A Monovacant Heteropolytungstate Thioderivative: Synthesis and Characterization of [(PW[sub 11]O[sub 39])[sub 2](H[sub 4]Mo[sub 4]S[sub 4]O[sub 6])][sup 10-] and Related Isomers.

[(PW[sub 11]O[sub 39])[sub 2](Mo[sub 4]S[sub 4]O[sub 4](OH[sub 2])[sub 2])][sup 10-] anions were obtained through the stereospecific addition of the [Mo[sub 2]S[sub 2]O[sub 2]][sup 2+] oxothiocation to the monovacant α-[PW[sub 11]O[sub 39]][sup 7-] anion. K[sub 10][(PW[sub 11]O[sub 39])[sub 2]Mo[sub 4]S[sub 4]O[sub 4](OH[sub 2])[sub 2])]·25H[sub 2]O has been isolated as crystals and characterized by X-ray diffraction. The structure revealed a "sandwich-like" dimer of two α-[PW[sub 11]O[sub 39]][sup 7-] subunits assembled by the noteworthy central cluster {H[sub 4]Mo[sub 4]S[sub 4]O[sub 6]}. The crystallization of the crude product produces an isomerically pure compound, which was characterized by [sup 31]P and [sup 183]W NMR. IR data were also supplied. In solution, the compound isomerizes, giving a second diastereoisomer. A kinetic experiment, carried out by [sup 31]P NMR, allowed the conditions of the thermodynamic equilibrium to be determined. A structural relationship between the two isomers is proposed, fully consistent with NMR data. Cisoid and transoid isomers result in the relative disposition of each [PW[sub 11]O[sub 39]][sup 7-] subunit, either staggered or eclipsed. An investigation of the formation of the [Mo[sub 2]O[sub 2]S[sub 2]][sup 2+] unit from the polycondensed cyclic precursor [Mo[sub 10]S[sub 10]O[sub 10](OH)[sub 10](H[sub 2]O)[sub 5]] and the aggregation process resulting in the oxothio [(PW[sub 11]O[sub 39])[sub 2](Mo[sub 4]S[sub 4]O[sub 4](OH[sub 2])[sub 2])][sup 10-] compound has been undertaken. The studies were monitored by [sup 31]P NMR and UV-vis spectroscopies. The reaction is quantitative in nearly stoichiometric conditions. [ABSTRACT FROM AUTHOR]