Gallium(III) polyhydroxocations in aqueous perchlorate media

The formation of polyhydroxo gallium(III) complexes has been investigated a t 30 degreesC and in a 3M (Na)ClO4 ionic medium by p[H] measurements. The g allium(III) concentration has been varied between 0.0054 and 0.043 M. Slow proton producing side reactions were hypothesized to be responsible for the erratic behaviour of the p[H] of gallium(III) hydrolyzed solutions and to obscure the experimental measurements to such an extent that the compositio n of quickly formed hydrolysis products can hardly be determined with certa inty. By imparting to the p[H] measurements a well defined time scale and b y employing the uncommon integral titration technique, the bias of slow hyd rolysis reactions has been excluded. Formally the data can satisfactorily b e explained either by assuming the single reaction: 13 Ga3+ + 33 H2O = Ga-13(OH)(33)(6+) + 33 H+ log beta (13.33) = -65.38 +/- 0.06 or the two "Core + Links" reactions : 13 Ga3+ + 32 H2O = Ga-13(OH)(33)(7+) + 32 H+ log beta (13.32) = -62.34 +/- 0.06 22 Ga3+ + 56 H2O = Ga-22(OH)(56)(10+) + 56 H+ log beta (22.6) = -108.2 +/- 0.06 Both models fit equally well the data but, comparing these models with lite rature Ga-71-NMR spectra of hydrolyzed solutions, we finally selected the s ingle species model to explain our data. In any case there may be no doubt that a Ga-13 cluster is quickly formed by hydrolyzing gallium(III) solution s and which unexpectedly is by far more stable than the analogous All clust er(3). Our results apply to freshly hydrolyzed gallium(III) solutions and i s by no means excluded that further polymerization takes place, although sl owly, if solutions are aged.