Structure of solvent cluster and solvation steric effect at the transition state

溶剂簇结构和过渡态溶剂化空间效应

基本信息

批准号：
10304057
负责人：
ISHIGURO Shin-ichi
金额：
$ 18.3万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

Organic solvent molecules coordinate to the metal ion to form solvation clusters in an aprotic donor solvent, and solvation steric effect operates between solvent molecules simultaneously coordinating to the metal ion. Solvation steric effect may also operate at the activated state of a complexation reaction in solution. The cobalt (II) ion forms a series of halogeno complexes in N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMA). The cobalt (II) ion is four-coordinated in both [CoCl_3 (solvent)]^- and [CoCl_4]^<2->, and activation enthalpy and entropy values for reaction, [CoCl_3 (solvent)]^- + Cl^- = [CoCl_4]^<2->+ solvent, have been determined from temperature dependence of the reaction rate. The activation enthalpy play a decisive role in the reaction rate, and the rate become slower with increasing enthalpy of activation. By combining thermodynamic parameters at the ground state, the activation enthalpy for the reverse reaction was also obtained. It is concluded that solvation steric effect operates more strongly at the activated state, and its aspect is different from that at the ground state. In the above reaction, the five-coordinated [CoCl_4 (solvent)]^<2-> is formed. By using enthalpies of transfer of related species from DMF to DMA and those of activation in these solvents, the enthalpy of transfer of [CoCl^4 (solvent)]^<2-> from DMF to DMA was estimated to be 26 kJ mol^<-1>, and this indicating that the Co^<2+>-O (DMA) bond length become longer than the Co^<2+>-O (DMF) bond length. On the other hand, the decrease in the entropy of activation is smaller for DMA than DMF, indicating that the decrease in freedom of motion is smaller for DMA than DMF, probably owing to longer Co^<2+>-O (DMA) bond length than the Co^<2+>-O (DMF) bond length.

有机溶剂分子与金属离子配位，在非质子供体溶剂中形成溶剂化簇，溶剂化空间效应在同时与金属离子配位的溶剂分子之间起作用。溶剂化空间效应也可以在溶液中络合反应的激活状态下起作用。钴(II)离子在N,N-二甲基甲酰胺(DMF)和N,N-二甲基乙酰胺(DMA)中形成一系列卤代络合物。钴 (II) 离子在 [CoCl_3（溶剂）]^- 和 [CoCl_4]^<2-> 中均为四配位，反应的活化焓和熵值 [CoCl_3（溶剂）]^- + Cl^ -＝[CoCl_4]^<2->+溶剂，已由反应速率的温度依赖性确定。活化焓对反应速率起决定性作用，随着活化焓的增大，反应速率变慢。通过结合基态热力学参数，还获得了逆反应的活化焓。得出结论，溶剂化空间效应在激活态下作用更强，其方面与基态下有所不同。在上述反应中，形成五配位的[CoCl_4(溶剂)]^<2->。通过使用相关物质从 DMF 到 DMA 的转移热函以及这些溶剂中的活化热函，[CoCl^4（溶剂）]^<2-> 从 DMF 到 DMA 的转移热函估计为 26 kJ mol^ <-1>，这表明Co^2+-O(DMA)键长变得比Co^2+-O(DMF)键长长。另一方面，DMA 的活化熵的降低比 DMF 更小，表明 DMA 的运动自由度降低比 DMF 更小，这可能是由于 Co^<2+>-O (DMA) 键更长长度比Co^ 2+ -O(DMF)键长。