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Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study

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Abstract

The uranyl(VI) ‘Pacman’ complex [(UO2)(py)(H2L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp2Ti(η2-Me3SiC[triple bond, length as m-dash]CSiMe3) and [Cp2TiCl]2 to oxo-titanated uranyl(V) complexes [(py)(Cp2TiIIIOUO)(py)(H2L)] 1 and [(ClCp2TiIVOUO)(py)(H2L)] 2. Combination of ZrII and ZrIV synthons with A yields the first ZrIV–uranyl(V) complex, [(ClCp2ZrOUO)(py)(H2L)] 3. Similarly, combinations of Ae0 and AeII synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(V) complexes [(py)2(ClMgOUO)(py)(H2L)] 4, [(py)2(thf)2(ICaOUO)(py) (H2L)] 5; the zinc complexes [(py)2(XZnOUO)(py)(H2L)] (X = Cl 6, I 7) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(V) complexes; monomeric [(py)3(RbOUO)(py)(H2L)] 8 and hexameric [(MOUO)(py)(H2L)]6 (M = Rb 8b or Cs 9). In these uranyl(V) complexes, the pyrrole N–H atoms show strengthened hydrogen-bonding interactions with the endo-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M4 edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(V) in 7 (ZnI)) to compare the covalent character in the UV–O and O–M bonds and show the 5f orbitals in uranyl(VI) complex A are unexpectedly more delocalised than in the uranyl(V) 7 (ZnI) complex. The Oexo–Zn bonds have a larger covalent contribution compared to the Mg–Oexo/Ca–Oexo bonds, and more covalency is found in the U–Oexo bond in 7 (ZnI), in agreement with the calculations.

Graphical abstract: Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study

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Publication details

The article was received on 21 Dec 2018, accepted on 26 Aug 2019 and first published on 06 Sep 2019


Article type: Edge Article
DOI: 10.1039/C8SC05717F
Chem. Sci., 2019, Advance Article
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    Differential uranyl(V) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study

    M. Zegke, X. Zhang, I. Pidchenko, J. A. Hlina, R. M. Lord, J. Purkis, G. S. Nichol, N. Magnani, G. Schreckenbach, T. Vitova, J. B. Love and P. L. Arnold, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C8SC05717F

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