Be2+ hydration in concentrated aqueous solutions of BeCl2

Neutron diffraction experiments were carried out on concentrated aqueous solutions of beryllium chloride at three concentrations: 1.5, 3, and 6 molal. By working with a specific ("null") mixture of heavy water (D2O) and water (H2O), information on the local structure around Be2+ ions was extracted directly. For all three BeCl2 solutions, the results show that the Be2+ ion has a well-defined 4-fold coordination shell that is dominated by oxygen atoms. There is also a relatively small probability (10-15%) that there are direct contacts between Be2+ and Cl- at a distance of approximately 2.2 angstroms. The oxygen atoms of the highly structured Be2+ first hydration shell are found to be situated at 2.6 angstroms apart, and form a pyramidal structure, in agreement with recent MD simulation results. The Cl- ions have approximately seven oxygen atoms (water molecules) in their hydration shells sited at 3.2 angstroms.