Triaqua(1,10-phenanthroline-2,9-dicarboxylato)cobalt(II) dihydrate

The title compound, [Co(C14H6N2O4)(H2O)3]·2H2O, has twofold crystallographic symmetry. The CoII atom is in a distorted pentagonal-bipyramidal coordination environment with two N atoms and two O atoms from a tetradentate 1,10-phenanthroline-2,9-dicarboxylate ligand and one O atom from a water molecule forming the pentagonal plane, and two O atoms from two water molecules occupying axial positions. In the crystal, adjacent molecules are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, [Co(C 14 H 6 N 2 O 4 )(H 2 O) 3 ]Á2H 2 O, has twofold crystallographic symmetry. The Co II atom is in a distorted pentagonal-bipyramidal coordination environment with two N atoms and two O atoms from a tetradentate 1,10-phenanthroline-2,9-dicarboxylate ligand and one O atom from a water molecule forming the pentagonal plane, and two O atoms from two water molecules occupying axial positions. In the crystal, adjacent molecules are linked by O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Comment
In recent years, the research of coordination compounds has been one of the most attractive fields due to their peculiar structures and properties (Zhao et al., 2008;Poulsen et al., 2005). Many multi-carboxylate or heterocyclic carboxylic acids are used for this purpose (Luo et al., 2009;Han et al., 2009). In the designed synthesis of the coordination compounds, H 2 PDA is an excellent dicarboxylate ligand (Xie et al., 2005). In order to extend the investigation, we have prepared the Co II complex of H 2 PDA, and report its crystal structure here.
The title compound ( Fig. 1) is located on a twofold axis of symmetry which passes through the Co and O3 atoms, which is (Park et al., 2001). The seven-coordinated Co atom is in a distorted pentagonal bipyramidal geometry. Two N and two O atoms from PDA and one O atom from a water molecule define the pentagonal plane, and the two axial positions are occupied by O atoms derived from two water molecules. . This is probably due to the high rigidity of PDA as well as the high affinity of the Co II ion to water molecules (Zhang & Chen, 2009). The carboxylate groups of the PDA ligand are almost coplanar with the phenanthroline unit as indicated by the O1-C1-C2-N6 torsion angle of 2.6 (3)°. All bond distances and angles are similar to those observed in other seven-coordinated Co II complexes (Newkome et al., 1984;Rajput & Biradha, 2007). Adjacent molecules are linked by O-H···O hydrogen bonds, forming a three-dimensional network.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.