Ancillary Ligand Dependent Shifts in Charge Distribution for Cobalt–Quinone Complexes

The length of the carbon chain between the N-donor centers of the bidentate amine ligand NN ( = Me2N(CH2)nNMe2) determines the charge distribution in the redox isomers of cobalt complexes of the type [CoIII(NN)(sq)(cat)] and [CoII(NN)-(sq)2] with semiquinone (sq) and catecholate (cat) as additional ligands. Complexes with tmmda (n = 1) and tmeda (n = 2; 1) exist as CoIII isomers at temperatures below 350 K. The addition of a third methylene group (tmpda, n = 3; 2) to the chelate ring results in a dramatic drop in the CoIII/CoII transition temperature of 200 K.