4-(Dimethyl­amino)­pyridinium tetra­chloridoferrate(III)

The title salt, (C₇H₁₁N₂)[FeCl₄], consists of one essentially planar (the r.m.s. deviation for all non-H atoms being 0.004 Å) 4-(dimethyl­amino)­pyridinium cation and a tetra­hedral tetra­chloridoferrate(III) anion. The cations and anions are arranged in layers parallel to (010). Besides electrostatic inter­actions, the crystal packing features N—H...Cl and C—H...Cl hydrogen bonds between cations and anions, forming a three-dimensional network.

Bis(3-amino­pyrazine-2-carboxyl­ato-κ²N¹,O)di­aqua­nickel(II) dihydrate

In the title compound, [Ni(C₅H₄N₃O₂)₂(H₂O)₂]·2H₂O, the Ni^II ion lies on an inversion center and is coordinated in an slightly distorted octa­hedral environment by two N,O-chelating 3-amino­pyrazine-2-carboxyl­ate (APZC) ligands in the equatorial plane and two trans-axial aqua ligands. In the crystal, O—H...O, N—H...O and O—H...N hydrogen bonds involving the solvent water mol­ecules, aqua and APZC ligands form layers parallel to (010). These layers are linked further via O—H...O, N—H...O and C—H...O hydrogen bonds involving the axial aqua ligands, amino groups and the carboxyl­ate groups of the APZC ligands, forming a three-dimensional network.

Bis[4-(di­methyl­amino)­pyridinium] tetra­chlorido­cuprate(II)

The asymmetric unit of the title salt, (C₇H₁₁N₂)₂[CuCl₄], comprises half a tetrahedral tetra­chlorido­cuprate anion, being located on a twofold axis, and a protonated 4-(di­methyl­amino)­pyridine cation. The geometry around the Cu^II ion is highly distorted with the range of Cl—Cu—Cl angles being 94.94 (1)–141.03 (1)°. The crystal structure is stabilized by N—H...Cl and C—H...Cl hydrogen bonds. In the three-dimensional network, cations and anions pack in the lattice so as to generate chains of [CuCl₄]²⁻ anions separated by two orientations of cation layers, which are inter­locked through π–π stacking contacts between pairs of pyridine rings, with centroid–centroid distances of 3.7874 (7) Å.