A Study of Silver (I) Ion−Organonitrile Complexes:  Ion Structures, Binding Energies, and Substituent Effects

Density functional calculations at B3LYP/DZVP are used to obtain the binding enthalpies and free energies for the reaction Ag⁺ + XCN → AgNCX⁺, where X = H, CH<INF>3</INF>, NH<INF>2</INF>, OH, F, CF<INF>3</INF>, CN, NO<INF>2</INF>, N(CH<INF>3</INF>)<INF>2</INF>, C<INF>6</INF>H<INF>5</INF>, p-C<INF>6</INF>H<INF>4</INF>N(CH<INF>3</INF>)<INF>2</INF>, p-C<INF>6</INF>H<INF>4</INF>NO<INF>2</INF>, and p-C<INF>6</INF>H<INF>4</INF>NH<INF>2</INF>. The calculated binding enthalpies at 298 K range from 52.2 kcal mol^-1 for X = p-C<INF>6</INF>H<INF>4</INF>N(CH<INF>3</INF>)<INF>2</INF> to 21.3 kcal mol^-1 for X = NO<INF>2</INF>. Calculations at this level of theory are also used to optimize the structures of Ag(NCCH<INF>3</INF>)<INF>n</INF><INF></INF>⁺ and Ag(NCH)<INF>n</INF><INF></INF>⁺ ions, where n = 1−6. The binding enthalpies for the addition of the first and second molecules of CH<INF>3</INF>CN are 40.1 and 35.3 kcal mol^-1, whereas for HCN, they are calculated to be 31.2 and 28.3 kcal mol^-1, respectively. The binding enthalpies of the third and fourth ligands are much smaller at 15.9 and 10.8 kcal mol^-1 for CH<INF>3</INF>CN and 13.5 and 9.7 kcal mol^-1 for HCN. The 5- and 6-coordinate structures have positive free energies of formation with both ligands. Electrospraying a solution of AgNO<INF>3</INF> and acetonitrile in water shows the dominant ions to be Ag⁺, AgNCCH<INF>3</INF>⁺, and Ag(NCCH<INF>3</INF>)<INF>2</INF>⁺, with the Ag(NCCH<INF>3</INF>)<INF>3</INF>⁺ ion being observed only in very small amounts and only under relatively mild conditions. Energy-resolved collision-induced dissociation (CID) experiments confirm the Ag(NCCH<INF>3</INF>)<INF>3</INF>⁺ ion to be a loosely bound species, while the Ag(NCCH<INF>3</INF>)<INF>2</INF>⁺ and AgNCCH<INF>3</INF>⁺ ions have substantially higher and comparable binding energies. Using the threshold method, we determined the binding energies at 0 K of NCCH<INF>3</INF> to Ag⁺ and of NCCH<INF>3</INF> to AgNCCH<INF>3</INF>⁺ to be 38.7 and 34.6 kcal mol^-1, respectively; the corresponding energies at 298 K are 39.4 and 34.7 kcal mol^-1.