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

Uranyl ion complexation by mixtures ofzwitterionic andanionic dicarboxylate ligands endowed with a range of flexibilityand curvature gives two monoperiodic, ribbon-like coordination polymers,a case of polycatenated, ring-containing chains, and unique examplesof a heteroleptic, binuclear uranyl polycarboxylate coordination cageand a diperiodic arrangement based on woven uranyl carboxylate chains. Combiningthe flexible zwitterionic dicarboxylate 4,4 & PRIME;-bis-(2-carboxylatoethyl)-4,4 & PRIME;-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 isolationof five uranyl ion complexes by synthesis under solvo-hydrothermalconditions. [(UO2)(2)(L)-(ipht)(2)] (1) and [(UO2)(2)(L)-(1,2-pda)(2)]& BULL;2H(2)O (2) have the same stoichiometry,and both crystallize as monoperiodic coordination polymers containingtwo uranyl-(anionic carboxylate) strands united by L linkersinto a wide ribbon, all ligands being in the divergent conformation.Complex 3, [(UO2)(2)(L)-(1,3-pda)(2)]& BULL;0.5CH(3)CN, with the same stoichiometry butligands in a convergent conformation, is a discrete, binuclear specieswhich is the first example of a heteroleptic uranyl carboxylate coordinationcage. 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; twofamilies of chains run along different directions and are woven intodiperiodic layers. Modification of the synthetic conditions leadsto [(UO2)(4)(LH)(2)(1,4-pda)(5)]& BULL;H2O & BULL;2CH(3)CN (5), amonoperiodic polymer based on tetranuclear (UO2)(4)(1,4-pda)(4) rings; intrachain hydrogen bonding of the terminalLH(+) ligands results in diperiodic network formation throughparallel polycatenation involving the tetranuclear rings and the LH+ rods. Complexes 1-3 and 5 are emissive, with complex 2 having the highestphotoluminescence quantum yield (19%), and their spectra show themaxima positions usual for tris-& kappa;(2) O,O & PRIME;-chelated uranyl cations.

Automated summary

Mixtures of zwitterionic and anionic dicarboxylate ligands with flexibility and curvature can form various types of uranyl ion complexes, including coordination polymers, polycatenated chains, and coordination cages. These complexes were synthesized under solvo-hydrothermal conditions and exhibit different stoichiometries and conformations.