Résumé
A computational study of the relative stability of the monolacunary Keggin polyoxotungstates alpha and beta(3)-[XW(11)O(39)](m-) (X = P, m = 7; X = Si, m = 8) was performed. The influence of the nature of different grafted cations and of the central anion XO(4)(n-) on the relative stabilities of the lacunary isomers was analyzed. From these results, an interpretation of the structural difference in the metallic frameworks of alpha-[PW(11)O(39){Ru(DMSO)(3)(H(2)O)}](5-), alpha-[PW(11)O(3){Ru(C(6)H(6))(H(2)O)}](5-), and beta(3)-[SiW(11)O(39){Ru(DMSO)(3)(H(2)O)}](6-) is proposed, and conclusions are drawn as to how to favor the formation of beta(3) derivatives in future syntheses.