Thiocyanate Complexes of Uranium in Multiple Oxidation States: A Combined Structural, Magnetic, Spectroscopic, Spectroelectrochemical, and Theoretical Study

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• 作者：Emtithal Hashem ; James A. Platts ; Franti拧ek Hartl ; Giulia Lorusso ; Marco Evangelisti ; Carola Schulzke ; Robert J. Baker
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：August 18, 2014
• 年：2014
• 卷：53
• 期：16
• 页码：8624-8637
• 全文大小：624K
• ISSN：1520-510X

文摘

A comprehensive study of the complexes A₄[U(NCS)₈] (A = Cs, Et₄N, ⁿBu₄N) and A₃[UO₂(NCS)₅] (A = Cs, Et₄N) is described, with the crystal structures of [ⁿBu₄N]₄[U(NCS)₈]路2MeCN and Cs₃[UO₂(NCS)₅]路O_0.5 reported. The magnetic properties of square antiprismatic Cs₄[U(NCS)₈] and cubic [Et₄N]₄[U(NCS)₈] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, 渭_eff = 1.21 渭_B and 0.53 渭_B, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et₄N]₄[U(NCS)₈] has been explored using IR and UV鈥搗is spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc⁺, followed by an irreversible oxidation to form dithiocyanogen (NCS)₂ which upon back reduction regenerates thiocyanate anions coordinating to UO₂²⁺. NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)₈]^{4鈥?/sup> is delocalized over all NCS鈥?/sup> ligands. Reduction of the uranyl(VI) complex [Et₄N]₃[UO₂(NCS)₅] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)₈]4鈥?/sup> (An = Th, U) and [UO₂(NCS)₅]3鈥?/sup> has been explored by a combination of DFT and QTAIM analysis, and the U鈥揘 bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)鈥揘CS ion is more ionic than what was found for U(IV)鈥揅l complexes.}