ION-PAIR CHARGE-TRANSFER COMPLEXES OF A DITHIOOXALATE ZINC DONOR COMPONENT WITH VIOLOGENS - SYNTHESIS, STRUCTURAL AND ELECTRONIC CHARACTERIZATION

Bipyridinium and phenanthrolinium accepters of different reduction pot entials form with zinc 1,2-dithiooxalates (dto) ion-pair charge-transf er complexes of the general formula {A(2+) [Zn(dto)(2)](2-)}. The cont act ion pairs exhibit absorptions in the range 390-490 nm which can be attributed to the ion-pair charge-transfer (IPCT) type. On the base o f spectroscopic, electrochemical and quantum-chemical investigations t he relation between optical and thermal electron transfer within the i on pair applying the Hush theory is discussed. The mean reorganization energy of 12 complexes is 180 kJ mol(-1) and exceeds the values found for the dithiolene systems. Due to the diminished donor ability of th e dithiooxalate unit, a hypsochromic shift of the position of the IPCT band, compared with the metal dithiolenes, results. The extent of ele ctron delocalization from [Zn(dto)(2)](2-) to PQ(2+), as described by the parameter alpha(2), is calculated as 4.1 x 10(-6). X-ray analyses of BQ[Zn(dto)(2)] and DP[Zn(dto)(2)] reveal that the solid-state struc ture is largely determined by the geometry of the acceptor component.