Crystal structure of (nitrato-κO)bis(1,10′-phenanthroline-κ2 N,N′)copper(II) nitrate gallic acid monosolvate monohydrate

The coordination sphere of the CuII atom in the title compound is trigonal–bipyramidal, with two N atoms of two 1,10-phenanthroline ligands occupying the axial sites, and the remaining N atoms of the ligands, as well as one O atom of a nitrate anion occupying the equatorial positions.

In a project to combine phen and nitrate ligands with gallic acid as an additional co-ligand for coordination to a Cu II atom, we obtained the title compound, [Cu(NO 3 )(C 12 H 8 N 2 ) 2 ]NO 3 Á-C 7 H 6 O 5 ÁH 2 O. However, as revealed by single crystal X-ray diffraction analysis, gallic acid does not coordinate to the metal but is incorporated as a solvent molecule.

Structural commentary
The coordination sphere around copper in the complex cation, [Cu(NO 3 )(C 12 H 8 N 2 ) 2 ] + , comprises one oxygen atom (O1) of one nitrate anion and four nitrogen atoms (N1, N2, N3, N4) of two N,N'-chelating phen ligands (Fig. 1, Table 1). The conformation of the resulting N 4 O coordination set is distorted trigonal-bipyramidal, as revealed by the structural parameter 5 (Addison et al., 1984), which is defined as = ( À ) /60 where and are the two greatest angles of the coordinated atom. For a perfect square-pyramidal coordination, is 0, and for perfect trigonal-bipyramidal coordination, becomes 1.0. In the title compound, the largest angles are = 178.59 (10) for N1- and = 132.61 (9) for O1-Cu-N2. Thus, is 0.76, indicating a considerable distortion. Each phen ligand provides an equatorial (N2, N4) and an axial (N1, N3) nitrogen donor atom, forming five-membered chelate rings. The fifth coordination site is occupied by an equatorial oxygen atom (O1) from one of the nitrate anions.
The axial distances are shorter than the equatorial distances; relevant bond lengths and angles are collated in Table 1. The dihedral angle between two phen planes around the metal cation is 64.45 (7) .
There is an additional interaction of the copper cation with atom O2 of the nitrate ligand. This interaction is rather weak [2.782 (2) Å ], and the result of a bond-valence-sum calculation (Brown & Altermatt, 1985) reveals a valence unit of 0.047 for O2, which is lower than the limit of 0.06 for a cation-donor contact to be considered as a weak bonding interaction (Liebau, 2000).

Supramolecular features
As already noted in Section 1, gallic acid does not coordinate to the metal but is involved in numerous hydrogen-bonding interactions, including one intramolecular hydrogen bond 1578 Shen and Lush [Cu(NO 3  The asymmetric unit of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity.  Hydrogen-bond geometry (Å , ).

D-HÁ
between one of the hydroxy groups (O5) and neighbouring O6. In the crystal, intermolecular O-HÁ Á ÁO bonds between the other OH functions of gallic acid as well as of the water solvent molecule are present. The latter also is hydrogenbonded to O2 of the coordinating nitrate group and to O10 of the non-coordinating nitrate counter-anion (Table 2), establishing a three-dimensional network that is consolidated by further C-HÁ Á ÁO hydrogen-bonding interactions ( Table 2, Figs. 2 and 3). In addition to these classical and non-classical hydrogen-bonding interactions,ring stacking between benzene and pyridine rings with centroid-to-centroid distances in the range 3.471 (2)-3.992 (2)Å is observed, the shortest distance being between Cg8(C4-C7/C11-C12) and its symmetry-related counterpart [symmetry code: 1 À x, 1 À y, Àz]. Finally, C-HÁ Á Á interactions (

Synthesis and crystallization
The reagents Cu(NO 3 ) 2 Á6H 2 O, gallic acid and phen were used as commercially received. A warm solution of phen (0.180 g, 1 mmol) and gallic acid (0.170 g, 1mmol) in a ethanol/water mixture (20 ml) was added to a solution of Cu(NO 3 ) 2 Á6H 2 O (0.296 g, 1 mmol) in the same solvent (20 ml). The mixture was refluxed for 1 h and the green solution filtered. Upon slow evaporation of the solvent at room temperature, a green crystalline solid appeared several weeks later and was separated by filtration.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3 Parts of the crystal structure of the title compound sustained by O-HÁ Á ÁO hydrogen bonds (dotted lines).

Figure 3
Intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (dotted lines), as well as C-HÁ Á Á interactions in the crystal structure of the title compound.  software used to prepare material for publication: PLATON (Spek, 2009).

(Nitrato-κO)bis(1,10′-phenanthroline-κ 2 N,N′)copper(II) nitrate gallic acid monosolvate monohydrate
Crystal data [Cu(NO 3   Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs 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.