Bimetallic iron-iron and iron-zinc complexes of the redox-active ONO pincer ligand

A new bimetallic platform comprising a six-coordinate Fe(ONO)₂ unit bound to an (ONO)M (M = Fe, Zn) has been discovered ((ONO^cat)H₃ = bis(3,5-di-tert-butyl-2-phenol)amine). Reaction of Fe(ONO)₂ with either (ONO^cat)Fe(py)₃ or with (ONO^q)FeCl₂ under reducing conditions led to the formation of the bimetallic complex Fe₂(ONO)₃, which includes unique five- and six-coordinate iron centers. Similarly, the reaction of Fe(ONO)₂ with the new synthon (ONO^sq˙)Zn(py)₂ led to the formation of the heterobimetallic complex FeZn(ONO)₃, with a six-coordinate iron center and a five-coordinate zinc center. Both bimetallic complexes were characterized by single-crystal X-ray diffraction studies, solid-state magnetic measurements, and multiple spectroscopic techniques. The magnetic data for FeZn(ONO)₃ are consistent with a ground state S = 3/2 spin system, generated from a high-spin iron(ii) center that is antiferromagnetically coupled to a single (ONO^sq˙)^2- radical ligand. In the case of Fe₂(ONO)₃, the magnetic data revealed a ground state S = 7/2 spin system arising from the interactions of one high-spin iron(ii) center, one high-spin iron(iii) center, and two (ONO^sq˙)^2- radical ligands.