THERMODYNAMIC SND KINETIC STUDY ON SOLVATION STERIC INTERACTIONS

金属离子以溶剂化配合物的形式存在于非质子给体溶剂中，如二甲基甲酰胺（DMF）、二甲基乙酰胺（DMA）和六甲基磷酸三酰胺（HMPA）。溶剂化金属配合物的配位结构和分子内相互作用与水合金属配合物有很大的不同，这种差异在非质子溶剂中的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给体溶剂的溶剂化立体效应。由于非水溶液中金属络合的动力学方面尚未揭示，我们新引入了一种止流分光光度计，并对Ni-Cl-bpy体系进行了动力学分析，并对其进行了精确的热力学分析。发现在DMF中，氯离子共存时，三联吡啶镍（II）配合物的形成速率降低。在Ni-Cl-bpy三元体系中，[NiCl (bpy)_2]^+和[NiCl_2bpy_2]配合物明显形成，与[NiCl (bpy)_2]^<2+>相比，这些配合物的通过速度较慢，表明中间体[NiCl (bpy)_3]^+之间存在特定的相互作用，其中一个bpy坐标为单齿状。溶剂化立体效应与金属离子的离子半径密切相关。考察了铍、铝、镉和锰离子在DMF和DMA中的卤化络合作用，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，较大的六配位镉离子表现出明显的空间位阻效应。更大的镧系离子也表现出明显的位阻效应，EXAFS表明，与DMF相比，DMA中的配位数减少了1。^<89>Y NMR也表明，在DMF-DMA混合物中，配位数随着DMA含量的增加而逐渐降低。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