Keggin型有机硅取代的多金属氧酸盐衍生物[XW_(11)O_(40)(SiR)_2]^(n-)(X=Co^(III),P;R=CH=CH_2,OH)的合成和表征

Synthesis and Characterization of Organosilyl Derivatives of Keggin Polyoxometalates [XW_(11)O_(40)(SiR)_2]^(n-)(X=Co^(III), P; R=CH=CH_2,OH)

以CoIIIW11和有机硅烷为原料,在pH=1,乙醇-水(体积比=2∶1)的混合溶剂中,首次合成了Keggin型有机硅取代的钨钴酸盐[CoIIIW11O40(SiR)2]5-(CoIIIW11(SiR)2,R=CH=CH2,OH).这里,乙醇作为共溶剂增加硅烷在溶液中的溶解度,使CoIIIW11在转化为饱和结构之前能够快速与硅烷相遇并反应.产物的组成和结构用IR,UV-Vis,NMR,TG-DTA,元素分析等技术进行了全面表征.结果显示,两个SiR基团进入了CoIIIW11的空位,并形成Si—O—Si桥,得到与先前报道的硅取代钨硅酸盐和钨磷酸盐相似的结构.还运用此条件成功合成了以往需要在固-液相转移条件下合成的[PW11O40(SiR)2]3-[PW11(SiR)2,R=CH=CH2,OH],进一步证明了此方法在合成有机硅取代的多金属氧酸盐方面的可行性和通用性.

The Keggin-type organosilyl substituted tungstocobaltates [CoIIIWIIO40（SiR）2]5- （ConIIIW11（SiR）2, R=CH-CH2, OH） were synthesized for the first time by using ComWll and organosilane as starting materials. The syntheses were carried out in an ethanol-water mixing solvent with volume ratio of 2 ： 1 and pH 1. Ethanol was employed as a cosolvent here to increase the solubility of organosilane in the reactive system, so that the organosilane was accessible and could react with CollIWll before it was converted to CoIIIwI2. The mixture was stirred at room temperature for 20 h, and then the product was obtained as tetramethylammonium （TMA） salt precipitate by adding tetramethylammonium chloride （TMACI）. The structure and composition of the products were characterized by IR, UV-Vis, NMR, TG-DTA and elemental analysis techniques. The IR spectra showed that the Keggin units in the products were close to the saturated structure. Two SiR groups were inserted into the vacancy of ColIIWll and a Si--O--Si bridge was formed between two Si atoms, similar to those reported previously in organosilyl substituted tungstosilicate and tungstophosphate. This insertion of SiR groups was also confirmed by 29Si, 1H and 13C NMR of the products, but the Z9Si signal exhibited a large chemical shift compared with those of organosilyl substi- tuted tungstosilicate and tungstophosphate possibly due to the paramagnetism of CoIII. UV-Vis spectra of the products also indicated the conversion of the structural symmetry and the retainment of CoIII in the synthesis. The decomposing processes of the products were suggested by TG-DTA curves, which also revealed that, the anion in CoIIIIW11（SiOH）2 possesses a higer stability than that in CoIIIWll （SiCH=CH2）2. Furthermore, [PW11O40（SiR）2]3- [PW11（SiR）2, R=CH=CH2, OH], which were synthesized previously by the procedure of solid-liquid phase transfer, were also synthesized under the same conditions, in- dicating this method is a feasible and general approach for the synthesis of organosilyl substituted polyoxometalates.