浓氯化钙水溶液中高配位Ca-Cl离子团簇:分子动力学模拟研究

High-Coordinated Ca(Ⅱ)-Chloro Ion Clusters in the Concentrated CaCl2 Aqueous Solution: A Molecular Dynamics Simulation Study

采用分子动力学(MD)模拟研究了5.55 mol·kg-1氯化钙溶液的微观结构特征,尤其是溶液中高配位Ca-Cl离子团簇的结构与性质,探究了温度对于高配位Ca-Cl离子团簇的影响。结果显示,5.55 mol·kg-1氯化钙溶液中,除形成[CaCl]+、[CaCl 2]0离子对外,还存在一些高配位[CaCl x]2-x(x=3~6)离子团簇。高配位[CaCl x]2-x(x=3~6)离子团簇在5.55 mol·kg^-1氯化钙溶液中介稳存在,易解离或进一步缔合形成更大Ca-Cl离子团簇,这可能与溶液中大量未完全水合Ca^ 2+对高配位[CaCl x]2-x(x=3~6)离子团簇水壳层的扰动破坏有关。温度升高,氯化钙溶液中Ca-Cl离子缔合增强,但高配位Ca-Cl离子团簇的平均存在时间(t av)减小,这表示高温下溶液中Ca-Cl离子团簇频繁地解离与缔合,离子团聚趋势更为显著。本工作观测到的高配位[CaCl x]2-x(x=3~6)离子团簇可能是浓氯化钙溶液Ca-Cl离子缔合过程中一种热力学不稳定结构,但这些高配位Ca-Cl离子团簇的形成可能对溶液结晶及相关化学过程产生不利影响。

Molecular dynamics simulation was employed to investigate the structural characteristics of 5.55 mol·kg-1 CaCl 2 solution,especially the high-coordinated Ca-Cl ion clusters observed in the solution.The results show that there may be some highly coordinated[CaCl x]2-x(x=3~6)ion clusters formed in 5.55 mol·kg^-1 CaCl 2 solution,apart from the[CaCl]+and[CaCl 2]0 ion pairs.The highly coordinated Ca-Cl ion clusters remain meta-stable in 5.55 mol·kg^-1 CaCl 2 solution and easily disassociate into smaller structures or associate with other ions to form the larger Ca-Cl ion clusters,which may be related to the disturbing damage of the numerous Ca 2+,without adequate hydration,to the outer shells of the high-coordinated Ca-Cl ion clusters in the concentrated CaCl 2 solution.As the temperature rises,Ca-Cl ion association increases in 5.55 mol·kg^-1 CaCl 2 solution,but the average lifetime(t av)of the[CaCl x]2-x(x=3~6)ion clusters decreases,indicating that at elevated temperature the Ca-Cl ion clusters frequently disassociate and associate,and the tendency of ionic aggregation in the solution is more pronounced.The highly coordinated[CaCl x]2-x(x=3~6)ion clusters observed in this work may be a thermodynamically unstable structure during the ion association in 5.55 mol·kg^-1 CaCl2 solution,but the formation of the high-coordinated Ca-Cl ion clusters can exert some negative influences on the crystallization of the CaCl 2 solution and other related chemical processes.