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Three three-dimensional polymers, namely, [Zn(bpea)(H2O)]n (1), [Cd(bpea)(H2O)]n (2), and [Ni(bpea)(4,4′-bipyridine)(pyridine)]n (3) have been synthesized by the hydrothermal reaction of ZnII, CdII, or NiII salts with biphenylethene-4,4′-dicarboxylic acid. Complexes 1 and 2 have a 2-fold interpenetrating three-dimensional (3D) structure with Pts topology, and complex 1 exhibits strong fluorescent emission bands at 435 and 459 nm in the solid state at room temperature. Complex 3 is a 3D structure with an unprecedented 9-fold interpenetrated Ths topology.

La0.6Sr0.4Co0.2Fe0.8O3–Ce0.7Bi0.3O2 (LSCF–CBO) composite electrode has been prepared by polymer–gel method. SEM results showed that the composite electrode formed good contact with Ce0.9Gd0.1O2−δ (CGO) electrolyte after sintering at 900 °C for 2 h. AC impedance spectroscopy and dc polarization measurements were used to study the composite electrode performances in different atmospheres. The ( p O 2 )1/2 relationship of Rp (polarization resistance) with oxygen partial pressure has been observed, which indicated that the oxygen adsorption/desorption process was the reaction rate limiting step. The polarization resistance decreased with increasing CBO contents. The optimum value of 35 vol.% CBO in LSCF resulted in 0.16 Ω cm2 area specific resistivity (ASR) at 706 °C in air, which indicated that the LSCF–CBO composite electrode was a promising cathode material in ITSOFC.

In the title complex, {[Ni(C16H10O4)(C12H8N2)(H2O)]·H2O}n, the NiII ion is in a distorted octa­hedral geometry and coordinated by two N atoms of a 1,10-phenanthroline (phen) ligand, three carboxylate O atoms of two different bpea2− ligands and one water mol­ecule. The [Ni(phen)H2O] units are connected by two different 4,4′-(ethene-1,2-di­yl)dibenzoate (bpea2−) bridges, forming a one-dimensional zigzag chain structure. One bpea2− ligand coordinates to Ni in a bis-monodentate fashion, while the other acts as a bis-bidentate chelate.

One of the two independent Zn atoms of the polymeric title compound, [Zn3(C16H10O4)3(C10H8N2)]n, lies on a special position of site symmetry 3 and the other on a special position of site symmetry \overline{3}. The carboxylate ends of the 4,4′-(ethene-1,2-di­yl)dibenzoate dianion, which lies on a special position of site symmetry \overline{1}, each bridge these two independent Zn atoms. The bipyridine-coordinated Zn atom on the threefold axis has a tetra­hedral geometry, whereas the other Zn atom is coordin­ated by the O atoms of six different dianions in an octa­hedral geometry.

In the title complex, [Mn(C4O4)(C12H8N2)(H2O)2]n, each MnII ion is octa­hedrally coordinated by two N atoms of a 1,10-phenanthroline ligand, two carboxylate O atoms of different acetyl­enedicarboxyl­ate (ace2−) ligands and two coordinated water mol­ecules, and the octa­hedral units are connected by ace2− bridges, which adopt a bis-monodentate coordination mode, to form a one-dimensional structure along the [101] direction. A three-dimensional supra­molecular architecture is constructed via hydrogen-bond and π–π inter­actions.

In the title complex, [Co(C4O4)(C12H8N2)(H2O)2]n, the CoII atom exhibits a slightly distorted octa­hedral coordination geometry involving two N atoms from 1,10-phenanthroline, two O atoms from two acetyl­enedicarboxyl­ate (ace2−) dianions and two water O atoms. The ace2− ligand acts in a bis-monodentate mode to connect two adjacent CoII atoms, forming chains along the b axis. A three-dimensional supra­molecular architecture is constructed via O—H⋯O hydrogen bonds and π–π inter­actions.

In the title coordination polymer, [Ca(2-OPA)2(H2O)2]n [2-OPA− is 2-oxo-1,2-di­hydro­pyridine-1-acetate, C7H6NO3], the Ca atom is eight-coordinated by six O atoms from four 2-OPA− ligands and two water mol­ecules, and displays a dodecahedral coordination geometry. Each 2-OPA− ligand bridges two adjacent Ca atoms, forming a chain along the a-axis direction. The Ca⋯Ca separation within the polymer is 4.1022 (8) A. A two-dimensional supramolecular framework is further constructed by hydrogen bonds and weak π–π stacking interactions.

In the title complex, [Cd2(C9H6O5)2(C7H6N2)4(H2O)2]·2H2O, the CdII atoms are linked by two 3-carboxy­phenoxy­acetate groups into a centrosymmetric dimer. Each CdII atom displays a distorted octa­hedral coordination geometry, with three carboxylate O atoms from different 3-carboxy­phenoxy­acetate groups, two N atoms from two benzimidazole co-ligands and one water mol­ecule. Inter­molecular hydrogen bonding leads to a two-dimensional supramolecular network.

The crystal structure of the title complex, [Co(C9H7O5)2(C10H8N2)2(H2O)2]·4H2O or [Co(4-CPOAH)2(4,4′-bipy)2(H2O)2]·4H2O (4,4′-bipy is 4,4′-bipyridine and 4-CPOAH− is the 4-carboxy­phenoxy­acetate monoanion), consists of two independent mononuclear mol­ecules that inter­act through the uncoordinated water mol­ecules. The CoII atoms lie on inversion centers and display an octa­hedral geometry defined by two oxyacetate O atoms of 4-CPOAH− groups, two N atoms of 4,4′-bipy ligands and two water mol­ecules. A three-dimensional supramolecular network structure is formed through hydrogen-bonding inter­actions.

The title mol­ecule, [Co2(C8H7O2)4(C12H8N2)2(H2O)], is a dinuclear CoII complex which is located on a twofold symmetry axis. Each CoII ion is six-coordinated by three O atoms of different phenyl­acetate ligands, two N atoms of the 1,10-phenanthroline ligands and one O atom of a water mol­ecule, giving a distorted octa­hedral geometry. The two CoII atoms are bridged by two phenyl­acetate groups and the water mol­ecule lying on the twofold axis. The Co⋯Co distance is 3.553 (2) A. A one-dimensional supramolecular chain is constructed by π–π stacking inter­actions between adjacent 1,10-phenanthroline mol­ecules.

In the title coordination polymer, [Zn(C9H6O5)(C8H12N2)]n, the ZnII atom is surrounded by two chelating 3-carboxyl­atophenoxy­acetate (3-CPOA) dianions and one 1,10-phenanthroline (phen) ligand. Adjacent ZnII atoms are bridged by 3-CPOA to form a zigzag chain structure. The polymeric chains are connected via π–π stacking inter­actions.

In the title complex, [Mn(C9H7O5)(C10H8N2)(H2O)3](C9H7O5)·H2O or [Mn(3-CPOAH−)(2,2′-bipy)(H2O)3](3-CPOAH−)·H2O (where 3-CPOAH− is the 3-carboxy­phenoxy­acetate monoanion and 2,2′-bipy is 2,2′-bipyridine), the MnII ion has a distorted octa­hedral geometry involving one O atom of the 3-CPOAH− group, two N atoms of the 2,2′-bipy ligand and three water mol­ecules. A three-dimensional supramolecular network is constructed via O—H⋯O hydrogen-bonding and π–π stacking inter­actions.

In the title coordination polymer, {[Ni(4-CPOA)(phen)(H2O)2]·H2O}n (phen is 1,10-phenanthroline, C12H8N2; 4-CPOA is the 4-carboxy­phenoxy­acetate dianion, C9H6O5), each NiII ion displays a distorted octa­hedral geometry, defined by two carboxyl O atoms from two different 4-CPOA ligands, two N atoms from one phen mol­ecule and two coordinated water mol­ecules. The NiII ions are bridged by carboxyl­ate groups of 4-CPOA to form a chain structure. Adjacent polymeric chains are connected via hydrogen bonds and π–π stacking to construct a three-dimensional supramolecular network.

In the title one-dimensional polymer, {[Zn(3-CPOA)(C3H4N2)2]·3H2O}n (3-CPOA2− is the 3-carboxyl­atophenoxy­acetate dianion, C9H6O5), the Zn atom shows tetra­hedral coordination, as it is linked to two N atoms from two imidazole mol­ecules and two carboxyl­ate O atoms from two different 3-CPOA2− groups. Adjacent Zn atoms are linked by 3-CPOA2− ligands into a helical chain. The chains are linked into a three-dimensional network by hydrogen bonds.

The dinuclear title complex, [Ag2(NO3)2(3-PyOH)4]·2H2O (3-PyOH is 3-hydroxy­pyridine, C5H5NO), situated across a crystallographic inversion centre, can be described as a dimeric structure, in which two [Ag(3-PyOH)2] groups are held together by the Ag⋯Ag inter­action [3.317 (1) A]. Each Ag atom is two-coordinate and exists in an approximately linear geometry. The two NO3− ions inter­act with the AgI atoms in a bridging mode through very weak Ag⋯O inter­actions [Ag⋯O = 2.862 (2) and 2.877 (2) A]. A three-dimensional supramolecular framework is formed by O—H⋯O hydrogen bonds.

In the mononuclear title complex, [Ag(NO3)(3-PyOH)2] (3-PyOH = 3-hydroxy­pyridine, C5H5NO), the AgI atom shows a linear geometry defined by two N atoms of the 3-PyOH ligands, and the NO3− anion inter­acts with the AgI atom in a chelating mode through very weak Ag⋯O bonds. A three-dimensional supramolecular framework is formed by both hydrogen bonds and π–π inter­actions.

In the title coordination polymer, [Cd(4-CPOA)(H2O)3]n (where 4-CPOA2− is the 4-carboxyl­ato­phenoxy­acetate dianion, C9H6O5), the CdII ion is seven-coordinate, involving four O atoms of two different 4-CPOA2− ligands and three water mol­ecules, arranged in a pentagonal–bipyramidal geometry. Adjacent CdII ions are linked by the 4-CPOA2− groups in bidentate mode, giving rise to a zigzag chain with a closest Cd⋯Cd distance of 10.310 (5) A. The chains are further linked by O—H⋯O hydrogen bonds to form a supramolecular three-dimensional network.

The CoII atom in the title coordination polymer, [Co(C9H6O5)(C12H8N2)(H2O)]n, displays a distorted octahedral geometry defined by three carboxyl O atoms from two independent 4-carboxy­phenoxy­acetate groups, two N atoms from one 1,10-phenanthroline mol­ecule and one water mol­ecule. The CoII atoms are bridged by carboxyl­ate groups in monodentate and bidentate modes, forming a chain structure. Adjacent polymeric chains are connected via hydrogen-bond interactions into a double-chain structure. Furthermore, these chains are stacked through π–π interactions to construct a two-dimensional supramolecular network.

The CdII atom in the title coordination polymer, [Cd(4-CPOA)(1,10-phen)(H2O)]n (1,10-phen is 1,10-phenanthroline, C12H8N2, and 4-CPOA2− is the 4-carboxy­phenoxy­acetate dianion, C9H6O5), shows a distorted octahedral geometry, defined by three carboxyl O-atom donors from two independent 4-CPOA2− groups, two N-atom donors from one 1,10-phen ligand, and one water molecule. The CdII ions are bridged by carboxyl­ate groups in mono- and bidentate modes, forming a chain structure. The polymeric chains are connected via O—H⋯O hydrogen bonds and π–π stacking interactions into a two-dimensional layer structure.

The asymmetric unit of the title one-dimensional coordination polymer, {[Co(C10H8N2)(H2O)4](C9H6O5)·H2O}n, comprises two half-cations, [Co(4,4′-bipy)(H2O)4]22+ (4,4′-bipy is 4,4′-bi­pyridine), one 3-carboxyl­ato­phenoxy­acetate (3-CPOA2−) dianion and one non-coordinated water mol­ecule. The CoII ions, both of which are located on inversion centres, have approximately octahedral geometries, involving two N atoms of the centrosymmetric 4,4′-bipy ligand and four water mol­ecules. Adjacent CoII atoms are linked by 4,4′-bipy ligands into a chain, the shortest Co⋯Co separation within the polymeric chain being 11.456 (2) A. The chains are further linked by hydrogen-bonding and π–π stacking interactions, generating a three-dimensional network.

In the title two-dimensional coordination polymer, [Cu(C9H6O5)(C7H6N2)]n, each CuII atom exists in a distorted square-pyramidal coordination environment, defined by one N atom from the terminal benz­imidazole mol­ecule and four carboxyl O atoms derived from three different 3-carboxyl­ato­phenoxy­acetate (3-CPOA) dianions. The tetradentate 3-CPOA ligand forms three bonds to adjacent Cu atoms to form chains that are linked to neighboring chains, via a fourth Cu—O bond, so as to form a layer structure that is further stabilized by hydrogen bonds.

In the title coordination polymer, [Cu(HIDC)(1,10-phen)]n (HIDC2− is the 4-carboxy­imidazole-5-carboxyl­ate dianion, C5H2N2O42−, and 1,10-phen is 1,10-phenanthroline, C12H8N2), the CuII atom shows a distorted octahedral coordination configuration, defined by two N atoms from a terminal 1,10-phen mol­ecule, two N atoms and two O atoms from two individual HIDC2− groups. Adjacent CuII atoms are bridged by HIDC2− groups, forming a one-dimensional chain structure. The Cu⋯Cu separation within the polymer is 6.132 (4) A. The chains are linked into a two-dimensional supramolecular network via π–π stacking interactions.

Each seven-coordinate CdII atom in the title coordination polymer, poly­[[bis(1H-imidazole-κN3)­cadmium(II)]-μ3-m-phenyl­enebis­(oxy­acetato)], [Cd(1,3-BDOA)(C3H4N2)2]n (1,3-BDOA2− is the benzene-1,3-dioxy­acetate dianion, C10H8O6), displays a distorted monocapped octahedral coordination geometry, defined by two N atoms from the imidazole ligands and five O atoms from three 1,3-BDOA2− anions. Adjacent CdII atoms are bridged by two 1,3-BDOA2− ligands, forming a one-dimensional double-chain structure, with Cd⋯Cd separations of 4.014 (3) A across the double chain and 13.105 (2) A along the chain. A network of N—H⋯O interchain hydrogen bonds is also present.

In the title coordination polymer, [Zn(C9H6O5)(C10H8N2)(H2O)]n, the ZnII ion displays a distorted octahedral coordination configuration, defined by two N atoms from the 2,2′-bi­pyridine ligand, three carboxyl­ate O atoms from two 4-carboxyl­ato­phenoxy­acetate dianions and one water mol­ecule. Adjacent ZnII atoms are linked by carboxyl­ate groups into zigzag chains with a Zn⋯Zn separation of 9.710 (3) A across the chains. Intermolecular hydrogen bonds serve to assemble the chains into a double-chain structure.

In the title compound, poly­[cadmium(II)-μ4-m-phenyl­enebis­(oxy­acetato)], [Cd(C10H8O6)]n, the CdII atom exists in a distorted monocapped octahedral coordination environment with seven O atoms from four carboxyl­ate groups. The Cd atoms are bridged by benzene-1,3-dioxy­acetate dianions with tridentate and tetradentate modes of the oxy­acetate groups, leading to a two-dimensional layer structure parallel to (001).

In the asymmetric unit of the title compound, [Mn(C10H8O6)(H2O)3]n, the two half-MnII atoms lie on inversion centres. One MnII atom is in an octahedral configuration, defined by two O atoms from two monodentate carboxyl­ate groups and four water mol­ecules, and the other MnII atom exists in a different octahedral coordination environment, defined by four O atoms from four monodentate carboxyl­ate groups and two water mol­ecules. The MnII atoms are bridged by a benzene-1,3-dioxy­acetate dianion in monodentate and bridging-bidentate modes, forming a two-dimensional layer structure.

In the title one-dimensional coordination polymer, {[Co(4-CPOA)(3-PyOH)2(H2O)2]·H2O}n [4-CPOA2− is the 4-carboxy­phenoxy­acetate dianion (C9H6O52−) and 3-PyOH is 3-hydroxy­pyridine (C5H5NO)], the CoII atom has a distorted octahedral coordination geometry, defined by two carboxyl O-atom donors from two 4-CPOA2− groups, two N-atom donors from two 3-PyOH co-ligands and two water mol­ecules. The CoII atoms are bridged by bis-monodentate carboxyl­ate groups, forming a one-dimensional chain structure. The Co⋯Co separation within the polymer is 10.862 (3) A. The chains are linked into a three-dimensional supramolecular network via O—H⋯O hydrogen bonds.

In the title complex {systematic name: aqua­[p-phenyl­enebis­(dioxy­acetato)-κO]­tetrakis(1H-imidazole-κN3)­nickel(II) mono­hydrate}, [Ni(C10H8O6)(C3H4N2)4(H2O)]·H2O, the NiII atom shows a distorted octahedral configuration, defined by one carboxyl O atom of the benzene-1,3-dioxy­acetate group, four N atoms from four imidazole ligands and one water mol­ecule. A three-dimensional supramolecular network is constructed by hydrogen-bonding and π–π stacking interactions.

In the title complex, [Zn(H2IDC)2(H2O)2] (where H2IDC− is the 5-carboxy-1H-imidazole-4-carboxyl­ate monoanion, C5H3N2O4), the ZnII atom is located on an inversion centre, is trans-coordinated by two N,O-bidentate H2IDC− ligands and two water mol­ecules and shows an approximately octahedral configuration. A three-dimensional supramolec­ular architecture is formed via hydrogen-bond interactions.

In the title one-dimensional coordination polymer, [Cd(HIDC)(1,10-phen)]n (where HIDC2− is the imidazole-4,5-di­carboxyl­ate dianion, C5H2N2O42−, and 1,10-phen is 1,10-phenanthroline, C12H8N2), the CdII atom has a distorted octahedral coordination geometry, defined by two N donors from a chelating 1,10-phen mol­ecule, two N-atom donors and two O-atom donors from two individual HIDC2− groups. Adjacent CdII ions are bridged by HIDC2− groups, resulting in a one-dimensional chain structure. The Cd⋯Cd separation within the polymer is 6.661 (2) A. The chains are linked into a two-dimensional supramolecular network via π–π stacking interactions.

The title complex crystallizes as a methanol solvate, [Cu2(C16H14O4N2)2(C5H5N)2]·2CH4O. The dinuclear complex is generated from the atoms of the asymmetric unit by inversion symmetry, resulting in a Cu⋯Cu separation of 3.497 (3) A. The copper(II) species has a square-pyramidal geometry, with the basal plane defined by two O atoms and one N atom from the hydrazone ligand and a pyridine N atom. The apical site is occupied by a phenolate O atom in the symmetry-generated hydrazone ligand, which also bonds to the second Cu atom. Intramolecular O—H⋯N hydrogen bonds are formed between the methanol solvent mol­ecules and the uncoordinated N atoms of the hydrazone ligand.

The title complex, [Co(2-OPA)2(H2O)4] [2-OPA− = (2-oxo-1,2-dihydropyridin-1-yl)­acetate, C7H6NO], is a neutral mononuclear compound. The CoII atom, located on an inversion center, has an octahedral coordination geometry involving two carbonyl O atoms of different 2-OPA− ligands and four water mol­ecules. A layer structure is formed via O—H⋯O intermolecular hydrogen bonds.

In the title complex, [Zn(1,4-BDOA)(H2O)4]n or [Zn(C10H8O6)(H2O)4]n (where 1,4-BDOA2− is the benzene-1,4-dioxy­acetate dianion), the ZnII atom and the 1,4-BDOA2− ligand build up a one-dimensional polymer chain along c. The ZnII atom, located on an inversion center, shows an octahedral coordination geometry, defined by two carboxyl O atoms of different benzene-1,4-dioxy­acetate ligands and four water mol­ecules. Adjacent ZnII atoms are bridged by bis-monodentate carboxyl­ate groups of the centrosymmetric 1,4-BDOA2− ligands, to furnish the one-dimensional chain along the c axis; the Zn⋯Zn separation within the polymer is 14.717 (3) A. A hydrogen-bonded supramolecular architecture is formed via O—H⋯O intermolecular hydrogen bonds.

The hydro­xide group in the centrosymmetric title complex, {[Zn4(C9H6O5)3(OH)2(C10H8N2)2]·2H2O}n, which adopts a three-dimensional network structure, bridges three Zn atoms. One of the symmetry-independent di­carboxyl­ate groups chelates to a Zn—OH—Zn unit through the carboxyl group on the aromatic ring, while its other oxy­acetate arm uses only one O atom for binding. The other di­carboxyl­ate dianion is disordered over a center of inversion and functions as a chelating ligand to two Zn—OH—Zn units. The modes of coordination by the hydro­xide, heterocycle and di­carboxyl­ate ligands give rise to tetrahedral coordination for one Zn atom and octahedral coordination for the other.

The Zn atom in the title mononuclear complex, [Zn(C2H3O3)2(C12H8N2)]·2H2O, exists in an octahedral coord­ination environment defined by two hydroxy O atoms, two carboxyl­ate O atoms from different glycolate (hydroxy­acetate) ligands and two N atoms from one phenanthroline (phen) ligand. The Zn atom occupies a special position with twofold symmetry. A layer structure is formed via O—H⋯O hydrogen bonds involving the water molecules.

In the title coordination polymer, [Cd(1,4-BDOA)(C3H4N2)3]n (1,4-BDOA2− is benzene-1,4-dioxy­acetate, C10H8O6), each CdII atom exists in a distorted octahedral coordination sphere, involving three carboxyl O atoms from different 1,4-BDOA2− groups and three N atoms from the imidazole co-ligands. The CdII ions are linked by carboxyl­ate groups into a one-dimensional infinite chain. The Cd⋯Cd separation within the polymer is 15.009 (2) A. N—H⋯O hydrogen bonds help to establish the crystal packing.

In the title coordination polymer, also called catena-poly­[[aqua­bis(1H-imidazole-κN3)copper(II)]-μ-phenyl­ene­dioxy­diacetato-κ2O:O′], [Cu(1,4-BDOA)(C3H4N2)2(H2O)]n (where 1,4-BDOA2− is benzene-1,4-dioxy­acetate, C10H8O6), the CuII atom is five-coordinate involving two O atoms of the 1,4-BDOA ligand, two N atoms of imidazole ligands and one water mol­ecule, displaying a distorted square-pyramidal coordination geometry. The CuII atoms are bridged by carboxyl­ate groups, forming a one-dimensional zigzag chain. The adjacent Cu⋯Cu distance is 12.656 (5) A. Furthermore, such chains are linked by hydrogen-bond interactions, resulting in a three-dimensional network.

The title compound, C16H16N2O 4·H2O, crystallizes as a monohydrate in which the water molecule forms bifurcated hydrogen bonds to the hydroxyl and methoxy O atoms of the methoxysalicyldehyde portion of the Schiff base. The molecule is approximately planar; hydrogen-bonding interactions involving the amino group and the water molecule give rise to a layer structure. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

In the crystal structure of the title 1:1 co-crystal, C7H8NO3+·NO3−·C7H7NO3, two cations inter­act with two zwitterions to form a hydrogen-bonded ring, the nitrate anions being located outside of the ring.

In the title one-dimensional coordination polymer {systematic name: catena-poly­[[[aqua(1,10-phenanthroline-κ2N,N′)­copper(II)]-μ-phenyl­enebis­(oxy­acetato)-κ2O:O′] dihydrate]}, {[Cu(C10H8O6)(C12H8N2)(H2O)]·2H2O}n, the CuII atom has a distorted square-pyramidal coordination geometry, defined by two carboxyl O-atom donors from two benzene-1,3-dioxy­acetate groups, two N-atom donors from the 1,10-phenanthroline ligand and one water mol­ecule. The CuII ions are bridged by benzene-1,3-dioxy­acetate dianions (1,3-BDOA2−), resulting in a one-dimensional chain structure. The intrachain Cu⋯Cu separation is 9.769 (4) A. The chains are linked into a three-dimensional supramolecular network via hydrogen bonds and π–π stacking interactions.

In the title complex, [CoCl2(C5H5NO)4], the Co atom is in an elongated octahedral environment, defined by two Cl− ions and four N atoms of 3-hydroxy­pyridine ligands. The Co atom lies on a special position with crystallographic twofold rotation symmetry. Individual mol­ecules are linked by intermolecular O—H⋯Cl hydrogen bonds into a layer structure.

In the title centrosymmetric dinuclear complex, [Cu2(C2H3O2)4(C5H5NO)2], the two CuII atoms are bridged by four atetate groups, the Cu⋯Cu separation being 2.6468 (7) A. Each CuII atom exists in a square-pyramidal coordination environment defined by four carboxyl acetate O atoms and one 4-pyridone O atom. Intermolecular hydrogen bonds give rise to a two-dimensional layer structure.

In the title complex, [Co(NO3)(C5H5NO)2(H2O)2](NO3), the Co atom exists in an octahedral environment, defined by four O atoms of two 4-pyridone ligands and a chelating nitrate ion, as well as two water mol­ecules. The Co atom and two nitrate ions lie on special positions with twofold rotation symmetry. A three-dimensional network structure is formed by intermol­ecular hydrogen bonds and π–π interactions.

The title compound, expected to be a betaine, 4-hydroxy­pyridinio­acetate, HOC5H4N+CH2CO2− or C7H7NO3, on the basis of its synthesis by the nucleophilic displacement of chloride from the chloro­acetate ion in water, exists as (4-oxo-1,4-di­hydro­pyridin-1-yl)­acetic acid. The acid H atom interacts with the oxo O atom of an adjacent molecule to form a linear helical chain [O⋯O = 2.451 (3) A].

The title complex, tetraaquabis[(2-oxo-1,2-dihydropyridin-1-yl)acetato]magnesium(II), [Mg(C7H6NO3)2(H2O)4], is a neutral mononuclear mol­ecule consisting of an MgII ion, two (2-oxo-4H-pyridin-1-yl)­acetate ligands and four coordinated water mol­ecules. The MgII atom, located on a symmetry center, has octahedral coordination involving two carbonyl O atoms of different (2-oxo-4H-pyridin-1-yl)­acetate ligands and four water mol­ecules. O—H⋯O intermolecular hydrogen bonds form a layer structure.

In the title compound, [Zn(C2H3O2)(C11H12N3O2)(C3H4N2)], the Zn atom is five-coordinate in a ZnN3O2 trigonal-bipyramidal enviroment. Adjacent mol­ecules are linked by an intermolecular hydrogen bond into a chain running along the a axis of the monoclinic cell.