The two liquid phase system NaAl(ethyl)4 – benzene–HMPA

Abstract

A detailed study of complexation of the sodium ion by HMPA2 has been made using the system[Formula: see text]where HMPA is observed to be a strong donor towards Na+ but does not complex AlEt4−. This system forms two liquid phases at low HMPA:Na+ molar ratios with the salt and the HMPA, up to a 4:1 HMPA:Na+ ratio, occurring only in the lower phase. Based on a variety of experimental techniques, reasonable proposals of the solute species in the lower phase as a function of HMPA:Na+ ratio are presented. A 2.5:1 ratio of HMPA:Na+ is observed to be particularly significant. This ratio is rationalized in terms of a bridging HMPA molecule resulting in a cationic species with the stoichiometry [2Na•5HMPA]2+. It is found that the 27Al and 1H nmr spectra are determined primarily by quadrupole relaxation of the 27Al nucleus rather than by exchange.