离子液体中Pb^2+／Pb^4+溶质局域结构的EXAFS研究

在超稀浓度条件下ωPb(OAc)2]或ωPb(OAc)4]<0.2,我们使用EXAFS方法对 溶解在离子液体中的铅化合物的局域结构进行了研究。从结果中可以看出,Pb (OAc)4的铅中心在（0.200±0.003）nm处有8个氧近邻,而Pb(OAc）2的铅中心在（ 0.225±0.003)nm处有6个氧近邻。但是溶解在离子液体中的铅化合物均具有较低的 配位数（一般小于4）,这显示出离子液体具有较低的配位性能。另一方面,铅中 心与最近邻氧的原子间距有较大的变化。例如：溶解于bmim]PF6的Pb^4+的Pb-O间 距为（0.186±0.005)nm,配位数仅为2.4,从Fourier变换谱上可清楚地看出有第 二配位壳层的贡献;溶解于bmim]PF6的Pb^2+的Pb-O间距也明显地小于纯样品中 Pb-O的间距。相比之下,溶解于 bmim]BF4的铅离子显示出的Pb-O间距与纯样品几 乎没有差别,对于Pb^2+为0.223nm,而对于Pb^4+为0.210nm。

Study on Stability of Nateglinide Polymorphism

Under the condition of ultra diluted concentration w;Pb(OAc)-2l or wPb(OAc)-4] < 0.2% , the local structure of lead complex dissolved in ionic liquids has been studied by Pb Z/m-edge EXAFS. Pb~4+ in bulk Pb (OAc)-4 shows 8 nearest oxygen neighbors at (0.200 ± 0.003) nm while Pb~2+ in bulk Pb(OAc)-2 shows 6 nearest oxygen neighbors at (0. 225 ± 0. 003) nm. However, both Pb~4+ and Pb~2+ dissolved in ionic liquids have very low coordination numbers, normally less than 4, indicating a low coordination property for the ionic liquids. On the other hand, the interatomic distance between Pb center and the nearest oxygen seems not comparable with each other. For example, the Pb-0 distance observed for Pb~2+ in bmim] PF-6 is only (0. 186 ± 0. 005) nm with a very low coordination number of 2.4, while the Fourier transform clearly indicates a second coordination shell for Pb ~+ in bmim]PF6. The Pb-0 distance observed for Pb~2+ in bmimJPFs, which is only (0. 211 ±0.005) nm, is also significantly shorter than that (0.225 nm) in bulk Pb(OAc)2- The Pb ions dissolved in bmim]BF-4, which are 0.223nm for Pb~ + and 0.210 nm for Pb~ + respectively, exhibit that the Pb- 0 distances are of no more difference with those in bulk samples.