Ammonia Solvation of Alkaline Earth Dications: Mg(II), Ca(II), Sr(II), and Ba(II); Hybrid Density Functional Theory Born-Oppenheimer Molecular Dynamics Studies

Structural and dynamical properties of Sr2+ and Ba2+ dications in ammonia microsolvation environments were studied through hybrid density functional theory Born-Oppenhemier molecular dynamics of [Sr(NH3)n]2+ and [Ba(NH3)n]2+ clusters with n = 2, 3, 4, 5, 6, 8, 10, and 27. The largest cluster models were used to explore bulk phase solvation of Sr2+ and Ba2+ in liquid ammonia for which experimental data are available. Results are discussed in the light of previous results obtained for the [Mg(NH3)n]2+ and [Ca(NH3)n]2+ systems with the same methodology. Vibrational and EXAFS spectra are reported for the first time for [Sr(NH3)n]2+ and [Ba(NH3)n]2+ systems. It was found that alkaline earth dications have coordination numbers (CN) in ammonia as follows: Mg2+ (6) < Ca2+ (8) < Sr2+ (8.3) < Ba2+ (9.4). The coordination structures found turn out to be rather flexible with CN greater than six and these structures depart from the simple geometry of hexamine in the solid phase.

Automated summary

The structural and dynamical properties of Sr2+ and Ba2+ dications in ammonia microsolvation environments were investigated using hybrid density functional theory Born-Oppenheimer molecular dynamics. The results were compared with previous studies on [Mg(NH3)n]2+ and [Ca(NH3)n]2+ systems. Vibrational and EXAFS spectra of [Sr(NH3)n]2+ and [Ba(NH3)n]2+ systems were reported for the first time. It was found that alkaline earth dications have coordination numbers in ammonia as follows: Mg2+ (6) < Ca2+ (8) < Sr2+ (8.3) < Ba2+ (9.4). The coordination structures exhibit greater flexibility and deviate from the simple hexamine geometry in the solid phase.