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An analysis of Mossbauer spectra from a model complex of known structure with an Fe(super 2+)(S1=2)-muOH-Cr(super 3+)(S2=3/2) center and of its Fe(super 3+)(S1=5/2)-muO-Cr(super 3+)(S2=3/2) analog reveals that effective S(super eff) = 1/2 and S(super eff) = 1 Hamiltonians successfully reproduce 4.2 K spectra, as antiferromagnetic spin coupling between Fe and Cr ions which results in S(super eff) = 1/2 and S(super eff) = 1 was confirmed. Analysis of the 4.2K spectra from the Fe(super 2+)(S1=2)-muOH-Cr(super 3+)(S2=3/2) center in terms of a spin Hamiltonian that includes the isotropic exchange and zero-field splittings was also conducted.

Photochemical or chemical oxidation of Fe(III)-hexadentate macrocyclic ligand complexes, FeLp or FeLo, involves the elimination of an electron from a phenolate ligand, leading to the formation of cationic complexes. FeLo and FeLp can be used as biocatalysts for the reaction of metal ions and radicals. These radicals show a homology to the protonated parent compounds, as revealed by Mossbauer, UV/vis and resonance Raman spectroscopies.

Bulky clusters containing eight high-spin iron(III) ions of the formula (((tacn)6Fe8(mu3-O)2(mu2-OH)12)Br7-(H2O))Br.H2O, Fe8, tacn = 1,4,7-triazacyclononane were used to determine the magnetic susceptibility of large clusters. Results showed that the S = 10 spin rate can be described in terms of a dominant spin configuration where the time spins for Fe5, Fe6, Fe7 and Fe8 are parallel to each other. The Fe8 ion cluster was found to possess the highest spin in the ground state.

Magnetization and ac-susceptibility investigation of Fe8 clusters were conducted to gain a deeper understanding of the physics underlying the resonant tunneling of magnetization. The clusters, made of eight iron ions, had a ground state S=10. Peaks in the curves of the samples were observed at fields H(sub n)=nH(sub o). These peaks were well described by the thermally assisted resonant quantum tunneling of magnetization.

The superoxidized Mn(super III)Mn(super IV) state of dimanganase catalase from Thermus thermophilus and a series of structurally similar Mn(super III)Mn(super IV) complexes were investigated using continuous wave (CW) and pulsed EPR spectroscopy at X- (9 GHz), Q- (34 GHz) frequencies. An important experimental aspect is the elimination of Mn(super II) impurities, which give rise to very intense lines superimposed to the spectrum of the Mn(super III)Mn(super IV) complex.

The observed metal-ligand bond lengths in the mixed-valence complex (ttacnMnII(mu-OH)(mu-pivolanto)2-MnIIIttacn)(ClO4)2 indicated a significant temperature dependence in the 20-298 K range. Spectroscopic and crystallographic studies show that this dependence is caused by a superposition of two orientations with different energies in the crystal, which are interconverted by electron transfer between the metal centers.