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

The isostructural diamagnetic CpCo(bdtodt)] and paramagnetic CpNi(bdtodt)] (Cp = η⁵-cyclopentadienyl, bdtodt:benzo1,3]dithiol-2-one-5,6-dithiolato) complexes were prepared by starting from the corresponding bis(dithiocarbonate): benzo1,2-d;4,5-d′]bis1,3]dithiole-2,6-dione. Both Co and Ni complexes are isostructural and crystallize in the orthorhombic system, space group Pbca. The formally M^III (16-electron for Co^III and 17-electron Ni^III) 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 (λ_max) 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.