Liao Zuolei, Deb Tapash, Nyman May
Energy Frontier Research Center, Materials Science of Actinides Department of Chemistry, Oregon State University , Gilbert Hall, Corvallis, Oregon 97331, United States.
Inorg Chem. 2014 Oct 6;53(19):10506-13. doi: 10.1021/ic501587g. Epub 2014 Sep 19.
Self-assembly of uranyl peroxide polyoxometalates (POMs) in alkaline peroxide solutions has been known for almost a decade, but in these dynamic solutions that contain high concentrations of base and peroxide the reaction pathway could never be discerned, mixed species are obtained, and reproducibility is sometimes a challenge. Here we elucidate the reaction mechanisms utilizing self-assembly of the U24 cluster, [UO2(O2)(OH)]24(24-), from monomers as a model system. Using Raman as our main spectroscopic probe, we learned that the monomeric species is persistent in water at room temperature indefinitely. However, if a redox-active transition metal catalyst (copper (Cu(2+)) or cobalt (Co(2+))) is added, self-assembly is accelerated in a significant manner, forming U24 peroxide clusters in several hours, which is a good time scale for studying reaction mechanisms. From semiquantitative treatment of the spectroscopic data, we elucidate reaction mechanisms that are consistent with prior structural and computational studies that suggest uranyl peroxide rings templated by alkalis are the building units of clusters. By understanding aqueous speciation and processes, we are moving toward assuming control over cluster self-assembly that has been mastered for decades now in the analogous transition-metal POM systems.
近十年来，人们已经知道过氧铀多金属氧酸盐（POMs）在碱性过氧化物溶液中会发生自组装，但在这些含有高浓度碱和过氧化物的动态溶液中，反应途径一直无法确定，会得到混合物种，并且重现性有时是一个挑战。在这里，我们以U24簇[UO2(O2)(OH)]24(24-)从单体自组装作为模型系统来阐明反应机制。以拉曼光谱作为主要光谱探针，我们了解到单体物种在室温下的水中能无限期地持续存在。然而，如果加入一种具有氧化还原活性的过渡金属催化剂（铜（Cu(2+)）或钴（Co(2+)）），自组装会显著加速，在数小时内形成U24过氧化物簇，这是研究反应机制的一个很好的时间尺度。通过对光谱数据的半定量处理，我们阐明了与先前结构和计算研究一致的反应机制，这些研究表明由碱模板化的过氧铀环是簇的构建单元。通过了解水相物种形成和过程，我们正朝着能够控制簇的自组装迈进，而在类似的过渡金属POM系统中，人们已经掌握这种自组装几十年了。
