Electron spin resonance behaviour of the [Fe3Pt3(CO)15]– carbonyl cluster anion

Abstract

The e.s.r. spectra of the paramagnetic [Fe₃Pt₃(CO)₁₅]^– monoanion have been recorded in solution and in the solid state at variable concentration and temperature. A comparison of e.s.r. and electronic diffuse-reflectance spectra with X-ray structural data of [Fe₃Pt₃(CO)₁₅]^n–(n= 1 or 2) clusters suggests that the unpaired electron is mainly located in a non-degenerate molecular orbital of the triplatinum system which, under an idealized D_3h symmetry, may primarily be the a₂′* combination of three d_xz platinum orbitals. The stability of the paramagnetic cluster probably derives from the unpaired electron being localised mostly on the platinum atoms, and from the steric properties of the µ-Fe(CO)₄ groups which hinder spin-pairing by dimerization.