Uranyl-Glycine-Water Complexes in Solution: Comprehensive Computational Modeling of Coordination Geometries, Stabilization Energies, and Luminescence Properties

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• 作者：Jing Su ; Kai Zhang ; W. H. Eugen Schwarz ; Jun Li
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：March 21, 2011
• 年：2011
• 卷：50
• 期：6
• 页码：2082-2093
• 全文大小：1112K
• 年卷期：v.50,no.6(March 21, 2011)
• ISSN：1520-510X

文摘

Comprehensive computational modeling of coordination structures, thermodynamic stabilities, and luminescence spectra of uranyl-glycine-water complexes [UO₂(Gly)_naq_m]²⁺ (Gly = glycine, aq = H₂O, n = 0鈭?, m = 0鈭?) in aqueous solution has been carried out using relativistic density functional approaches. The solvent is approximated by a dielectric continuum model and additional explicit water molecules. Detailed pictures are obtained by synergic combination of experimental and theoretical data. The optimal equatorial coordination numbers of uranyl are determined to be five. The energies of several complex conformations are competitively close to each other. In non-basic solution the most probable complex forms are those with two water ligands replaced by the bidentate carboxyl groups of zwitterionic glycine. The N,O-chelation in non-basic solution is neither entropically nor enthalpically favored. The symmetric and antisymmetric stretch vibrations of the nearly linear O鈭扷鈭扥 unit determine the luminescence features. The shapes of the vibrationally resolved experimental solution spectra are reproduced theoretically with an empirically fitted overall line-width parameter. The calculated luminescence origins correspond to thermally populated, near-degenerate groups of the lowest electronically excited states of ³螖_g and ³桅_g character, originating from (U鈭扥)蟽_u 鈫?(U-5f)未_u,_u configurations of the linear [OUO]²⁺ unit. The intensity distributions of the vibrational progressions are consistent with U鈭扥 bond-length changes around 5¹/₂ pm. The unusually high intensity of the short wavelength foot is explained by near-degeneracy of vibrationally and electronically excited states, and by intensity enhancement through the asymmetric O鈭扷鈭扥 stretch mode. The combination of contemporary computational chemistry and experimental techniques leads to a detailed understanding of structures, thermodynamics, and luminescence of actinide compounds, including those with bioligands.