A Combined Experimental and Computational Study of the Magnetic Superexchange within a Triangular (mu 3-O)-Pyrazolato-FeIII3 Complex

The triangular complex [Fe III3(μ 3-O) (μ-4-O 2N-C 3H 2N 2) 6Br 3] 2- has been characterized and studied by magnetic susceptibility measurements, 57Fe Mössbauer and electron paramagnetic resonance (EPR) spectroscopic methods. A combination of experimental and computational results has allowed the differentiation between two sets of acceptable isotropic exchange constants. The magnetic exchange within this complex has been modelled by a spin Hamiltonian involving antiferromagnetic exchange constants of average value J av = -81.4 cm -1 and an antisymmetric exchange |d z| = 1.40 cm -1. Pyrazolato bridges have both a structural role and a non-negligible participation in magnetic exchange in trinuclear oxido-iron complexes Copyright © 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Experimental and theoretical Mossbauer study of an extended family of [Fe8(μ4-O)4(μ-4-R-px)12X4] clusters.

Six [Fe(8)(μ(4)-O)(4)(μ-4-R-pyrazolato)(12)X(4)] complexes containing an identical Fe(8)(μ(4)-O)(4) core have been structurally characterized and studied by Mössbauer spectroscopy. In each case, an inner μ(4)-O bridged Fe(III) cubane core is surrounded by four trigonal bipyramidal iron centers, the two distinct sites occurring in a 1:1 ratio. The Mössbauer spectrum of each of the clusters consists of two quadrupole doublets, which, with one exception (X = NCS, R = H), overlap to give three absorption lines. The systematic variation of X and R causes significant changes in the Mössbauer spectra. A comparison with values for the same clusters computed using density functional theory allows us to establish an unequivocal assignment of these peaks in terms of a nested model for the overlapping doublets. The changes in Mössbauer parameters (both experimental and computed) for the 1-electron reduced species [Fe(8)(μ(4)-O)(4)(μ-4-Cl-pyrazolato)(12)Cl(4)](-) are consistent with a redox event that is localized within the cubane core