Li_2SO_4·20H_2O溶液结构的X射线衍射研究

An X - ray Diffraction Study on the Structure of Li_2SO_4·20H_2O Solution

用θ-2θ型X射线衍射仪研究了25℃Li_2SO_4·20H_2O溶液的结构.用经验公式r_(x-y)=0.618λ/sinθ进行溶液衍射曲线I-θ定性结构的分析,而用另一经验公式r_(x-y)=7.766/s计算加权结构函数曲线s·i(s)-s上某些强峰的原子间距.结构模型的精修研究表明,溶液中占优势的物种是四水合锂离子和八水合硫酸根离子.四面体水合锂离子Li-H_2O距离为0.20nm,配位数为4.四个顶点上水分子间距为0.321nm,相互作用数目为6.锂离子与第二配位层的水分子距离大约为0.425nm,配位数为12.水合硫酸根离子S-W距离为0.386nm,配位数为8.用对称模型描述了水合硫酸根离子中氧原子与水分子的四种相互作用,O_s-W(1),O_s-W(2),O_s-W(3)和O_s-W(4)距离分别精修为0.288nm,0.316nm,0.396nm和0,469nm.由于锂离子散射能力低,没有足够的证据表明溶液中存在接触离子对和溶剂共享离子对.

The structure of Li2SO4·20H2O solution has been investigated with a θ - 2θ type X - ray diffractometer. An empirical formula, rx-y = 0. 618λ/sinθ, has been applied to carry out qualitatively structural analysis of the diffraction curve, and another rx-y =7.766/s to calculate the interatomic distance of some strong peaks from the reduced intensity curve. The refinement results of structrural models show that the dominant species in the solution are tetraquolithium and octaaquosulfate ion. The Li - H2O distance is fixed at 0.20nm when the coordination number is 4. The water - water distance at four vertexes in the tetrahedron is 0.321nm with n= 6. The distance between lithium ion and water molecules on the second hydration shell was determined to be about 0.425nm, with n = 12. The S - W distance of hydrated sulfate ion with 8 water molecules is estimated to be 0. 386nm. Four interactions of oxygen atom Os in sulfate ion and the water molecules have been expounded by a symmetric hydration model and the distances of Os - W( 1), Os - W(2) , Os - W(3) and Os - W(4) were refined to be 0.288, 0.316, 0.396 and 0.469nm respectively. No reliable enough evidence shows that there are the contact ion - pair and the solvent - shared ion - pair in the solution owing to very low scattering power of lithium.