Interaction of metal cations with alkylnitriles in the gas phase: Solvation of metal ions by the hydrocarbon chain

Relative affnity measurements of monovalent metal ions (M=Li+, Na+, Cu+ and Ag+) toward aliphatic nitriles have been performed using the kinetic method by dissociation of metal-bound dimer ions of the type R1C≡N-M+-N≡CR2. It was found, particularly for Cu+ and Ag+, that the affnity toward nitriles having long chains (>C6) is markedly enhanced. This is attributed to a bidentate interaction of the metal ion with the nitrile moiety and the aliphatic chain. Theoretical calculations on the copper complexes show that these bidentate structures enjoy about 30% greater copper-ion affnities compared to their linear counterparts. Such aliphatic interactions also play a major role in the dissociation chemistry of copper-bound tetramers of the kind (RC≡N)4Cu2+• where the long aliphatic chain R curls around the copper ion to facilitate electron transfer or a redox reaction to produce (RC≡N)2Cu+ + RC≡N2+• + RC≡N.

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