PF5 and PCl5 interacting with water – Comparative study at the molecular level

Abstract

The isomeric structures formed by the interaction of PF5 and PCl5 with up to four water molecules were theoretically examined by employing the MP2 method and the aug-cc-pVDZ basis set. The additional effects of surrounding water molecules were approximated by employing the polarized continuum solvation model (PCM) within a self-consistent reaction field treatment. The calculations indicate that the global minimum resulting from the interaction of PF5 and one H2O molecule corresponds to the PF5–H2O adduct and remains the most stable isomer after addition of second and third H2O, whereas the presence of fourth H2O molecule renders the PF5OH−/H3O+/2H2O structure the most stable. On the contrary, the interaction of PCl5 and a single H2O molecule leads to the global minimum structure corresponding to the PCl3O phosphoryl chloride with two HCl moieties attached. The lowest energy isomers resulting from the interaction of PCl5 with two, three, and four H2O molecules indicate the tendency of PCl3O to subsequent replacement of the Cl ligands with OH groups resulting in formation of H3PO4 (with five surrounding HCl fragments) when the number of available H2O molecules is sufficient. The presence of the competitive isomers containing H3O+ fragments in the case of the PCl5 interacting with water molecules is also predicted and discussed.