N-Heterocyclic based new nickel–bis(dithiolene) complexes: Synthesis, characterization and properties

Abstract

Five new nickel–bis(dithiolene) complexes (PPh4)2[NiII(C8H2N2S2R2)2] (R=pyridin-2-yl (1), pyridin-3-yl (2), thiophen-2-yl (3), furan-2-yl (4)) and (PPh4)[NiIII(C8H2N2S2R2)2] (R=naphthalen-2-yl (5)), have been prepared by the treatment of N-heterocyclic based dithiolene ligands with sodium metal in dry methanol followed by the addition of nickel chloride salt. All these dithiolene ligands and metal coordination complexes are characterized by LC–MS-, 1H NMR- and HRMS-, IR-, UV–Vis–NIR-spectroscopy, routine elemental analysis and cyclic voltammetry. Compounds 2 and 3 are structurally characterized by single crystal X-ray crystallography. Complex 2 crystallizes in monoclinic space group P2(1)/c, whereas complex 3 crystallizes in triclinic space group P1¯. Both these complexes (2 and 3) exhibit two-dimensional supramolecular networks through C–H⋯N hydrogen bonding interactions in their crystal structures. Nickel(II) compounds 1–4 exhibit a oxidative response in the range of E1/2=+0.17 to +0.21V versus Ag/AgCl, whereas, nickel(III) complex 5 shows both oxidative and reductive responses. Compounds 1–4 show electronic absorptions in the region of 630–650nm, while compound 5 exhibits absorption band at 890nm. The positions of the absorption maxima in the electronic absorption spectra of compounds 1 and 2 depend on the solvent polarity, whereas absorption bands of complexes 3–5 are not influenced by the solvent polarity.