Woven, Polycatenated, or Cage Structures: Effect of Modulation of Ligand Curvature in Heteroleptic Uranyl Ion Complexes
Sotaro Kusumoto, Youssef Atoini, Shunya Masuda, Yoshihiro Koide, Kittipong Chainok, Yang Kim, Jack M. Harrowfield, P. Thuéry
Abstract
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.