A study of silver (I) ion-organonitrile complexes: Ion structures, binding energies, and substituent effects

Density functional calculations at B3LYP/DZVP an 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 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 (CTD) 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 It are 39.4 and 34.7 kcal mol(-1).