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 SO42-, and dinuclear complexes with a [Be2(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 and -6.2 kcal/mol, 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 SO42-, 10.9 and 13.6 kcal/mol, 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 density functional theory computations of the salient kinetic and thermodynamic quantities involving simple polarizable continuum solvent models, CPMD simulations are validated as a promising tool for studying the structures and speciation of beryllium complexes in aqueous solution.

Electrospray Ionization Mass Spectrometric Study of the Gas-Phase Coordination Chemistry of Be2+ Ions with 1,2- and 1,3-Diketone Ligands.

Electrospray ionization mass spectrometry (ESI MS) is a powerful technique for the study of coordination complexes because of its ability to analyze solution systems involving very low concentrations of metal complexes. In this work, the coordination chemistry of Be ions with a selection of well-known 1,3-diketone and related 1,2-diketone ligands has been investigated using ESI MS. With acetylacetone (Hacac), a range of acac-containing ions is observed, including [Be(acac)2H]+, [Be(acac)(MeOH) n]+ ( n = 1, 2), and polynuclear species such as the dinuclear [Be2(acac)3]+ and trinuclear [Be3O(acac)3]+. Density functional theory calculations indicate that the latter species has a central Be3(µ3-O) core, with each Be chelated (as opposed to being bridged) by an acac ligand. The effect of changing the substituents on 1,3-diketone was explored by an investigation of mixtures of Be2+ with other 1,3-diketones such as dibenzoylmethane (Hdbm), where the [Be(dbm)2H]+ ion showed a lesser tendency to undergo fragmentation and aggregation processes. Comparisons with the corresponding aluminum acetylacetone system were also made. In contrast, mixtures of Be2+ and the 1,2-diketones diacetyl and phenanthrenequinone showed poor metal-ligand interactions. Be2+ interacted with the 1,2-diketone benzil [PhC(O)C(O)Ph], forming the [Be(benzil) n]2+ ( n = 2-4) ions. The synthesis (from BeCl2) and X-ray structures of the dibenzoylmethanato (dbm) complex Be(dbm)2 and the benzil complex [BeCl2(benzil)] are also reported.