Iron and cobalt complexes of 2,6-diacetylpyridine-bis(R-thiosemicarbazone) (R = H, phenyl) showing unprecedented ligand deviation from planarity

The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four complexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone) (H2L1) and 2,6-diacetylpyridinebis(phenylthiosemicarbazone) (H2L2), including a cobalt dimer displaying a deviation from planarity which is unprecedented for this class of ligands and allows the ligand to occupy five positions of a pseudo-octahedral coordination sphere. This dimer reacts with KCN to produce a mononuclear complex of relevance to the active site of cobalt nitrile hydratase.