Hexaaquamagnesium(II) bis(pyridinium-2,6-dicarboxylate)

In the title compound, [Mg(H2O)6](C7H4NO4)2, a single six-coordinate Mg2+ cation (site symmetry 2/m) is bonded to six water molecules in a distorted octahedral geometry. The crystal packing between the complex cation and the zwitterionic organic cation (m symmetry) is stabilized by intermolecular O—H⋯O hydrogen bonds and weak intermolecular C—H⋯O interactions.

In the title compound, [Mg(H 2 O) 6 ](C 7 H 4 NO 4 ) 2 , a single sixcoordinate Mg 2+ cation (site symmetry 2/m) is bonded to six water molecules in a distorted octahedral geometry. The crystal packing between the complex cation and the zwitterionic organic cation (m symmetry) is stabilized by intermolecular O-HÁ Á ÁO hydrogen bonds and weak intermolecular C-HÁ Á ÁO interactions.

Structure Reports Online
In the title compound, [Mg(H 2 O) 6 ][pyH-2,6-dc] 2 , the cation is comprised of a six-coordinate Mg II ion bound by water molecules in a distorted octahedral geometry. The dianion is comprised of a pyridine-2,6-dicarboxylic acid group (Fig. 1).
Bond lengths and angles for Mg-O are in normal ranges. Crystal packing is stabilized by O-H···O intra and intermolecular hydrogen bonds and weak C-H···O intermolecular hydrogen bond interactions with the coordinated water molecules (Fig.   2). The pyridine ring in the dianion is protonated and the two carboxylic acid groups are deprotonated forming a proton transfer fragment.

Experimental
A solution of pyridine-2,6-dicarboxylic acid (pydcH 2 ) (0.1671 g, 1 mmol) in ethanol (20 ml) was added to a solution of pyridazine (pydz) (0.072 ml, 1 mmol) in ethanol (8 ml) and stirred for 2 hrs. Then an aqueous solution of Mg(NO 3 ) 2 .6H 2 O (0.1282 g, 0.5 mmol) was added to mixture of pydcH 2 -pydz and stirred for 1 h. 1 mL DMSO was then added to the mixture to clear the solution and stirred for more 2 hrs. Slow evaporation of the resulting solution gave colorless crystals of the title compound after three weeks which were suitable for X-ray analysis (decomposition > 260 °C).

Refinement
The hydrogen atoms from the water molecules and pyridinium group were found in a difference Fourier map and refined isotropically without restraint. The C-H protons of the aromatic ring were positioned geometrically and refined as riding atoms, with C-H = 0.93Å and U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of [Mg(H 2 O) 6 ][pyH-2,6-dc] 2 with displacement ellipsoids drawn at 30% probability level. Symmetry codes: (i: x, 1 -y, z; ii: 1 -x, y, -z; iv: 1 -x, -y, -z).