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 potentials form with zinc 1,2-dithiooxalates (dto) ion-pair charge-transfer complexes of the general formula {A(2+) [Zn(dto)(2)](2-)}. The contact 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 of spectroscopic, electrochemical and quantum-chemical investigations the relation between optical and thermal electron transfer within the ion 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 the dithiooxalate unit, a hypsochromic shift of the position of the IPCT band, compared with the metal dithiolenes, results. The extent of electron 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 structure is largely determined by the geometry of the acceptor component.