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

Racemic and enantiopure (1R,2R) forms of trans-1,2-cyclohexanedicarboxylic acid (H(2)chdc and R-H(2)chdc, 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)]center dot H2O (7) and [UO2Cu(R-chdc)(2)(bipy)]center dot 3H2O (8) crystallize as a 1D or a 2D species, respectively, while [UO2Cd(R-chdc)(2)(H2O)(2)]center dot H2O (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO2)(2)Na-2(chdc)(3)(H2O)(2)] (10), [(UO2)(2)Ag-2(chdc)(3)(H2O)(2)] (11), [(UO2)(2)Na-2(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.