A TRIANGULAR IRON(III) COMPLEX POTENTIALLY RELEVANT TO IRON(III)-BINDING SITES IN FERREASCIDIN

An asymmetric triangular Fe-III complex has been synthesized by an unu sual Fe-II-promoted activation of salicylaldoxime. Formation of the li gand 2-(bis(salicylideneamino)methyl)phenol in situ is believed to occ ur through the reductive deoximation of salicylaldoxime by ferrous ion s. The trinuclear ferric complex has been characterized on the basis o f elemental analysis, IR, variable-temperature magnetic susceptibility , and EPR and Mossbauer spectroscopies. The molecular structure establ ished by X-ray diffraction consists of a trinuclear structure with a [ Fe-3(mu(3)-O)(mu(2)-OPh)](6+) core. Two iron ions are in a distorted o ctahedral environment having FeN2O4 coordination spheres, and the five -coordinated third iron ion, with an FeNO4 coordination sphere, is in a trigonal bipyramidal environment. The magnetic susceptibility measur ements revealed an S-t=5/2 ground state with the antiparallel exchange interactions J=-34.3 cm(-1) J'=-4.7 cm(-1), and D=-0.90 cm(-1). The E PR results are consistent with a ground state of S=5/2 together with a negative D-5/2 value, The Mossbauer isomer shifts together with the q uadrupole splitting also provide evidence for the high-spin state of t he three ferric sites. Magnetic Mossbauer spectra lead to the conclusi on that the internal magnetic fields possibly lie in the plane of the three ferric ions.