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

Combining the flexible zwitterionic dicarboxylate 4,4ʹ-bis(2-carboxylatoethyl)-4,4ʹ-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. [(UO2)2(L)(ipht)2] (1) and [(UO2)2(L)(1,2-pda)2]2H2O (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, [(UO2)2(L)(1,3-pda)2]0.5CH3CN, 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, [(UO2)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 [(UO2)4(LH)2(1,4-pda)5]H2O2CH3CN (5), a monoperiodic polymer based on tetranuclear (UO2)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- 2 O,O'-chelated uranyl cations