Where are the protons in [alpha]-[[[H.sub.x][W.sub.12][O.sub.40]].sup.(8-x)-] (x = 2-4)?

A combination of [super 1]H and [super 183]W NMR evidence, elemental analysis, acid titration measurements, and H/D isotopomer assignments has established that in nonaqueous media the internal cryptand cavity of [alpha]-[[([H.sub.2])[W.sub.12][O.sub.40]].sup.6-] reversibly accommodates only one more proton to form [alpha]-[Q.sub.5]-[([H.sub.3])[W.sub.12][O.sub.40]]. The results have shown that the transformation is instantaneous by [super 1]H NMR, whereas the reverse process is slow.