A triangular iron(III) complex potentially relevant to iron(III)-binding sites in ferreascidin

An asymmetric triangular Fe¹¹¹ complex has been synthesized by an unusual Fe¹¹-promoted activation of salicylaldoxime. Formation of tile ligand 2(bis(salicylideneamino)methyl)phenol in situ is believed to occur through the reductive deoximation of salicylaldoxime by ferrous ions. The trinuclear ferric complex has been characterized on the basis of elemental analysis. IR, variable-temperature magnetic susceptibility, and EPR and Mossbauer spectroscopies. The molecular structure established by X-ray diffraction consists of a trinuclear structure with a [Fe₃(μ₃-O)(μ₂-OPh]⁶¹ core. Two iron ions are in a distorted octahedral 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 measurements revealed an S₁= 5/2 ground state with the antiparallel exchange interactions J = -34.3 cm¹ J = 4.7 cm¹ and D = - 0.90 cm¹. The EPR results are consistent with a ground state of S= 5/2 together with a negative D₅/₂ value. The Mossbauer isomer shifts together with the quadrupole splitting also provide evidence for the high-spin state of the three ferric sites. Magnetic Mossbauer spectra lead to the conclusion that the internal magnetic fields possibly lie in the plane of the three ferric ions.