Woven, Polycatenated, or Cage Structures: Effect of Modulation of Ligand Curvature in Heteroleptic Uranyl Ion Complexes.

Combining the flexible zwitterionic dicarboxylate 4,4'-bis(2-carboxylatoethyl)-4,4'-bipyridinium (L) and the anionic dicarboxylate ligands isophthalate (ipht 2- ) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda 2- ), of varying shape and curvature, has allowed isolation of five uranyl ion complexes by synthesis under solvo-hydrothermal conditions. [(UO 2 ) 2 (L)(ipht) 2 ] ( 1 ) and [(UO 2 ) 2 (L)(1,2-pda) 2 ]·2H 2 O ( 2 ) have the same stoichiometry, and both crystallize as monoperiodic coordination polymers containing two uranyl-(anionic carboxylate) strands united by L linkers into a wide ribbon, all ligands being in the divergent conformation. Complex 3 , [(UO 2 ) 2 (L)(1,3-pda) 2 ]·0.5CH 3 CN, with the same stoichiometry but ligands in a convergent conformation, is a discrete, binuclear species which is the first example of a heteroleptic uranyl carboxylate coordination cage. With all ligands in a divergent conformation, [(UO 2 ) 2 (L)(1,4-pda)(1,4-pdaH) 2 ] ( 4 ) crystallizes as a sinuous and thread-like monoperiodic polymer; two families of chains run along different directions and are woven into diperiodic layers. Modification of the synthetic conditions leads to [(UO 2 ) 4 (LH) 2 (1,4-pda) 5 ]·H 2 O·2CH 3 CN ( 5 ), a monoperiodic polymer based on tetranuclear (UO 2 ) 4 (1,4-pda) 4 rings; intrachain hydrogen bonding of the terminal LH + ligands results in diperiodic network formation through parallel polycatenation involving the tetranuclear rings and the LH + rods. Complexes 1 - 3 and 5 are emissive, with complex 2 having the highest photoluminescence quantum yield (19%), and their spectra show the maxima positions usual for tris-κ 2 O , O' -chelated uranyl cations.