Uranyl ion complexes with chiral malic and citramalic, and prochiral citric and tricarballylic acids. Influence of coligands and additional metal cations

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 Cd^II 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. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)