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) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda), of varying shape and curvature, has allowed isolation of five uranyl ion complexes by synthesis under solvo-hydrothermal conditions. [(UO)(L)(ipht)] () and [(UO)(L)(1,2-pda)]·2HO () 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 , [(UO)(L)(1,3-pda)]·0.5CHCN, 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)(L)(1,4-pda)(1,4-pdaH)] () 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)(LH)(1,4-pda)]·HO·2CHCN (), a monoperiodic polymer based on tetranuclear (UO)(1,4-pda) 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 - and are emissive, with complex having the highest photoluminescence quantum yield (19%), and their spectra show the maxima positions usual for tris-κ,-chelated uranyl cations.