Hydrothermal Crystallization of Uranyl Coordination Polymers Involving an Imidazolium Dicarboxylate Ligand: Effect of pH on the Nuclearity of Uranyl-Centered Subunits

Abstract

Four uranyl-bearing coordination polymers (1-4) have been hydrothermally synthesized in the presence of the zwitterionic 1,3-bis(carboxymethyl)imidazolium (= imdc) anion as organic linkers after reaction at 150 °C. At low pH (0.8-3.1), the form 1 ((UO2)2(imdc)2(ox)·3H2O; ox stands for oxalate group) has been identified. Its crystal structure (XRD analysis) consists of the 8-fold-coordinated uranyl centers linked to each other through the imdc ligand together with oxalate species coming from the partial decomposition of the imdc molecule. The resulting structure is based on one-dimensional infinite ribbons intercalated by free water molecules. By adding NaOH solution, a second form 2 is observed for pH 1.9-3.9 but in a mixture with phase 1. The pure phase of 2 is obtained after a hydrothermal treatment at 120 °C. It corresponds to a double-layered network (UO2(imdc)2) composed of 7-fold-coordinated uranyl cations linked via the imdc ligands. In the same pH range, a third phase ((UO2)3O2(H2O)(imdc)·H2O, 3) is formed: it is composed of hexanuclear units of 7-fold- and 8-fold-coordinated uranyl cations, connected via the imdc molecules in a layered assembly. At higher pH, the chain-like solid (UO2)3O(OH)3(imdc)·2H2O (4) is observed and composed of the infinite edge-sharing uranyl-centered pentagonal bipyramidal polyhedra. As a function of pH, uranyl nuclearity increases from discrete 8- or 7-fold uranyl centers (1, 2) to hexanuclear bricks (3) and then infinite chains in 4 (built up from the hexameric fragments found in 3). This observation emphasized the influence of the hydrolysis reaction occurring between uranyl centers. The compounds have been further characterized by thermogravimetric analysis, infrared, and luminescence spectroscopy.

Complexation of Uranyl Ion with Sulfonates: One‐ to Three‐Dimensional Assemblies with 1,5‐ and 2,7‐Naphthalenedisulfonates

“…While the maxima positions in uranyl emission spectra are known to be dependent on the number and nature of equatorial donors,, subtle factors are nevertheless obviously at play here since significant shifts are observed, even in a series of closely related species. The average vibronic splitting energies for the S 10 → S 0 ν transitions are in the range 821–897 cm –1 for complexes 2 and 4 , these values being in the range usually observed , …”

Tetrahedral and Cuboidal Clusters in Complexes of Uranyl and Alkali or Alkaline-Earth Metal Ions with rac- and (1R,2R)-trans-1,2-Cyclohexanedicarboxylate

“…71 The vibronic splitting energies for the S10  S0 transitions average 833(20) cm -1 , a value in agreement with those usually measured for uranyl carboxylate complexes. 54,69,[71][72][73]…”

Magnetic and luminescent coordination networks based on imidazolium salts and lanthanides for sensitive ratiometric thermometry

“…Only few examples of lanthanide-based networks obtained with charged ligands are reported in the literature [ 27 – 30 ]. Following this last point, we have chosen to synthesize lanthanide-based networks from positively charged imidazolium dicarboxylate salts [ 31 – 34 ]. Contrarily to the classical imidazolium salts or ionic liquids used in ionothermal syntheses [ 35 – 40 ], the functionalization of imidazolium moieties with coordinating functions reduces the influence of the imidazolium salt on the ligand for a better rationalization of the synthesis [ 31 – 34 ].…”