Synthesis and characterization of nickel-group bis(dithiocroconate) complexes and dicyanomethylene-substituted analogues

Two series of nickel-group metal bis(dithiolene) complexes with ligands 4,5-disulfanylcyclopent-4-ene-1,2,3-trionate (L(1)) and 2-dicyanomethylene-4,5-disulfanylcyclopent-4-ene-1,3-dionate (L(2)) have been prepared and characterized: [NBu(4)(n)](2)[M(L(i))(2)] (M = Ni, Pd or Pt; i = 1 or 2). Oxidation of the dianion complexes yielded paramagnetic monoanions with ESR spectra indicative of a delocalized b(3g) HOMO (highest occupied molecular orbital), like that previously found for comparable bis(dithiolene) complexes. The intense low-energy visible absorptions and multiple, reversible reductions exhibited by the dianions likewise suggest that the LUMO (lowest unoccupied molecular orbital) is a ligand-based a(u)(pi*) orbital, rather than the b(1g)(d(xy)) orbital as commonly found for such complexes. The stabilization of the ligand-based LUMO in this case is attributed to the strongly electron-withdrawing character of the ligand substituents. Iodination of [NBu(4)(n)](2)[Pd(L(2))(2)] in CH2Cl2 solution yielded the novel iodine inclusion compound [NBu(4)(n)](2)[Pd(L(2))(2)]. I-2, which crystallizes in space group <P(1)over bar> with Z = 1, a = 10.792(3), b = 13.995(5), c = 10.737(3) Angstrom, alpha = 105.48(1), beta = 115.15(1) and gamma = 76.51(2)degrees at 25 degrees C. The I-2 molecules are associated with the complex anions through short [3.1696(9) Angstrom] S ... I contacts; however, the observed I-I distance [2.7354(4) Angstrom] indicates that the degree of charge transfer associated with this interaction is small.