Bis­(μ-pyridine-2,3-dicarboxyl­ato)bis­[aqua­(3-carb­oxy­pyridine-2-carboxyl­ato)indium(III)] tetra­hydrate

In the binuclear centrosymmetric title compound, [In2(C7H3NO4)2(C7H4NO4)2(H2O)2]·4H2O, which contains both pyridine-2,3-dicarboxyl­ate and 3-carb­oxy­pyridine-2-carboxyl­ate ligands, the InIII atom is six-coordinated in a distorted octa­hedral geometry. One pyridine ligand is N,O-chelated while the other is N,O-chelated and at the same time bridging to the other via the second carboxyl group. In the crystal, an extensive O—H⋯O hydrogen-bonding network, involving the coordinated and lattice water mol­ecules and the carboxyl groups of the ligands, together with C—H⋯O and π–π inter­actions [centroid–centroid distance = 3.793 (1) Å], leads to the formation of a three-dimensional structure

Structural variation within uranium(VI) heterocyclic carboxylates: Solid and solution states studies

The solution chemistry and solid-state structures of two new uraniumVI metal–organic compounds, (tataH)2[(UO2)2(pdtc)2(l-OH)2].2H2O (1) and (AcrH)2[(UO2)(pydc)2] (2), [where tata = 1,3,5-triazine- 2,4,6-triamine, Acr = acridine, pydc = pyridine-2,6-dicarboxylate and pdtc = pyridine-2,6-bis(monothiocarboxylate)] have been investigated. These compounds were obtained via proton-transfer methodology by reacting UO2 2+ with the preformed proton-transfer systems (tataH)2(pdtc) and (AcrH)2(pydc), respectively, in aqueous solution, after evaporation of the solvent. Our results show that noncovalent interactions such as hydrogen bonds, sulfur...sulfur, and p...p interactions, when acting cooperatively, are driving forces for the selection of different structures. The protonation constants of Acr, tata, pdtcH2, and pydcH2, the building blocks of the proton-transfer systems (tataH)2(pdtc) and (AcrH)2(pydc), and the stability constants of these systems were determined by potentiometric studies in a dioxane/H2O (1:1 v/v) mixture. The stoichiometry and the formation stability constants of complexes formed on reacting pydcH2/Acr or pdtcH2/tata 1:1 molar mixtures with the UO2 2+ ion in dioxane/H2O (1:1 v/v) were investigated by potentiometric pH titration methods. The stoichiometries of the complex species formed in solution were compared with those observed for the crystalline metal ion complexes 1 and 2