Synthesis and characterization of metal tris-dithiocroconate complexes and dicyanomethylene-substituted analogues. 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 (dtcroc)(3)]. solvent (M = Cr, solvent = EtOH; M = Fe, solvent = DMF; M = Co, solvent = acetone; dtcroc = 3,4,5-trioxocyclopent-1-ene-1,2-dithiolato-) have been prepared and characterized. The magnetic properties of the paramagnetic Fe and Cr salts are consistent with strong-field octahedral coordination of the metal ion. The crystal structure of [Ph(4)P](3)[Co(dtcroc)(3)]. 0.6acetone confirms that the cobalt ion is octahedrally coordinated by the sulfur atoms of three chelating dithiocroconate 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 300 mV more anodic than those of any previously reported metal tris-dithiolene analogues. The [Fe(dtcroc)(3)](3-) ion also exhibits a quasi-reversible one-electron reduction. Reaction of [M(dtcroc)(3)](3-) ions with excess malononitrile in DMF solution yields dicyanomethylene-substituted analogues with the formula [M(dcmdtcroc)(3)](3-) (M = Cr, Fe, Co; dcmdtcroc = 4-dicyanomethylene-3 ,5-dioxocyclopent-1-ene-1,2-dithiolato). Replacement of the central oxo-group of each dithiocroconate ligand with the more electronegative dicyanomethylene group causes significant shifts in both the visible absorption bands and redox potentials of the complexes; however, the similar stabilities and magnetic properties of analogous [M(dcmdtcroc)(3)](3-) and [M(dtcroc)(3)](3-) complexes indicate that dicyanomethylene substitution on the ligand periphery does not dramatically alter the character of the metal-ligand interaction.