Single-Molecule-Magnet FeII4FeIII2 and Antiferromagnetic FeIII4 Coordination Clusters

A tetracobalt(II) cluster with a two vertex truncated dicubane topology endogenously supported by carboxylate-based (2-pyridyl)methylamine ligands: magneto-structural and DFT studies

A reaction between CoCl2 and L3-(CO2-)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [CoII4-{L3-(CO2-)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2-)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2-)2}Cl units connected by a dimeric CoII2(μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm-1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = -2.5 cm-1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm-1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin-orbit coupling (λ = -158 cm-1) and axial distortion (energy gap Δ = -975 cm-1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.

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.

Heterobimetallic cyanide-bridged FeIII(μ-CN)MII complexes (M = Mn and Cu): synthesis, structure and magnetism

Systematic magneto-structural studies reveal ‘[FeIII(Tp)(CN)2(μ-CN)MnIICl(L1/L2)]′ (both antiferromagnetic) and [FeIII(Tp)(CN)2(μ-CN)CuII(L1/L2)]+′(L1 ferro- and L2 antiferromagnetic).

Dimeric Mn(ii), Co(ii), Ni(ii) and Cu(ii) complexes of a common carboxylate-appended (2-pyridyl)alkylamine ligand: structure, magnetism and DFT study

Weak anti- (1) and ferro-magnetic (2–4) interactions are observed in [MII2(L3)2(S)2]2+ (Mn 1, Co 2, Ni 3) (S = MeOH) and Cu 4 (S = none).

Synthesis and Structural Characterization of the Tetranuclear Iron(Iii) Cluster with Salicylic Acid

A new tetra-homonuclear iron(III) cluster, [Fe4O2(Sal)4(H2O)6]·4DMA·0.75H2O, where Sal= salicylic acid and DMA= N,N-dimethylacetamide consolidated via two µ3-oxo- and four salicylate-bridges was synthesized and characterized by IR spectroscopic method as well as by single crystal X-ray diffraction analysis. The structure of the obtained tetranuclear compound consists of four FeIII atoms in a “butterfly” arrangement. The coordination sphere of each of the two central FeIII atoms is generated by two μ3-oxo-bridging atoms and four oxygen atoms provided by the tridentate-bridging Sal2- ligands, while the coordination polyhedron of another two iron atoms involve six oxygen atoms from three water molecules, two salicylic and one μ3-oxigen atom. The Fe-O distances within Fe-O-Fe bridge are of 2.102(3) Å (for wing-body) and 2.038(3) Å (for body-body).

Li4Ru2OCl10·10H2O: crystal structure, magnetic properties and bonding interactions in ruthenium-oxo complexes

The results of the structural determination, magnetic characterization, and theoretical calculations of a new ruthenium-oxo complex, Li₄[Ru₂OCl₁₀]·10H₂O, are presented. Single crystals were grown using solvent methods and the crystal structure was characterized by single crystal X-ray diffraction. Li₄[Ru₂OCl₁₀]·10H₂O crystallizes into a low-symmetry triclinic structure (P1) due to the much smaller Li⁺ cation compared to K⁺ cation in the tetragonal complex K₄[Ru₂OCl₁₀]·H₂O. The X-ray photoelectron spectra confirm only the single valent Ru⁴⁺ in Li₄[Ru₂OCl₁₀]·10H₂O even though two distinct Ru sites exist in the crystal structure. Magnetic measurements reveal the diamagnetic property of Li₄[Ru₂OCl₁₀]·10H₂O with unpaired electrons existing on Ru⁴⁺. Furthermore, the molecular orbital analysis matches well with the observed UV and magnetic measurements.