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Two new coordination polymers with 3-pyridyl-4-yl-benzoic acid (3,4-HPybz), namely, [Zn(3,4-Pybz)2 · 2H2O] n (I) and [Ag(3,4-Pybz)(3,4-HPybz)] n (II), have been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. Compound I crystallizes in the triclinic system and has P1 space group. Complex I is an infinite 1D chain polymer and the infinite chains array uniformly in a 3D supramolecular network which posesses abundant O-H...O hydrogen-bonding interactions among the occupied and unoccupied carboxylate O atoms and the coordinated water molecules; compound II crystallizes in the triclinic system and has $$P\bar 1$$ space group, II is an infinite chain with the repeat sequence of Ag1(I)-Ag2(I)-Ag1(I), in which weak intermolecular interactions play a key role in forming the final 3D supramolecular architectures. The photoluminescences and lifetime of I and II in the solid state have been investigated.

Three new coordination polymers based on 2-ethyl-imidazole-4,5-dicarboxylate with 1,10-phenanthroline as ligands, Pb(HEIDC)(phen)2 (1), [Zn(EIDC)(phen)] n (2), and {[Ba(H2EIDC)2(phen)] · (phen)2 · [Ba(H2EIDC)(HEIDC)(phen)]} n (3) (H3EIDC = 2-ethyl-1-Himidazole-4,5-dicarboxylate; phen = 1,10-phenanthroline), have been synthesized under hydrothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Complex 1 displays a tetranuclear square constructed of four Pb(II) centers, four HEIDC, and eight phen, resulting in a 3-D network with a 1-D open channel along the c-axis via C–H ··· O hydrogen bonds, C–H ··· π, and π–π stacking interactions. Complex 2 is an infinite zigzag chain resulting in the final 3-D supramolecular framework via C–H ··· O and π–π stacking interactions. Complex 3 is composed of two individual Ba chains, exhibiting a 3-D framework via O–H ··· O, O–H ··· N hydrogen bonds, and π–π stacking interactions....

Two new isostructural coordination polymers, namely, [Ln(nbtc)·2H2O]n [Ln = Eu (1), Tm (2)] (H3nbtc = 5-nitrobenzene-1,2,3-tricarboxylic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. Both compounds are sandwich-like 2D layered network built by the 1D Ln-carboxylate chains and nbtc3− linkers, displaying the same 3D supramolecular network via intermolecular hydrogen bonds. The photoluminescence and lifetime of 1 in the solid state has also been investigated.

In the present study, through a transmission experiment, the effects of europium complex and Eu3+ on the pearl colour in the pearl oyster Pinctada martensii were evaluated. Europium complex and europium salt were respectively enriched by dietary green algae platymonas subcordiformi, and their toxicity to algae were analysed by the 96-h acute toxic experiment. Then, the green algae enriched europium complex and europium salt were respectively fed pearl oysters for 2 months, and the surface microstructures of cultured pearls were presented with scanning electron microscopy (SEM) and atomic force microscope(AFM). The results show that toxicity of europium complex to algae is much lower than Eu3+ from lowest no observable effect concentration LNOEC values and 96h-EC50 values and two compounds can modify pearl structure and optimize pearl colour from SEM and AFM images. Taken together, our results, for the first time, show that rare earth complex can improve the pearl quality. This study provides an innovative approach for additional investigation of the influence of rare earth elements on pearls.

The 3D heterometallic 3d–4f coordination polymer, [EuZn(gly)(ox)2(H2O)2]n, 1, (gly = glycinate, ox = oxalate), was the product of the hydrothermal synthesis of glycinate from the reaction of tetrazole-1-acetic acid, sodium oxalate, zinc and europium salts in the presence of a trace quantity of nitric acid. Coordination polymer 1 exhibits an unusual 3D heterometallic coordination framework that is built up by heterometallic dinuclear EuZn secondary building units and mixed ox and gly linkers in a uninodal 6-connected vme {33.43.58.6} net. The solid-state photoluminescence and lifetime characteristics of 1 reveal intense red luminescence.

A series of new coordination polymers, namely, [Sr(H2EIDC)2(H2O)2]n (1),{[Pb(H2EIDC)2(H2O)](H2O)3}n (2), [Ag(H2EIDC)]n (3), and [Ba(H2EIDC)2(H2O)]n (4) (H2EIDC = 2-ethyl-1H-imidazole-4,5-dicarboxylate), were synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, X-ray diffraction and thermogravimetric analyses. Complex 1 is a 2D infinite gridlike (4,4)topological layer structure. Complex 2 is a 2D corrugated layer constructed by PbII atoms and H2EIDC– anions. Complex 3 is a 2D corrugated sheet consisting of 1D chains linked by short Ag···Ag interactions, and the three complexes are extended into 3D supramolecular structures by weak intermolecular forces such as hydrogen bonds and π–π stacking interactions. Complex 4 exhibits a 3D framework with 1D channels. Furthermore, the luminescent properties of complexes 1, 2, and 3 are also investigated.

The title molecule, C13H8N4, is is essentially planar [r.m.s. deviation for all non-H atoms = 0.025 (3) Å]. In the crystal, molecules are connected through one weak bifurcated N—H...(N,N) hydrogen bond and three π–π stacking interactions between pyridine and imidazole rings [centroid–centroid distance = 3.631 (8) Å] and between pyridine and benzene rings [centroid–centroid distances = 3.675 (5) and 3.666 (2) Å].

In the title compound, [Cd(C10H7N6)2(H2O)2], the CdII atom lies on an inversion centre and is coordinated by four N atoms from 5-[4-(1H-imidazol-1-yl)phenyl]tetrazol-1-ide ligands and two O atoms from the coordinated water molecules in an octahedral arrangement. The complex polymeric chains are interconnected via intermolecular water O—H...N hydrogen bonds into a three-dimensional network.

In the title compound, [Co(C7H7N2O4)2(H2O)2]·3H2O, the CoII cation, located on an inversion center, is N,O-chelated by two 5-carboxy-2-ethyl-1H-imidazole-4-carboxylate anions and further coordinated by two water molecules in a distorted octahedral geometry. Only one carboxy group of the anion is deprotonated, and the two carboxyl groups of the same anion are linked via an intramolecular O—H...O hydrogen bond. One of the lattice water molecules is located on an inversion center, its H atom equally disordered over two positions. One of H atoms of another lattice water molecules is also equally disordered over two sites. Water H atoms and the amino H atom all are involved in an intermolecular hydrogen-bonded network in the crystal.

In the title complex polymer, [Sr(C10H7N6)2(H2O)2]n, the SrII atom lies on an inversion centre and is coordinated by four N atoms from two bidentate bridging trans-related 5-[4-(1H-imidazol-1-yl)phenyl]tetrazolide ligands [Sr—N = 2.387 (4) Å for the tetrazolide moiety and Sr—N = 2.273 (5) Å for the imidazole moiety], and by two O atoms from water molecules [Sr—O = 2.464 (4) Å], giving a distorted octahedral coordination. Pairs of ligand bridges link the complex units, forming chains which extend along [111] and are inter-associated through Owater—H...N hydrogen bonds, giving a two-dimensional network structure parallel to (001). Weak π–π stacking interactions between the benzene and imidazole rings are also present [minimum ring centroid separation = 3.691 (4) Å].

In the title compound, [Mn(C10H7N6)2(H2O)4]·2H2O, the Mn2+ lies on a twofold rotation axis and is six-coordinated by two N atoms from the cis-related monodentate 5-[4-(imidazol-1-yl)phenyl]tetrazolide ligands and four O atoms from the coordinated water molecules. The complex molecules are connected via water O—H...O and O—H...N hydrogen bonds and weak π–π stacking interactions between the benzene rings [minimum ring centroid separation = 3.750 (6) Å] into a three-dimensional polymeric structure. The imidazolyl group of the ligand is partially disordered over two sets of sites with refined occupancies of 0.531 (7):0.469 (7).

In the title compound, [Cd(C(10)H(7)N(6))(2)(H(2)O)(2)], the Cd(II) atom lies on an inversion centre and is coordinated by four N atoms from 5-[4-(1H-imidazol-1-yl)phen-yl]tetra-zol-1-ide ligands and two O atoms from the coordinated water mol-ecules in an octa-hedral arrangement. The complex polymeric chains are inter-connected via inter-molecular water O-H⋯N hydrogen bonds into a three-dimensional network.

In the title complex, [Cd(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·2C(3)H(7)NO, the six-coordinate Cd(II) ion is in a slightly distorted octa-hedral environment, defined by two O atoms from two coordinated water mol-ecules and two carboxyl-ate O atoms and two N atoms from two N,O-bidentate 5-carb-oxy-2-propyl-1H-imidazole-4-carboxyl-ate ligands. In the crystal, complex mol-ecules and dimethyl-formamide solvent mol-ecules are linked by O-H⋯O and N-H⋯O hydrogen bonds into a two-dimensional supra-molecular structure. The propyl groups of the ligands are disordered over two conformations with refined occupancies of 0.680 (7) and 0.320 (7).

The title compound, [Sr(C10H6NO2)2(H2O)2]n, contains an eight-coordinate SrII ion displaying a distorted square-antiprismatic geometry, two quinoline-3-carboxylate ligands and two terminal water molecules. The SrII atom is surrounded by six carboxylate O atoms from four separate quinoline-3-carboxylate ligands and two O atoms from two coordinated water molecules. The bridging carboxylate O atoms [Sr—O = 2.498 (3) and 2.495 (3) Å] link SrII atoms, forming a chain substructure extending along the c axis. The chains are linked by O—H...N and O—H...O hydrogen bonds, giving a three-dimensional framework structure

In the title complex, [Co(C8H9N2O4)2(H2O)2]·3.5H2O, the CoII cation is six-coordinated by two H2pimda− ligands (H3pimda is 2-propyl-1H-imidazole-4,5-carboxylic acid) and two water molecules in a distorted octahedral environment. The crystal structures features a three-dimensional network stabilized by extensive O—H...O and N—H...O hydrogen bonds. The propyl groups of the ligands are disordered over two sets of sites with refined occupancies of 0.673 (8):0.327 (8) and 0.621 (17):0.379 (17). One of the water molecules is located on a site with half-occupancy.

In the centrosymmetric dinuclear anions of the title bimetallic complex, {[Mg(H(2)O)(6)][Cu(2)(C(8)H(2)NO(7))(2)]·2H(2)O}(n), each Cu(II) ion is strongly coordinated by four O atoms in a distorted square-planar geometry. Two of these O atoms belong to phenolate groups and the other two to carboxylate groups from 5-nitro-2-oxidoisophthalate (L1) trianions, derived from 5-nitrobenzene-1,2,3-tricarboxylic acid (O(2)N-H(3)L). The phenolate O atoms bridge the two Cu(II) ions in the anion. In addition, each Cu(II) cation interacts weakly with a symmetry-related carboxylate O atom of an adjacent L1 ligand, giving a square-pyramidal coordination geometry. The copper residue forms a ladder-like linear coordination polymer via L1 ligands. The [Mg(H(2)O)(6)](2+) cations sit on centres of inversion. The polymeric anions, cations and free water molecules are self-assembled into a three-dimensional supramolecular network via O-H···O hydrogen bonds.

In the title complex, [Ca(C10H6NO2)2(H2O)2]n, the CaII ion is eight-coordinated by six carboxylate O atoms from four separate quinoline-3-carboxylate ligands, two of which are bidentate chelate and two bridging, and two water molecules in a distorted square-antiprismatic geometry. The bridging groups form a polymeric chain substructure extending along the c axis, the chains being connected by coordinated-water O—H...N and O—H...Ocarboxylate hydrogen bonds into a three-dimensional framework structure.

In the title complex, [Ca(C(10)H(6)NO(2))(2)(H(2)O)(2)](n), the Ca(II) ion is eight-coordinated by six carboxyl-ate O atoms from four separate quinoline-3-carboxyl-ate ligands, two of which are bidentate chelate and two bridging, and two water mol-ecules in a distorted square-anti-prismatic geometry. The bridging groups form a polymeric chain substructure extending along the c axis, the chains being connected by coordinated-water O-H⋯N and O-H⋯O(carboxyl-ate) hydrogen bonds into a three-dimensional framework structure.

In the title complex, [Mn(C8H9N2O4)2(H2O)2]·3.5H2O, the MnII cation is six-coordinated by two N,O-bidentate H2pimda− ligands (H2pimda− = 5-carboxy-2-propyl-1H-imidazole-4-carboxylate) and two water molecules in a distorted octahedral environment. The complete solid-state structure can be described as a three-dimensional supramolecular framework stabilized by a wide range of O—H...O and N—H...O hydrogen bonds. The propyl groups of H2pimda− are disordered over two sets of sites with refined occupancies of 0.759 (5):0.241 (5) and 0.545 (7):0.455 (7).

In the title complex, [Cu(C8H9N2O4)2(H2O)2]·2C3H7NO, the CuII ion, lying on an inversion center, is six-coordinated in a slightly distorted octahedral geometry. Two N atoms and two O atoms from two H2pimda (H3pimda is 2-propyl-1H-4,5-dicarboxylic acid) ligands are in the equatorial plane. The axial positions are occupied by two O atoms from two water molecules. A two-dimensional supramolecular network parallel to (001) is constructed by N—H...O and O—H...O hydrogen bonds. An intramolecular O—H...O hydrogen bond is also observed.

In the title complex, [Ni(C8H9N2O4)2(H2O)2]·4H2O, the NiII ion is coordinated in a slightly distorted octahedral environment formed by two bis-chelating H2pimda (H3pimda is 2-propyl-1H-4,5-dicarboxylic acid) ligands and two coordinated water molecules. In the crystal structure, a three-dimensional framework is formed by intermolecular O—H...O and N—H...O hydrogen bonds involving the solvent water molecules, coordinated water molecules, carboxylate O atoms and the protonated N atoms of the H2pimda ligands. The propyl groups of each H2pimda ligand are disordered over two sets of sites with refined occupancies of 0.50 (2):0.50 (2) and 0.762 (11):0.238 (11). In one water solvent molecule, one of the H atoms was refined as disordered over two sites of equal occupancy.

In the title complex, [Mn(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·3.5H(2)O, the Mn(II) cation is six-coordinated by two N,O-bidentate H(2)pimda(-) ligands (H(2)pimda(-) = 5-carb-oxy-2-propyl-1H-imidazole-4-carboxyl-ate) and two water mol-ecules in a distorted octa-hedral environment. The complete solid-state structure can be described as a three-dimensional supra-molecular framework stabilized by a wide range of O-H⋯O and N-H⋯O hydrogen bonds. The propyl groups of H(2)pimda(-) are disordered over two sets of sites with refined occupancies of 0.759 (5):0.241 (5) and 0.545 (7):0.455 (7).

In the title complex, [Cu(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·2C(3)H(7)NO, the Cu(II) ion, lying on an inversion center, is six-coordinated in a slightly distorted octa-hedral geometry. Two N atoms and two O atoms from two H(2)pimda (H(3)pimda is 2-propyl-1H-4,5-dicarb-oxy-lic acid) ligands are in the equatorial plane. The axial positions are occupied by two O atoms from two water mol-ecules. A two-dimensional supra-molecular network parallel to (001) is constructed by N-H⋯O and O-H⋯O hydrogen bonds. An intra-molecular O-H⋯O hydrogen bond is also observed.

In the title complex, [Ni(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·4H(2)O, the Ni(II) ion is coordinated in a slightly distorted octa-hedral environment formed by two bis-chelating H(2)pimda (H(3)pimda is 2-propyl-1H-4,5-dicarb-oxy-lic acid) ligands and two coordinated water mol-ecules. In the crystal structure, a three-dimensional framework is formed by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds involving the solvent water mol-ecules, coordinated water mol-ecules, carboxyl-ate O atoms and the protonated N atoms of the H(2)pimda ligands. The propyl groups of each H(2)pimda ligand are disordered over two sets of sites with refined occupancies of 0.50 (2):0.50 (2) and 0.762 (11):0.238 (11). In one water solvent mol-ecule, one of the H atoms was refined as disordered over two sites of equal occupancy.

In the title complex, [Ni(C8H9N2O4)2(H2O)2]·2C3H7NO, the NiII atom is six-coordinated by two N,O-bidentate 5-carboxy-2-propyl-1H-imidazole-4-carboxylate ligands and two water molecules in a distorted octahedral environment. The methyl C and H atoms of the two ligands are disordered over two sets of sites in 0.74 (2):0.26 (2) and 0.57 (8):0.43 (8) ratios. A supramolecular network is stabilized by intra- and intermolecular N—H...O and O—H...O hydrogen bonds involving the ligands, coordinated water molecules and dimethylformamide solvent molecules.

In the title compound, {[Cd(C9H4N2O4)(C3H7NO)(H2O)]·2H2O}n, the CdII atom is coordinated by one N atom and three O atoms from four different 1H-benzimidazole-5,6-dicarboxylate (Hbidc) ligands, one O atom from one dimethylformamide ligand, and one O atom from a water molecule in a distorted octahedral geometry. The Hbidc ligands connect the Cd atoms into a two-dimensional network parallel to (001). N—H...O and O—H...O hydrogen bonds involving the water molecules are observed in the crystal structure.

In the title compound, {[Cd(C(9)H(4)N(2)O(4))(C(3)H(7)NO)(H(2)O)]·2H(2)O}(n), the Cd(II) atom is coordinated by one N atom and three O atoms from four different 1H-benzimidazole-5,6-dicarboxyl-ate (Hbidc) ligands, one O atom from one dimethyl-formamide ligand, and one O atom from a water mol-ecule in a distorted octa-hedral geometry. The Hbidc ligands connect the Cd atoms into a two-dimensional network parallel to (001). N-H⋯O and O-H⋯O hydrogen bonds involving the water molecules are observed in the crystal structure.

In the title complex, [Ca(C8H9N2O4)2(H2O)2]n, the CaII atom is eight-coordinated in a distorted square-antiprismatic environment. The water-coordinated Ca atom is N,O-chelated by the monocarboxylate anion; the carboxyl –CO2 portion engaged in chelation bears an acid hydrogen. The free –CO2 portion engages in bonding to adjacent Ca atoms. The CaII centres are connected through the ligand, forming a layer structure; the layers are linked by hydrogen bonds into a three-dimensional network.

In the title complex, [Mn(C8H9N2O4)2(H2O)2]·2C3H7NO, the MnII atom, lying on an inversion centre, is six-coordinated by two N,O-bidentate 5-carboxy-2-propyl-1H-imidazole-4-carboxylate ligands and two water molecules in a distorted octahedral environment. In the crystal structure, the complex molecules and dimethylformamide solvent molecules are linked by N—H...O and O—H...O hydrogen bonds into a two-dimensional supramolecular network parallel to (001).

In the title complex, [Ca(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)](n), the Ca(II) atom is eight-coordinated in a distorted square-anti-prismatic environment. The water-coordinated Ca atom is N,O-chelated by the monocarboxyl-ate anion; the carboxyl -CO(2) portion engaged in chelation bears an acid hydrogen. The free -CO(2) portion engages in bonding to adjacent Ca atoms. The Ca(II) centres are connected through the ligand, forming a layer structure; the layers are linked by hydrogen bonds into a three-dimensional network.

In the mononuclear title compound, [Co(C9H4N2O4)2(H2O)4]·2C3H7NO·2H2O, the CoII atom, which lies on a center of inversion, is coordinated by four water molecules and two N atoms from two two symmetry-related 1H-benzimidazole-5,6-dicarboxylate ligands in a distorted octahedral geometry. The packing is governed by intermolecular O—H...O and N—H...O hydrogen-bonding interactions.

In the title complex polymer, [Sr(C10H7N6)2(H2O)2]n, the SrIIatom lies on an inversion centre and is coordinated by four N atoms from two bidentate bridgingtrans-related 5-[4-(1H-imidazol-1-yl)phenyl]tetrazolide ligands [Sr—N = 2.387 (4) Å for the tetrazolide moiety and Sr—N = 2.273 (5) Å for the imidazole moiety], and by two O atoms from water molecules [Sr—O = 2.464 (4) Å], giving a distorted octahedral coordination. Pairs of ligand bridges link the complex units, forming chains which extend along [111] and are inter-associated through Owater—H...N hydrogen bonds, giving a two-dimensional network structure parallel to (001). Weak π–π stacking interactions between the benzene and imidazole rings are also present [minimum ring centroid separation = 3.691 (4) Å].

In the title compound, [Mn(C10H7N6)2(H2O)4]·2H2O, the Mn2+lies on a twofold rotation axis and is six-coordinated by two N atoms from thecis-related monodentate 5-[4-(imidazol-1-yl)phenyl]tetrazolide ligands and four O atoms from the coordinated water molecules. The complex molecules are connectedviawater O—H...O and O—H...N hydrogen bonds and weak π–π stacking interactions between the benzene rings [minimum ring centroid separation = 3.750 (6) Å] into a three-dimensional polymeric structure. The imidazolyl group of the ligand is partially disordered over two sets of sites with refined occupancies of 0.531 (7):0.469 (7).

In the title compound, [Co(C7H7N2O4)2(H2O)2]·3H2O, the CoIIcation, located on an inversion center, isN,O-chelated by two 5-carboxy-2-ethyl-1H-imidazole-4-carboxylate anions and further coordinated by two water molecules in a distorted octahedral geometry. Only one carboxy group of the anion is deprotonated, and the two carboxyl groups of the same anion are linkedviaan intramolecular O—H...O hydrogen bond. One of the lattice water molecules is located on an inversion center, its H atom equally disordered over two positions. One of H atoms of another lattice water molecules is also equally disordered over two sites. Water H atoms and the amino H atom all are involved in an intermolecular hydrogen-bonded network in the crystal.

In the title complex, [Cd(C8H9N2O4)2(H2O)2]·2C3H7NO, the six-coordinate CdII ion is in a slightly distorted octa­hedral environment, defined by two O atoms from two coordinated water mol­ecules and two carboxyl­ate O atoms and two N atoms from two N,O-bidentate 5-carb­oxy-2-propyl-1H-imidazole-4-carboxyl­ate ligands. In the crystal, complex mol­ecules and dimethyl­formamide solvent mol­ecules are linked by O—H⋯O and N—H⋯O hydrogen bonds into a two-dimensional supra­molecular structure. The propyl groups of the ligands are disordered over two conformations with refined occupancies of 0.680 (7) and 0.320 (7).

The title compound, [Sr(C(10)H(6)NO(2))(2)(H(2)O)(2)](n), contains an eight-coordinate Sr(II) ion displaying a distorted square-anti-prismatic geometry, two quinoline-3-carboxyl-ate ligands and two terminal water mol-ecules. The Sr(II) atom is surrounded by six carboxyl-ate O atoms from four separate quinoline-3-carboxyl-ate ligands and two O atoms from two coordinated water mol-ecules. The bridging carboxyl-ate O atoms [Sr-O = 2.498 (3) and 2.495 (3) Å] link Sr(II) atoms, forming a chain substructure extending along the c axis. The chains are linked by O-H⋯N and O-H⋯O hydrogen bonds, giving a three-dimensional framework structure.

In the title compound, C7H8N2O4·H2O, the imidazole N atom is protonated and one of the carboxylate groups is deprontonated, forming a zwitterion. The two carboxyl groups are are approximately coplanar with the imidazole ring [O—C—C—C torsion angles = −176.8 (2) and 2.9 (4)° for one group and −4.6 (3) and 176.4 (2)° for the other] and have an intramolecular O—H...O hydrogen bond between them. The water molecule is linked to the organic molecules via an N—H...O hydrogen bonds. Intermolecular O—H...O and N—H...O hydrogen bonds are found in the crystal structure.

In the title complex, [Co(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·3.5H(2)O, the Co(II) cation is six-coordinated by two H(2)pimda(-) ligands (H(3)pimda is 2-propyl-1H-imidazole-4,5-carboxylic acid) and two water mol-ecules in a distorted octa-hedral environment. The crystal structures features a three-dimensional network stabilized by extensive O-H⋯O and N-H⋯O hydrogen bonds. The propyl groups of the ligands are disordered over two sets of sites with refined occupancies of 0.673 (8):0.327 (8) and 0.621 (17):0.379 (17). One of the water mol-ecules is located on a site with half-occupancy.

In the title complex, [Mn(C8H9N2O4)2(H2O)2]·3.5H2O, the MnII cation is six-coordinated by two N,O-bidentate H2pimda− ligands (H2pimda− = 5-carb­oxy-2-propyl-1H-imidazole-4-carboxyl­ate) and two water mol­ecules in a distorted octa­hedral environment. The complete solid-state structure can be described as a three-dimensional supra­molecular framework stabilized by a wide range of O—H⋯O and N—H⋯O hydrogen bonds. The propyl groups of H2pimda− are disordered over two sets of sites with refined occupancies of 0.759 (5):0.241 (5) and 0.545 (7):0.455 (7).

In the title complex, [Ni(C8H9N2O4)2(H2O)2]·4H2O, the NiII ion is coordinated in a slightly distorted octa­hedral environment formed by two bis-chelating H2pimda (H3pimda is 2-propyl-1H-4,5-dicarb­oxy­lic acid) ligands and two coordinated water mol­ecules. In the crystal structure, a three-dimensional framework is formed by inter­molecular O—H⋯O and N—H⋯O hydrogen bonds involving the solvent water mol­ecules, coordinated water mol­ecules, carboxyl­ate O atoms and the protonated N atoms of the H2pimda ligands. The propyl groups of each H2pimda ligand are disordered over two sets of sites with refined occupancies of 0.50 (2):0.50 (2) and 0.762 (11):0.238 (11). In one water solvent mol­ecule, one of the H atoms was refined as disordered over two sites of equal occupancy.

In the title compound, {[Cd(C9H4N2O4)(C3H7NO)(H2O)]·2H2O}n, the CdII atom is coordinated by one N atom and three O atoms from four different 1H-benzimidazole-5,6-dicarboxyl­ate (Hbidc) ligands, one O atom from one dimethyl­formamide ligand, and one O atom from a water mol­ecule in a distorted octa­hedral geometry. The Hbidc ligands connect the Cd atoms into a two-dimensional network parallel to (001). N—H⋯O and O—H⋯O hydrogen bonds involving the water molecules are observed in the crystal structure.

In the title compound, C10H8N6, the tetrazole and benzene rings are close to being coplanar [dihedral angle = 9.90 (16)°], but the imidazole ring is rotated 37.18 (09)° out of the benzene plane. In the crystal, molecules are connected through tetrazole–imidazole N—H...N hydrogen bonds, giving rise to zigzag chains, which extend along [010].

The title compound, C13H9NO4, crystallizes in a zwitterionic form with the pyridine N atom protonated and the carboxyl OH group deprotonated. The benzene and pyridinium rings are inclined with a dihedral angle of 31.42 (14)° between them. A previous report of this stucture claims, we believe incorrectly, that neither of the carboxylate groups is deprotonated [Zhang et al. (2010). Acta Cryst. E66, o2928–o2928]. In the crystal, intermolecular O—H...O, N—H...O and weak C—H...O hydrogen-bonding interactions link adjacent molecules into a three-dimensional supramolecular network.

In the title complex, [Cu(C8H9N2O4)2(H2O)2]·2C3H7NO, the CuII ion, lying on an inversion center, is six-coordinated in a slightly distorted octa­hedral geometry. Two N atoms and two O atoms from two H2pimda (H3pimda is 2-propyl-1H-4,5-dicarb­oxy­lic acid) ligands are in the equatorial plane. The axial positions are occupied by two O atoms from two water mol­ecules. A two-dimensional supra­molecular network parallel to (001) is constructed by N—H⋯O and O—H⋯O hydrogen bonds. An intra­molecular O—H⋯O hydrogen bond is also observed.

In the title complex, [Ni(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·2C(3)H(7)NO, the Ni(II) atom is six-coordinated by two N,O-bidentate 5-carb-oxy-2-propyl-1H-imidazole-4-carboxyl-ate ligands and two water mol-ecules in a distorted octa-hedral environment. The methyl C and H atoms of the two ligands are disordered over two sets of sites in 0.74 (2):0.26 (2) and 0.57 (8):0.43 (8) ratios. A supra-molecular network is stabilized by intra- and inter-molecular N-H⋯O and O-H⋯O hydrogen bonds involving the ligands, coordinated water mol-ecules and dimethyl-formamide solvent mol-ecules.

In the title complex, [Ca(C8H9N2O4)2(H2O)2]n, the CaII atom is eight-coordinated in a distorted square-anti­prismatic environment. The water-coordinated Ca atom is N,O-chelated by the monocarboxyl­ate anion; the carboxyl –CO2 portion engaged in chelation bears an acid hydrogen. The free –CO2 portion engages in bonding to adjacent Ca atoms. The CaII centres are connected through the ligand, forming a layer structure; the layers are linked by hydrogen bonds into a three-dimensional network.

In the title complex, [Mn(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·2C(3)H(7)NO, the Mn(II) atom, lying on an inversion centre, is six-coordinated by two N,O-bidentate 5-carb-oxy-2-propyl-1H-imidazole-4-carb-oxyl-ate ligands and two water mol-ecules in a distorted octa-hedral environment. In the crystal structure, the complex mol-ecules and dimethyl-formamide solvent mol-ecules are linked by N-H⋯O and O-H⋯O hydrogen bonds into a two-dimensional supra-molecular network parallel to (001).

In the mononuclear title compound, [Co(C(9)H(4)N(2)O(4))(2)(H(2)O)(4)]·2C(3)H(7)NO·2H(2)O, the Co(II) atom, which lies on a center of inversion, is coordinated by four water mol-ecules and two N atoms from two two symmetry-related 1H-benzimidazole-5,6-dicarboxyl-ate ligands in a distorted octa-hedral geometry. The packing is governed by inter-molecular O-H⋯O and N-H⋯O hydrogen-bonding inter-actions.