SYNTHESIS AND CHARACTERIZATION OF METAL TRIS-DITHIOCROCONATE COMPLEXES AND DICYANOMETHYLENE-SUBSTITUTED ANALOGS - CRYSTAL AND MOLECULAR-STRUCTURE OF [PH(4)P](3)[CO(DTCROC)(3)]CENTER-DOT-0.6ACETONE

Metal tris-dithiolene compounds with the composition [Ph(4)P](3)[M (dt croc)(3)]. solvent (M = Cr, solvent = EtOH; M = Fe, solvent = DMF; M = Co, solvent = acetone; dtcroc = 3,4,5-trioxocyclopent-1-ene-1,2-dithi olato-) have been prepared and characterized. The magnetic properties of the paramagnetic Fe and Cr salts are consistent with strong-field o ctahedral coordination of the metal ion. The crystal structure of [Ph( 4)P](3)[Co(dtcroc)(3)]. 0.6acetone confirms that the cobalt ion is oct ahedrally coordinated by the sulfur atoms of three chelating dithiocro conate ligands. Each [M(dtcroc)(3)](3-) (M = Cr, Fe, Co) ion undergoes reversible or quasi-reversible one-electron oxidation in acetonitrile solution at 25 degrees C; the measured E(1/2)(-2/-3) values are ca 30 0 mV more anodic than those of any previously reported metal tris-dith iolene analogues. The [Fe(dtcroc)(3)](3-) ion also exhibits a quasi-re versible one-electron reduction. Reaction of [M(dtcroc)(3)](3-) ions w ith excess malononitrile in DMF solution yields dicyanomethylene-subst ituted analogues with the formula [M(dcmdtcroc)(3)](3-) (M = Cr, Fe, C o; dcmdtcroc = 4-dicyanomethylene-3 ,5-dioxocyclopent-1-ene-1,2-dithio lato). Replacement of the central oxo-group of each dithiocroconate li gand with the more electronegative dicyanomethylene group causes signi ficant shifts in both the visible absorption bands and redox potential s of the complexes; however, the similar stabilities and magnetic prop erties of analogous [M(dcmdtcroc)(3)](3-) and [M(dtcroc)(3)](3-) compl exes indicate that dicyanomethylene substitution on the ligand periphe ry does not dramatically alter the character of the metal-ligand inter action.