Hayton Trevor W
Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
Dalton Trans. 2018 Jan 23;47(4):1003-1009. doi: 10.1039/c7dt04123c.
The structure of the uranyl ion (UO) has been the topic of investigation for almost a century. Since the first structural study of uranyl in 1935, over 4000 uranyl complexes have been characterized by X-ray crystallography. The vast majority of these complexes feature a linear uranyl group (e.g., O-U-O = 180°); however, there are a handful of complexes that feature much more acute O-U-O angles. In fact, the smallest experimentally observed O-U-O angles are ca. 161°. This Frontier Article catalogs every reported uranyl complex that features an O-U-O angle below 172°, and attempts to rationalize the origins of the observed O-U-O bending. In particular, I describe two distinct causes of O-U-O bending: (1) bending that occurs as a result of unfavourable steric interactions between the equatorial co-ligands and the uranyl oxo groups; and (2) bending that appears to have an electronic origin. In addition, I describe several possible avenues for future investigation. Understanding the effect that O-U-O bending has on uranyl electronic structure could ultimately provide insight into several unique aspects of the uranyl ion, such as the inverse trans influence and the involvement of the "pseudo-core" U6p orbitals in U-O bonding.
铀酰离子（UO）的结构已成为近一个世纪以来的研究课题。自1935年首次对铀酰进行结构研究以来，已有4000多种铀酰配合物通过X射线晶体学进行了表征。这些配合物中的绝大多数具有线性铀酰基团（例如，O-U-O = 180°）；然而，有少数配合物具有小得多的O-U-O键角。事实上，实验观察到的最小O-U-O键角约为161°。这篇前沿文章列出了每一个报道的O-U-O键角低于172°的铀酰配合物，并试图对观察到的O-U-O弯曲的起源作出合理的解释。特别是，我描述了O-U-O弯曲的两个不同原因：（1）由于赤道配位体与铀酰氧基团之间不利的空间相互作用而发生的弯曲；（2）似乎具有电子起源的弯曲。此外，我还描述了未来研究的几个可能途径。了解O-U-O弯曲对铀酰电子结构的影响最终可能会深入了解铀酰离子的几个独特方面，例如反位效应和“准核心”U6p轨道在U-O键合中的作用。
