Crystal structures of two Ca(II) complexes with imidazole-4,5-dicarboxylate and water ligands

The structure of compound I: poly-diaqua(μ-imidazole-4,5-dicarboxylato- N,O; -O′; -O″, -O‴) calcium(II) monohydrate [Ca(C ₅H₂N₂O₄)(H₂O) ₂·H₂O] is built of molecular sheets in which imidazole-4,5-dicarboxylate ligands bridge the metal ions using both carboxylate groups, each bidentate. Ca(II) is coordinated by six oxygen atoms and one hetero-ring nitrogen atom distributed at the apices of a capped tetragonal bipyramid. The basal plane of the pyramid is formed by two carboxylate oxygen atoms [d(Ca-O2 = 2.374(1) Å, d(Ca-O4) = 2.412(1) Å] and two water oxygen atoms [d(Ca-O5) = 2.384(1) Å, d(Ca-O6) = 2.455(1) Å], the capped position is occupied by the carboxylate oxygen atom O3 [d(Ca-O3) = 2.325(1) Å], the hetero-ring nitrogen atom [d(Ca-N2) = 2.523(1) Å] and the carboxylate oxygen atom O4 [d(Ca-O2) = 2.412(1) Å] form the apices of the prism. The solvation water molecule plays a significant role in a framework of hydrogen bonds responsible for the stability of the crystal. The structure of compound II: trans-tetraquadi(H-imidazole-4,5-dicarboxylato-N,O) calcium(II) monohydrate, [Ca(C₅H₃N₂O ₄)₂(H₂O)₄·H₂O] consists of monomers in which the Ca(II) ion is located on a centre of symmetry. The coordination around the Ca(II) is a strongly deformed pentagonal bipyramidal with the imidazole-4,5-dicarboxylate (4,5-IDA) ligands in the trans arrangement forming a dihedral angle of 68.3°. An imidazole-ring nitrogen atom [d(Ca-N) = 2.632(2) Å] and one carboxylate O atom [d(Ca-O) = 2.531(2) Å] from each ligand coordinate to the metal ion. The coordination is completed by four water oxygen atoms [d(Ca-O) = 2.393(2) Å] and [d(Ca-O) = 2.367(2) Å]. The coordinated water molecules act as hydrogen bond donors and acceptors to the unbonded carboxylate oxygen atoms in adjacent monomers giving rise to a three-dimensional molecular network.