A molecular picture of metal ion solvation: Infrared spectroscopy of Cu+(NH3)n and Ag+(NH3)n in the gas phase

Infrared spectroscopy is applied to mass-selected Cu+(NH3)n and Ag+(NH3)n in the gas phase for investigating coordination chemistry of ammonia solvated noble-metal ions. The Cu+(NH3)3 ion prefers a three-coordinated structure but two-coordinated isomers are of growing importance until becoming predominant at n = 8 and 9. The first shell of the Ag+ ion is filled with four NH3 molecules and the resulting tetrahedral Ag+(NH3)4 complex is solvated by subsequent NH3 molecules through hydrogen bonding. A coordination number of 2 for Cu+ can be ascribed to extensive 4s-3d hybridization in Cu+, which causes the twofold linear coordination. A larger coordination number of 4 for Ag+ can be attributed to its larger ionic size and more importantly to inefficient 5s-4d hybridization in Ag+.