Binuclear trivalent and tetravalent uranium halides and cyanides supported by cyclooctatetraene ligands

Abstract

Abstract Although the first organoactinide chloride Cp3UCl (Cp=η5-C5H5) was synthesized more than 50 years ago, binuclear uranium halides remain very rare in organoactinide chemistry. Herein, a series of binuclear trivalent and tetravalent uranium halides and cyanides with cyclooctatetraene ligands, (COT)2U2X n (COT=η8-C8H8; X=F, Cl, CN; n=2, 4), have been systematically studied using scalar-relativistic density functional theory (DFT). The structures with bridging halide or cyanide ligands were predicted to be the most stable complexes of (COT)2U2X n , and all the complexes show weak antiferromagnetic interactions between the uranium centers. However, for each species, there is no significant uranium-uranium bonding interaction. The bonding between the metal and the ligands shows some degree of covalent character, especially between the metal and terminal halide or cyanide ligands. The U-5f and 6d orbitals are predominantly involved in the metal-ligand bonding. All the (COT)2U2X n species were predicted to be more stable compared to the mononuclear half-sandwich complexes at room temperature in the gas phase such that (COT)2U2X4 might be accessible through the known (COT)2U complex. The tetravalent derivatives (COT)2U2X4 are more energetically favorable than the trivalent (COT)2U2X2 analogs, which may be attributed to the greater number of strong metal-ligand bonds in the former complexes.