Binding interactions of mono- and diatomic silver cations with small alkenes: experiment and theory

Temperature-dependent equilibrium methods were used to measure sequential association energies and entropies for the attachment of C2H4 and C3H6 ligands to ground-state Ag+(1S, 4d10) and Ag2+(2Σg, 4d20 σ(5s)1). Experimental bond dissociation energies (BDEs) of Ag+(C2H4)n are 32.2, 30.1, 13.6, 6.5 and 4.4 kcal/mol for n = 1-5, respectively, with the BDE of the sixth ligand estimated to be 3.3 kcal/mol. The BDEs of Ag2+(C2H4)n are 24.7, 22.5, 12.5, 7.7 and 2.9 kcal/mol for n = 1-5, respectively. The BDEs of Ag+(C3H6)n are 39.2, 32.9, 13.3, 7.0 and 3.0 kcal/mol and the BDEs of Ag2+(C3H6)n are 28.1, 25.8, 12.4, 9.3 and 4.2 kcal/mol for n = 1-5, respectively. A first solvation shell of four is observed for the attachment of both C2H4 and C3H6 ligands to both the Ag+ and Ag2+ core ions with all subsequent ligand additions taking place in the second solvation shell. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of all the observed Ag+ and Ag2+ clusters as well as the nature of the bonding of these clusters and its variation with core ion coordination.