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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.

The homometal cluster [Fe(DMF)6][W2(μ2-S)2S4] (I) was successfully synthesized by low-temperature solid-state reactions. X-ray single-crystal diffraction studies suggest that compound I is a dinuclear anion cluster. The compound was characterized by elemental analyses, IR spectra, and UV-Vis spectra. The third-order nonlinear optical (NLO) properties of the cluster were also investigated and exhibited nice nonlinear saturation absorption (α2 0) and self-defocusing property (n 2 < 0) and self-defocusing performance with modulus of the hyperpolarizabilities (9.547 × 10−31 esu) for I.

The title complex mol­ecule, [Mn2(C7H4ClO2)4(C12H8N2)2(H2O)], possesses crystallographically imposed C2 symmetry. Each MnII atom is coordinated by three carboxyl O atoms from three 4-chloro­benzoate ligands, two N atoms from one 1,10-phenanthroline ligand and one bridging water mol­ecule in a distorted octa­hedral coordination geometry. The Mn⋯Mn separation is 3.512 (3) A. Symmetrically related dinuclear mol­ecules form chains parallel to the c axis via π–π stacking inter­actions.

In the title complex, [Co(C7H4ClO2)2(C12H8N2)(H2O)2], the CoII atom is six-coordinated in a distorted octa­hedral geometry by two O atoms from two 4-chloro­benzoate ligands, two N atoms from one 1,10-phenanthroline ligand and two water mol­ecules. The mol­ecules form O—H⋯O hydrogen-bonded centrosymmetric dimers that are extended by additonal intra- and inter­molecular hydrogen-bonding inter­actions to form infinite chains of dimers parallel to the a axis.

The molecular structure of the title compound, [Zn(C8H7O2)2(C7H6N2)2]·2C8H8O2, is composed of a mononuclear ZnII complex, which possesses twofold rotation symmetry, and two uncoordinated 4-methylbenzoic acid molecules. The ZnII atom displays a four-coordinate distorted tetrahedral configuration, formed by two carboxylate O atoms of two monodentate 4-methylbenzoate ligands and two N atoms of two benzimidazole molecules. In the crystal structure, complex molecules are linked by the 4-methylbenzoic acid molecules via N—H...O and O—H...O hydrogen bonds, giving rise to the formation of a supramolecular structure.

In the title complex, [Mn(C7H2N2O7)(C10H8N2)] n , the MnII atom has a distorted octahedral coordination geometry, defined by two N atoms from the 2,2′-bipyridine ligand and four O atoms from two 3,5-dinitrosalicylate dianions. One carboxylate O atom acts as a bridge between adjacent metal centres to form a one-dimensional chain. The Mn...Mn distance is 4.315 (6) Å. The crystal packing is stabilized by intermolecular C—H...O hydrogen interactions.

In the title coordination polymer, [Ca(C7H2N2O7)(H2O)]n, the CaII atom is seven-coordinate by six O atoms from four 3,5-dinitro­salicylatate ligands and one water mol­ecule, and displays a distorted penta­gonal–bipyramidal geometry. Centrosymmetrically related dinuclear calcium units with a Ca⋯Ca separation of 3.8665 (8)A form layers which are self-assembled into a three-dimensional network by inter­molecular O—H⋯O hydrogen bonds.

In the title coordination polymer, [Zn(C7H2N2O7)(C12H8N2)]n, the ZnII atom has a distorted trigonal–bipyramidal coordination geometry, defined by two N atoms from one phenanthroline ligand and three O atoms from two different 3,5-dinitro­salicylate ligands. The crystal packing is governed by weak intra- and inter­molecular C—H⋯O hydrogen bonds.

The CoII atom in the mononuclear title complex, [Co(C8H5Cl2O3)2(C3H4N2)2(H2O)2], lies on an inversion center. The CoII atom has an octa­hedral coordination, involving two carboxylate O atoms of two monodentate 2,4-dichloro­phenoxy­acetate ligands, two N atoms of imidazole ligands and two water mol­ecules. Inter­molecular O—H⋯O hydrogen bonds give rise to chains, which are linked by N—H⋯O hydrogen bonds, forming a sheet structure. The mol­ecules are further linked by π–π stacking inter­actions, generating a two-dimensional supra­molecular network.

The title complex, [Mn(C8H5Cl2O3)2(H2O)2]n, is a coordination polymer containing the flexible 2,4-dichloro­phenoxy­acetate ligand. The MnII atom, which lies on a centre of inversion, is coordinated by four O atoms from two 2,4-dichloro­phenoxy­acetate ligands and two water mol­ecules and displays an octa­hedral geometry. An ideal three-dimensional framework is formed by the flexible phenoxy­acetate ligands via intra­molecular hydrogen-bond inter­actions.

In the title coordination polymer, [Cd(C8H5Cl2O3)2(H2O)2]n, each CdII atom lies on an inversion center. The CdII atom exists in a slightly distorted octa­hedral coordination polyhedron, involving four carboxyl O atoms from different 2,4-dichloro­phenoxy­acetate ligands and two water mol­ecules. The CdII ions are bridged by carboxyl­ate groups in a bis­(mono­dentate) mode, leading to a two-dimensional layer structure. This supra­molecular network is consolidated by inter­molecular hydrogen-bonding inter­actions.

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(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, [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 coordination polymer, {[Ba(C(7)H(2)N(2)O(7))(H(2)O)(2)]·H(2)O}(n), the Ba(II) atom is ten-coordinated by seven O atoms from four 3,5-dinitro-salicylatate ligands, two μ(2)-bridging aqua ligands and one water mol-ecule. The coordination mode is best described as a bicapped square-anti-prismatic geometry. The 3,5-dinitrosalicylatate ligands bridge three Ba atoms. Centrosymmetrically related dinuclear barium units, with a Ba⋯Ba separation of 4.767 (5) Å, form infinite chains, which are further self-assembled into a supra-molecular network through inter-molecular O-H⋯O hydrogen-bonding inter-actions between O atoms of 3,5-dinitro-salicylatate ligands and water mol-ecules.

Corrigendum to Acta Cryst. (2007), E63, o2296., In the paper by Hong, Song & Wu [Acta Cryst. (2007), E63, o2296], the scheme shows the wrong structure. The correct scheme is shown below and the compound name is corrected to "poly[[di-μ2-aqua-diaqua-hemi-μ6-oxalato-barium(II)] 2,4,6-trinitro­phenolate monohydrate", {[Ba(C2O4)0.5(H2O)4]C6H2N3O7·H2O}n.

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, [Co(C10H7N2O2)2(H2O)4], the CoIIatom lies on an inversion centre and displays a slightly distorted octahedral geometry. The coordination sphere is defined by two mutuallytransN atoms from two 4-(imidazol-1-yl)benzoate ligands and the O atoms from four water molecules. The crystal structure is stabilized by O—H...O hydrogen bonds.

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, {[Na(C7H7N2O4)(H2O)2]·H2O}n, the NaI atom exhibits a distorted octa­hedral geometry and is six-coordinated in an NO5 environment. The equatorial plane is defined by three O atoms and one N atom from two distinct 5-carb­oxy-2-ethyl-1H-imidazole-4-carboxyl­ate (H2EIDC) ligands and one coordinated water mol­ecule, and the apical sites are occupied by one carboxyl O atom from one H2EIDC ligand and one O atom from the other coordinated water mol­ecule. The NaI atoms are linked by H2EIDC ligands, generating an infinite double chain along the a axis. These chains are further connected via O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional supra­molecular network.

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, [Zn(C8H9N2O4)2(H2O)2]·3.5H2O, the ZnII ion is coordinated by two N,O-bidentate H2pimda ligands (H3pimda = 2-propyl-1H-imidazole-4,5-dicarb­oxy­lic acid) and two water mol­ecules in a distorted octa­hedral environment. In the crystal structure, extensive inter­molecular O—H⋯O and N—H⋯O hydrogen bonds stabilize the three-dimensional supra­molecular network. Intra­molecular O—H⋯O hydrogen bonds between the carboxyl groups are also observed. The propyl groups of the two H2pimda ligands are disordered each over two sites, with occupancy factors of 0.752 (5):0.248 (5) and 0.519 (7):0.481 (7). One of the water mol­ecules is half-occupied.

In the title complex, [Cd(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·3.5H(2)O, the Cd(II) is coordinated by two water mol-ecules and N,O-chelated by two 5-carb-oxy-2-propyl-1H-imidazole-4-carboxyl-ate anions in a distorted octa-hedral geometry. The two imidazole rings are oriented to each other with a dihedral angle of 75.1 (2)°. Strong O-H⋯O hydrogen bonds between protonated and deprotonated carboxyl-ate groups occur in the mol-ecular structure. In the crystal structure extensive O-H⋯O and N-H⋯O hydrogen bonds help to stabilize the three-dimensional supra-molecular framework. The propyl groups of anions are disordered over two sites with refined occupancies of 0.768 (6):0.232 (6) and 0.642 (8):0.358 (8).

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.

Each of the carboxyl-ate -CO(2) fragments of the dianion ligand in the title compound, {[Sr(C(9)H(4)N(2)O(4))(H(2)O)(2)]·H(2)O}(n), chelates to a Sr(II) atom and at the same time, one of the two O atoms coordinates to a third Sr(II) atom. The μ(4)-bridging mode of the dianion generates a square-grid layer motif; adjacent layers are connected by O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, forming a three-dimensional network. The eight-coordinate Sr atom exists in a distorted square-anti-prismatic geometry. The crystal studied was a non-merohedral twin with a minor twin component of 24%.

In the title complex, [Ag2La(C6H4NO2)4(ClO4)(H2O)5]n, the LaIII atom, lying on a twofold rotation axis, is eight-coordinated by four O atoms from four nicotinate (nic) ligands and four water mol­ecules in a distorted square-anti­prismatic coordination geometry. The AgI atom is coordinated in an almost linear fashion by two pyridyl N atoms of two nic ligands. The linear coordination is augmented by weak inter­actions with one O atom from a half-occupied ClO4− anion and a water mol­ecule lying on a twofold axis. Two Ag(nic)2 units connect two La atoms, forming a cyclic unit. These units are further extended into an infinite zigzag chain. The chains are bridged by the disordered perchlorate ions via weak Ag—O [2.678 (2) A] inter­actions. O—H⋯O hydrogen bonds, weak Ag⋯Ag [3.3340 (15) A] inter­actions and π–π inter­actions between the pyridyl rings [centroid–centroid distance = 3.656 (2) A] lead to a three-dimensional network.

In the title compound, {[Ag2Pr(C6H4NO2)4(H2O)4]ClO4·H2O}n, the PrIII atom, lying on a twofold rotation axis, has a distorted square-anti­prismatic coordination geometry, defined by four O atoms from four nicotinate (nic) ligands and four water mol­ecules. The AgI atom is coordinated in an almost linear fashion by two pyridyl N atoms from two nicotinate ligands. The linear coordination is augmented by weak inter­actions with three O atoms from one perchlorate anion, one uncoordinated water mol­ecule and one carboxyl­ate group. Two Pr atoms link two {Ag(nic)2}+ units into a ring, which is further extended into an infinite zigzag chain by sharing the Pr atoms. These chains are further connected into a three-dimensional network via weak Ag⋯O inter­actions, O—H⋯O hydrogen bonds, Ag⋯Ag inter­actions [3.357 (2) A] and π–π inter­actions between the pyridyl rings [centroid–centroid distance = 3.685 (4) A].

In the title dinuclear complex, [Ni(2)(C(8)H(7)O(2))(4)(C(12)H(8)N(2))(2)(H(2)O)], each Ni(II) atom is six-coordinated by three carboxylate O atoms from three 4-methyl-benzoate ligands, two N atoms from two 1,10-phenanthroline ligands, and one μ(2)-bridging aqua ligand. The dimeric complex is located on a crystallographic twofold axis and each Ni atom displays a distorted octa-hedral coordination geometry. The crystal structure is stabilized via intra-molecular hydrogen bonding of the bridging water mol-ecule and the uncoordinated carboxyl-ate O atoms, and by C-H⋯O and π-π stacking inter-actions [centroid-centroid distances between neighbouring phenanthroline ring systems and between the benzene ring of a 4-methyl-benzoate unit and a phenanthroline ring system are 3.662 (2) and 3.611 (3) Å, respectively].

In the title compound, [Cd(C(8)H(7)O(2))(2)(C(3)H(4)N(2))(2)(H(2)O)], the Cd(II) atom is coordinated by four carboxyl-ate O atoms from two bidentate chelating 4-methyl-benzoate ligands, two N atoms from two imidazole ligands and one water mol-ecule in a distorted penta-gonal bipyramidal geometry. Inter-molecular O-H⋯O hydrogen bonds between the coordinated water mol-ecule and the carboxyl-ate O atoms of 4-methyl-benzoate lead to an infinite chain. These chains are further self-assembled into a two-dimensional layer through N-H⋯O hydrogen bonds between the imidazole ligands and carboxyl-ate groups. One of the imidazole ligands is disordered over two positions with site-occupancy factors of 0.737 (4) and 0.263 (4).

The title complex, [Er(C5H5NO)(C2O4)(H2O)]n, is a new erbium polymer based on oxalate and 4-oxidopyridinium ligands. The ErII center is coordinated by six O atoms from three oxalate ligands, one O atom from a 4-oxidopyridinium ligand and one water mol­ecule, and displays a distorted square-anti­prismatic coordination geometry. The oxalate ligands are both chelating and bridging, and link ErII ions, forming Er–oxalate layers in which the attached water and 4-oxidopyridinium units point alternately up and down. A mirror plane passes through the Er atom, one C, the oxide O and two oxalate O atoms. The layers are assembled into a three-dimensional supra­molecular network via inter­molecular hydrogen bonding and π–π stacking inter­actions [centroid–centroid distances of 3.587 (2) Å between parallel pyridinium rings]. Both the water mol­ecule and the 4-oxidopyridinium ligand are disordered over two sites in a 1:1 ratio.

A new coordination polymer, [Cu(C(7)H(2)N(2)O(7))(C(5)H(5)NO)](n), exhibits a double-chain structure, in which 3,5-dinitro-2-oxidobenzoate and 3-hydroxy-pyridine both act as bridging ligands, -connecting adjacent copper(II) centers to form an infinite double-stranded chain. The asymmetric unit contains one Cu(II) ion, one 3,5-dinitro-2-oxidobenzoate ligand and a 3-hydroxy-pyridine ligand. Coordination by one N atom and three O atoms from two different 3,5-dinitro-2-oxidobenzoate ligands and a 3-hydroxy-pyridine ligand creates a square-planar Cu(II) center, which is augmented by a less tightly bonded fifth phenol O atom to form a square-pyramidal five-coordinate complex with an essentially planar base. The double-stranded chains are stabilized by intra-chain π-π inter-actions [the centroid-to-centroid distance between adjacent aromatic rings is 3.719 (7) Å], and further linked through O-H⋯O hydrogen bonds, forming a three-dimensional supra-molecular network.

The title erbium coordination polymer, {[Er2(C8H4O4)3(H2O)2]·H2O} n , was obtained by the hydrothermal reaction of ErCl3 with benzene-1,3-dicarboxylic acid (1,3-BDC) in alkaline aqueous solution. Each of the two crystallographically independent ErIII ions is seven-coordinate and has a distorted pentagonal–bipyramidal geometry. One Er centre is coordinated by seven O atoms from six 1,3-BDC ligands and the other Er centre is surrounded by five O atoms from five 1,3-BDC ligands and two water molecules. The bridging ligands, which have two different coordination modes, link the metal centres to form a three-dimensional network with channels parallel to the b axis in which solvent water molecules are located. The crystal structure is stabilized by intra- and intermolecular O—H...O hydrogen-bonding interactions. One benzene ring and the solvent water molecule are independently disordered over two positions each, with occupancy ratios of 0.595 (2):0.405 (2) and 0.661 (1):0.339 (1), respectively.

In the title compound, [Mn(C7H3N2O7)(C12H8N2)2(H2O)](C7H2N2O7), the MnII ion is chelated by two phenanthroline ligands, a water mol­ecule and a carboxyl­ate group in an octa­hedral geometry; the two O atoms involved in bonding are cis to each other. The coordinated water mol­ecule links the cation and the carboxyl­ate anion into a linear chain through hydrogen bonds.

In the title complex, [Cu(C5H3N2O2)2(NH3)4], the CuII atom lies on a site of symmetry 2/m and has distorted elongated octa­hedral coordination geometry defined by four N atoms from ammonia mol­ecules and another two N atoms from two pyrazine-2-carboxyl­ate ligands. The crystal packing is governed by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds.

The title compound, C10H9N2+·C7H3N2O7−, has been synthesized under hydro­thermal conditions. The crystal packing is governed by hydrogen bonding and π–π stacking.

In the title compound, [Cd(C8H7O2)2(C3H4N2)2(H2O)], the CdII atom is coordinated by four carboxyl­ate O atoms from two bidentate chelating 4-methyl­benzoate ligands, two N atoms from two imidazole ligands and one water mol­ecule in a distorted penta­gonal bipyramidal geometry. Inter­molecular O—H⋯O hydrogen bonds between the coordinated water mol­ecule and the carboxyl­ate O atoms of 4-methyl­benzoate lead to an infinite chain. These chains are further self-assembled into a two-dimensional layer through N—H⋯O hydrogen bonds between the imidazole ligands and carboxyl­ate groups. One of the imidazole ligands is disordered over two positions with site-occupancy factors of 0.737 (4) and 0.263 (4).

The title complex, C7H6N2 +·C6H2N3O7 −, has been synthesized under hydrothermal conditions. The packing is governed by intermolecular N—H...O hydrogen-bonding interactions.

The title complex, [Zn(C3H4N2)4](C7H3N2O7)2, consists of a tetra­kis(1H-imidazole-κN3)zinc(II) cation and two 2-hydr­oxy-3,5-dinitro­benzoate anions. In the cation, the ZnII atom, located on a twofold axis, is tetra­hedrally coordinated by four N atoms from four imidazole ligands. Inter­molecular hydrogen bonds between cations and anions form a supra­molecular network.

In the title complex, [Mn(C5H3N3)2(H2O)2], the MnII atom, located on an inversion center, is coordinated by four N atoms from two 5-(2-pyrazin­yl)tetra­zolate ligands and two water mol­ecules in a distorted octa­hedral geometry. The packing is governed by inter­molecular O—H⋯N hydrogen bonds.

The title complex, [Cd(C5H3N6)2(H2O)2], possesses a crystallographically imposed inversion centre. The CdII atom is coordinated by four N atoms [Cd—N = 2.2794 (16) and 2.4155 (16) A] from two 5-(pyrazin-2-yl)tetra­zolate ligands and two water mol­ecules [Cd—O = 2.263 (2) A] in a distorted octa­hedral geometry. The crystal packing is governed by inter­molecular O—H⋯N hydrogen bonds.

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.