THERMODYNAMIC SND KINETIC STUDY ON SOLVATION STERIC INTERACTIONS

金属离子以溶剂化络合物的形式存在于二甲基甲酰胺(DMF)、二甲基乙酰胺(DMA)和六甲基磷三胺(HMPA)等非质子化给体溶剂中。溶剂化金属络合物的配位结构和分子内相互作用与水合金属络合物有很大的不同，这种差异在热力学和动力学方面起着关键作用。在本研究中，我们特别关注了一些非质子化给体溶剂中的溶剂化空间效应。由于非水溶液中金属络合的动力学方面尚未被揭示，我们引进了停流分光光度计，并对已完成精确热力学分析的Ni-Cl-bpy体系进行了动力学分析，发现在DMF中，当溶液中氯离子共存时，三联吡啶镍(II)络合物的生成速度降低。在Ni-Cl-bpy三元体系中的…此外，[NiCl(Bpy)_2]^+和[NiCl2bpy_2]形成了明显的络合物，与通过[NiCl(Bpy)_2]^&lt；2+&gt；相比，这些络合物的穿透速度较慢，这表明在中间体[NiCl(Bpy)_3]^+中存在特定的相互作用，其中一个bpy以单齿配位。溶剂化空间效应与金属离子的离子半径密切相关。研究了铍、铝、镉和锰离子在DMF和DMA中的卤代络合作用，并比较了它们的热力学参数。四配位的小铍离子没有明显的空间效应。另一方面，相对较大的六配位镉离子表现出显著的空间效应。即使较大的稀土离子也表现出明显的空间效应，EXAFS表明，在DMA中的配位数比在DMF中的配位数减少了1个；而在DMF-DMA混合物中，随着DMA含量的增加，配位数逐渐减少。较少

Metal ions exist as solvated complexes in aprotic donor solvents such as dimethylformamide (DMF), dimethylacetamide (DMA), and hexamethylphosphoric triamide (HMPA). The coordination structure and intramolecular interactions of the solvated metal complexes are largely different from those of hydrated metal complexes, and the difference play a key role in thermodynamic and kinetic complexation aspects in these aprotic solvents. In the present study, we particularly focused our attention on solvation steric effects in some aprotic donor solvents. As kinetic aspects on metal complexation in nonaqueous solution have not been revealed yet, we newly introduced a stopped-flow spectrophotometer, and kinetic analyzes have been carried out for the Ni-Cl-bpy systems for which precise thermodynamic analyzes have been accomplished.It is found that in DMF the rate of formation of the tris-bipyridine nickel (II) complex is reduced when chloride ions coexist in solution. In the Ni-Cl-bpy ternary system … More , the [NiCl (bpy)_2]^+ and [NiCl_2bpy_2] complexes are significantly formed and the pass through these complexes was found to be slow compared to the pass through [NiCl (bpy)_2]^<2+>, suggesting a presence of a specific interaction within the intermediate [NiCl (bpy)_3]^+, in which one bpy coordinates as monodentate. Solvation steric effect exhibited a strong relationship to the ionic radius of metal ions. Halogeno complexation of beryllium, aluminum, cadmium and manganese ions were examined in DMF and DMA,and their thermodynamic parameters were compared. The four-coordinated small beryllium ion show no appreciable steric effect. One the other hand, relatively large and six-coordinated cadmium ion exhibits a significant steric effect. Even larger lanthanide ions show also significant steric efffect, and it is indicated by EXAFS that the coordination number in DMA is reduced by one compared with that in DMF.It is also indicated by ^<89>Y NMR that in DMF-DMA mixtures, the coordination number reduced gradually with increasing DMA content. Less