowledge FONDECYT 1170887, Proyecto Brechin, E. K.; McInnes, E. J. L. Molecular Nanoclusters as Magnetic Anillo CONICYT ACT 1404 grant, CONICYT-FONDE- Refrigerants: The Case of Fe14 with Very Large Spin Ground-State. QUIP/PPMS/EQM130086, CONICYT-FONDEQUIP/ Polyhedron 2005, 24, 2573−2578. (17) McCusker, J. K.; Christmas, C. A.; Hagen, P. M.; Chadha, R. K.; EQM140060, Chilean-French International Associated Labo- Harvey, D. F.; Hendrickson, D. N. Spin Frustration: A Hexanuclear ratory for Multifunctional Molecules, and Materials LIAM3- Ferric Complex with a S = 5 Ground State. J. Am. Chem. Soc. 1991, 113, CNRS N°1027 for financial support. The authors also 6114−6124. acknowledge Financiamiento Basal, AFB180001, CEDENNA (18) Weighardt, K.; Pohl, K.; Jibril, I.; Huttner, G. Hydrolysis and Laboratory of Analyses of Solids (L.A.S-UNAB). JFM Products of the Monomeric Amine Complex (C6H15N3)FeCl3: The acknowledges financial support from the Spanish Agencia Structure of the Octameric Iron(III) Cation of {[(C6H15N3)6Fe8(μ3- Estatal de Investigación (AEI) through Project No. RTI2018- O)2(μ2-OH)12]Br7(H2O)}Br·8H2O. Angew. Chem., Int. Ed. Engl. 1984, 095303-B-C51 and the Comunidad de Madrid through Project. 23, 77−78. NANOMAGCOST-CM P2018/NMT-4321. NM acknowl- (19) Konar, S.; Clearfield, A. 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