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Some new heteropolyoxometalates of large organic cations with molybdotungstosilicic acids (general formula:(CTMA)_4SiMo_x W_(12-x)O_(40)·mH_2O·nDMF,x=0,2,4,6,8,10,12)were prepared by the reaction of cetyltrimethylammonium bromide(CTMAB,C_(16)H_(33)N(CH_3)_3Br)with H_4SiMo_x W_(12-x)O_(40)(x=0,2,4,6,8,10,12) in aqueous solution and recrystallization in DMF,and characterized by elemental analysis,IR spectra,TG- DTA and XRD techniques.The IR spectrum confirms the presence of Keggin structure and organic cations in these compounds,and it is indicated that the stretching vibration of the M-Od,M-Ob-M and Si-Oa becomes more red-shifted when molybdenum is gradually substituted for the tungsten atom.In particular,the thermal decomposition of the heteropolyoxometalates was studied in nitrogen atmosphere.The TG-DTA curves show that their thermal behaviors not only contain the release of water molecule,DMF molecule,CTMA and its fragments but also contains simultaneous collapse of Keggin anion.Their end products of the thermal decomposition are the mixture of WO_3,MoO_3 and SiO_2.And from the final decomposition temperature of view,it is found that the thermal stability of these compounds gradually is decreased when the number of molybdenum atoms is increased.
Some new heteropolyoxometalates of large organic cations with molybdotungstosilicic acids (general formula: (CTMA) _4SiMo_xW_ (12-x) O_ (40) · mH_2O · nDMF, x = 0,2,4,6,8,10,12) were prepared by the reaction of cetyltrimethylammonium bromide (CTMAB, C_ (16) H_ (33) N (CH_3) _3Br) with H_4SiMo_xW_ (12-x) O_ (40) , 12) in aqueous solution and recrystallization in DMF, and characterized by elemental analysis, IR spectra, TG-DTA and XRD techniques. IR spectrum confirms the presence of Keggin structure and organic cations in these compounds, and it is indicated that the stretching vibration of the M-Od, M-Ob-M and Si-Oa becomes more red-shifted when molybdenum is gradually substituted for the tungsten atom. In particular, the thermal decomposition of the heteropolyoxometalates was studied in nitrogen atmosphere. The TG-DTA curves show that their thermal behaviors not only contain the release of water molecule, DMF molecule, CTMA and its fragments but also contains collapse collapse of Keggin anion. Th eir end products of the thermal decomposition are the mixture of WO_3, MoO_3 and SiO_2.And from the final decomposition temperature of view, it is found that the thermal stability of these compounds gradually is decreased when the number of molybdenum atoms is increased.