The chemistry of uranium. Part 20. Tetraphenylphosphonium pentachloro-oxouranate(VI): crystal structure and bonding characteristics

Abstract

The crystal structure of the title complex has been determined from three-dimensional X-ray diffraction data collected on a four-circle automatic diffractometer. The complex crystallises in space group P4/n, with a=b= 13.264(5), c= 7.621(5)Å, and Z= 2. The structure has been solved by Patterson and Fourier methods and refined to a final R of 0.024. The structure consists of octahedral anions and of cations with (S₄) symmetry, both ions forming linear stacks parallel to c: U–O is 1.76(1)Å, four Cl atoms form an equatorial plane with U–Cl 2.536(2)Å, while the axial U–Cl bond, trans to U–O, is 2.433(4)Å. The results are discussed in relation to structural data for similar actinoid complexes with metal oxidation states IV–VI; strong evidence is adduced that the bonding in such complexes is predominantly ionic in character and strongly influenced by ligand-ligand repulsion.