GROUND-STATE ELECTRONIC-STRUCTURES OF BINUCLEAR IRON(II) SITES - EXPERIMENTAL PROTOCOL AND A CONSISTENT DESCRIPTION OF MOSSBAUER, EPR, AND MAGNETIZATION MEASUREMENTS OF THE BIS(PHENOLATE)-BRIDGE COMPLEX [FE2(SALMP)2]2-

A class of proteins containing oxygen-bridged exchange-coupled binucle ar iron sites can exist in various oxidation states, including the Fe2 +.Fe2+ form. A variety of techniques such as magnetic circular dichroi sm, EPR, Mossbauer spectroscopy, and magnetization measurements are ge nerally being used to study the electronic structure of the low-lying levels of these clusters. Because Fe2+ sites exhibit large zero-field splittings, large quadrupole splittings, and substantial anisotropies of the magnetic hyperfine interactions, researchers are faced with sol ving a difficult multiparameter problem. In order to develop an experi mental protocol for the study of iron-oxo proteins, we have investigat ed a structurally well-defined Fe2+.Fe2+ center with EPR, Mossbauer sp ectroscopy, and saturation magnetization. Here we report a consistent set of exchange, fine structure, and hyperfine structure parameters fo r the Fe2O6N2 coordination unit of [Fe2(salmp)2]2-, where salmp is bis (salicylidenamino)-2-methylphenolate(3-). The techniques employed yiel d J = -14 cm-1 (H(ex) = JS1.S2) for the exchange coupling constant. Th e Mossbauer data indicate that the two ferrous sites are equivalent. A ligand field analysis shows that the ferrous sites experience a trigo nal distortion of the octahedral coordination unit. The data obtained by the three techniques have been fitted with a spin Hamiltonian over a wide range of applied magnetic fields and temperatures.