Structure and stereochemistry in f-block complexes of high co-ordination number. Part 3. The [M(bidentate ligand)2(unidentate ligand)4] system : crystal structures of tetrakis(isothiocyanato)bis(octamethylpyrophosphoramide-OO″)uranium(IV) and tetrachlorobis(octamethylpyrophosphoramide-OO″)thorium(IV)

Abstract

The crystal structures of octamethylpyrophosphoramide (ompp) adducts of uranium(IV) thiocyanate and thorium(IV) chloride have been determined and the complexes shown to be [U(NCS)₄(ompp)₂](1) and [ThCl₄(ompp)₂](2). The structures were refined by least squares to residuals of 0.043 [(1), 2 926 ‘observed’ reflections] and 0.060 [(2), 2 209 ‘observed’ reflections] for X-ray diffraction data measured at 295 K. For (1), crystals are orthorhombic, space group Fdd2, with unit-cell dimensions a= 44.26(2), b= 20.69(1), c= 9.110(5)Å, and Z= 8; for (2), crystals are monoclinic, space group P2₁/n, with unit-cell dimensions a= 18.714(7), b= 10.883(3), c= 18.999(7)Å, R = 105.01(3)°, and Z= 4. In each case the metal atom is eight-co-ordinated by the four unidentate ligands and a pair of bidentate octamethylpyrophosphoramide ligands. In (1) the metal atom lies on a crystallographic two-fold axis; U–N are 2.423(9) and 2.466(10)Å and U–0 2.297(6) and 2.414(7)Å. In (2) the molecule has no crystallographically imposed symmetry and Th-O range between 2.412(16) and 2.455(16)Å and Th-CI between 2.725(8) and 2.763(7)Å. The two compounds are two different structural isomers of the system [M(bidentate ligand)₂(unidentate ligand)₄]. The stereochemistry about the metal atom in (1) is square antiprismatic, whereas in (2) it is dodecahedral.