Ion-pair charge-transfer complexes of a dithiooxalate zinc donor component with viologens. Synthesis, structural and electronic characterization

Abstract

Bipyridinium and phenanthrolinium acceptors 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 U 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 α 2, is calculated as 4.1 × 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.