Ab initio molecular dynamics investigation of beryllium complexes

Structures of aqueous [Be(H₂O)₄]²⁺, its outer-sphere and inner-sphere complexes with F^-, Cl^- and SO₄^2-, as well as dinuclear complexes with a [Be(κ-OH)(κ-SO₄)]⁺ core have been studied through Car-Parrinello molecular dynamics (CPMD) simulations with the BLYP functional. According to constrained CPMD/BLYP simulations and pointwise thermodynamic integration, the free energy of deprotonation of [Be(H₂O)₄]²⁺ and its binding free energy with F^- are 9.6 kcal mol^-1 and -6.2 kcal mol^-1, respectively, in good accord with available experimental data. The computed activation barriers for replacing a water ligand in [Be(H₂O)₄]²⁺ with F^- and SO₄^2-, 10.9 kcal mol^-1 and 13.6 kcal mol^-1, respectively, are also in good qualitative agreement with available experimental data. These ligand substitution reactions are indicated to follow associative interchange mechanisms with backside (SN2-like) attack of the anion relative to the aquo ligand it is displacing. Outperforming static DFT computations of the salient kinetic and thermodynamic quantities involving simple polarizable continuum solvent models, CPMD simulations are validated as a promising tool to study structures and speciation of beryllium complexes in aqueous solution.