DITHIOLENES REVISITED - AN ELECTRON-SPIN-RESONANCE STUDY OF SOME 5-CO-ORDINATE COBALT COMPLEXES AND THE CRYSTAL-STRUCTURES OF [CO(S2C2(CF3)(2))(2)(P(OPH)(3))] AND [CO(S2C2(CF3)(2))(2)(PPH(3))]

Isotropic and frozen-solution ESR spectra in CH2Cl2-ClCH2CH2Cl have be en recorded for the five-co-ordinate. formally cobalt(iv) complexes [C o(S(2)C(2)R(2))(2)L] [R = CN, L= PEt(3),; R = CF3 or Ph, L = PPh(3) or P(OPh)(3); R = C(6)H(4)Me-4, L- PPh(3) or PEt(3); R = C(6)H(4)OMe-4. L = PPh(3)]. The spectra can be described by approximately axial g and Co-59 hyperfine matrices with g parallel to = g(x) approximate to 1.9 9. g perpendicular to approximate to 2.03 and A parallel to = A(y) = 6 1 X 10(-4) cm-1. A perpendicular to approximate to 7 x 10(-4) cm(-1). These parameters are interpreted to show that the cobalt electronic st ructure is best regarded as low-spin d(5), formally Co-IV, but the sin gly occupied molecular orbital is extensively delocalized with only ab out 25% cobalt 3d(xz) character. The g and A principal axes are displa ced in the xy plane by the angle alpha which varies from 2 to 31 degre es, increasing with the steric bulk of R and L. This angle is related to the degree; of d(xz)/d(yz) hybridization resulting from molecular d istortion from C,, symmetry. The structures of [Co{S2C2(CF3)(2)}2L] [L = P(OPh)(3) or PPh(3)] were determined by X-ray diffraction methods. Both complexes are approximately square pyramidal, but for L= P(OPh)(3 ) (diamagnetic in the solid state) the molecules are packed in the cry stal as face-to-face pairs (Co...Co 4.11 Angstrom). Extended-Huckel mo lecular-orbital calculations performed for [Co{S2C2-(CF3)(2)}(2){P(OH) (3)}] support the interpretation of the ESR results.