Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with <i>rac</i>- and (1<i>R</i>,2<i>R</i>)-<i>trans</i>-1,2-Cyclo­hexane­dicarboxylates: Consequences of Chirality

Racemic and enantiopure (1R,2R) forms of trans-1,2-cyclohexanedicarboxylic acid (H2chdc and R-H2chdc, respectively) have been used in the synthesis of a series of 13 uranyl ion complexes, all obtained under solvo-hydrothermal conditions and in the presence of additional metal cations and/or N-donor ligands. While the homometallic complex [UO2(R-chdc)] (1) was only obtained with the enantiopure ligand, complexes [UO2(chdc)­(THF)] (2), [UO2(chdc)­(DMF)] (3), and [UO2(chdc)­(NMP)] (4), with a coordinated solvent molecule, were obtained from the racemic form only; all crystallize as two-dimensional (2D) assemblies. The two complexes [UO2(chdc)­(bipy)]­(5) and [UO2(R-chdc)­(bipy)] (6), where bipy is 2,2′-bipyridine, are isomorphous since 5 crystallizes as a racemic conglomerate; they are both one-dimensional (1D) homochiral, helical polymers. The heterometallic complexes [UO2Cu­(chdc)2(bipy)­(H2O)]·H2O (7) and [UO2Cu­(R-chdc)2(bipy)]·3H2O (8) crystallize as a 1D or a 2D species, respectively, while [UO2Cd­(R-chdc)2(H2O)2]·H2O (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO2)2Na2(chdc)3(H2O)2] (10), [(UO2)2Ag2(chdc)3(H2O)2] (11), [(UO2)2Na2(R-chdc)3(H2O)2] (12), and [(UO2)2Pb­(R-chdc)3(H2O)4] (13) are closely related, all of them containing tetranuclear, pseudo­tetrahedral [(UO2)4(chdc/R-chdc)6]4– cage motifs, that are assembled into a three-dimensional (3D) framework by bridging counterions (Na+, Ag+, or Pb2+). These cages define a new pathway to assembly of such species based on the unique coordination geometry of uranyl ion, differing from the widely exploited use of octahedral metal ions.