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, CH3, NH2, OH, F, CF3, CN, NO2, N(CH3)2, C6H5, p-C6H4N(CH3)2, p-C6H4NO2, and p-C6H4NH2. The calculated binding enthalpies at 298 K range from 52.2 kcal mol-1 for X = p-C6H4N(CH3)2 to 21.3 kcal mol-1 for X = NO2. Calculations at this level of theory are also used to optimize the structures of Ag(NCCH3) n + and Ag(NCH) n + ions, where n = 1−6. The binding enthalpies for the addition of the first and second molecules of CH3CN 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 CH3CN 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 AgNO3 and acetonitrile in water shows the dominant ions to be Ag+, AgNCCH3 +, and Ag(NCCH3)2 +, with the Ag(NCCH3)3 + ion being observed only in very small amounts and only under relatively mild conditions. Energy-resolved collision-induced dissociation (CID) experiments confirm the Ag(NCCH3)3 + ion to be a loosely bound species, while the Ag(NCCH3)2 + and AgNCCH3 + ions have substantially higher and comparable binding energies. Using the threshold method, we determined the binding energies at 0 K of NCCH3 to Ag+ and of NCCH3 to AgNCCH3 + 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.