Isostructural diamagnetic cobalt(III) and paramagnetic nickel(III) dithiolene complexes with an extended benzenedithiolate core [CpMIII(bdtodt)] (M = Co and Ni)

The isostructural diamagnetic [CpCo(bdtodt)] and paramagnetic [CpNi(bdtodt)] (Cp = η5-cyclopentadienyl, bdtodt:benzo[1,3]dithiol-2-one-5,6-dithiolato) complexes were prepared by starting from the corresponding bis(dithiocarbonate): benzo[1,2-d;4,5-d′]bis[1,3]dithiole-2,6-dione. Both Co and Ni complexes are isostructural and crystallize in the orthorhombic system, space group Pbca. The formally MIII (16-electron for CoIII and 17-electron NiIII) complexes were investigated by X-ray structure analyses and exhibit the same two-legged piano-stool geometry. The CV of the radical [CpNi(bdtodt)] resulted in well-defined reversible reduction and oxidation waves. On the other hand, oxidation of [CpCo(bdtodt)] leads to dimerization in CH2Cl2 or reaction in the more coordinating CH3CN solvent. The absorption maximum (λmax) of [CpNi(bdtodt)] (741 nm) showed a more red shift compared with [CpCo(bdtodt)] (595 nm) in dichloromethane solution. The structural similarities, and electrochemical, spectroscopic and magnetic differences between various [CpCo(dithiolene)] and [CpNi(dithiolene)] complexes are further analyzed.