Three isomorphous 2,6-dibromopyridinium tetrabromidometallates: (C(5)H(4)Br(2)N)(2)[MBr(4)].2H(2)O (M = Cu, Cd and Hg).

The structures of three isomorphous compounds, namely bis(2,6-dibromopyridinium) tetrabromidocuprate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[CuBr(4)].2H(2)O, bis(2,6-dibromopyridinium) tetrabromidocadmate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[CdBr(4)].2H(2)O, and bis(2,6-dibromopyridinium) tetrabromidomercurate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[HgBr(4)].2H(2)O, show a crystal supramolecularity represented by M-Br...H-O-H...Br-M intermolecular interactions along with (pi)N-H...OH(2) hydrogen-bonding interactions forming layers connected via aryl-aryl face-to-face stacking of cations, leading to a three-dimensional network. The anions have significantly distorted tetrahedral geometry and crystallographic C(2) symmetry. The stability of this crystal lattice is evidenced by the crystallization of a whole series of isomorphous compounds.

Three-dimensional framework structures: isomorphous bis(2,6-diamino-3,5-dibromopyridinium) tetrabromidometallate(II) salts with Cd(II) and Mn(II).

In the structural motifs of two isomorphous triclinic salts, (C5H6Br2N3)2[MBr4] (M = Cd(II) and Mn(II)), each [MBr4]2- anion interacts with eight surrounding 2,6-diamino-3,5-dibromopyridinium cations through intermolecular C/N-H...Br and Br...Br interactions, leading to a three-dimensional framework structure. The cations show a minor degree of pi-pi stacking, adding extra stability to the three-dimensional architecture.

2,5-Dibromo-pyridine.

In the title compound, C(5)H(3)Br(2)N, C-H⋯N hydrogen-bonding inter-actions and Br⋯Br inter-actions [3.9418 (3) and 3.8986 (3) Å] connect the mol-ecules into planar sheets stacked perpendicular to the b axis. In addition, pyrid-yl-pyridyl inter-sheet π-π stacking inter-actions [centroid-centroid distance = 4.12 (1) Å] result in a three-dimensional network.

Bis(2,6-diamino-3,5-dibromo-pyridinium) hexa-bromidostannate(IV).

The asymmetric unit of the title compound, (C(5)H(6)Br(2)N(3))(2)[SnBr(6)], contains one cation and one half-anion in which the Sn atom is located on a crystallographic centre of inversion and is in a quasi-octa-hedral geometry. The crystal structure is assembled via hydrogen-bonding inter-actions of two kinds, N(pyridine/amine)-H⋯Br-Sn, along with C-Br⋯Br-Sn interactions [3.4925 (19) Å]. The cations are involved in π-π stacking, which adds an extra supra-molecularity as it presents a strong case of offset-face-to-face motifs [centroid-centroid distance = 3.577 (3) Å]. The inter-molecular hydrogen bonds, short Br⋯Br inter-actions and π-π stacking result in the formation of a three-dimensional supra-molecular architecture.

Bis(2,6-dimethyl-pyridinium) tetra-bromido-cobaltate(II).

In the crystal structure of the title compound, (C(7)H(10)N)(2)[CoBr(4)], the [CoBr(4)](2-) anion is connected to two cations through N-H⋯Br and H(2)C-H⋯Br hydrogen bonds to form two-dimensional cation-anion-cation layers normal to the crystallographic b axis. Inter-actions of the π-π type are absent between cations in the stacks [centroid-centroid separation = 5.01 (5) Å]. Significant inter-molecular Br-aryl inter-actions are present in the structure, especially an unusually short Br-ring centroid inter-action of 3.78 (1) Å. The coordination geometry of the anion is approximately tetrahedral and a twofold rotation axis passes through the Co atom.

Bis-(2-amino-6-methyl-pyridinium) tetra-bromido-cuprate(II).

In the crystal structure of the title compound, (C(6)H(9)N(2))(2)[CuBr(4)], the geometry around the Cu atom is inter-mediate between tetra-hedral (T(d)) and square planar (D(4h)). Each [CuBr(4)](2-) anion is connected non-symmetrically to four surrounding cations through N-H⋯X (pyridine and amine proton) hydrogen bonds, forming chains of the ladder-type running parallel to the crystallographic b axis. These layers are further connected by means of offset face-to-face inter-actions (parallel to the a axis), giving a three-dimensional network. Cation π-π stacking [centroid separations of 3.69 (9) and 3.71 (1) Å] and Br⋯aryl inter-actions [3.72 (2) and 4.04 (6) Å] are present in the crystal structure. There are no inter-molecular Br⋯Br inter-actions.

Bis(2-bromo-pyridinium) hexa-bromido-stannate(IV).

The asymmetric unit of the title compound, (C(5)H(5)BrN)(2)[SnBr(6)], contains one cation and one half-anion. The [SnBr(6)](2-) anion is located on an inversion center and forms a quasi-regular octa-hedral arrangement. The crystal structure consists of two-dimensional supra-molecular layers assembled via hydrogen-bonding inter-actions of N-H⋯Br-Sn [D⋯A = 3.375 (13)-3.562 (13) Šand D-H⋯A = 127-142°, along with C-Br⋯Br synthons [3.667 (2) and 3.778 (3) Å]. These layers are parallel to the bc plane and built up from anions inter-acting extensively with the six surrounding cations.

3-Ammonio-pyridinium tetra-bromido-mercurate(II) monohydrate.

The asymmetric unit of the title compound, (C(5)H(8)N(2))[HgBr(4)]·H(2)O, consists of one cation, one anion and one water mol-ecule. The anion exhibits a distorted tetra-hedral arrangement about the Hg atom. The crystal structure contains alternating sheets of cations (in the ac plane) and stacks of anions. Several strong hydrogen-bonding inter-actions (pyN-H⋯Br and C-H⋯Br; py is pyridine), along with O-H⋯Br inter-actions, connect the sheets of cations to the stacks of anions. Cation-cation π-π stacking is also present (C⋯C distances in the range 3.424-3.865 Å). The shortest Br⋯Br distance is 3.9527 (9) Å.

Bis(2-amino-4-methyl-pyridinium) tetra-chloridocuprate(II).

The asymmetric unit of the title compound, (C(6)H(9)N(2))(2)[CuCl(4)], consists of one cation and one half-anion, bis-ected by a twofold rotation axis through the metal center. The anion exhibits a geometry that is inter-mediate between a T(d) and D(4h) arrangement about the Cu atom. The crystal structure contains chains of cations alternating with stacks of anions. The cationic groups inter-act via offset face-to-face π-π stacking, forming chains running along the c axis. The anion stacks are parallel to the cation chains, with no significant inter- nor intra-stack Cl⋯Cl inter-actions. There are several anion-cation hydrogen-bonding inter-actions of the (N-H)(pyridine)⋯Cl and (N-H)(amino)⋯Cl types, connecting the chains of cations to the stacks of anions. Both the N-H⋯Cl and π-π stacking inter-actions [centroid-centroid distances 3.61 (8) and 3.92 (2) Å] contribute to the formation of a three-dimensional supra-molecular architecture.