trans-Diaquabis(1H imidazolium-4,5-dicarboxylato-κ2 O 4,O 5)magnesium

The title compound, [Mg(C5H3N2O4)2(H2O)2], consists of centrosymmetric neutral monomers in which two O,O′-bidentate imidazolinium-4,5-dicarboxylate ligands are bonded to the MgII ion. One of the carboxyl protons is transferred to the N atom of the imidazole ring. The octahedral metal-ion coordination is completed by two trans water O atoms. In the crystal, molecules are linked by N—H⋯(O,O) and O—H⋯O hydrogen bonds.

The title compound, [Mg(C 5

Related literature
For the crystal structures of two Ca II complexes with imidazole-4,5-dicarboxylate and aqua ligands, see: Starosta et al. (2006) and for the structure of a Ba II complex, see: Starosta et al. (2007).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB6745).  (Starosta et al., 2006). The polymeric structure of a Ba II complex with the title ligand can be described as built of monomeric structural units in which a Ba II ion, like in the Ca II complex, is coordinated by two ligands via N,O chelating sites. Their second O atoms are protonated and make a short hydrogen bond of 2.495 (2) Å to the O atoms in the adjacent carboxylate group (Starosta et al., 2007).
Experimental 1 mmol of magnesium(II) nitrate hexahydrate and 2 mmol s of imidazole-4,5-dicarboxylic acid (Aldrich) were dissolved in 20 ml of doubly distilled water, stirred for two hours, closed in a preasure vessel and kept at 363 K for three days.
Then, the vessel was slowly cooled to room temperature. The deposited colourless blocks were washed with cold distilled water and dried in the air.

Refinement
Water and attached to nitrogen hydrogen atoms were located in a difference map and refined isotropically, while the H atom attached to imidazole C atom was located at a calculated position and treated as riding on the parent atom with C-H=0.93 Å and U iso (H)=1.2U eq (C).

Figure 2
Packing diagram of the structure. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.