Crystal structure of a calcium(II) complex with pyrazine-2,3-dicarboxylate,nitrate and water ligands

The structure of catena-tris(aquo-O)(nitrato-O,O′)(µ-hydrogen pyrazine-2,3-dicarboxylato-O,N–O′,N′)calcium(II)]tetra(aquo-O)(μ-hydrogen pyrazine-2,3-dicarboxylato-O,N–O′,N′) calcium(I)] nitrate, {CaH(2,3-PZDC)](H₃O)₃(NO₃)}{CaH(2,3-PZDC)](H₂O)₄}⁺ (NO₃)^?, is composed of molecular ribbons in which calcium atoms are bridged by both N,O-bonding moieties of singly deprotonated ligand molecules. The hydrogen atom donated by one carboxylic group is linked by a short intramolecular hydrogen bond of 2.37 Å to an oxygen atom of the second carboxylic group of the same ligand. Two crystallographically independent Ca(II) ions exhibit different coordination modes. One is coordinated by two bonding moieties of the bridging ligand molecules, three water oxygen atoms and two oxygen atoms of a nitrate ligand. The other calcium ion is chelated by two bonding moieties donated by the bridging ligand molecules and four water oxygen atoms, forming a positively charged assembly with a nitrate anion located nearby. The coordination polyhedron of the first calcium ion is a strongly deformed bicapped pentagonal bipyramid with nine-coordinated atoms; the second calcium ion is also in a strongly deformed pentagonal bipyramid with one apex on one side of the equatorial plane and two apices on the other. Coordinated water oxygen atoms act as donors in a hydrogen-bond network.