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The binding energies at 0 K of sodium and silver ions to ammonia, methylamine, ethylamine, acetonitrile, and benzonitrile were determined using threshold collision-induced dissociation (CID) and molecular orbital calculations at the ab initio and density functional theory levels. There is good agreement between experimental and calculated binding energies. For the five ligands, threshold CID/CCSD(t)(fu)/6-311++G(2df,p)//MP2(fu)/6-311++G(d,p) Na⁺ binding energies are the following:  ammonia, 25.6 ± 2.8/24.8; methylamine, 27.0 ± 1.4/25.9; ethylamine, 27.7 ± 2.3/27.1; acetonitrile, 30.0 ± 2.3/30.3; and benzonitrile, 32.7 ± 1.4/35.0 (B3LYP/6-311++G(d,p)//B3LYP/6-311++G(d,p)) kcal/mol. Threshold CID and B3LYP/DZVP Ag⁺ binding energies are the following:  ammonia, 40.6 ± 3.0/38.9; methylamine, 41.5 ± 2.3/41.1; ethylamine, 42.9 ± 1.4/43.2; acetonitrile, 40.8 ± 2.0/39.3; and benzonitrile, 41.5 ± 2.8/43.1 kcal/mol. Wherever comparisons with literature data are possible, the Na⁺ binding energies determined in this study are in good agreement with established data. For Ag⁺ binding energies, agreement with the few published theoretical values is not as good. A comparison of Na⁺ and Ag⁺ binding energies for the five N-containing ligands in this study and those for water, methanol, and ethanol published earlier (El Aribi, H.; Shoeib, T.; Ling, Y.; Rodriquez, C. F.; Hopkinson, A. C.; Siu, K. W. M. J. Phys. Chem. A 2002, 106, 2908−2914) shows that for every ligand the Ag⁺ binding energy is higher than the Na⁺ binding energy. As a group, the amines exhibit the largest differences between Ag⁺ and Na⁺ binding energies, followed by the nitriles; the alcohols exhibit the smallest differences. These results are in line with previous observations that Ag⁺ prefers binding with nitrogen to binding with oxygen.

The binding enthalpies at 0 K of the silver ion to water, methanol, ethanol, diethyl ether, and acetone were calculated using density functional theory (DFT) using the hybrid B3LYP level of theory with the DZVP basis set; they were also measured using the threshold collision-induced dissociation (CID) method. There is good agreement between the two sets of data. For the five ligands, the DFT/threshold CID values are:  water, 28.1/31.6 ± 2.5; methanol, 30.1/33.0 ± 3.7; ethanol, 32.0/33.9 ± 3.5; diethyl ether, 33.3/33.2 ± 1.5; and acetone, 36.2/38.0 ± 1.4 kcal/mol. The average of the absolute differences between the DFT and threshold CID results is 2.0 kcal/mol, a value smaller than the average experimental uncertainty of 2.5 kcal/mol. For identical ligands, the silver ion binding energies are lower than the lithium ion binding energies, but higher than the sodium ion binding energies.

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.