Crystal structure of μ-4-oxidobenzoato-κ2 O 1:O 4-bis[bis(1,10-phenanthroline-κ2 N,N′)copper(II)] bis(4-hydroxybenzoate) 7.5-hydrate

In the hydrated complex composed of dinuclear CuII complex cations, uncoordinated 4-hydroxybenzoate anions and water molecules of crystallization, the CuII ions are bridged by a 4-oxidobenzoate ligand, each metal ion is five-coordinated by two chelated 1,10-phenanthroline (phen) molecules and one anion O atom in distorted trigonal bipyramid geometry.


Chemical context
In some biological systems,stacking between aromatic rings is correlated with the elctron-transfer process (Deisenhofer & Michel, 1989). To study the effect ofstacking, the title complex, (I), incorporating 1,10-phenanthroline (phen), has been prepared and its crystal structure is presented here.

Structural commentary
The crystal structure of (I) is composed of dinuclear Cu II complex cations, noncoordinating 4-hydroxybenzoate anions and solvent water molecules, as shown in Fig. 1. The molecular structure of the dinuclear Cu II complex cation is shown in Fig. 2. Two Cu II atoms (Cu1 and Cu2) are bridged by one 4oxidobenzoate anion through oxido and carboxy O atoms (O53 and O51, respectively), with a Cu1-O53 bond length of 1.941 (3) Å and a Cu2-O51 bond length of 1.979 (3) Å . Each Cu II atom is five-coordinated, displaying a distorted trigonalbipyramidal geometry (Table 1). The Cu1 atom is coordinated by two chelating phen rings (N1, N2, N3 and N4) intersecting at an angle of 71.35 (5) . The out-of-plane Cu1-N1 and Cu-N3 bond lengths are 2.002 (3) and 2.027 (3) Å , respectively, The structures of the molecular entities of (I), shown with 30% probability displacement ellipsoids. Dashed lines indicate hydrogen bonds. H atoms have been omitted for clarity.
dinuclear Cu II complex cations (complex-layer), the other consisting of noncoordinating 4-hydroxybenzoate anions and solvent water molecules (solvent-layer). Abundant hydrogenbonding interactions occur within the solvent-layer and among the solvent-and complex-layers (  Thestacking (dashed lines) between neighbouring dinuclear Cu II complex cations, forming a two-dimensional supramolecular system parallel to (100

Synthesis and crystallization
Each reagent was available commercially and was of analytical grade. CuCl 2 Á2H 2 O (0.17 g, 1 mmol), 4-hydroxybenzoic acid (0.28 g, 2 mmol), 1,10-phenanthroline (0.20 g, 1 mmol) and NaOH (0.16 g, 4 mmol) were dissolved in 20 ml water. The resulting solution was refluxed for 4 h and was then cooled to room temperature and filtered. Dark-green single crystals were obtained from the filtrate after five weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The disordered water O8W atom was refined isotropically with a fixed occupacy of 0.5. Aromatic and hydroxy H atoms were placed in calculated positions, with C-H = 0.93 Å and O-H = 0.82 Å , and were included in the final cycles of refinement in riding mode, with U iso (H) = 1.2 and 1.5U eq (parent), respectively. Water H atoms were located in difference Fourier map, and were refined with fixed positions and a fixed isotropic displacement parameter of 0.1 Å 2 . The H atoms of the water molecules O6W, O7W and O8W were not assigned. The peak corresponding to the maximum electron density in the difference Fourier map was close (1.01 Å ) to atom O8W.

µ-4-Oxidobenzoato-κ 2 O 1 :O 4 -bis[bis(1,10-phenanthroline-κ 2 N,N′)copper(II)] bis(4-hydroxybenzoate) 7.5-hydrate
Crystal data  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.