Synthesis, properties and characterization of Dawson-type tungstophosphate heteropoly complexes substituted by titanium and peroxotitanium†
Abstract
Twelve new compounds α2-MaHb[P2W18 – nTinO62]·xH2O and α-1,2,3-MaHb[P2W18 – n(TiO2)nO62 – n]·xH2O (M = K+, NEt4+ or NBu4+; n = 1, a + b = 8; n = 3, a + b = 12) were synthesized from vacant heteropolytungstate precursors α2-[P2W17O61]10– and α-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 O22– at ca. –0.08 V and that of Ti4+ at ca. –0.20 V. The characteristic charge-transfer absorption band O22–→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.