Bis­[hex­aqua­magnesium(II)] pyrazine-2,3,5,6-tetra­carboxyl­ate tetrahydrate

The unit cell of the title compound, [Mg(H₂O)₆]₂(C₈N₂O₈)·4H₂O, contains two hex­aqua­magnesium(II) cations, one fully deprotonated pyrazine-2,3,5,6-tetra­carboxyl­ate [(2,3,5,6-PZTC)^4-] anion with its geometrical centre situated at the inversion centre and four solvent water mol­ecules. The magnesium(II) ion is surrounded by six water mol­ecules with their O atoms located at the apices of a fairly regular octahedron. Mg-O bond distances range from 2.036 (1) to 2.113 (1) Å (mean value 2.065 Å). The carboxyl­ate groups are inclined to the pyrazine ring by 22.8 (1)and 99.1 (1)°. A three-dimensional network of hydrogen bonds is built up between the coordinated water mol­ecules and the carboxyl­ate O atoms.