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In the title compound, [PdBr(2)(C(10)H(8)N(2))]·CH(2)Cl(2), the Pd(2+) ion is four-coordinated in a slightly distorted square-planar environment by two N atoms of the chelating 2,2'-bipyridine ligand and two bromide ions. The compound displays intra-molecular C-H⋯Br hydrogen bonds and pairs of complex mol-ecules are assembled by inter-molecular C-H⋯Br hydrogen bonds. These pairs are connected by additional C-H⋯Br hydrogen bonds, forming a layer structure extending parallel to (011). Inter-molecular π-π inter-actions between the pyridine rings of the ligand are also present, the shortest centroid-centroid distance being 4.090 (9) Å.

The asymmetric unit of the title compound, [Pd(C(6)H(4)NO(2))(4)]·2H(2)O, consists of a quarter of a neutral Pd(IV) complex and half of a solvent water mol-ecule. In the complex, the Pd(IV) ion is located on a fourfold inversion axis and eight-coordinated in a distorted dodeca-hedral environment by four N and four O atoms from four symmetry-related pyridine-2-carboxyl-ate (pic) anionic ligands. In the crystal, the water mol-ecule is involved in O-H⋯O hydrogen bonding, and weak inter-molecular C-H⋯O hydrogen bonds occur. There are also inter-molecular π-π inter-actions between adjacent pyridine rings, with a centroid-centroid distance of 3.715 (3) Å.

In the dication of the title salt, C(6)H(16)N(2) (2+)·2C(6)H(4)NO(2) (-), the two ammonium groups are in the equatorial positions of the chair-shaped cyclo-hexyl ring. In the crystal, the cations and anions are linked by N-H⋯O and N-H⋯N hydrogen bonds, forming a layer network parallel to the ac plane. Weak π-π inter-actions between adjacent pyridine rings with a centroid-centroid distance of 3.589 (2) Å are also present.

The asymmetric unit of the title compound, C(10)H(26)N(4) (2+)·2C(6)H(4)NO(2) (-)·2H(2)O, consists of half of a doubly protonated 1,4,8,11-tetra-azacyclo-tetra-decane (cyclam) dication, a pyridine-2-carboxyl-ate anion and a solvent water mol-ecule. The complete dication is generated by a crystallographic centre and adopts an endodentate conformation which may be influenced by intra-molecular N-H⋯N hydrogen bonding. The carboxyl-ate group of the anion appears to be delocalized on the basis of the C-O bond lengths [1.257 (2) and 1.250 (2) Å]. In the crystal structure, the components are linked by inter-molecular N-H⋯O, N-H⋯N and O-H⋯O hydrogen bonds.

In the title compound, C(12)H(12)N(2) (2+)·2ClO(4) (-), the dihedral angle between the two outer pyridine rings of the dication is 44.8 (1)°. In the crystal, weak intermolecular C-H⋯O hydrogen bonds occur.

The asymmetric unit of the title compound, C(4)H(14)N(2) (2+)·2C(6)H(4)NO(2) (-)·H(2)O, consists of half of a doubly protonated tetra-methyl-enediammonium dication, a pyridine-2-carboxyl-ate anion and half of a solvent water mol-ecule; the dication is located on a centre of inversion and a twofold rotation axis passes through the O atom of the water mol-ecule. The carboxyl-ate group of the anion appears to be delocalized on the basis of the C-O bond lengths. In the crystal structure, the components are linked by inter-molecular N-H⋯O, N-H⋯N and O-H⋯O hydrogen bonds.

In the title compound, C(10)H(26)N(4) (2+)·2Cl(-)·0.5H(2)O, the cyclam (1,4,8,11-tetra-azacyclo-tetra-decane) dication adopts an endodentate conformation which my be inflenced by intra-molecular N-H⋯N hydrogen bonding. In the crystal structure, the components are linked by N-H⋯Cl and O-H⋯Cl hydrogen bonds into chains along [100]. The water molecule is disordered over two sites in a 50:50 ratio.

The asymmetric unit of the title compound, [MnBr(2)(C(6)H(4)NO(2))(H(2)O)(2)](n), contains one monomeric unit of the neutral linear coordination polymer. The Mn(3+) ions are bridged by anionic pyridine-2-carboxyl-ate (pic) ligands, thereby forming a chain-like structure along the c axis, and are six-coordinated in a distorted octa-hedral environment by two O atoms of the two different carboxyl-ate groups, two O atoms of two water mol-ecules and two Br atoms. The complex displays inter-molecular O-H⋯Br, O-H⋯N, O-H⋯O, C-H⋯O and C-H⋯Br hydrogen bonding. There may also be inter-molecular π-π inter-actions between adjacent pyridine rings, with a centroid-centroid distance of 3.993 (8) Å.

In the title complex, [PdBr(2)(C(7)H(8))], the Pd(II) ion lies in a distorted square-planar environment defined by the two Br atoms and the mid-points of the two π-coordinated double bonds of bicyclo-[2.2.1]hepta-2,5-diene. The complex is disposed about a crystallographic mirror plane parallel to the ac plane passing through the Pd, Br atoms and the centre of the diene ligand.

The title compound, C(6)H(18)N(2) (2+)·2C(6)H(4)NO(2) (-), consists of a doubly protonated hexa-methyl-enediammonium dication and two pyridine-2-carboxyl-ate anions. These ions inter-act by means of inter-molecular N-H⋯O and N-H⋯N hydrogen bonds to form a two-dimensional array. The carboxyl-ate groups of the anions appear to be delocalized on the basis of the C-O bond lengths.

The asymmetric unit of the title compound, [PtCl(2)(C(6)H(4)NO(2))(2)]·CH(3)CN, contains a neutral Pt(IV) complex and an acetonitrile solvent mol-ecule. In the complex, the Pt(4+) atom is six-coordinated in a distorted octa-hedral environment by two N atoms and two O atoms from two pyridine-carboxyl-ate (pic) ligands and two Cl atoms. The Cl atoms are cis with respect to each other. The compound displays inter- and intra-molecular C-H⋯O and C-H⋯Cl hydrogen bonding.

In the title compound, [PdCl(2)(C(10)H(8)N(2))]·CH(2)Cl(2), the Pd(2+) ion is four-coordinated in a slightly distorted square-planar environment by two N atoms of the 2,2'-bipyridine (bipy) ligand and two chloride ions. The compound displays intra-molecular C-H⋯Cl hydrogen bonds and pairs of complex mol-ecules are connected by inter-molecular C-H⋯Cl hydrogen bonds. Inter-molecular π-π inter-actions are present between the pyridine rings of the ligand, the shortest centroid-centroid distance being 4.096 (3) Å. As a result of the electronic nature of the chelate ring, it is possible to create π-π inter-actions to its symmetry-related counterpart [3.720 (2) Å] and also with a pyridine ring [3.570 (3) Å] of the bipy unit. The present structure is a redetermination of a previous structure [Vicente et al. (1997 ▶). Private communication (refcode PYCXMN02). CCDC, Cambridge, England]. In the new structure refinement all H atoms were located in a difference Fourier synthesis. Their coordinates were refined freely, together with isotropic displacement parameters.

The asymmetric unit of the title compound, {(C(6)H(18)N(2))(0.5)[MnBr(2)(C(6)H(4)NO(2))(H(2)O)]}(n), contains the repeat unit of the complex anion and one-half of a hexane-1,6-diammonium cation that is located on a twofold rotation axis. In the anionic polymer, the Mn(2+) ions are bridged by the pyridine-carboxyl-ate (pic) anion ligand, forming a chain structure along the c axis. The Mn(2+) ion is six-coordinated in a distorted octa-hedral environment by one N atom of the pyridine ring, two O atoms of the two carboxyl-ate groups, one O atom of the water mol-ecule and two Br atoms. The compound displays inter-molecular N-H⋯O, N-H⋯Br, O-H⋯Br and O-H⋯O hydrogen bonding. There may also be inter-molecular π-π inter-actions between adjacent pyridine rings, with a centroid-centroid distance of 3.992 (4) Å.

The asymmetric unit of the title compound, [Mn(2)Cl(4)(C(30)H(36)N(6))], contains one-half of the formula unit; a centre of inversion is located at the mid-point of the mol-ecule. The two Mn(2+) ions are bridged by the dual tri-dentate N,N,N',N'-tetra-kis(2-pyridylmeth-yl)hexane-1,6-diamine ligand to form a dinuclear complex. Each Mn atom is five-coordinated in an approximately square-pyramidal geometry by three N atoms from the ligand and two Cl atoms. Inter-molecular π-π inter-actions between adjacent pyridine rings with a centroid-centroid distance of 3.576 (2) Å are reported.

In the title complex, [PtCl(4)(C(12)H(8)N(2))]·H(2)O, the Pt(4+) ion is six-coordinated in a distorted octa-hedral environment by two N atoms of a 1,10-phenanthroline ligand and by four Cl atoms. As a result of the different trans effects of the N and Cl atoms, the Pt-Cl bonds trans to the N atom are slightly shorter than those trans to the Cl atom. The compound displays inter-molecular π-π inter-actions between the six-membered rings, with a centroid-centroid distance of 3.834 Å. There are also weak intra-molecular C-H⋯Cl hydrogen bonds. According to the IR spectrum, solvent water was present in the crystal, but owing to the high thermal motion of the uncoordinated O atom, the H atoms could not be detected.

The asymmetric unit of the title compound, [PtCl(4)(C(12)H(8)N(2))]·0.5CH(3)CN, contains two crystallographically independent Pt(IV) complexes with very similar geometry and one solvent mol-ecule. In the complexes, each Pt(IV) ion is six-coordinated in a distorted octa-hedral environment by two N atoms of the 1,10-phenanthroline ligand and four Cl atoms. Because of the different trans effects of the N and Cl atoms, the Pt-Cl bonds trans to the N atom are slightly shorter than those trans to the Cl atom. The compound displays numerous inter-molecular π-π inter-actions between six-membered rings, with a shortest centroid-to-centroid distance of 3.654 Å. There are also weak intra- and inter-molecular C-H⋯Cl hydrogen bonds.

In the title complex, [PtCl(2)(C(10)H(8)N(2))(2)]Cl(2)·H(2)O, the Pt(4+) ion is six-coordinated in a distorted octa-hedral environment by four N atoms from the two 2,2'-bipyridine ligands and two Cl atoms. As a result of the different trans influences of the N and Cl atoms, the Pt-N bonds trans to the Cl atom are slightly longer than those trans to the N atom. The compound displays inter-molecular hydrogen bonding between the water mol-ecule and the Cl anions. There are inter-molecular π-π inter-actions between adjacent pyridine rings, with a centroid-centroid distance of 3.962 Å.