SYNTHESIS AND CHARACTERIZATION OF NICKEL-GROUP BIS(DITHIOCROCONATE) COMPLEXES AND DICYANOMETHYLENE-SUBSTITUTED ANALOGS

Two series of nickel-group metal bis(dithiolene) complexes with ligand s 4,5-disulfanylcyclopent-4-ene-1,2,3-trionate (L(1)) and ethylene-4,5 -disulfanylcyclopent-4-ene-1,3-dionate (L(2)) have been prepared and c haracterized: [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 occup ied 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 sug gest that the LUMO (lowest unoccupied molecular orbital) is a ligand-b ased a(u)(pi) orbital, rather than the b(1g)(d(xy)) orbital as common ly found for such complexes. The stabilization of the ligand-based LUM O in this case is attributed to the strongly electron-withdrawing char acter 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) An gstrom, alpha = 105.48(1), beta = 115.15(1) and gamma = 76.51(2)degree s at 25 degrees C. The I-2 molecules are associated with the complex a nions through short [3.1696(9) Angstrom] S ... I contacts; however, th e observed I-I distance [2.7354(4) Angstrom] indicates that the degree of charge transfer associated with this interaction is small.