The asymmetric unit of the title compound, C12H14N2 2+·2C7H5O5 −·1.5H2O, contains two 4,4′-ethyl­enedipyridinium cations, four gallate anions and three water mol­ecules. In the 4,4′-ethyl­enedipyridinium cations, the dihedral angles between the pyridinium rings are 4.3 (3) and 18.6 (3)°. Extensive classical N—H⋯O and O—H⋯O hydrogen bonding and weak C—H⋯O hydrogen bonding and C—H⋯π inter­actions are present in the crystal structure. π–π stacking is also observed, the centroid–centroid separations between the benzene and pyridine rings being 3.611 (3), 3.448 (3) and 3.536 (3) Å.

Key indicators: single-crystal X-ray study; T = 294 K; mean (C-C) = 0.005 Å; R factor = 0.028; wR factor = 0.066; data-to-parameter ratio = 15.4.The asymmetric unit of the title heterometallic coordination polymer, [ anions and three water molecules. One Cu II atom is located on an inversion center and is N,O-chelated by two pdc 2À anions in the equatorial plane and further coordinated by two carboxylate O atoms from another two pdc anions in the axial positions, with an elongated octahedral geometry [Cu-O = 2.409 (3) Å in the axial direction]; the other Cu atom is N,Ochelated by two pdc anions in the coordination basal plane and coordinated by a carboxyl O atom at the apical position with a distorted square-pyramidal geometry [Cu-O = 2.359 (3) Å in the apical direction]. The Eu atom is eightcoordinated with a distorted square-antiprismatic geometry formed by five carboxylate O atoms from five pdc anions and three water molecules. The carboxylate anions bridge adjacent Eu and Cu atoms, forming the coordination polymer. Interand intramolecular O-HÁ Á ÁO hydrogen bonding occurs in the structure. -stacking further consolidates the crystal structure, the centroid-centroid distance between parallel pyridine rings being 3.367 (2) Å . Related literature

In the title coordination polymer, [Pb(C7H3NO4)]n, the PbII ion is eight-coordinated in a distorted square-anti­prismatic geometry formed by one pyridine N atom and seven carboxyl­ate O atoms from four pyridine-2,3-dicarboxyl­ate (pda) anions. In the pda anion, the dihedral angles between the pyridine ring and carboxyl­ate groups are 19.5 (6) and 73.3 (6)°. The carboxyl­ate groups of the pda anions bridge the Pb ions, forming a two-dimensional coordination polymer parallel to (100). Weak inter­molecular C—H⋯O hydrogen boning is present in the crystal structure.

In the polymeric title compound, {[La2(C7H3NO4)2(C2O4)(H2O)6]·H2O}n, the La3+ cation is nine-coordinated in a distorted LaNO8 tricapped trigonal–prismatic geometry formed by three pyridinedicarboxylate anions, one oxalate anion and three water mol­ecules. The oxalate anion is located on an inversion center. The oxalate and pyridine­dicarboxyl­ate anions bridge the La3+ cations, forming a two-dimensional polymeric complex parallel to (010). Inter­molecular O—H⋯O hydrogen bonding and weak C—H⋯O hydrogen bonding is present in the crystal structure and π–π stacking [centroid–centroid distance = 3.571 (3) Å] is observed between parallel pyridine rings of adjacent mol­ecules. The uncoordinated water molecule shows an occupancy of 0.5.

In the polymeric title compound, {[Ce2(C7H3NO4)2(C2O4)(H2O)6]·H2O}n, the Ce3+ cation is nine-coordinated in a distorted CeNO8 tricapped trigonal–prismatic geometry, formed by three pyridine-2,4-dicarboxyl­ate anions, one oxalate anion and three water mol­ecules. The mid-point of the oxalate anion is located on an inversion center. The oxalate and pyridine-2,4-dicarboxyl­ate anions bridge the Ce3+ cations, forming a two-dimensional polymeric complex parallel to (010). Inter­molecular classical O—H⋯O hydrogen bonding and weak C—H⋯O hydrogen bonding are present in the crystal structure and π–π stacking [centroid–centroid distance = 3.558 (2) Å] is observed between parallel pyridine rings of adjacent mol­ecules. The uncoordinated water mol­ecule shows an occupancy of 0.5.