Synthesis, characterization and crystal structures of nickel complexes with dissymmetric tetradentate ligands containing a mixed-donor sphere

Four new nickel(II) complexes of dissymmetric tetradentate ligands, contain ing mixed-ligand donor sets of NSNS or NSNO, have been synthesized. These c omplexes were prepared by facile template reactions of the appropriate alde hyde and amine in the presence of [Ni(H2O)(6)](BF4)(2), resulting directly in the desired nickel compounds. The nickel compounds were characterized by analytical, spectroscopic and electrochemical methods. The structures of [ Ni(pyzs)]BF4, [Ni(pyrs)]BF4 and [Ni(pyzo)]BF4 (see Scheme 1) have been dete rmined by single-crystal X-ray crystallography, showing the geometry of the nickel ion to be square-planar. Vis-NIR spectra show that the phenolate-co ntaining complexes [Ni(pyzo)]BF4 and [Ni(pyro)]BF4 (see Scheme 1) are essen tially square-planar in nitromethane, but tetragonal octahedral in methanol , whereas the thiophenolate-containing compounds [Ni(pyzs)]BF4 and [Ni(pyrs )]BF4 remain square-planar in both solvents. Titration of the thiophenolate -containing complexes with 1-methylimidazole results in diamagnetic five-co ordinated complexes. Electrochemistry shows quasi-reversible reductions to Ni(I) to occur for [Ni(pyzo)]BF4, [Ni(pyrs)]BF4 and [Ni(pyro)]BF4. (C) 2000 Elsevier Science B.V. All rights reserved.