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

Abstract

Twelve new compounds α₂-M_aH_b[P₂W_18 – nTi_nO₆₂]·xH₂O and α-1,2,3-M_aH_b[P₂W_18 – n(TiO₂)_nO_62 – 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 O₂^2– at ca. –0.08 V and that of Ti⁴⁺ at ca. –0.20 V. The characteristic charge-transfer absorption band O₂^2–→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.