Solvation structure and dynamics of Ag+ in aqueous ammonia solutions: A molecular simulation study

We present an ab initio-based force-field for silver ion interactions withwater and ammonia. Compared to quantum calculations, our model allows for rather large-scale molecular dynamics simulations of silver solutions of aqueous ammonia. For a series of NH3:H2O ratios ranging from 1 to 20 mol.%, Ag+ ions were mainly found as octahedral [Ag(NH3)(x)(H2O)](6-x)(+) coordination complexes with preferential values of x ranging from 0 to 3. In the first coordination structure, water <-> ammonia exchanges occur within a 1-3 ps time scale and, depending on the NH3 concentration, imply significant fluctuations of x covering the whole range from 0 to 6. Based on ns-scale molecular dynamics simulations, chemical potentials are derived for all Ag+ coordination species as functions of temperature and ammonia concentration. Moreover, we compare the diffusion constants of the [Ag(H2O)(6)](+) to [Ag(H2O)(3)(NH3)(3)](+) coordination complexes, based on the solutions of the corresponding ammonia content. Published by AIP Publishing.