Synthesis, properties and characterization of Dawson-type tungstophosphate heteropoly complexes substituted by titanium and peroxotitanium

Twelve new compounds a(2)-MaHb[P2W18-nTinO62]. xH(2)O and a-1,2,3-MaHb[P2W18-n(TiO2)(n)O62-n]. xH(2)O(M = K+, NEt4+ or NBu4+; n = 1, a + b = 8; n = 3,a + b = 12) were synthesized from vacant heteropolytungstate precursors a(2)-[P2W17O61](10-) and a-1,2,3-[P2W15O56](12-). The products were characterized by IR, UV spectroscopy, polarography, cyclic voltammetry and X-ray photoelectron spectroscopy. Tungsten-183 NMR studies showed that the titanium atoms or the peroxotitanium group in the anions are at 'polar' sites. The polarographic results indicated that there was a polarographic reduction potential of O-2(2-) at ca -0.08 V and that of Ti4+ at ca -0.20 V. The characteristic charge-transfer absorption band O-2(2-)-->Ti at 318 nm occurs in the UV spectra. The peroxotitanium (TiO2) groups show two additional characteristic bands at ca. 870 and ca. 490 cm(-1) in the IR spectra.