Second Generation Octahedral Coordination Chemistry based on Hexametal Cluster Units

八面体六金属簇合物是已知的各种过渡金属离子。其中，具有d^4金属离子的化合物如Re（III）、Mo（II）和W（II）特别稳定，具有12个电子精确的金属-金属单键。在这个项目中，d^4八面体六核簇合物被认为是第二代八面体金属配位化学的目标。本研究的目的是阐明八面体簇合物与简单单核八面体簇合物之间的异同。结果总结如下。(i)配体取代性质。配体取代反应的动力学研究表明，吡啶配体比氯离子更快地被取代。这与单核络合物的趋势相反，在单核络合物中，更少的碱性氯化物配体更容易被取代。(ii)氧化还原反应。六铼（III）配合物进行单电子氧化。氧化还原 关于我们 在混合末端吡啶-氯化物体系中，随着末端吡啶配体数目的增加，电位向正方向移动。这与通过考虑配体碱度的预期相反。这两个事实（i）和（ii）表明了六金属簇的独特特征：与典型的低自旋d^6单核金属中心相比，六金属簇具有良好的π接受性和较差的π施主性。(iii)排放d^4八面体团簇具有很强的红光发射。详细的温度依赖性的排放揭示了奇怪的行为的发射寿命和发射能量。通过考虑四个激发态子能级成功地分析了这些结果。(iv)自组装单分子膜。利用强的Au-S键将六铼团簇成功地固定在金电极表面。将S-位点引入到连接到六核单元的配体吡啶衍生物中。此外，无论是在溶液中还是在金表面上，六铼原子簇单元都被化学结合到以氧为中心的三钌单元中。研究了六铼原子簇和三铼-六铼杂化配合物的表面电化学。这些结果（i）-（iv）揭示了八面体六金属簇合物和简单单核金属中心的重要差异和相似之处。少

Octahedal hexametal clusters are known for various transition metal ions. Among them, those with d^4 metal ions such as Re(III), Mo(II) and W(II) are particularly stable with twelve electron-precise metal-metal single bonds. In this project, d^4 octahedral hexanuclear cluster complexes are considered as a target of a second generation of octahedral metal coordination chemistry. The purpose of this study is to clarify the similarity and difference between the octahedral cluster complexes and simple mononuclear octahedral complexes. The results are summarized as follows. (i) Ligand substitution properties. Kinetic study of the ligand substitution reactions at the terminal sites of the hexarhenium(III) clusters revealed that pyridine ligand is more rapidly substituted than chloride. This is in reverse trend from that of mononuclear complexes where less basic chloride ligand is replaced more easily. (ii) Redox reactions. Hexarhenium(III) complexes undergo one-electron oxidation. The redox … More potential shifts to positive direction as the number of terminal pyridine ligands increases in the mixed terminal pyridine-chloride system. This is in reverse direction from the expectation by considering the ligand basicity. The two facts, (i) and (ii), manifest unique characteristics of the hexametal clusters ; good π accepting and poor π donoating properties as opposed to typical low-spin d^6 mononuclear metal centers. (iii) Emissions. The d^4 octahedral clusters exhibit strong red emissions. Detailed temperature dependence of the emissions revealed curious behavior of emission life-times and emission energies. These results were successfully analyzed by considering four excited state sublevels. (iv) Self-assembled monolayers. Hexarhenium clusters were successfully fixed onto the gold electrode surfaces by using strong Au-S bond. The S-site was introduced to the ligand pyridine derivatives attached to the hexanuclear unit. Also the hexarhenium cluster unit was chemically combined to oxo-centered triruthenium unit both in solution and on the gold surface. The surface electrochemistry of the hexarhenium clusters and triruthenium-hexarhenium hybrid complexes have been studied. These results (i) - (iv) revealed important differences and similarities of the octahedral hexametal cluster complexes and simple mononuclear metal centers. Less