SOLVENT TRAPPED VALENCY IN THE (PENTAAMMINERUTHENIUM)(MU-1,4-DICYANAMIDOBENZENE)] TRICATION

Cyclic voltammetry measurements show an unprecedented solvent dependen ce of metal-metal coupling for the symmetric mixed valence [3,2] compl ex, [{(NH3)(5)Ru}(2)(mu-dicyd)](3+), where dicyd(2-) is the 1,4-dicyan amidobenzene dianion. The comproportionation constant was determined t o be K-c = 10 and 68 400 in aqueous and acetonitrile solution, respect ively, The intervalence absorption band was deconvoluted from the low energy Ru(IIl)-cyanamide LMCT band by curve fitting analysis which gav e for the [3,2] complex assuming a gaussian IT band, E(op) = 8190 cm(- 1), Delta $($) over bar$$nu(1/2) = 4090 cm(-1) and epsilon(max) = 2590 M(-1) cm(-1) in aqueous solution and in acetonitrile solution E(op) = 6910 cm(-1), Delta $($) over bar$$nu(1/2) = 2640 cm(-1) and epsilon(m ax) = 19 400 M(-1) cm(-1). It is suggested that donor-acceptor interac tions between the solvent and ammine protons weakens the Ru(III)-cyana mide pi bond. Because the interaction between Ru(III) and the cyanamid e group is crucial to superexchange, metal-metal coupling is also weak ened. The acceptor properties of water may also play a role.