Synthesis, Characterization, and Solid-State Structural Chemistry of Uranium(IV) Aliphatic Dicarboxylates

Abstract

Examinations of uranium­(IV) complexation by aliphatic dicarboxylates, ranging from the three-carbon malonate to the six-carbon adipate, yielded six novel phases. Single crystals of the compounds were prepared through either evaporation or solvent layering, and the structures were determined via single-crystal X-ray diffraction. The compounds were further characterized via IR and Raman spectroscopies. For the phases synthesized via solvent layering, correlations between the solution- and solid-state speciation were probed using UV–visible absorption spectroscopy. In the presence of malonate (MA), [U­(MA)2(H2O)3] n (U-1a) was isolated. As the crystals were not suitable for structure determination, reactions of MA with thorium were pursued. These efforts yielded polymorphs, Th-1a and Th-1b; in both An-1a (An = Th, U) and Th-1b, the An­(IV) metal centers are bridged via the MA ligands into 2D sheets. Upon increasing the length of the aliphatic backbone, monodentate and bridging bidentate binding modes are observed. Two distinct ligand-bridged extended networks that vary in metal ion nuclearity were observed for succinate (SA): [UCl2(SA)­(H2O)2] n (U-2) and [U6O4(OH)4(SA)4(H2O)10]·4Cl·mH2O (U-3). Whereas U-2 consists of mononuclear U­(IV) atoms that are bridged through the organic carboxylate into a 3D network, U-3 is built from hexanuclear U­(IV)-hydroxo-oxo clusters that are further bridged into a 3D network. From glutarate (GA) ligand systems, two phases were isolated including [UCl2(HGA)2(H2O)2] n (U-4) that consists of ligand-bridged one-dimensional chains and [U2Cl6(HGA)2(H2O)2] n (U-5), which is built from chloride-bridged {U2Cl2} dimers that are further linked via GA into two-dimensional sheets. Finally, in the presence of adipate (AA), [U6O4(OH)4(AA)4(H2O)8]·4Cl·7­(H2O) (U-6) is observed; the structure consists of hexameric [U6O4(OH)4]12+ clusters that are propagated into one-dimensional chains via the AA and uranium-bound water molecules that directly link adjacent clusters. Taken together, this work provides a systematic examination of the influence of the identity of the dicarboxylate backbones on actinide structural chemistry and highlights the role that the organic ligand plays in stabilizing unique tetravalent actinide structural units.

Structures and Properties of a Series of High-Spin [CoII2] Complexes Supported by Ancillary Benzoate, Ortho-Hydroxybenzoate, and Para-Hydroxybenzoate Ligands

“…The differences between ν as (COO – ) and ν s (COO – ) stretches (Δ) of 199 and 110 cm –1 for 1 , 224 and 90 cm –1 for 2 , and 200 and 96 cm –1 for 3 which are the characteristic features of monodentate terminal and μ:η 1 :η 1 - syn - syn bidentate coordination of carboxylate groups, respectively, are in agreement with previous studies. − The band detected at higher stretching frequencies of 1605, 1609, and 1608 cm –1 for 1 , 2 , and 3 respectively, which can be attributed to ν­(CN) vibration of the pyridine moiety of the ligand backbone, is most probably overlapped with one of the asymmetric modes of benzoate groups. Furthermore, the characteristic stretching frequencies of 3420, 3416, and 3397 cm –1 for 1 , 2 , and 3 , respectively, are indicative of the noncoordinating hydroxyl ν­(O–H) groups of lattice waters/moisture …”

Uranium(IV) and Thorium(IV) Coordination Polymers Based on Tritopic Carboxylic Acids

“…In contrast, the synthesis of new polymeric networks of U­(IV) is considerably less developed with most previously reported U­(IV) polymer based either on oxalate or phosphonate ligands. − In particular, the use of aromatic polycarboxylic linkers remains rare in U­(IV) chemistry despite the fact that has proven a convenient strategy for the synthesis of stable three-dimensional (3D) frameworks with different topologies and permanent porosity. ,,− Monotopic aromatic carboxylates (benzoate), reported by us and others, lead to the controlled assembly of molecular oxo clusters of diverse nuclearity {U 6 } {U 10 },{U 12 },{U 13 }­{U 16 } and {U 24 }, depending on the reaction stoichiometry, solvent, and temperature. − Using a different approach, Loiseau and Falaise showed that the use of ditopic aromatic carboxylates in solvothermal conditions leads to the formation of 3D networks based on the hexanuclear uranium-centered motif [U 6 O 4 (OH) 4 (H 2 O) 6 ] . Very recently, Long et al reported a similar permanently porous uranium­(IV) framework based on a ditopic aromatic carboxylate that showed self-adjusting binding pockets that enhance CH 4 and H 2 absorption .…”