title: (18-Crown-6)-mu-oxo-hexakis(tetrahydroborato)diuranium(IV): an unprecedented asymmetric dinuclear complex.
abstract: In the title compound, (1,4,7,10,13,16-hexaoxacyclooctadecane-1kappa6O)-mu-oxo-1:2kappa2O:O-hexakis(tetrahydroborato)-1kappa3H;2kappa2H;2kappa2H;2kappa3H;2kappa3H;2kappa3H-diuranium(IV), [U2(BH4)6O(C12H24O6)], one of the U atoms (U1), located at the centre of the crown ether moiety, is bound to the six ether O atoms, and also to a tridentate tetrahydroborate group and a mu-oxo atom in axial positions. The other U atom (U2) is bound to the same oxo group and to five tetrahydroborate moieties, three of them tridentate and the other two bidentate. The two metal centres are bridged by the mu-oxo atom in an asymmetric fashion, thus giving the species (18-crown-6)(kappa3-BH4)U=(mu-O)-U(kappa3-BH4)3(kappa2-BH4)2, in which the U1=O and U2-O bond lengths to the mu-O atom [1.979 (5) and 2.187 (5) angstroms, respectively] are indicative of the presence of positive and negative partial charges on U1 and U2, respectively.
authors.affiliation: CEA/Saclay, DSM/DRECAM/SCM (CNRS URA 331), Bâtiment 125, 91191 Gif-sur-Yvette, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Villiers
authors.forename: Pierre
authors.initials: P
authors.lastname: Thuéry
authors.forename: Michel
authors.initials: M
authors.lastname: Ephritikhine