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

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 mu-hydroxobis[Fe(III) porphyrin] with the smallest known Fe-O(H)-Fe angle [142.5(2)degrees] 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-N-p, Fe-O and Fe center dot center dot center dot Ct(p) 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 mu-oxo dimer (-J = 126.6 cm(-1)) is attenuated to only 4.5 cm(-1) simply by protonation to give the,mu-hydroxo complex.