A new polymorph of aquabis(1,10-phenanthroline-κ2 N,N′)copper(II) dinitrate

The title molecule, [Cu(C12H8N2)2(H2O)](NO3)2, is a new polymorph of a compound which up to now has been reported to crystallize space groups in C2/c and Cc. The crystal studied was twinned by non-merohedry (final BASF factor of 0.40043) with the structure being solved and refined in P-1. The CuII atom is coordinated by four N atoms from two 1,10-phenanthroline ligands and an O atom from a water molecule in an approximate trigonal–bipyramidal geometry. Discrete entities of one cation and two nitrate anions are formed by water–nitrate O—H⋯O hydrogen bonds. The components are further assembled into a three-dimensional network by C—H⋯O hydrogen bonds.

The title molecule, [Cu(C 12 H 8 N 2 ) 2 (H 2 O)](NO 3 ) 2 , is a new polymorph of a compound which up to now has been reported to crystallize space groups in C2/c and Cc. The crystal studied was twinned by non-merohedry (final BASF factor of 0.40043) with the structure being solved and refined in P1. The Cu II atom is coordinated by four N atoms from two 1,10phenanthroline ligands and an O atom from a water molecule in an approximate trigonal-bipyramidal geometry. Discrete entities of one cation and two nitrate anions are formed by water-nitrate O-HÁ Á ÁO hydrogen bonds. The components are further assembled into a three-dimensional network by C-HÁ Á ÁO hydrogen bonds.

Comment
The reported structure of complex (I) is a polymorph of previously reported material. It crystallizes as a non-merohedral twin in the triclinic system with the space group P1, contrary to what has been observed in other structural analyses which three times report the crystal symmetry to correspond to the space group C2/c (Nakai & Deguchi (1975);Szpakolski et al. (2010); Zhou (2011)), while the fourth crystal structure was reported in the space group Cc (Catalan et al., 1995).
Compound (I) has a discrete structure containing monomeric [Cu(H 2 O)(1,10′-phen)] 2+ cations and two counter-balanced nitrate anions which are connected to the cation via O-H···O hydrogen bonds. The Cu(II) ion is coordinated by two 1,10′phenantroline molecules each acting as a bidentate ligand (through the four nitrogen atoms (N1,N2, N4,N3)) and one water molecule O1w (Fig. 1). The geometry around the metal is of distorted trigonal bipyramidal geometry and all distances are in a normal range. The dihedral angle between the two 1,10′-phenantroline molecules is 34.92 (3)°, while the dihedral angle varies in its analogous between 37.89 (3)° and 53.46 (3)°. In the crystal, molecules are linked by extensive hydrogen bonds involving the nitrate anions and phenantroline and water molecules, producing a threedimensional network (Fig 2).

Experimental
A methanolic solution containing Cu(NO 3 ) 2 × 3 H 2 O (0.1208 g, 0.5 mmol) was added with stirring to a methanolic solution containing 1,10′-phenantroline (0.9 g, 0.5 mmol). After a few minutes a blue green precipitate appears and was filtrated. The blue green filtrate was kept for several weeks at room temperature. Green crystals suitable for X-ray analysis were obtained (yield: 0.20 g, 70% on the basis of Cu(NO 3 ) 2 .3H 2 O).

Refinement
Water hydrogen atoms were tentatively found in the difference density Fourier map and were refined with an isotropic displacement parameter of U iso (H) = 1.5 U eq (O1W). O-H distances were restrained to be 0.9 Å within a standard View of the title compound with the atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level.

Figure 2
Partial view of the crystal structure of the title compound showing the hydrogen bonds.

Crystal data
[Cu (C 12 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.