CRYSTAL-STRUCTURE OF SODIUM TRIS(TETRAMETHYLAMMONIUM) PENTAMOLYBDODISULFATE(VI) TETRAHYDRATE, NA[NME4]3S2MO5O23.4H2O

The structure of Na[NMe4]3S2Mo5O23-4H2O has been determined by the single-crystal X-ray method: monoclinic, space group P2/c, a = 29.25(2), b = 12.85(1), c = 18.24(1) angstrom, and beta = 123.89(2)" and Z = 6. The structure was refined by full-matrix least squares to R' = 0.0678 for 5532 reflections. The existence of the Strandberg-type heteropolyion [S2Mo5O23]4- 1 in the crystals has been confirmed. The geometry of 1 was compared systematically with various analogues containing S(IV)O3(3-), PO4(3-), MePO3(2) or NH3C2H4PO3- as the central polyhedron. The UV spectrum of the salts Na[NMe4]3S2Mo5O33.4H2O and [NMe4]4S2Mo5O23 in neat MeCN, hence the kernel heteropolyion 1 showed absorption maxima at lambda 213 and 243 nm (epsilon = 3.2 x 10(4) and 3.3 x 10(4) dm3mol4 cm-1). Spectroscopic measurements also indicate that 1 and [Mo6O19]2- form simultaneously in aqueous-MeCN media containing Mo(VI) and H2SO4.