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Structure of solvent clusters and its effect on metal-ion reactivity in non-aqueous solvent mixtures

非水溶剂混合物中溶剂簇的结构及其对金属离子反应性的影响

基本信息

批准号：
13440222
负责人：
ISHIGURO Shinichi
金额：
$ 9.47万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

Solvation of the metal-ion and its complexation in some nonaqueous solvents and their mixtures have been studied by means of titration spectrophotometry, catorimetry and Roman spectrometry, all these are on-line controlled for the titration procedure and data acquisition. In the present project, we investigated solvation steric effect (SSE) in the initial and transition states of the metal-ion complexation in nonaqueous solvent mixtures. Solvents used are tetramethylurea (TMU), N,N-dimethylformanmide (DMF), N,N-dimethylacetamide (DMA), N,N-dimethylpropionamide (DMPA), etc. TMU and DMPA show a strong SSE, i.e., the solvation number of the metal ion is reduced, while DMF and DMA show a weak SSE, i.e., the solvation number is kept the same as that in water. It is found that DMPA has two conformational isomers. The two isomers coexist in equilibrium, and the equilibrium constant, and the corresponding enthalpy and entropy values were obtained. The conformational equilibrium largely changes when the solvent molecules simultaneously coordinate to the metal ion, which is ascribed to the conformational change arising from the strong solvation steric effect. This leads to a remarkable difference in the complexation behavior of the manganese(II) ion in TMU and DMPA, despite that the metal ion is five-solvated in both the solvents. The solvation energy of an activated species formed at the transition state of metal-ion complexation is also investigated from the view-point of solvation steric effect. The solvation enthalpy difference of an activated species is defined as the enthalpy of transfer of the activated species from solvent A to B, which is evaluated from the enthalpies of activated measured in the solvents and the enthalpy of transfer of reactants at the initial state from solvent A to B. We found that the solvation steric effect operates significantly at the transition state.

本文用滴定分光光度法、比色法和罗曼光谱法研究了金属离子在几种非水溶剂及其混合溶剂中的溶剂化和络合作用，并对滴定过程和数据采集进行了在线控制。本课题研究了非水溶剂体系中金属离子络合反应初始态和过渡态的溶剂化空间效应。使用的溶剂是四甲基脲（TMU）、N，N-二甲基甲酰胺（DMF）、N，N-二甲基乙酰胺（DMA）、N，N-二甲基丙酰胺（DMPA）等。TMU和DMPA显示出强SSE，即，金属离子的溶剂化值降低，而DMF和DMA显示出弱的SSE，即，溶剂化值保持与在水中相同。发现DMPA有两种构象异构体。两种异构体平衡共存，求得了平衡常数和相应的焓、熵值。当溶剂分子同时与金属离子配位时，构象平衡发生了很大的变化，这归因于强溶剂化空间效应引起的构象变化。这导致TMU和DMPA中锰（II）离子的络合行为的显着差异，尽管金属离子在这两种溶剂中是五溶剂化的。本文还从溶剂化空间效应的角度研究了在金属离子络合过渡态形成的活化物种的溶剂化能。活化物种的溶剂化焓差定义为活化物种从溶剂A到B的转移焓，其由在溶剂中测量的活化的焓和反应物在初始状态下从溶剂A到B的转移焓来评估。我们发现，溶剂化的空间效应在过渡态的操作显着。