Oxygen and nitrogen Lewis base adducts of [UO2(OTf)2].: Crystal structures of polypyridine complexes with out-of-plane uranyl equatorial coordination

Dissolution of [UO2(OTf)(2)] (1) in anhydrous thf, dme or py led to the formation of the complexes [UO2(OTf)(2)(thf)(3)] (2), [UO2(OTf)(2)(dme)] (3) and [UO2(OTf)(2)(py)(3)] (4), respectively. Compounds 2 and 4 are neutral monomers in the solid state as well as the chloride [UO2Cl2(py)(3)] (5) which was prepared in a similar way as for 4 from the dimer [{UO2Cl2(thf)(2)}(2)]. Addition of 4 equivalents of triphenylphosphine oxide (tppo) to 1 afforded, in pyridine, the dicationic species [UO2(tppo)(4)][OTf](2) (6). The bi- or terdentate nitrogen molecules 2,2'-bipy, phen or terpy reacted with 1 in acetonitrile or pyridine to give [UO2(OTf)(2)(bipy)(2)] (7), [UO2(phen)(3)][OTf](2) (8), [UO2(OTf)(2) (terpy)] (9) and [UO2(terpy)(2)][OTf](2) (10), respectively. The hydroxide compound [{UO2(OH)(terpy)}(2)][OTf](2) (11) was obtained by hydrolysis in air of 1 in a mixture of acetonitrile and ethanol in the presence of terpyridine. The X-ray crystal structures of 7, 8 and 10 reveal a novel coordination geometry for the uranyl ion, the uranium atom being in a rhombohedral environment; the six coordinating ligands atoms of the {UO2}(2+) ion are separated into two parallel and staggered equilateral triangles and the UO2 axis is perpendicular to these triangles, passing through their centre. The structures of the mono(terpy) complexes 9 and 11 show the uranium atoms in a distorted pentagonal bipyramidal configuration with the nitrogen atom of the central pyridine ring of the terpy ligand significantly displaced from the equatorial plane.