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 (Hchdc and R-Hchdc, 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 [UO(R-chdc)] (1) was only obtained with the enantiopure ligand, complexes [UO(chdc)(THF)] (2), [UO(chdc)(DMF)] (3), and [UO(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 UO(chdc)(bipy) and [UO(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 [UOCu(chdc)(bipy)(HO)]·HO (7) and [UOCu(R-chdc)(bipy)]·3HO (8) crystallize as a 1D or a 2D species, respectively, while [UOCd(R-chdc)(HO)]·HO (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO)Na(chdc)(HO)] (10), [(UO)Ag(chdc)(HO)] (11), [(UO)Na(R-chdc)(HO)] (12), and [(UO)Pb(R-chdc)(HO)] (13) are closely related, all of them containing tetranuclear, pseudotetrahedral [(UO)(chdc/R-chdc)] cage motifs, that are assembled into a three-dimensional (3D) framework by bridging counterions (Na, Ag, or Pb). 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.