The physical properties and structures of a series of six complexes of the type (NiN(2)S(2))W(CO)(4) have been used to establish electronic and steric parameters for square planar NiN(2)S(2) complexes as bidentate, S-donor ligands. According to the nu(CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of the tungsten carbonyl adducts, there is little difference in donor abilities of the five neutral NiN(2)S(2) metallodithiolate ligands in the series. The dianionic Ni(ema)(2)(-) (ema = N,N'-ethylenebis(2-mercaptoacetamide)) complex transfers more electron density onto the W(CO)(4) moiety. A ranking of donor abilities and a comparison with classical bidentate ligands is as follows: Ni(ema)(=) > {[NiN(2)S(2)](0)} > bipy approximately phen > Ph(2)PCH(2)CH(2)PPh(2) > Ph(2)PCH(2)PPh(2). Electrochemical data from cyclic voltammetry find that the reduction event in the (NiN(2)S(2))W(CO)(4) derivatives is shifted to more positive potentials by ca. 0.5 V compared to the ca. -2 V Ni(II/I) redox event in the free NiN(2)S(2) ligand, consistent with the electron drain from the nickel-dithiolate ligands by the W(CO)(4) acceptor. Differences in Ni(II/I) DeltaE(1/2) values appear to have a ligand dependence which is related to a structural feature of the hinge angle imposed by the (mu-SR)(2) bridges. Thus the angle formed by the intersection of NiN(2)S(2)/WS(2)C(2) planes has been established by X-ray diffraction analyses as a unique orientational feature of the nickel-dithiolate ligands in contrast to classical diphosphine or diimine ligands and ranges in value from 136 to 107 degrees . Variable-temperature (13)C NMR studies show that the spatial orientations of the ligands remained fixed with respect to the W(CO)(4) moiety to temperatures of 100 degrees C.

In pursuit of an analogy between bidentate diphosphane ligands and cis-dithiolato nickel complexes, the easily prepared [bis(mercaptoethane)diazacycloheptane]nickel complex, Ni-1Ј, has been treated with Pd II and Ni II sources. With the latter, trinickel species are observed with typical slantchair structures; for palladium(ii) chloride, a basket-type structure is realized in which the floor of the basket is a PdS 4 unit and the sides are N 2 S 2 units. One chloride atom is held

The metal binding affinity of an (N2S2)Ni bridging metallothiolate ligand (Zn2+ < Ni2+ < Cu+) gives precedent for the observed heterogeneity in ACS/CODH.

Monomeric five-coordinate nickel−cysteine complexes were prepared using anionic tris(3,5-disubstituted pyrazolyl)borates (Tp* - and TpPhMe-) and l-cysteine (ethyl ester and amino acid forms). Tp*NiCysEt crystallizes with a single methanol of solvation in the monoclinic space group P21:  a = 7.8145(18), b = 24.201(6), c = 7.9925(14) Å; β = 117.991(16)°. [Tp*NiCys-][K+] and TpPhMeNiCysEt show magnetic and electronic characteristics similar to Tp*NiCysEt, so that the trigonal bipyramidal coordination geometry confirmed for Tp*NiCysEt in the solid state likely applies to all three. All three complexes have high spin magnetic ground states at room temperature (μeff = 2.9−3.2 μB, S =1). Their electronic spectra are dominated by sulfur to nickel charge-transfer bands (388−430 nm in chloroform) with energies that correlate to respective thiolate basicities and TpX- donor strengths. The Tp* derivatives undergo a rapid reaction with molecular oxygen. Stoichiometric, infrared, and electronic spectroscopy measurements are consistent with formation of a sulfinate as a result of reaction with dioxygen. Kinetics measurements for the reaction of Tp*NiCysEt and O2 fit the following composite rate law:  rate = k 1[Tp*NiCysEt] + k 2[O2][Tp*NiCysEt] with k 1 = 0.013(1) min-1 and k 2 = 4.8(1) M-1·min-1 at 22 °C. Increased nucleophilicity of the nickel−sulfur center enhanced by electron donation from Tp*- (vs TpPhMe-) and encouraged by a trigonal bipyramidal geometry (vs square planar Ni(CysEt)2) is hypothesized as the reason for the susceptibility of Tp*NiCys complexes to oxygen.

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