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.

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Keywords Ammine complexes, Dicyanamido complexes, Electrochemistry, Mixed valence complex, Ruthenium complexes
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Journal Inorganica Chimica Acta
Naklicki, M.L. (Mark L.), & Crutchley, R. (1994). Solvent trapped valency in the [bis(pentaammineruthenium)-(μ-1,4-dicyanamidobenzene)] trication. Inorganica Chimica Acta, 225(1-2), 123–127. doi:10.1016/0020-1693(94)04038-9