Poly[bis-[µ(2)-(dimethyl-aza-nium-yl)methyl-enediphospho-nato]magnesium].

The title compound, [Mg(C(3)H(10)NO(6)P(2))(2)](n), synthesized by a hydro-thermal method, adopts a one-dimensional polymeric chain structure and is isotypic with the previously reported Cd complex based on the ligand N,N-dimethyl-amino-methane-1,1-diphospho-nic acid (H(4)L). The asymmetric unit contains one half Mg(2+) ion and one H(3)L(-) anion. The unique Mg(2+) ion lies on an inversion center and is octa-hedrally coordinated by O atoms from six phospho-nate groups of four different H(3)L(-) anions. Each H(3)L(-) anion, with one protonated N atom and two phospho-nate OH groups, serves as a tridentate ligand. Two of its six phospho-nate O atoms chelate to a Mg(2+) cation in a bidentate fashion, while a third O atom bridges to a neighbouring Mg(2+) ion. The inter-connection of Mg(2+) ions by the H(3)L(-)anions leads to the formation of a polymer chain along the a axis in which the adjacent Mg(2+) ions are doubly bridged by two equivalent H(3)L(-) anions. These discrete chains are further assembled into a three-dimensional supra-molecular network via O-H⋯O and N-H⋯O hydrogen bonds involving the non-coordin-ated phospho-nate O atoms and the protonated N atoms.