catena-Poly[[[bis(nitrato-κO)copper(II)]-bis[μ-1,3-bis(imidazol-1-yl)-5-methylbenzene-κ2 N 3:N 3′]] dihydrate]

In the title complex, {[Cu(NO3)2(C13H12N4)2]·2H2O}n, the CuII atom is located on a crystallographic center of symmetry and adopts an N4O2 octahedral coordination geometry with four imidazole N atoms in the equatorial sites and two O atoms in the axial sites. The dihedral angles between the central benzene ring and the imidazole rings are 4.93 (11) and 46.08 (12)°. The 1,3-bis(imidazol-1-yl)-5-methylbenzene ligand is bis-monodentate, linking symmetry-related CuII atoms into sheets in the bc plane. These sheets are further bridged into a three-dimensional supramolecular structure by O—H⋯O and C—H⋯O hydrogen bonds.

In the title complex, {[Cu(NO 3 ) 2 (C 13 H 12 N 4 ) 2 ]Á2H 2 O} n , the Cu II atom is located on a crystallographic center of symmetry and adopts an N 4 O 2 octahedral coordination geometry with four imidazole N atoms in the equatorial sites and two O atoms in the axial sites. The dihedral angles between the central benzene ring and the imidazole rings are 4.93 (11) and 46.08 (12) . The 1,3-bis(imidazol-1-yl)-5-methylbenzene ligand is bis-monodentate, linking symmetry-related Cu II atoms into sheets in the bc plane. These sheets are further bridged into a three-dimensional supramolecular structure by O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds.

Guang-Xiang Liu Comment
Imidazole has been well used in crystal engineering, and some zeolite-like porous frameworks with divalent and tetrahedral metal ions with this ligand have been reported (Huang et al., 2006;Wang et al., 2008;Tian et al., 2007).
Meanwhile, a large number of imidazole-containing flexible ligands have been extensively studied, and many fascinating coordination polymers based on such poly(imidazole) ligands have been synthesized (Jin et al., 2008). However, to the best of our knowledge, the research on imidazole ligands bearing rigid spacers is still less developed (Qi et al., 2008;Li et al., 2007;Zhang et al., 2008).
Single-crystal X-ray diffraction analysis reveals that the title compound (I) crystallizes in the monoclinic space group P2 1 /c. The geometry of the Cu II ion is surrounded by four imidazole rings of distinct L ligands and two nitrate anions, which illustrates a slightly distorted octahedral coordination environment (Fig. 1). Notably, as shown in Fig. 2, the fourcoordinated Cu II center is connected by the bent ligand L into a two-dimensional sheets in the bc plane. Within the ligand, the dihedral angle between the central benzene ring and terminal imidazole ring is 4.93 (11) and 46.08 (12), respectively.
These sheets are further bridged into a three-dimensional supramolecular structure by O-H···O and C-H···O hydrogen bonds (Fig. 3).

Experimental
The ligand was obtained according to the reported procedure (Altman et al., 2006). A mixture of CH 3 OH and H 2 O (1:1, 8 ml), as a buffer layer, was carefully layered over a solution of Cu(NO 3 ) 2 (0.02 mmol) in H 2 O (6 ml). Then a solution of 5methyl-1,3-bis(imidazol-1-yl)benzene (L, 0.06 mmol) in CH 3 OH (6 ml) was layered over the buffer layer, and the resultant reaction was left to stand at room temperature. After two weeks, blue blocks of (I) appeared at the boundary.

Refinement
H atoms were positioned geometrically, with C-H = 0.93 and 0.96 Å for aromatic and methyl H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = xUeq(C), where x = 1.5 for methyl H and x = 1.2 for aromatic H atoms.  The title complex with displacement ellipsoids shown at the 30% probability level. Hydrogen atoms are omitted for clarity.

Figure 2
Lateral view of the two-dimensional sheet in the bc plane of the title complex. Hydrogen atoms, water molecules and nitrate anions are omitted for clarity.  The packing diagram of the title complex, showing the hydrogen bonding as dashed lines.

catena-Poly[[[bis(nitrato-κO)copper(II)]-bis[µ-1,3-bis(imidazol-1-yl)-5-methylbenzene-κ 2 N 3 :N 3′ ]] dihydrate]
Crystal data [Cu(NO 3 ) 2 (C 13 H 12 N 4 ) 2 ]·2H 2 O M r = 672.12 Monoclinic, P2 1 /c Hall symbol: -P 2ybc a = 11.585 (4)  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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq