Bis(μ-4-chloro-2-oxidobenzoato)bis[(1,10-phenanthroline)copper(II)] dihydrate

The structure of the the title compound, [Cu2(C7H3ClO3)2(C12H8N2)2]·2H2O, consists of a dimeric unit involving a planar Cu2O2 group arranged around an inversion center. The coordination sphere of the CuII atom can be described as an elongated distorted square pyramid where the basal plane is formed by the two N atoms of the 1,10-phenanthroline molecule and the two O atoms of the hydroxychlorobenzoate (hcbe) anion. The long apical Cu—O distance of 2.569 (2) Å involves the O atom of a symmetry-related hcbe anion, building up the dinuclear unit. Each dinuclear unit is connected through O—H⋯O hydrogen bonds involving two water molecules, resulting in an R 4 2(8) graph-set motif and building up an infinite chain parallel to (10). C—H⋯O interactions further stabilize the chain.

The structure of the the title compound, [Cu 2 (C 7 H 3 ClO 3 ) 2 -(C 12 H 8 N 2 ) 2 ]Á2H 2 O, consists of a dimeric unit involving a planar Cu 2 O 2 group arranged around an inversion center. The coordination sphere of the Cu II atom can be described as an elongated distorted square pyramid where the basal plane is formed by the two N atoms of the 1,10-phenanthroline molecule and the two O atoms of the hydroxychlorobenzoate (hcbe) anion. The long apical Cu-O distance of 2.569 (2) Å involves the O atom of a symmetry-related hcbe anion, building up the dinuclear unit. Each dinuclear unit is connected through O-HÁ Á ÁO hydrogen bonds involving two water molecules, resulting in an R 4 2 (8) graph-set motif and building up an infinite chain parallel to (101). C-HÁ Á ÁO interactions further stabilize the chain.

Comment
As part of our ongoing investigation on the nature of π-π stacking (Su & Xu, 2004;Xu et al., 2007), the title Cu II compound incorporating 2-hydroxy-4-chlorobenzoate (hcbe) ligand has recently been prepared in the laboratory and its crystal structure is reported here.
The structure of the the title compound, (C 19 H 11 ClCuN 2 O 3 ).(H 2 O), consists of a dimeric unit involving a planar Cu 2 O 2 group arranged around inversion center The coordination sphere of the Cu II can be described as an elongated distorted square pyramid where the basal plane is formed by the two N atoms of the 1,10-phenanthroline molecule and the two O atoms of the hydroxychlorobenzoate (hcbe) anion. The long apical Cu-O3 distance of 2.569 (2)A involves the O3 atom of the symmetry related hcbe anion [symmetry code (i) i-x,1-y,1-z] building up the dinuclear unit ( Fig. 1).
This apical Cu-O3 distance is 0.674 (3) Å longer than Cu-O3 bond distance in the basal coordination plane, showing the Jahn-Teller distorted square-pyramidal coordination geometry around the Cu II cation. A patially overlapped arrangement is observed between the nearly parallel C2-C7 phenyl ring and C11-C19 phen ring system [dihedral angle 14.25°]. The centroid to centroid distance is 3.649 (3) Å and the perpendicular distance of the centroid to the rings is 3.456 and 3.571 Å respectively suggesting a weak π-π stacking comparable to that found in the related Cu II complexes (Garland et al., 1987;Li et al., 1995;Fan & Zhu, 2005;Song et al., 2007) and also to the Ni II complex of 2,4-dihydroxybenzoate (Yang et al., 2006).
Each dinuclear unit are connected through O-H···O hydrogen bonds involving two water molecules resulting in a R 2 4 (8) graph set motif ( Etter et al., 1990, Bernstein et al., 1995 and building up an infinite chain parallel to the (1 0 -1) plane.

Experimental
An ethanol-water solution (20 ml, 1:3) containing 2-hydroxy-4-chlorobenzoic acid (0.173 g, 1 mmol), Na 2 CO 3 (0.053 g, 0.5 mmol) and CuCl 2 .2H 2 O (0.085 g, 0.5 mmol) was refluxed for 6 h, then phenanthroline hydrate (0.99 g, 1 mmol) was added into the solution and the mixture was refluxed for further 0.5 h. After cooling to room temperature the solution was filtered. Single crystals of the title compound were obtained from the filtrate after one week.

Refinement
Water H atoms were located in a difference Fourier map and refined as riding in as-found relative positions with U iso (H) = 1.5U eq (O). Other H atoms were placed in calculated positions with C-H = 0.93 Å and refined in riding mode with U iso (H) = 1.2U eq (C).  Fig. 1. The dinuclear molecular structure of the title compound with 30% probability displacement (arbitrary spheres for H atoms) [symmetry code: (i) 1-x, 1-y, 1-z].

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.