Synthesis and characterization of metal tris-dithiocroconate complexes and dicyanomethylene-substituted analogues. Crystal and molecular structure of [Ph 4P] 3[Co(dtcroc) 3]·)0.6acetone

Abstract

Metaltris-dithiolene compounds with the composition [Ph 4P] 3[M(dtcroc) 3]·solvent (M s= Cr, solvent s= EtOH; M s= Fe, solvent s= DMF; M s= Co, solvent s= 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 4P] 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 s= Cr, Fe, Co) ion undergoes reversible or quasi-reversible one-electron oxidation in acetonitrile solution at 25°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 s= Cr, Fe, Co; dcmdtcroc s= 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.