Excess Proton Hydrate Structures with Large Proton Polarizability, Screened by Tris(2-ethylhexyl) Phosphate

Abstract

Complexes of tris(2-ethylhexyl) phosphate (EHPO) with HAuCl4 and its hydrates with various amounts of water were studied by FT-IR spectroscopy. In the water free solution of HAuCl4 in EHPO homoconjugated PO···H+···OP hydrogen bonds with proton polarizability are formed. We demonstrate that in the 1:1 and 1:2 mixture with water only the H5O2+ species is present and no H3O+ species is formed. In the 1:1 mixture with water in addition to the H5O2+ species, 50% homoconjugated hydrogen bonds of protonated EHPO are still present. This homoconjugated hydrogen bond, as well as the central bond in H5O2+ shows large proton polarizability, as indicated by IR continua. In the 1:3 mixture of the homoconjugated complex with water a cyclic hydrogen-bonded system with a three-minima proton potential is present. The proton polarizability of this system is the largest, as indicated by a particularly intense IR continuum. In the case of the 1:4 mixture, a cyclic hydrogen-bonded arrangement with a four-minima proton potential is present, in which the barriers between the minima are larger than in the three-minima potential.