Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with rac-and (1R,2R)-trans-1,2- Cyclohexanedicarboxylates: Consequences of Chirality
Résumé
Racemic and enantiopure (1R,2R) forms of trans-1,2-cyclo-hexanedicarboxylic 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 [UO 2 (R-chdc)] (1) was only obtained with the enantiopure ligand, complexes [UO 2 (chdc)(THF)] (2), [UO 2 (chdc)(DMF)] (3), and [UO 2 (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 2 (chdc)(bipy)](5) and [UO 2 (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 [UO 2 Cu(chdc) 2 (bipy)(H 2 O)]·H 2 O (7) and [UO 2 Cu(R-chdc) 2 (bipy)]·3H 2 O (8) crystallize as a 1D or a 2D species, respectively, while [UO 2 Cd(R-chdc) 2 (H 2 O) 2 ]·H 2 O (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO 2) 2 Na 2 (chdc) 3 (H 2 O) 2 ] (10), [(UO 2) 2 Ag 2 (chdc) 3 (H 2 O) 2 ] (11), [(UO 2) 2 Na 2 (R-chdc) 3 (H 2 O) 2 ] (12), and [(UO 2) 2 Pb(R-chdc) 3 (H 2 O) 4 ] (13) are closely related, all of them containing tetranuclear, pseudotetrahedral [(UO 2) 4 (chdc/R-chdc) 6 ] 4− cage motifs, that are assembled into a three-dimensional (3D) framework by bridging counterions (Na + , Ag + , or Pb 2+). 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.