Qin Jian-Wei, Zhang Peng, Pu Zhen, Hu Yin, Zhang Ping, Shuai Mao-Bing, Hu Shu-Xian
Science and Technology on Surface Physics and Chemistry Laboratory , Mianyang 621908 , China.
Beijing Computational Science Research Center , Beijing 100193 , China.
J Phys Chem A. 2019 Aug 15;123(32):6958-6969. doi: 10.1021/acs.jpca.9b02923. Epub 2019 Jul 31.
Uranium(III) compounds are very reactive and exhibit a broad range of chemical-bonding tendencies owing to the spatially diffused valence orbitals of uranium. A systematic study on the geometries, electronic structures, and chemical bonding of NU-XO (X = C, N, O) is performed using relativistic quantum chemistry approaches. The NU-CO and NU-NO complexes have an end-on structure, that is, (NU) (η-CO) and (NU) (η-NO), whereas NU-OO adopts a side-on ((NU) (η-O)) structure. The electronic structure analysis shows that UN exhibits efficient activation reactivity to molecules, especially to NO and O, because of the significant U 7s/5f → XO 2π* electron transfer. Thus, the oxidation state of U is +V with the dianion ligand NO and O in NU-NO and NU-OO, respectively. Instead, U retains its usual +III oxidation state in NU-CO with a neutral CO ligand. The significant stability of NU-XO (X = C, N, O) is determined by the covalent U-X bonding which contains both X → U σ-, π-donation from the X lone pair and U 5f → XO 2π* back-donation contributions. The significant back-donation to the antibonding X-O 2π* orbital results in the obvious weakening of the X-O bonding.
铀（III）化合物具有很高的反应活性，由于铀的价轨道在空间上呈弥散状，因而展现出广泛的化学键合倾向。利用相对论量子化学方法，对NU-XO（X = C、N、O）的几何结构、电子结构和化学键进行了系统研究。NU-CO和NU-NO配合物具有端连结构，即(NU)(η-CO)和(NU)(η-NO)，而NU-OO采用侧连（(NU)(η-O)）结构。电子结构分析表明，由于U 7s/5f向XO 2π的显著电子转移，UN对分子，尤其是对NO和O表现出高效的活化反应性。因此，在NU-NO和NU-OO中，U与双负离子配体NO和O的氧化态分别为+V。相反，在含有中性CO配体的NU-CO中，U保持其通常的+III氧化态。NU-XO（X = C、N、O）的显著稳定性由共价U-X键决定，该键包含X孤对电子向U的σ、π给予以及U 5f向XO 2π的反馈给予。对反键X-O 2π*轨道的显著反馈给予导致X-O键明显减弱。
