Synthesis and X-ray crystal structure of the first mononuclear nickel(II) alkane thiolate complex with a mixed (S,N,N,O) ligand field

The six-step synthesis of a chiral, pentadentate dihydrosalen Ligand, carrying a mercaptomethyl group as additional binding site, is described. When this ligand was treated with nickel(II) salts, a planar tetracoordinated nickel chelate was obtained, and not the expected pentacoordinated species. This complex was fully characterized, including X-ray crystallography. The crystal structure revealed that the nickel ion is coordinated by the thiolate anion, both the amine and the imine nitrogen atoms of the Ligand, and by one phenolate anion. The second phenolic oxygen atom of the Ligand does not participate in the coordination of the nickel ion. This chelate is the first mononuclear nickel(II) thiolate complex having a mixed (S,N,N,O) Ligand field. Cyclic voltammetry did not indicate a reduction up to -2.1 V (vs. Fc/Fc(+)). In the anodic range, no reversible but two irreversible oxidation processes were observed.