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.

The uranyl(vi) 'Pacman' complex [(UO)(py)(HL)] (L = polypyrrolic Schiff-base macrocycle) is reduced by CpTi(η-MeSiC[triple bond, length as m-dash]CSiMe) and [CpTiCl] to oxo-titanated uranyl(v) complexes [(py)(CpTiOUO)(py)(HL)] and [(ClCpTiOUO)(py)(HL)] . Combination of Zr and Zr synthons with yields the first Zr-uranyl(v) complex, [(ClCpZrOUO)(py)(HL)] . Similarly, combinations of Ae and Ae synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)(ClMgOUO)(py)(HL)] , [(py)(thf)(ICaOUO)(py) (HL)] ; the zinc complexes [(py)(XZnOUO)(py)(HL)] (X = Cl , I ) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with generate the first mono-rubidiated and mono-caesiated uranyl(v) complexes; monomeric [(py)(RbOUO)(py)(HL)] and hexameric [(MOUO)(py)(HL)] (M = Rb or Cs ). In these uranyl(v) complexes, the pyrrole N-H atoms show strengthened hydrogen-bonding interactions with the -oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M 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 (ZnI)) to compare the covalent character in the U-O and O-M bonds and show the 5f orbitals in uranyl(vi) complex are unexpectedly more delocalised than in the uranyl(v) (ZnI) complex. The O-Zn bonds have a larger covalent contribution compared to the Mg-O/Ca-O bonds, and more covalency is found in the U-O bond in (ZnI), in agreement with the calculations.