Large spin differences in structurally related Fe6 molecular clusters and their magnetostructural explanation

Direct and remote control of electronic structures and redox potentials in μ-oxo diferric complexes

Non-heme diiron enzymes activate O2 for the oxidation of substrates in the form of peroxo FeIII2 or high-valent FeIV2 intermediates. We have developed a dinucleating bis(tetradentate) ligand system that stabilizes peroxo and hydroperoxo FeIII2 complexes with terminal 6-methylpyridine donors, while the peroxo FeIII2 intermediate is reactive with terminal pyridine donors presumably via conversion to a fluent high-valent FeIV2 intermediate. We present here a derivative with electron-donating methoxy substituents at the pyridine donors and its diferric complexes with an {FeIIIX(μ-O)FeIIIX} (X- = Cl-, OAc-, and OH-) or an {FeIII(μ-O)(μ-OAc)FeIII} core. The complex-induced oxidation of EtOH with H2O2 provides μ-OAc-, and in acetone, the complex with mixed OH-/OAc- exogenous donors is obtained. Both reactivities indicate a reactive fluent peroxo FeIII2 intermediate. The coupling constant J and the LMCT transitions are insensitive to the nature of the directly bound ligands X- and reflect mainly the electronic structure of the central {FeIII(μ-O)FeIII} core, while Mössbauer spectroscopy and d-d transitions probe the local FeIII sites. The remote methoxy substituents decrease the potential for the oxidation to FeIV by ∼100 mV, while directly bound OH- in {FeIII(OH)(μ-O)FeIII(OH)} with a short 1.91 Å FeIII-OOH bond decreases the potential by 590 mV compared to {FeIII(OAc)(μ-O)FeIII(OAc)} with a 2.01 Å FeIII-OOAc bond. Interestingly, this FeIII-OH bond is even shorter (1.87 Å) in the mixed OH-/OAc- complex but the potential is the mean value of the potentials of the OH-/OH- and OAc-/OAc- complexes, thus reflecting the electron density of the central {FeIII(μ-O)FeIII} core and not of the local FeIII-OH unit.

Semiempirical Magnetostructural Correlation for High-Nuclearity MnIII-Oxo Complexes: Accommodation of Different Relative Jahn-Teller Axis Orientations

The previous development of a magnetostructural correlation (MSC) for polynuclear FeIII/oxo clusters has now been extended to one for polynuclear MnIII/oxo clusters. A semiempirical model estimating each pairwise Mn2 exchange constant (Jij) from the Mn-O bond lengths and Mn-O-Mn angles has been formulated based on the angular overlap model. The extra complication, compared with the FeIII/oxo MSC, of different relative orientations of the Jahn-Teller distortion axes typical of high-spin MnIII in near-octahedral geometry was accommodated by developing a separate MSC variant for each possible situation. The final coefficients of the three MSC variants were determined by using reliable crystal structure data and experimentally determined Jij values from the literature. The estimated JMSC values from the new MnIII/oxo MSC have been employed to successfully rationalize the magnetic properties of a number of MnIII clusters in the nuclearity range Mn3-Mn10. These properties include relative spin vector alignments in the ground state, the presence of spin frustration effects, and the resulting overall ground state spin. In addition, the JMSC values can be used to simulate the direct-current magnetic susceptibility versus temperature data and provide realistic input values for fits of these data to minimize false-fit problems. A protocol for the use of the new MSC is also reported.

Odd and Even Numbered Ferric Wheels

The structurally related odd and even numbered wheels [FeIII 11 ZnII 4 (tea)10 (teaH)1 (OMe)Cl8 ] (1) and [FeIII 12 ZnII 4 (tea)12 Cl8 ] (2) can be synthesized under ambient conditions by reacting FeIII and ZnII salts with triethanolamine (teaH3 ), the change in nuclearity being dictated by the solvents employed. An antiferromagnetic exchange between nearest neighbors, J = -10.0 cm-1 for 1 and J = -12.0 cm-1 for 2, leads to a frustrated S = 1/2 ground state in the former and an S = 0 ground state in the latter.

Synthesis, Structure, and Magnetic Properties of an Fe36 Dimethylarsinate Cluster: The Largest "Ferric Wheel"

The synthesis and characterization of a high-nuclearity Fe^III/O/arsinate cluster is reported within the salt [Fe₃₆O₁₂(OH)₆(O₂AsMe₂)₆₃(O₂CH)₃(H₂O)₆](NO₃)₁₂ (1). The compound was prepared from the reaction of Fe(NO₃)₃·9H₂O, dimethylarsinic acid (Me₂AsO₂H), and triethylamine in a 1:2:4 molar ratio in acetonitrile. The Fe₃₆ cation of 1 is an unprecedented structural type consisting of nine Fe₄ butterfly units of two types, three {Fe^III₄(μ₃-O)₂} units A, and six {Fe^III₄(μ₃-O)(μ₃-OH)} units B, linked by multiple bridging Me₂AsO₂^- groups into an Fe₃₆ triangular wheel/loop with C₃ crystallographic and D₃ virtual symmetry that looks like a guitar plectrum. The unusual structure has been rationalized on the basis of the different curvatures of units A and B, the presence of intra-Fe₃₆ hydrogen bonding, and the tendency of Me₂AsO₂^- groups to favor μ₃-bridging modes. The cations stack into supramolecular nanotubes parallel to the crystallographic c axis and contain badly disordered solvent and NO₃^- anions. The cation of 1 is the highest-nuclearity "ferric wheel" to date and also the highest-nuclearity Fe/O cluster of any structural type with a single contiguous Fe/O core. Variable-temperature direct-current magnetic susceptibility data and alternating-current in-phase magnetic susceptibility data indicate that the cation of 1 possesses an S = 0 ground state and dominant antiferromagnetic interactions. The Fe₂ pairwise J_i,j couplings were estimated by the combined use of a magnetostructural correlation for high-nuclearity Fe^III/oxo clusters and density functional theory calculations using broken-symmetry methods and the Green's function approach. The three methods gave satisfyingly similar J_i,j values and allowed the identification of spin-frustration effects and the resulting relative spin-vector alignments and thus rationalization of the S = 0 ground state of the cation.

Magnetic Properties of High-Nuclearity Fex-oxo (x = 7, 22, 24) Clusters Analyzed by a Multipronged Experimental, Computational, and Magnetostructural Correlation Approach

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [Fe₇O₃(O₂CPh)₉(mda)₃(H₂O)] (1), [Fe₂₂O₁₄(OH)₃(O₂CMe)₂₁(mda)₆](ClO₄)₂ (2), and [Fe₂₄O₁₅(OH)₄(OEt)(O₂CMe)₂₁(mda)₇](ClO₄)₂ (3), where mdaH₂ is N-methyldiethanolamine. 1 was prepared from the reaction of [Fe₃O(O₂CPh)₆(H₂O)₃](NO₃) with mdaH₂ in a 1:2 ratio in MeCN, whereas 2 and 3 were prepared from the reaction of FeCl₃/NaO₂CMe/mdaH₂ in a 2:∼13:2 ratio and FeCl₃/NaO₂CMe/mdaH₂/pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of 1 consists of a central octahedral Fe^III ion held within a nonplanar Fe₆ loop by three μ₃-O^2- and three μ₂-RO^- arms from the three mda^2- chelates. The cores of the cations of 2 and 3 consist of an A:B:A three-layer topology, in which a central Fe₆ (2) or Fe₈ (3) layer B is sandwiched between two Fe₈ layers A. The A layers structurally resemble 1 with the additional Fe added at the center to retain virtual C₃ symmetry. The central Fe₆ layer B of 2 consists of a {Fe₄(μ₄-O)₂(μ₃-OH)₂}⁶⁺ cubane with an Fe on either side attached to cubane O^2- ions, whereas that of 3 has the same cubane but with an {Fe₃(μ₃-O)(μ-OH)} unit attached on one side and a single Fe on the other. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling in all complexes leading to ground-state spins of S = ⁵/₂ for 1 and S = 0 for 2 and 3. All Fe₂ pairwise exchange parameters (J_ij) for 1-3 were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity Fe^III/O complexes. The two approaches gave satisfyingly similar J_ij values, and the latter allowed rationalization of the experimental ground states by identification of the spin frustration effects operative and the resultant relative spin vector alignments at each Fe^III ion.

An [FeIII8] molecular oxyhydroxide

An [Fe^III₈] hexagonal bipyramid displays antiferromagnetic exchange between the two capping tetrahedral ions and the six ring octahedral ions resulting in a spin ground state of S = 10.

An [FeIII30] molecular metal oxide

Dissolution of FeBr₃ in a mixture of acetonitrile and 3,4-lutidine in the presence of an amine results in the formation of an [Fe₃₀] molecular metal oxide containing alternating layers of tetrahedral and octahedral Fe^III ions. Mass spectrometry suggests the cluster is formed quickly and remains stable in solution, while magnetic measurements and DFT calculations reveal competing antiferromagnetic exchange interactions.

[Fe15]: a frustrated, centred tetrakis hexahedron

The combination of two different Fe^III salts in a solvothermal reaction with triethanolamine results in the formation of a high symmetry [FeIII15] cluster whose structure conforms to a centred, tetrakis hexahedron.

Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF₄)₂·6H₂O with each ligand (H₂ L1 and H₄ L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe₃-μ₃-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ₃-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H₄ L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe₃-μ₃-O] and [Fe₃-μ₃-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe₃-μ₃-O···H···μ₃-O-Fe₃] species inferred crystallographically from the very short μ₃-O···μ₃-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.

Spin-Orbit Coupling Changes the Identity of the Hyper-Open-Shell Ground State of Ce+, and the Bond Dissociation Energy of CeH+ Proves to Be Challenging for Theory

Cerium (Ce) plays important roles in catalysis. Its position in the sixth period of the periodic table leads to spin-orbit coupling (SOC) and other open-shell effects that make the quantum mechanical calculation of cerium compounds challenging. In this work, we investigated the low-lying spin states of Ce⁺ and the bond energy of CeH⁺, both by multiconfigurational methods, in particular, SA-CASSCF, MC-PDFT, CASPT2, XMS-PDFT, and XMS-CASPT2, and by single-configurational methods, namely, Hartree-Fock theory and unrestricted Kohn-Sham density functional theory with 34 choices of the exchange-correlation functional. We found that only CASPT2, XMS-CASPT2, and SA-CASSCF (among the five multiconfigurational methods) and GAM, HCTH, SOGGA11, and OreLYP (among the 35 single-configuration methods) successfully predict that the SOC-free ground spin state of Ce⁺ is a doublet state, and CASPT2 and GAM give the most accurate multireference and single-reference calculations, respectively, of the excitation energy of the first SOC-free excited state for Ce⁺. We calculated that the ground doublet state of Ce⁺ is an intra-atomic hyper-open-shell state. We calculated the spin-orbit energy (E^SO) of Ce⁺ by the five multiconfigurational methods and found that E^SO calculated by CASPT2 is the closest to the experimental value. Taking advantage of the availability of an experimental D₀ for CeH⁺ as a way to provide a unique test of theory, we showed that all the multiconfigurational methods overestimate D₀ by at least 246 meV (5.7 kcal/mol), and only three functionals, namely, SOGGA, MN15, and GAM, have an error of D₀ that is less than 200 meV (5 kcal/mol).

Iron(III)-Oxo Cluster Chemistry with Dimethylarsinate Ligands: Structures, Magnetic Properties, and Computational Studies

A program has been initiated to develop Fe^III/oxo cluster chemistry with the "pseudocarboxylate" ligand dimethylarsinate (Me₂AsO₂^-) for comparison with the well investigated Fe^III/oxo/carboxylate cluster area. The synthesis and characterization of three polynuclear Fe^III complexes are reported, [Fe₁₂O₄(O₂C^tBu)₈(O₂AsMe₂)₁₇(H₂O)₃]Cl₃ (1), Na₂[Fe₁₂Na₂O₄(O₂AsMe₂)₂₀(NO₃)₆(Me₂AsO₂H)₂(H₂O)₄](NO₃)₆ (2), and [Fe₃(O₂AsMe₂)₆(Me₂AsO₂H)₂(hqn)₂](NO₃) (3), where hqnH is 8-hydroxyquinoline. The Fe₁₂ core of 1 is a type never previously encountered in Fe^III carboxylate chemistry, consisting of two Fe₆ units each of which comprises two {Fe₃(μ₃-O^2-)} units bridged by three Me₂AsO₂^- groups and linked into an Fe₁₂ loop structure by two anti-anti η¹:η¹:μ Me₂AsO₂^- groups, a bridging mode extremely rare with carboxylates. 2 also consists of two Fe₆ units, differing in their ligation from those in 1, and this time linked together into a linear structure by a central {Na₂(NO₃)₂} bridging unit. 3 is a linear Fe₃ complex with no monatomic bridges between Fe^III ions, a very rare situation in Fe^III chemistry with any ligands and unprecedented in Fe carboxylate chemistry. The distinct differences observed in arsinate vs carboxylate ligation modes are rationalized largely based on the greater basicity of the former vs the latter. Variable-temperature dc and ac magnetic susceptibility data reveal all Fe₂ pairwise interactions to be antiferromagnetic. For 1 and 2, the different J_ij couplings were estimated by use of a magnetostructural correlation for high nuclearity Fe^III-oxo clusters and by density functional theory calculations using broken symmetry methods, allowing identification of their relative spin vector alignments and thus rationalization of their S = 0 ground states. The J_ij values were then used as input values to give excellent fits of the experimental χ_MT vs T data. For 3, the fits of the experimental χ_MT vs T data to the Van Vleck equation or with PHI gave a very weak J₁₂ = -0.8(1) cm^-1 (H = -2JŜ_i·Ŝ_j convention) between adjacent Fe^III ions and an S = ⁵/₂ ground state. These initial Fe^III arsinate complexes also provide structural parameters that help validate literature assignments of arsinate binding modes to iron oxide/hydroxide minerals as part of environmental concerns of using arsenic-containing herbicides in agriculture.

A New FeIII Substituted Arsenotungstate [FeIII2(AsIIIW6O23)2(AsIIIO3H)2]12−: Synthesis, Structure, Characterization and Magnetic Properties

The iron(III)-containing arsenotungstate [FeIII2(AsIIIW6O23)2(AsIIIO3H)2]12− (1) was prepared via a simple, one-pot reaction in aqueous basic medium. The compound was isolated as its sodium salt, and structurally-characterized by Single Crystal X-ray Diffraction (SCXRD), Powder X-ray Diffraction (PXRD), Fourier-Transform Infrared (FT-IR) spectroscopy, Thermogravimetric Analysis (TGA) and elemental analysis. Its magnetic properties are reported; the antiferromagnetic coupling between the two FeIII centers is unusually weak as a result of the bridging geometry imposed by the rigid arsenotungstate metalloligands.

Inorganic Approach to Stabilizing Nanoscale Toroidicity in a Tetraicosanuclear Fe18Dy6 Single Molecule Magnet

Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe₁₈Dy₆ CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe₁₈Ln₆(μ-OH)₆(ampd)₁₂(Hampd)₁₂(PhCO₂)₂₄](NO₃)₆·38MeCN for Ln = Dy^III (1), Lu^III (2), or Y^III (3), where H₂ampd = 2-amino-2-methyl-1,3-propanediol, are reported. These can be described in terms of the cyclization of six {Fe₃Ln(μOH)(ampd)₂(Hampd)₂(PhCO₂)₄}⁺ units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy₃ triangles sandwiching a strongly antiferromagnetically coupled Fe₁₈ ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far.

Theoretical Studies on Hexanuclear [M3(μ3-O/OH)]2 (M = Fe(III), Mn(III), and Ni(II)) Clusters: Magnetic Exchange, Magnetic Anisotropy, and Magneto-Structural Correlations

Controlling spin Hamiltonian parameters such as magnetic exchange and magnetic anisotropy of polynuclear clusters is of great interest in the area of single molecule magnets (SMMs). Among large polynuclear clusters, hexanuclear clusters offer the best compromise in terms of size as they are often rigid, solution stable, and chemically amenable. The {M₆O₂} core is one of the common architectures known for many hexanuclear clusters and generally reported to possess a diamagnetic S_T = 0 spin ground state, barring a few exceptions. In these clusters, there are several open questions that are poorly understood: (a) What controls the nature of magnetic exchange, which in turn dictates the ground state spin values? (b) For clusters possessing a nonzero spin ground state, what dictates the magnetic anisotropy? Here, using density functional methods, we have attempted to shed light on these two question by evaluating the exchange coupling constants in [Fe₆^IIIO₂(OH)₂{(C₄N₂H₂SMe)₂C(OH)O}₂( ^tBuCO₂)₁₀] (1), [Fe₆^III(O)₂(O₂CH₂)(O₂CCH₂ ^tBu)₁₂(py)₂] (2), [Fe₆^III(O₂)(O)₂(O₂CCMe₃)₁₂(py)₂] (3), [Fe^III₆O₃(O₂CMe)₉(OEt)₂(bpy)₂]ClO₄ (4), [Mn^III₆O₂(O₂CH₂)(O₂CPe ^t)₁₁(HO₂CPe ^t)₂(O₂CMe)] (5), and [Ni^II₆(OH)₄(O₂C ^tBu)₈( ^tBuCO₂H)₄] (6) complexes. We have estimated all the eight near-neighbor exchange coupling constants in these clusters. Our calculations not only agree with the experimental results but also offer insight on the origin of the spin ground state. Extensive magneto-structural correlations developed by varying M-O-M angles and M-O distances reveal that J values are extremely sensitive to small structural distortions. Correlations developed indicate that both the parameters are important for Fe(III), but for Mn(III) and Ni(II), the angles were found to play a dominant role. Quite interestingly, the computed zero-field splitting parameter D _S=5 of complex 1 reveals that the exchange contribution to the anisotropy controls the sign of the ground state D value-an observation which differs from the general perception that the ground state D is controlled by the single-ion zero-field splitting parameter.

Hexanuclear iron(iii) α-aminophosphonate: synthesis, structure, and magnetic properties of a molecular wheel

A new hexanuclear molecular iron phosphonate complex, [Fe₆(HAIPA)₁₂(OH)₆]·nH₂O (1·nH₂O) (H₂AIPA = NH₂(CH₃)₂CP(O)(OH)₂, (2-aminopropan-2-yl)phosphonic acid), was synthesized from Fe²⁺ and Fe³⁺ salts in water by interaction with the ligand sodium salt.

Syntheses, crystal structures, magnetic properties and ESI-MS studies of a series of trinuclear CuIIMIICuII compounds (M = Cu, Ni, Co, Fe, Mn, Zn)

Six homo/heterotrinuclear Cu^IIM^IICu^II (M = Mn–Zn) compounds derived from salicylaldehyde-trans-1,2-diaminocyclohexane, which is a rarely utilized ligand, are reported.

Unprecedented family of heterometallic LnIII[18-metallacrown-6] complexes: syntheses, structures, and magnetic properties

Herein, a new family of Ln^III[18-metallacrown-6] compounds with the formula [Fe₆O₂Ln(tBu-sao)₆(OH)(MeO)₄(MeOH)(H₂O)]·6MeOH [Ln = Dy^III (1), Tb^III (2), Gd^III (3), and Y^III (4), tBu-saoH₂ = 3,5-di-tert-butylsalicylaldoxime] was synthesized through one-pot reactions using tBu-saoH₂, Fe(ClO₄)₃·6H₂O, and Ln(NO₃)₃·6H₂O. The four compounds are isostructural, and the encapsulation of a Ln ion in the ring cavity of 18-metallacrown-6 (18-MC-6) was exhibited for the first time. The structural analysis shows a ship-like 18-MC-6 core with a beset lanthanide ion connecting six ring oxygen atoms (O_MC). Magnetic measurements reveal domain antiferromagnetic coupling interactions between metal ions and field-dependent slow magnetic relaxation in 1-3.

Binding of ligands containing carbonyl and phenol groups to iron(iii): new Fe6, Fe10 and Fe12 coordination clusters

The initial use of ligands 2'-hydroxyacetophenone (HL¹), 2-hydroxybenzophenone (HL²) and 2,2'-dihydroxybenzophenone (H₂L³) in iron(iii) chemistry is described. The syntheses and crystal structures are reported for five iron(iii) clusters: [Fe₁₀O₄(OMe)₁₄(L¹)₆(MeOH)₂](NO₃)₂·3MeOH (1·3MeOH), [Fe₁₂O₄(OH)(OMe)₁₇(L¹)₈](ClO₄)₂·2H₂O (2·2H₂O), [Fe₁₀O₄(OMe)₁₄Cl₄(L²)₄(MeOH)₂] (3), [Fe₁₀O₄(OMe)₁₄(L²)₆(py)₂](ClO₄)₂·MeOH (4·MeOH), where py = pyridine, and [Fe₆O₂(OEt)₆(O₂CMe)₂(L³)₂(HL³)₂] (5). The molecular structures of the decanuclear clusters 1, 3 and 4 are organized around a {Fe₁₀(μ₄-O)₄(μ₃-OMe)₂(μ-OMe)₁₂}⁸⁺ core consisting of ten {Fe₃O₄} face-sharing defective cubane units. The core of 2 consists of a {Fe₁₂(μ₄-O)₄(μ₃-OMe)₄(μ-OH)(μ-OMe)₁₃}¹⁰⁺ unit composed of twelve {Fe₃O₄} face-sharing defective cubanes. The ligands (L¹)^- and (L²)^- in 1-4 adopt the O,O'-bidentate chelating coordination mode and their roles are to terminate the further aggregation of the Fe^III/O^2-/RO^- cores. Complex 5 contains the {Fe₆(μ₄-O)₂(μ-OEt)₆(μ-O_carbonyl)₂}⁴⁺ core, where the μ-O_carbonyl atoms are the bridging carbonyl oxygens of the two η¹:η²:η¹:μ (L³)^2- ligands; the (HL³)^- groups behave as O_phenolate, O_carbonyl-bidentate chelating ligands with the neutral hydroxyl group being unbound to the Fe^III atoms. The core is composed of four {Fe₃O₄} face-sharing defective cubanes. The Fe^III atoms in 1-5 are all six-coordinate with distorted octahedral geometries. The IR spectra of the complexes are discussed in terms of the known coordination modes of the ligands and the ionic character of nitrates and perchlorates. Variable-temperature magnetic susceptibility and variable-field magnetization measurements establish that 2, 3 and 5 have S = 3, 0 and 5 ground states, respectively. The susceptibility data for 5 were fitted using a 3-J model indicating the simultaneous presence of both antiferromagnetic and ferromagnetic Fe^IIIFe^III exchange interactions. Known magnetostructural correlations in oxido-bridged iron(iii) systems have been applied to rationalise the magnetic behaviour of the three clusters. The results of the present study demonstrate the utility of HL¹, HL² and H₂L³ in the stabilisation of robust iron(iii)/oxido/alkoxido clusters.

Nine members of a family of nine-membered cyclic coordination clusters; Fe6Ln3 wheels (Ln = Gd to Lu and Y)

We report a family of isostructural nonanuclear Fe^III–Ln^III cyclic coordination clusters, [FeIII6LnIII3(μ-OMe)₉(vanox)₆ (benzoate)₆], with a planar core structure built up from three [Fe₂Ln] units to give a giant Ln₃ triangle embedded into an Fe₆ ring.

Design and synthesis of a dinucleating ligand system with varying terminal donor functions that provides no bridging donor and its application to the synthesis of a series of FeIII–μ-O–FeIII complexes

We have developed the dinucleating ligands H₄julia, susan, and H₄hilde^Me2 and present their μ-oxo diferric complexes.

A single molecule magnet to single molecule magnet transformation via a solvothermal process: Fe4Dy2 → Fe6Dy3

Under ambient and solvothermal conditions four new compounds [FeIII4LnIII2(μ₃-OH)₂(mdea)₄(m-NO₂C₆H₄COO)₈]·3MeCN and [FeIII6LnIII3(μ₄-O)₃(μ₃-O)(mdea)₅(m-NO₂C₆H₄COO)₉]·3MeCN (Ln = Y and Dy) have been synthesised and their magnetic properties investigated.

A Strongly Spin-Frustrated Fe(III) 7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2

A disk-shaped [Fe(III) 7 (Cl)(MeOH)6 (μ3 -O)3 (μ-OMe)6 (PhCO2 )6 ]Cl2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral Fe(III) is 0.733 Å above the almost co-planar Fe(III) 6 wheel, to which it is connected through three μ3 -oxide bridges. For this iron-oxo core, the magnetic susceptibility analysis proposed a Heisenberg-Dirac-van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The (57) Fe Mössbauer (MS) analysis verifies that the central Fe(III) ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe(III) ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology.

A trigonal prismatic Cu6-pyrazolato complex containing a μ6-F ligand

The encapsulation of a fluoride ion in a trigonal prismatic CuII6-pyrazolato cage results in a small expansion of the Cu₆-host.

Syntheses, crystal structures and magnetic properties of a series of μ-phenoxo-μ1,1-carboxylato-μ1,3-carboxylato trinickel(II) compounds

The work in this report describes the syntheses, characterization, crystal structures and magnetic properties of eight linear trinickel(ii) compounds of the composition [Ni(II)3(L(sal-pyr))2(propionate)4] (), [Ni(II)3(L(sal-pyr))2(benzoate)4]·CH3CN (), [Ni(II)3(L(sal-pip))2(acetate)4]·2CH3CN (), [Ni(II)3(L(sal-pip))2(propionate)4] (), [Ni(II)3(L(sal-pip))2(benzoate)4]·CH2Cl2 (), [Ni(II)3(L(sal-mor))2(propionate)4] (), [Ni(II)3(L(sal-mor))2(benzoate)4]·3CH2Cl2 () and [Ni(II)3(L(sal-mor))2(o-Cl-benzoate)4]·2CH3CN·2H2O (), where HL(sal-pyr), HL(sal-pip) and HL(sal-mor) are the 1 : 1 condensation products of salicylaldehyde and 1-(2-aminoethyl)-pyrrolidine, 1-(2-aminoethyl)-piperidine and 4-(2-aminoethyl)-morpholine, respectively. One-half of the trinuclear core in each complex is symmetry related to the second part due to the presence of an inversion centre on the central metal ion and so the terminal nickelcentral nickelterminal nickel angle is 180°. The terminal and central nickel(ii) ions are triply bridged by a phenoxo, a μ1,1-carboxylato and a μ1,3-carboxylato moiety. The μ1,1-carboxylato also acts as a chelating ligand for the terminal metal ion. Both the variable-temperature (2-300 K) susceptibilities at a fixed field strength of 0.1 T and variable-field (up to 7 T) magnetization at different fixed temperatures (2-10 K) were recorded. The magnetic data indicate the ferromagnetic interaction in all the cases with J (Ĥ = -2Jij∑SiSj) values ranging between 2.37 and 3.89 cm(-1) and the single-ion zero-field parameter (D) ranging between 7.21 and 8.94 cm(-1). Satisfactorily simulation of both the χMT vs. T and M vs. H data has been obtained. Comparison of the structures and magnetic properties of compounds with those of the previously published related systems reveals some interesting aspects.

Magnetic refrigeration and slow magnetic relaxation in tetranuclear lanthanide cages (Ln = Gd, Dy) with in situ ligand transformation

Three tetranuclear lanthanide cages featuring either hemicubane (1 and 2) or distorted hemicubane (3) like cores are reported. Magnetic studies reveal significant magnetic entropy changes for complex 1 and a slow relaxation of magnetisation for 3.

Heptanuclear antiferromagnetic Fe(III)-D-(-)-quinato assemblies with an S = 3/2 ground state-pH-specific synthetic chemistry, spectroscopic, structural, and magnetic susceptibility studies

Iron is an essential metal ion with numerous roles in biological systems and advanced abiotic materials. D-(-)-quinic acid is a cellular metal ion chelator, capable of promoting reactions with metal M(II,III) ions under pH-specific conditions. In an effort to comprehend the chemical reactivity of well-defined forms of Fe(III)/Fe(II) toward α-hydroxycarboxylic acids, pH-specific reactions of: (a) [Fe3O(CH3COO)6(H2O)3]·(NO3)·4H2O with D-(-)-quinic acid in a molar ratio 1:3 at pH 2.5 and (b) Mohr's salt with D-(-)-quinic acid in a molar ratio 1:3 at pH 7.5, respectively, led to the isolation of the first two heptanuclear Fe(III)-quinato complexes, [Fe7O3(OH)3(C7H10O6)6]·20.5H2O (1) and (NH4)[Fe7(OH)6(C7H10O6)6]·(SO4)2·18H2O (2). Compounds 1 and 2 were characterized by analytical, spectroscopic (UV-vis, FT-IR, EPR, and Mössbauer) techniques, CV, TGA-DTG, and magnetic susceptibility measurements. The X-ray structures of 1 and 2 reveal heptanuclear assemblies of six Fe(III) ions bound by six doubly deprotonated quinates and one Fe(III) ion bound by oxido- and hydroxido-bridges (1), and hydroxido-bridges (2), all in an octahedral fashion. Mössbauer spectroscopy on 1 and 2 suggests the presence of Fe(III) ions in an all-oxygen environment. EPR measurements indicate that 1 and 2 retain their structure in solution, while magnetic measurements reveal an overall antiferromagnetic behavior with a ground state S = 3/2. The collective physicochemical properties of 1 and 2 suggest that the (a) nature of the ligand, (b) precursor form of iron, (c) pH, and (d) molecular stoichiometry are key factors influencing the chemical reactivity of the binary Fe(II,III)-hydroxycarboxylato systems, their aqueous speciation, and ultimately through variably emerging hydrogen bonding interactions, the assembly of multinuclear Fe(III)-hydroxycarboxylato clusters with distinct lattice architectures of specific dimensionality (2D-3D) and magnetic signature.