CHARGE-TRANSFER COMPLEXES OF METAL DITHIOLENES .15. ION-PAIR CHARGE-TRANSFER COMPLEXES OF DITHIOLENE METALATES WITH DIQUATERNARY 2,2'-BIIMIDAZOLES

Cycloalkylated biimidazolium dications (A(2+)) Of reduction potentials from -0.4 to -1.4 V form ion pair charge-transfer complexes {A(2+)[M( mnt)(2)](2-)} with dithiolene metalates, M = Zn, Ni, Pd, Pt, mnt(2-) = maleonitrile-2,3-dithiolate, X-ray analyses of {P(2)BBIm(2+)[Ni(mnt)( 2)](2-)} [P(2)BBIm(2+) = 1,1',3,3'-bis(prop ane-1,3-diyl)bibenzimidazo lium] and {B(2)BIm(2+) [Pd(mnt)(2)](2-)} [B(2)BIm(2+) = 1,1',3,3'-bis( butane-1,4-diyl)biimidazolium] reveal that the solid-state structure i s largely determined by the geometry of the acceptor. When the latter is strongly twisted, the usually observed mixed donor-acceptor columns are modified to a chain-like arrangement. In the case of the bibenzim idazolium dication P(2)BBIm(2+) the otherwise planar [Ni(mnt)(2)](2-) becomes tetrahedrally distorted. By the application of the Hush model a reorganization energy of about 67 kJ/mol is estimated for the therma l electron transfer from [M(mnt)(2)](2-) to A(2+) when M = Ni, Pd, Pt, but considerable deviations from this model are observed when M = Zn. Irradiation of the free biimidazolium accepters in the presence of ED TA affords the strongly reducing radical cations which reduce water to hydrogen in the presence of colloidal platinum. Attempts to sensitize this reaction by irradiating into the charge-transfer band of {A(2+)[ M(mnt)(2)](2-)} have failed until now. The molar absorptivity of one b iimidazolium radical cation is measured by spectroelectrochemistry.