title: 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.
authors: Unité de Catalyse et Chimie du Solide (UCCS)-UMR CNRS 8181, Université de Lille, ENSCL , Bat C7, BP 90108, 59652 Villeneuve d'Ascq, France.
authors: Nicolas P
authors: NP
authors: Martin
authors: Unité de Catalyse et Chimie du Solide (UCCS)-UMR CNRS 8181, Université de Lille, ENSCL , Bat C7, BP 90108, 59652 Villeneuve d'Ascq, France.
authors: Clément
authors: C
authors: Falaise
authors: Unité de Catalyse et Chimie du Solide (UCCS)-UMR CNRS 8181, Université de Lille, ENSCL , Bat C7, BP 90108, 59652 Villeneuve d'Ascq, France.|Institut Universitaire de France , 1 rue Descartes, 75231 Paris Cedex 05, France.
authors: Christophe
authors: C
authors: Volkringer
authors: Unité de Catalyse et Chimie du Solide (UCCS)-UMR CNRS 8181, Université de Lille, ENSCL , Bat C7, BP 90108, 59652 Villeneuve d'Ascq, France.
authors: Natacha
authors: N
authors: Henry
authors: Département de Chimie des Matériaux Inorganiques, IPCMS UMR7504 CNRS-UNISTRA , 23, rue du Loess, BP43, Strasbourg Cedex 2, France.
authors: Pierre
authors: P
authors: Farger
authors: Département de Chimie des Matériaux Inorganiques, IPCMS UMR7504 CNRS-UNISTRA , 23, rue du Loess, BP43, Strasbourg Cedex 2, France.
authors: Camille
authors: C
authors: Falk
authors: Département de Chimie des Matériaux Inorganiques, IPCMS UMR7504 CNRS-UNISTRA , 23, rue du Loess, BP43, Strasbourg Cedex 2, France.
authors: Emilie
authors: E
authors: Delahaye
authors: Département de Chimie des Matériaux Inorganiques, IPCMS UMR7504 CNRS-UNISTRA , 23, rue du Loess, BP43, Strasbourg Cedex 2, France.
authors: Pierre
authors: P
authors: Rabu
authors: Unité de Catalyse et Chimie du Solide (UCCS)-UMR CNRS 8181, Université de Lille, ENSCL , Bat C7, BP 90108, 59652 Villeneuve d'Ascq, France.
authors: Thierry
authors: T
authors: Loiseau