Publication | Open Access
Differential uranyl(<scp>v</scp>) 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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Citations
84
References
2019
Year
The uranyl(vi) 'Pacman' complex [(UO<sub>2</sub>)(py)(H<sub>2</sub>L)] <b>A</b> (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp<sub>2</sub>Ti(η<sup>2</sup>-Me<sub>3</sub>SiC[triple bond, length as m-dash]CSiMe<sub>3</sub>) and [Cp<sub>2</sub>TiCl]<sub>2</sub> to oxo-titanated uranyl(v) complexes [(py)(Cp<sub>2</sub>Ti<sup>III</sup>OUO)(py)(H<sub>2</sub>L)] <b>1</b> and [(ClCp<sub>2</sub>Ti<sup>IV</sup>OUO)(py)(H<sub>2</sub>L)] <b>2</b>. Combination of Zr<sup>II</sup> and Zr<sup>IV</sup> synthons with <b>A</b> yields the first Zr<sup>IV</sup>-uranyl(v) complex, [(ClCp<sub>2</sub>ZrOUO)(py)(H<sub>2</sub>L)] <b>3</b>. Similarly, combinations of Ae<sup>0</sup> and Ae<sup>II</sup> synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)<sub>2</sub>(ClMgOUO)(py)(H<sub>2</sub>L)] <b>4</b>, [(py)<sub>2</sub>(thf)<sub>2</sub>(ICaOUO)(py) (H<sub>2</sub>L)] <b>5</b>; the zinc complexes [(py)<sub>2</sub>(XZnOUO)(py)(H<sub>2</sub>L)] (X = Cl <b>6</b>, I <b>7</b>) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with <b>A</b> generate the first mono-rubidiated and mono-caesiated uranyl(v) complexes; monomeric [(py)<sub>3</sub>(RbOUO)(py)(H<sub>2</sub>L)] <b>8</b> and hexameric [(MOUO)(py)(H<sub>2</sub>L)]<sub>6</sub> (M = Rb <b>8b</b> or Cs <b>9</b>). In these uranyl(v) complexes, the pyrrole N-H atoms show strengthened hydrogen-bonding interactions with the <i>endo</i>-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M<sub>4</sub> 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 <b>7</b> (ZnI)) to compare the covalent character in the U<sup>V</sup>-O and O-M bonds and show the 5f orbitals in uranyl(vi) complex <b>A</b> are unexpectedly more delocalised than in the uranyl(v) <b>7</b> (ZnI) complex. The O<sub>exo</sub>-Zn bonds have a larger covalent contribution compared to the Mg-O<sub>exo</sub>/Ca-O<sub>exo</sub> bonds, and more covalency is found in the U-O<sub>exo</sub> bond in <b>7</b> (ZnI), in agreement with the calculations.
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