Uranyl complexes conformation

ESR spectra, 511 Uranium(VI) complexes dioxoneocupferron, 512 Uranium hexaalkoxides physical properties, 347 Uranyl complexes cupferron, 512 formamide, 491 glycolic acid, 472 hexafluoroacetylacetone, 373, 377 photochemistry, 385 rearrangement, 384 maleic acid conformation, 467 neutral 1,3-diketones, 402 poly ketones, 399 Urea... 

An early X-ray structure of 8 crystallized from pyridine indicated it to have a pleated loop conformation (see ref. 1, p. 70), and rather similar conformations have been observed for its complexes with calcium and uranyl cations. In a more recent study, however, the X-ray structure of a complex of 8 with eight pyridine molecules showed it to assume a twisted conformation, something approaching the pinched conformation suggested in the early 1980s before an X-ray structure had been obtained. Complexes of 8 " with various metal ions, including lanthanides, thorium, and molybdenum, also reveal a conformation different from a pleated loop and approximately described as a 1,2,3,4-alternate. 

Labarre JF (1978) Conformational Analysis in Inorganic Chemistry Semi-Empirical Quantum Calculation vs. Experiment 35 1-35 hammers M, Follmann H (1983) The Ribonucleotide Reductases A Unique Group of Metallo-enzymes Essential for Cell Proliferation. 54 27-91 Le Brun NE, Thomson AJ, Moore GR (1997) Metal Centres of Bacterioferritins or Non-Heam-Iron-Containing Cytochromes (>557. 88 103-138 Leciejewicz J, Alcock NW, Kemp TJ (1995) Carboxylato Complexes of the Uranyl Ion Effects of Ligand Size and Coordinat. Geometry Upon Molecular and Crystal Structure. 82 43-84 Lecomte C, see Guilard R (1987) 64 205-268 Lee YJ, see Scheldt WR (1987) 64 1-70 Lehmann H, see Schultz H (1991) 74 41-146... 

Binding of hard anions occurs strongly at the hard Lewis acidic uranyl center, whereas cation- tt interactions are established between the aromatic side arms and the cation counterpart of the ion pair. Thus, complexation of alkali metal salts (MX) such as CsCl and RbCl with 15 resulted in the formation of isomorphous supramolecular assemblies in the solid state. In the dimeric [15-CsCl], each cation is coordinated to six oxygens, three from each receptor, thus creating a pseudo-crown-ether-Uke environment for the cation. Additionally, each metal ion in the dimeric unit is coordinated to both halide ions and, most importantly, to two aromatic side arms, one from each of the receptors giving decacoordination for the cation. The closest metal ion-aromatic carbon distances of 3.44(1) A for CsCl, 3.34-3.38(1) A for RbCl, and 3.58(1) A for CsF are observed in the respective alkali halide complexes [15 MX] indicating the conformational flexibility of the side arms and adaptability of the receptors 15 and 16 to form multiple cation- rt interactions with the hosted cations. 

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