A Remarkably Bent Diiron(III)-μ-Hydroxo Bisporphyrin: Unusual Stabilization of Two Spin States of Iron in a Single Molecular Framework

Abstract

A novel diiron(III) bisporphyrin bridged by a hydroxo group between two cofacial Fe centers is reported. X-ray structural characterization revealed the remarkably bent μ-hydroxobis[Fe(III) porphyrin] with the smallest known Fe−O(H)−Fe angle [142.5(2)°] reported to date in an iron porphyrin. The close approach of the two rings in the molecule results in an unequal core deformation, and as a result, the geometrical parameters (such as the Fe−Np, Fe−O and Fe···Ctp distances) are all different for the two Fe(III) centers, leading for the first time to a natural way of stabilizing two different spins of iron in a single molecular framework with complete retention of their own spectroscopic identities in both the solid state and solution. The strong antiferromagnetic coupling between the two Fe(III) centers in the μ-oxo dimer (−J = 126.6 cm−1) is attenuated to only 4.5 cm−1 simply by protonation to give the μ-hydroxo complex.