Tetrakis(1H-benzimidazole-κN 3)(nitrato-κO)copper(II) nitrate

In the title salt, [Cu(NO3)(C7H6N2)4]NO3, one nitrate anion is coordinated to the CuII atom, which is also coordinated by the N atoms of four N-heterocycles. The geometry at the metal atom is a square pyramid in which the O atom of the anion occupies the apical position [Cu—O = 2.468 (5) and 2.590 (7) Å in the two independent formula units]. The cation lies on a twofold rotation axis; the coordinated nitrate anion is also disordered about this symmetry element. The lattice anion is also disordered about a twofold rotation axis. In the crystal, the cations are linked to the coordinated and free anions by N—H⋯O hydrogen bonds.

In the title salt, [Cu(NO 3 )(C 7 H 6 N 2 ) 4 ]NO 3 , one nitrate anion is coordinated to the Cu II atom, which is also coordinated by the N atoms of four N-heterocycles. The geometry at the metal atom is a square pyramid in which the O atom of the anion occupies the apical position [Cu-O = 2.468 (5) and 2.590 (7) Å in the two independent formula units]. The cation lies on a twofold rotation axis; the coordinated nitrate anion is also disordered about this symmetry element. The lattice anion is also disordered about a twofold rotation axis. In the crystal, the cations are linked to the coordinated and free anions by N-HÁ Á ÁO hydrogen bonds.
ates four to six imidazole ligands, the space sphere is not large enough to fit a similar number of the related benzimidazole ligands. In the copper nitrate-tetrakis(imidazole) adduct, the nitrate ion is involved in coordination (McFadden et al., 1976) but in the hexakis(imidazole) adduct, the nitrate ion is not (McFadden et al., 1975). The tetrakis(benzimidazole)copper species has been reported for the perchlorate (Dobrzyńska et al., 2010) and the sulfate (Sierón, 2007) only. These two, as well the present nitrate (Scheme I), have the Cu II atom in a square pyramidal geometry but with the square pyramid being distorted because the ligand crowds out the donor atom of the anion.
In the crystal of the salt, Cu(NO 3 )(C 7 H 6 N 2 ) 4 . NO 3 , one nitrate anion is coordinated to the Cu II atom, which is also coordinated by the N atoms of four N-heterocycles (Fig. 1). The geometry at the metal atom is a square pyramid in which the O atom of the anion occupies the apical position [Cu-O 2.468 (5), 2.590 (7) Å in the two independent formula units].
The coordinated and lattice nitrates are disordered about this symmetry element. The disorder, which requires space for the anions to rattle around, probably accounts for the somewhat large solvent-accessible voids. Nevertheless, the cations interact with the anions through N-H···O hydrogen bonds (Table 1).

Experimental
Copper nitrate trihydrate (0.246 g), 1,3-benzimidazole (0.473 g) and water (2 ml) were placed in a 25-ml, Teflon-lined Parr bomb. The bomb was heated at 413 K for 5 days. Blue prismatic crystals were isolated after the bomb was cooled to room temperature over the course of a day.