Considerations of the rates and lifetimes of intermediate complexes for the association of various ligands to metal ions: Ag+ and Cu+

Rates were measured for the association of CO, CH4, CH3F, NH3, ND3, CH3Cl, and CH3Br onto Ag+ and Cu+ at 298 K. In the order given above, the three-body association rate constants for Ag+ range from 2.5×10−30 to 3.9×10−27 cm6 s−1. The rate constants for Cu+ are about four to six times larger for a given neutral reactant. The rate constants display trends in the order expected considering the relative bond energies of the clusters, although the enormous range of reactivity is not reflected simply by differences in dipole moments and polarizabilities. There is a very large isotope effect, where the rate constant for ND3 association was found to be about three times greater than NH3 in the case of both ions. (Results for Na+ follow the same trend.) This suggests a coupling of ligand vibrations with orbiting motion which leads to enhanced lifetimes of the cluster intermediates. The trend found for the methyl halides also supports the involvement of this effect.