Uranium, tetrakis structure

Uranium, pentakis(dimethyl sulfoxide)dioxy-stereochemistry, I, 74 Uranium, pentakis(urea)dioxy-stereochemistry, 1,74 Uranium, tetrakis(bipyridyl)-stereochemistry, I, 94 structure, 1, 24... 

Uranium, tctrakis(dibcnzoylmclhane)-stereochemistry, l, 94 Uranium, tetrakis(oxalato)-structure, 1, 99... 

Uranium. tetrakis(phenoxy)bis[ethylenebis-(dimethylphosphine)]-structure, 1,89... 

The pyrrolyl ligand is interesting in that it can function as both a u-bonded amido group or a yr-bonded multihapto ligand. The pyrrolyl group appears to be a weaker electron donor than the cyclopentadienide anion 90). In the tetrakis-(2,5-dimethylp3u rolyl)uranium(IV) complex a preliminary structure has been revised with a tris(monohapto) (pentahapto) structure now assigned from variable temperature PMR spectra 90). 

Thus the structures of tetrakis(N-isopropyl-3,3-dimethylbutano-and -2,2-dimethylpropano)hydroxamatothorium(IV) have been determined by single crystal X-ray diffraction (77). Keeping the pH as low as possible, these compounds precipitate upon the addition of an aqueous solution of thorium tetrachloride to an aqueous solution of the sodium salt of the hydroxamic acid. The analogous uranium(IV) complexes were prepared similarly under an inert atmosphere using deaerated solvents. In addition to their hydrocarbon solubility, the bulky alkyl substituents impart other interesting properties to these complexes. They melt at 127-8 and 116-7°C and, under a vacuum of 10 3 torr, sublime at 95 and 100°C, respectively ... 

Uranium forms tris and tetrakis-cyclopentadienyls CpjU and Cp U. In the latter there are four fy -cyclopentadienyl groups so that the metal atom is formally 12-coordinate. This high coordination number is consistent with essentially ionic (electrostatic) bonding. This may also apply to the complexes MCp (M = Ti, Zr) where the structures apparently depend on the size of the metal atom and, for Cp Zr, the 18-electron rule does not apply. 

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