Uranyl Ion Complexes with Chiral Malic and Citramalic, and Prochiral Citric and Tricarballylic Acids: Influence of Coligands and Additional Metal Cations
Résumé
Seven homo- or heterometallic uranyl ion complexes with R,S-malic (H3ml), R-citramalic (H3cml), citric (H4cit) and tricarballylic (H3tca) acids were obtained under (solvo-)hydrothermal conditions and characterized by their crystal structure and, for five of them, their uranyl emission spectrum. All the malate, citramalate and citrate complexes contain the frequently observed 2:2 dimeric uranyl subunit in which the alkoxide group is bridging, these subunits being generally assembled into one-dimensional (1D) polymeric chains by bridging carboxylate groups. [(UO2)4(ml)2(C2O4)(NMP)4] (1) and [(UO2)2Cu2(ml)2(C2O4)(phen)2] (2), which contain oxalate anions formed in situ, crystallize as two-dimensional (2D) networks, the increase in dimensionality being provided by uranyl or copper oxalate bridges. [(UO2)2Ni(cml)2(cyclam)] (3) is also a 2D species, while [(UO2)2Cd(cml)2(bipy)(H2O)2] (4) crystallizes as a three-dimensional (3D) framework (even if CdII cations are disregarded). [(UO2)2Zn(Hcit)2(bipy)2(H2O)] (5) is a 1D polymer with decorating Zn(bipy)2(H2O)2+ groups, while [(UO2)2Cd(Hcit)2(bipy)2] (6) is a 2D network. [(UO2)2Pb(tca)2(H2O)4] (7), in which the three carboxylate groups are chelating and two of them further bridging, is a 3D framework. The uranyl emission spectra of complexes 3–6 are in agreement with a previously described trend, the largest blue-shift being found for the eight-coordinate complex 7
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