Valence Fluctionality of Trinuclear Ruthenium Complex Dimers

点击翻译按钮获取中文摘要

lntramolecular electron transfers within the mixed valence states of the ligand bridged hexaruthenium clusters Ru_3(mu_3-O)(mu-CH_3CO_2)_6(CO)(L)(mu-L')Ru_3(mu_3-O)(mu-CH_3CO_2)_6(CO)(L)(L' = 1,4-pyrazine ; L = 4-dimethyl-aminopyridine (1), pyridine (2), 4-cyanopyridine (3), or L' = 4,4'-bipyridine ; L = 4-dimethyl-aminopyridine (4), pyridine (5), 4-cyanopyridine (6) were examined. Two discrete and reversible single electron reductions are evident by cyclic voltammetry in the redox chemistry of 1 - 5, and the inter-cluster charge transfer complexes are well defined. The splitting of the reduction waves, E, is related to the electronic coupling H_<AB> between the triruthenium clusters, and varies from 80 mV for 5 to 440 mV for 1. In the case of 6, the splitting of the reduction waves, E, is < 50 mV and the inter-cluster charge transfer complex is not defined. The mixed valence states of 1 - 3 also exhibit intervalence charge transfer (ICT) bands in the region 12,100 cm^<-1> (1) to 10,80 … More 0 cm^<-1> (3) which provide spectroscopic estimates of H_<AB> in the range 2180 cm^<-1> (1) to 1310 cm^<-1> (3). The magnitude of the electronic coupling H_<AB> is found to strongly influence the IR spectra of the singly reduced (-1) mixed valence states of 1 - 6 in the n(CO) region. In the case of relatively weak electronic coupling (4 - 6), two v(CO) bands are clearly resolved. In the cases of strong electronic coupling (1 - 3), these bands broaden to a single v(CO) absorption band. These data allow the rate constants, kappa_c, for electron transfer in the mixed valence states of 1, 2, and 3 to be estimated by simulating dynamical effects (Bloch type equations) on v(CO) absorption bandshape at 9 x 10^<11> s^<-1>, 5 x l0^<11> s^<-1>, and ca . 1 x 10^<11> s^<-1>, respectively. The less strongly coupled 4,4'-bipyridine bridged complexes 4 - 6 exhibit IR lineshapes in the -1 mixed valence states that are not as strongly affected by electron transfer dynamics. The rate constant for the -1 mixed valence state of 4 is close to the lower limit that can be estimated by this approach, between 1 x 10^<10> and 1 x 10^<11> s^<-1>. Less