Hydrogen bonding promotes diversity in nitrite coordination modes at a single iron(II) center

A low-valent[FeN5(OTf)(2)]complex and its bisnitrite adduct,[FeN5(NO2)(2)], have been synthesized in the interest of extending the reactivity of Fe complexes featuring redox-active ligands with secondary coordination sphere hydrogen-bond donors to nitrite reduction. Crystallographic characterization of[FeN5(NO2)(2)]reveals that the nitrite ligands demonstrate both eta(1)-NO2(N-nitro) and eta(1)-ONO (O-nitrito) coordination modes. H-bonding between nitrite ligands and the protons on secondary amine moieties in theN(5)ligand play a pivotal role in positioning the nitrite ligands in multiple coordination modes. These results provide insights into the role of H-bonding in supporting disparate coordination modes of this substrate that can be translated to mechanisms of nitrite reduction in biological systems.