Novel N2S2 tetradentate chelate ligand H(2)tsalamo, which contains both thiol groups and C=N moieties, was synthesized as a remarkably stable compound. Complexation between H2tsalamo and nickel(II) acetate gave a square planar complex [Ni(tsalamo)] as dark brown crystals, whose structure was determined by X-ray crystallography. In contrast, the corresponding N2O2 ligands, salamo and 3-MeOsalamo, gave trinuclear and mononuclear complexes, respectively, in which all the nickel atoms have octahedral geometry.