Octahedral monodithiolene complexes of cobalt(III) and chromium(III). Spectroscopic and density functional theoretical characterization of S,S'-coordinated benzene-1,2-dithiolate(1-) pi radicals.

The reaction of [M(tren)Cl(2)]Cl (M = Co(III), Cr(III)) with benzene-1,2-dithiol, H(2)(bdt), and 3,6-bis(trimethylsilyl)benzene-1,2-dithiol, H(2)(tmsdt), in a water/methanol mixture in the presence of potassium tert-butoxide produced green crystals of M(tren)(bdt)(1/2)(Cl)(1/2).H(2)O (1(PF(6))(1/2)(Cl)(1/2).H(2)O, M = Co; 2(PF(6))(1/2)(Cl)(1/2).H(2)O, M = Cr) and M(tren)(tmsdt)(1/2)(Cl)(1/2).H(2)O (1a(PF(6))(1/2)(Cl)(1/2).H(2)O, M = Co; 2a(PF(6))(1/2)(Cl)(1/2).H(2)O, M = Cr), respectively, upon addition of KPF(6). The structures of 1(PF(6))(1/2)(Cl)(1/2).H(2)O and 2(PF(6))(1/2)(Cl)(1/2).H(2)O have been determined by X-ray crystallography. Octahedral 1 and 1a are diamagnetic whereas 2 and 2a possess an S = (3)/(2) ground state. Cyclic voltammetry of 1a and 2a in CH(2)Cl(2) solution established that both species undergo a reversible one-electron oxidation generating the stable dications Co(III)(tren)(tmsdt(*)) (S = (1)/(2)) and Cr(III)(tren)(tmsdt(*)) (S = 1) where (tmsdt(*))(1-) represents the pi radical monoanion of oxidized (tmsdt)(2-). The electrochemical oxidations are ligand centered processes. These dications have been investigated by UV-vis and EPR spectroscopy and density functional calculations using the B3LYP functional. The S,S'-coordinated benzene-1,2-dithiolate(1-) radical has been identified and unambiguously characterized. Comparison with the corresponding o-benzosemiquinonate(1-) complexes shows that the S,S'-coordinated benzene-1,2-dithiolate(1-) radical is a sulfur centered radical whereas its oxygen containing analogue carries approximately 65% of the spin density on the six-membered ring.