Structure and stereochemistry in f-block complexes of high co-ordination number. Part 1. The [M(unidentate ligand X)(unidentate ligand Y)7] system : crystal structure of bis[chloroheptakis(dimethylformamide)uranium(IV)] tris[tetrachlorodioxouranate(VI)]

Abstract

A reaction product of uranium tetrachloride and dimethylformamide (dmf) from acetone solution has been studied crystallographically and shown to have the stoicheiometry [U^IVCl(dmf)₇]₂[U^VIO₂Cl₄]₃; for the 4 295 ‘observed’X-ray diffraction data at 295 K the final residual was 0.046. Crystals are monoclinic, space group P2₁/n, with a= 14.132(4), b= 26.160(6), c= 12.092(2)Å, β= 97.83(2)°, and Z= 2. The asymmetric unit comprises one cation, one full anion, and one half-anion, the uranium of which lies on a crystallographic inversion centre. Within the anions, the stereochemistry about the uranium atoms is pseudo-octahedral, UO ranging from 1.73(1) to 1.77(1)Å while U–Cl lie between 2.650(7) and 2.672(5)Å. The uranium of the cation is eight-co-ordinated by the chloride [U–Cl 2.665(5)Å] and seven dimethylformamide ligands [U–O 2.30(1)–2.40(1)Å]. The stereochemistry is dodecahedral with the chloride in one of the ‘B’ sites, as expected from repulsion-energy calculations.