Uranyl Ion Complexes with Chiral Malic and Citramalic, and Prochiral Citric and Tricarballylic Acids: Influence of Coligands and Additional Metal Cations

Abstract

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 structures, and for five of them, by their uranyl emission spectra. All of 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. Complexes [(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. The complex [(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). The complex [(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. The complex [(UO2)2Pb(tca)2(H2O)4] (7), in which the three carboxylate groups are chelating and two of them are further bridging, is a 3D framework. The uranyl emission spectra of complexes 3–6 are in agreement with a previously described trend, the largest blueshift being found for the eight‐coordinate complex 7.