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A new tetranuclear [2 × 2] cluster of Cu(II) with a symmetric carbohydrazone based ligand, [Cu 4 L 4 ](NO 3 ) 4 ·1.6(H 2 O) ( 1 ), {where HL donates bis-[( E )- N’ -(1-(pyridin-2-yl)ethylidene)]carbohydrazide} was synthesized and characterized by spectroscopic methods and X-ray analysis. The EPR spectra were performed on single crystals of complex 1 at various temperatures and allowed the identification and separation of two types of magnetic objects contributing to magnetism: single atoms of Cu(II) and a tetranuclear Cu 4 cluster. The main values of the g -factor and hyperfine structure were determined for single ions of Cu(II). The copper atoms in the tetramer are coupled antiferromagnetically with an isotropic antiferromagnetic exchange J = 215 K (149.4 cm −1 ). A small anisotropic exchange of the order of 0.06 K (0.04 cm −1 ) is responsible for the initial zero-field splitting of the energy levels in the tetramer spectrum. Magnetic measurements of complex 1 confirmed the existence of a strong antiferromagnetic exchange coupling between four Cu(II) ions. Complex 1 showed high potential for the catalytic and selective oxidation of cis -cyclooctene with aqueous H 2 O 2 . [ABSTRACT FROM AUTHOR]

We prepared crystalline [RE III (hfac) 3 (TMIO) 2 ] (RE = Gd, Y; abbreviated as RE-TMIO 2 ), where TMIO and hfac stand for 1,1,3,3-tetramethylisoindolin-2-oxyl and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, respectively. Two compounds are isomorphous in a C 2/ c space group. The paramagnetic TMIO ligand serves as an O-donor, and there are two TMIO moieties related with twofold symmetry in each molecule. The discrete molecular system guarantees the three- or two-centered exchange-coupling model. Magnetic study clarified that Gd-TMIO 2 behaved as a ground S total = 5/2 species with the intramolecular exchange couplings 2 J Gd-TMIO / k B = −12.5(4) K and 2 J TMIO–TMIO / k B = −27(2) K from an isosceles triangle model. Superexchange interaction across the diamagnetic Y ion was characterized in Y-TMIO 2 with 2 J TMIO–TMIO / k B = −21.3(2) K from the singlet–triplet model. DFT calculation on Y-TMIO 2 and a series of model compounds involving Rb + , Sr 2+ , Y 3+ , and Zr 4+ suggests a possible mechanism involving ligand-to-metal charge transfer interaction for the relatively strong radical–radical couplings. [ABSTRACT FROM AUTHOR]

In present work, a new approximation method has been proposed to calculate the exchange couplings in the Lanthanum Copper Manganate La 2 CuMnO 6 Double Perovskite, that verify the experimental Curie temperature T C exp , using Monte Carlo simulation under Metropolis algorithm in the frame of Ising model. Internal energy per site, Magnetization per site, Susceptibility and Specific heat have been established as a function of temperature and as a function of different values of the parameter α. [Display omitted] This paper presents a theoretical study of exchange couplings in double Perovskite La 2 CuMnO 6 , using Monte Carlo simulation. The Numerical method used in this project, is based on the relation between the internal energy and the magnetization per site in the framework of Ising model. To determine the exchange couplings, we have accepted the experimental Curie temperature observed under an external field h = 0.5 T , and we have adopted a new parameter titled α. In addition, in this project, the Internal energy of each magnetic configuration has been calculated, alongside the magnetization per site, the magnetic susceptibility and the specific heat. The Exchange couplings obtained are J Cu - M n = 12.058 m e V , J Cu - C u = - 9.135 m e V and J Mn - M n = 1.461 m e V. [ABSTRACT FROM AUTHOR]

Abstract: On the basis of the experimentally synthesized [(PY5Me2)4Mn4Re(CN)7]5+, the theoretically modeled clusters of [(PY5Me2)4V4Re(CN)7]5+ and [(PY5Me2)4Ni4Re(CN)7]5+ both have strong magnetic anisotropy energy barriers. [Copyright &y& Elsevier]

Abstract: DFT broken-symmetry calculations at the B3LYP level were carried out to evaluate the exchange coupling constants defined by the Heisenberg–Dirac–van Vleck spin Hamiltonian (HDvV), Ĥ =−2JŜaŜb, in a 1D chain of iron basic carboxylate cores [Fe3O(Piv)6(H2O)] bridged by dicyanamide, and two related trinuclear Fe3O moieties. The chain complex was modeled as two Fe3O units that preserve all features of the repetitive unit in the infinite real system. All geometries were taken from the crystallographic data previously reported. The obtained calculated values for the J constants are in good agreement with experimental results. The weak anti-ferromagnetic inter-Fe3O core interaction along the chain is also reasonably accounted by the calculations. This methodology appears as a useful tool in the theoretical evaluation of exchange coupling constants in 1D systems. [Copyright &y& Elsevier]

Abstract: The reaction of α-benzoinoxime, H2BNO with FeCl3 in the presence of Et3N as a base gives the mononuclear Fe(III) complex, Fe(HBNO)3 (1). Treatment of 1 with a methanolic solution of KOH at room temperature leads to a dinuclear Fe(III)–Fe(III) complex, [Fe(HBNO)2OH]2 (2). The complexes were initially characterized on the basis of their elemental, mass and thermal analyses. The IR studies were useful in assigning the coordination mode of the benzoinoxime ligand to the iron metal. In addition, the presence of a hydroxo-bridge in the dimeric complex 2 is inferred from the IR spectral studies. Room-temperature Mössbauer studies indicated octahedral, high-spin iron(III). Variable-temperature magnetic susceptibility measurements supported the existence of the μ-dihydroxo-bridging structure core, FeIII(μ-OH)2FeIII in the dinuclear complex 2. Theoretical modelling of the magnetic data indicated a weak antiferromagnetic spin exchange between the iron(III) centers (J =−8.35cm−1, g =2.01, ρ =0.02 and TIP= 1.7×10−4 cm3 mol−1 for H =−2JS 1 · S 2). The electronic spectra of the complexes revealed two bands due to d–d transitions and one band assignable to an oxygen (pπ)→Fe(dπ∗) LMCT transition observed in each complex. An additional charge-transfer transition, assignable to μ-hydroxo(pπ)→Fe(dπ∗), was observed for the dimeric complex 2. The structural and vibrational behaviors of these complexes have been elucidated with quantum mechanical methods. [Copyright &y& Elsevier]

Abstract: The synthesis, variable-temperature electronic absorption spectroscopy, magnetic susceptibility of a novel valence tautomer are presented, and thermodynamic parameters for the valence tautomeric equilibrium were determined. The dioxolene used is a semiquinone–nitronylnitroxide donor–acceptor ligand. Due to the ferromagnetic coupling inherent in the semiquinone–nitronylnitroxide donor–acceptor biradical, the CoIII form of the valence tautomer may display an additional stabilization of the high-spin ground state resulting from valence delocalization. As such, this would represent a unique example of double exchange in an organic system. [Copyright &y& Elsevier]

Abstract: Theoretical methods based on density functional theory have been employed to study the exchange interactions in a Fe11 complex. This molecule shows 10 different exchange coupling constants. The theoretical J values obtained agree well with the information available for similar complexes, being the single μ3-O bridging ligands those that present the strongest antiferromagnetic coupling. Monte Carlo simulations performed with the calculated J values reproduce fairly well the experimental data and the S value of 11/2 corresponding to the ground state. [Copyright &y& Elsevier]

Abstract: The preparation, structure and magnetic properties of two mono-N-substituted ethylenediammonium copper chloride salts are reported. Both [(MEDA)Cl]2CuCl4 and [(EEDA)Cl]2CuCl4 assume monoclinic layered perovskite A2CuCl4 type structures (here MEDA2+ is the N-methylethylenediammonium dication and EEDA2+ is the N-ethylethylenediammonium dication). In these structures, planar ions are linked together into layers of corner-sharing distorted octahedra via semi-coordinate Cu⋯Cl bonds. The magnetic studies reveal the presence of dominant ferromagnetic coupling in both compounds and analysis of the higher temperature data yielded J/k =19.29(1)K and 19.0(4)K for the methyl and ethyl derivatives, respectively. Further ac susceptibility studies reveal the onset of ferromagnetic ordering below 9.0K for both compounds. The ferromagnetic ordering is further confirmed by the presence of hysteresis loops with rapid saturation in both compounds. [Copyright &y& Elsevier]

Abstract: A series of mixed-metal solid solutions M x Cu1− x (hfac)2L (M=Mn, Ni, and Co) liable to undergo thermally induced spin transitions have been synthesized. The structure and magnetic properties of the compounds have been investigated. By varying the metal to be incorporated in the complex (Mn, Ni, or Co) and the value of x, one can control the character of the magnetic anomaly. [Copyright &y& Elsevier]

Frontier orbital perturbation theory analysis provides insight into a donor–acceptor contribution to ferromagnetic exchange in biradicals having two, chemically distinct paramagnetic groups. [Copyright &y& Elsevier]

Cu(hfac)2LH, Cu(hfac)2L1H, Cu(hfac)(CF3COO)LH, Cu(LH)2(NO3)2, and Cu(L1H)2(NO3)2, where LH and L1H are nitronyl- and iminonitroxides, respectively, containing an imidazol-4-yl substituent in the side chain have been synthesized. In the solid state, the molecules are linked by intermolecular N&z.sbnd;H⋯O hydrogen bonds, leading to the formation of dimers, bands, or polymer layers. The antiferromagnetic exchange interactions between the odd electrons of the paramagnetic centers are concentrated in the Cu(II)-coordinated nitroxide exchange clusters. The energies of these interactions are between −154 and −350 cm−1. [Copyright &y& Elsevier]