Transition-metal complexes with sulfur ligands. 55. Nickel complexes with thiolato-thioether ligands including nitrogen and oxygen donors in S6, S5, OS4, NS4, and S4 donor sets. Syntheses, properties, and x-ray structure determinations of [Ni('S6')], [Ni('S5')], [Ni('OS4')]2, [Ni('S4-C5')]2, and [Ni('S4-C3')]