Solvent trapped valency in the [bis(pentaammineruthenium)-(μ-1,4-dicyanamidobenzene)] trication

Cyclic voltammetry measurements show an unprecedented solvent dependence of metal-metal coupling for the symmetric mixed valence [3,2] complex, [{(NH3)5Ru}2(μ-dicyd)]3+, where dicyd2- is the 1,4-dicyanamidobenzene dianion. The comproportionation constant was determined to be Kc=10 and 68 400 in aqueous and acetonitrile solution, respectively. The intervalence absorption band was deconvoluted from the low energy Ru(III)-cyanamide LMCT band by curve fitting analysis which gave for the [3,2] complex assuming a gaussian IT band, Eop=8190 cm-1, Δν 1 2=4090 cm-1 and ε{lunate}max=2590 M-1 cm-1 in aqueous solution and in acetonitrile solution Eop=6910 cm-1, Δν 1 2=2640 cm-1 and ε{lunate}max=19 400 M-1 cm-1. It is suggested that donor-acceptor interactions between the solvent and ammine protons weakens the Ru(III)-cyanamide π bond. Because the interaction between Ru(III) and the cyanamide group is crucial to superexchange, metal-metal coupling is also weakened. The acceptor properties of water may also play a role