trans-Tetraaquabis(pyridazine-4-carboxylato-κO)magnesium(II) dihydrate

The crystal structure of the title compound, [Mg(C5H3N2O2)2(H2O)4]·2H2O, is composed of centrosymmetric monomers in which an MgII ion is coordinated by two carboxylate O atoms from the two pyridazine-4-carboxylate ligands. The monomers linked by O—H⋯O and O—H⋯N hydrogen bonds into layers which are held together by hydrogen bonds in which solvent water O atoms act as donors and acceptors, resulting in a three-dimensional network.

The crystal structure of the title compound, [Mg(C 5

Related literature
For the crystal structure of a Pb(II) complex with pyridazine-4-carboxylate and water ligands, see: Starosta & Leciejewicz, (2009). The structure of pyridazine-4-carboxylic acid hydrochloride was determined earlier (Starosta & Leciejewicz, 2008). The structure of a Mg II complex with pyridazine-3carboxylate and water ligands has been also reported by Gryz et al. (2006).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KP2307).

Comment
The structure of the title compound (I) is built of monomeric molecules in which the Mg +2 located in an inversion centre is chelated by two carboxylate atoms each donated by one of symmetry ralated ligand molecules and by two pairs of aqua O atoms resulting in a slightly distorted octahedral geometry. The carboxylate O1, O1 (i) and aqua O3, O3 (i) atoms form an equatorial plane, aqua O4 and O4 (i) atoms are at the axial positions. The observed Mg-O bond lengths and bond angles are almost the same as reported for the complex with pyridazine-3-carboxylate and water ligands (Gryz et al., 2006). The pyridazine ring is planar with r.m.s. of 0.0046 (1) Å. The observed bond distances and angles are close to those reported for the parent acid (Starosta & Leciejewicz, 2008). The carboxylate group is rotated from the mean plane by 8.1 (1)°.
Hydrogen bonds link the monomers to form molecular sheets. They operate between coordinated water O atoms as donors and uncoordinated carboxylate O atoms and pyridazine-N atoms in adjacent monomers as acceptors. The sheets are held together by hydrogen bonds in which crystal water molecules act as donors and acceptors resulting in a three-dimensional network. The coordination mode reported in the structure of a Mg II complex with pyridazine-3-carboxylate and water ligands is also octahedral but the Mg II ion is coordinated by a pair of symmetry related N,O-chelating groups of the ligands and a pair of water O atoms (Gryz et al., 2006). The Pb(II) complex with the title ligand shows entirely different coordination mode. Two symmetry related metal ions form a dimer in which they are bridged by hetero-ring N atoms of two symmetry related ligands amd two aqua-O atoms. Each Pb(II) ion is also coordinated by both carboxylate O atoms of another ligand whose hetero-ring N atoms do not coordinate to Pb(II). (Starosta & Leciejewicz, 2009).

Experimental
The title compound was obtained by mixing boiling aqueous solutions, one containig 2 mmols of pyridazine-4-carboxylic acid (Aldrich), the other 1 mmol of magnesium diacetate tetrahydrate (Aldrich). The mixture was boiled under reflux for two h, then cooled to room temperature and left to crystallise. A few days latter, colourless crystalline plates were found after evaporation to dryness. They were recrystallised from water several times until well formed single crystals were obtained.
Crystals were washed with cold ethanol and dried in the air.

Refinement
Water hydrogen atoms were located in a difference map and were allowed to ride on the parent atom with U iso (H)=1.5U eq (O).
H atoms attached to pyridazine-ring C atoms were positioned at calculated positions and were treated as riding on the parent atoms, with C-H=0.93 Å and U iso (H)=1.5U eq (C).