Synthesis And Characterization Of New-type Organic-Polyoxometalate Charge-Transfer Salts

Polyoxometalate acid is a kind of electron acceptor, which can combine with organic electron donor to form an electron donor-acceptor compound. Charge transfer may happen from organic donor to polyoxometalate acceptor in the organic-polyoxometalate compound when the compound is excited by the light with certain wavelength. In the procedure of charge transfer, photochromism may probably be observed. Therefore, the organic-polyoxometalate compounds may become a new type of photosensitive material, which will have a very promising prospect in material field. However, the reported researches for the photochemistry of solid polyoxometalate charge transfer salts are rarely. Considering the diversity of organic donors, the functional materials with certain photochemistry feature, based on solid polyoxometalate charge transfer salts, have the potential to be developed further. Herein, we describe our main job as below:1. We synthesized three series of new-type unreported polyoxometalate charge-transfer salts, totally 13 salts, using polyoxometalate acids with Keggin structure as acceptors and three series of organic compounds as donors. Namely, (I) 3 charge-transfer salts combining tungstophosphoric anion and organic cation of basic dye (crystal violet, safranine T, methylene blue BB, respectively); (II) 7 charge-transfer salts combining phosphomolybdic anion and organic cation of phenanthroline-M (M=NiII, FeIII, CuII, MnII, CdII, MgII, CoII,) complex; (III)3 charge-transfer salts combining polyoxometalate anion (tungstophosphoric, phosphomolybdic, tungstosilicic, respectively) and the organic cation of methyl viologen.2.Element analysis and IR spectra analysis indicate: the N atom with lone-pair electron of basic dye combined with the H+ proton of polyoxometalate acid to form the cation of the basic dye- polyoxometalate compounds (coumpunds (I)). The N atom with lone-pair electron of phenanthroline combined with the metal cation to form complex, and then the complex combined with the polyoxometalate anion to form phenanthroline-M- polyoxometalate compounds (coumpunds (II)) bymetathetical reaction. methyl viologen and polyoxometalate acid formed compounds (III) by metathetical reaction at room temperature .3.TG-DTA and IR spectra analysis indicate: The decomposition of compounds (I) and (III)had two stages: firstly, the decomposition of the organic cation; secondly, the decomposition of polyoxometalate anion at about 450~470℃, which was lower than the decomposition temperature of corresponding polyoxometalate acid. That proved the introduction of the organic cation, basic dye or methyl viologen, to the polyoxometalate acid decreased the thermal stability of polyoxometalate anion. The decomposition of compounds (II) had one stage: the organic cation and phosphomolybdic anion decomposed at about 400-600℃.4.IR spectra analysis indicates that the characteristic peaks of polyoxometalate anion still existed in the new compounds. But the position of the peaks had red shift or blue shift with different extent. That proved that the basic structure of the polyoxometalate anion was not changed, whereas, the bond strength of the polyoxometalate anion had been changed, which was probably induced by steteohindrance effect and conjugation effect of organic cation.5.UV-vis spectra analysis indicates that the characteristic peaks of organic-polyoxometalate compound in the ultraviolet region were formed by the overlap of the absorption peak of organic cation and the absorption peak of polyoxometalate anion in the ultraviolet. Furthermore, a new absorption peak was observed in the new compound in the visible region, which was induced by IVCT transition(W(V)- W(VI) or Mo(V) -Mo(VI)). That showed the electron had transferred from organic cation to polyoxometalate anion during the excitement of light. That is a powerful proof for the existence of charge transfer salts.6. We use the reaction of decomposition of dyes as probe reaction to test the photo catalysis character of organic- polyoxometalate compounds. The results indicate that comp...