Structure and stereochemistry in f-block complexes of high co-ordination number. Part 2. The [M(unidentate ligand X)4(unidentate ligand Y)4] system : crystal structure of tetrakis(hexamethylphosphoramide)tetrakis(isothiocyanato)uranium(IV)

Abstract

The crystal structure of the title compound [U^IV(NCS)₄{OP(NMe₂)₃}₄] has been determined from X-ray diffraction data at 295 K, the structure being refined by least squares to a residual of 0.059 for 7 356 ‘observed’ reflections. Crystals are monoclinic, space group P2/c, with a= 25.06(1), b= 21.50(1), c= 22.64(1)Å, β= 117.94(3)°, and Z= 8. The structure comprises discrete molecules of the complex, all of which have eight-co-ordinate uranium atoms lying on crystallographic two-fold symmetry axes, with U–O ranging from 2.276(13) to 2.357(10)Å and U–N from 2.410(15) to 2.526(17)Å. The stereochemistry and relative stability of the different isomers of [M(unidentate ligand X)₄(unidentate ligand Y)₄] have been examined by repulsion theory.