Probing the Electronic Structure and Chemical Bonding in Tricoordinate Uranyl Complexes UO2X3鈥?/sup> (X = F, Cl, Br, I): Competition between Coulomb Repulsion and U鈥揦 Bondin

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• 作者：Jing Su ; Phuong Diem Dau ; Yi-Heng Qiu ; Hong-Tao Liu ; Chao-Fei Xu ; Dao-Ling Huang ; Lai-Sheng Wang ; Jun Li
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：June 3, 2013
• 年：2013
• 卷：52
• 期：11
• 页码：6617-6626
• 全文大小：399K
• 年卷期：v.52,no.11(June 3, 2013)
• ISSN：1520-510X

文摘

While uranyl halide complexes [UO₂(halogen)_n]^2鈥?i>n (n = 1, 2, 4) are ubiquitous, the tricoordinate species have been relatively unknown until very recently. Here photoelectron spectroscopy and relativistic quantum chemistry are used to investigate the bonding and stability of a series of gaseous tricoordinate uranyl complexes, UO₂X₃^{鈥?/sup> (X = F, Cl, Br, I). Isolated UO₂X₃鈥?/sup> ions are produced by electrospray ionization and observed to be highly stable with very large adiabatic electron detachment energies: 6.25, 6.64, 6.27, and 5.60 eV for X = F, Cl, Br, and I, respectively. Theoretical calculations reveal that the frontier molecular orbitals are mainly of uranyl U鈥揙 bonding character in UO₂F₃鈥?/sup>, but they are from the ligand valence np lone pairs in the heavier halogen complexes. Extensive bonding analyses are carried out for UO₂X₃鈥?/sup> as well as for the doubly charged tetracoordinate complexes (UO₂X₄2鈥?/sup>), showing that the U鈥揦 bonds are dominated by ionic interactions with weak covalency. The U鈥揦 bond strength decreases down the periodic table from F to I. Coulomb barriers and dissociation energies of UO₂X₄2鈥?/sup> 鈫?UO₂X₃鈥?/sup> + X鈥?/sup> are calculated, revealing that all gaseous dianions are in fact metastable. The dielectric constant of the environment is shown to be the key in controlling the thermodynamic and kinetic stabilities of the tetracoordinate uranyl complexes via modulation of the ligand鈥搇igand Coulomb repulsions.}