[Spectral study of three compounds of tungstosilicic salt with Keggin structure].

ABSTRACT

Three compounds of tungstosilicic acid and tungstosilicic salt K3H[SiW(VI)12O40].3H2O(I), (H3O)4[H3SiW(VI)9W(V)3O40].2H2O(II) and [(CH3)4N]4[SiW(VI)12O40].4.5H2O(III), with Keggin structure, have been synthesized. The relationship between their properties and structures was studied by using FTIR, NIR FT-Raman, UV-Vis and flurescence etc. They possess isolated [SiW12O40] cage anion, which combines with cation and water by static electric action and weak hydrogen bond; The study of their FTIR and Raman spectra shows that the vibrational frequencies of the group are related to the structure of the materials. For the compound II, the vibrational frequency of vas(W=Od) decreases as part of W6+ are reduced to W5+, and the charges of anion group affect vas(W-Oc-W), vas(Si-Oa) and delta(Oa-Si-Oa) etc. apparently. In UV-Vis spectra of compound I and II, there are two characteristic peaks at 200 and 260 nm, respectively. The fluorescence spectra of compound I were studied, and showed that the emission peak is at 350, 440, 520 and 675 nm excited by 220, 350 and 440 nm.