Diaqua(2,2′-bipyridine-κ2 N,N′)bis(perchlorato-κO)copper(II)

The central CuN2O4 motif of the title compound, [Cu(ClO4)2(C10H8N2)(H2O)2], exhibits a Jahn–Teller-distorted octahedral geometry around the metal atom, showing a considerably long Cu—O bond distance of 2.5058 (12) Å towards the second perchlorate group, giving a (4 + 1+1)-type coordination mode. In the crystal, the components are linked via intermolecular O—H⋯O hydrogen bonds, forming layers parallel to (001). Additional stabilization within these layers is provided by π–π [centroid–centroid distances of 3.7848 (9)–4.4231 (9) Å] stacking interactions.

The asymmetric unit of (I), and the atomic numbering used, is illustrated in Fig. 1. The Cu II atom is located in a Jahn-Teller distorted octahedral coordination environment with two N atoms from one 2,2'-bipyridine ligand (N1, N2) (d(Cu-N) = 1.9723 (13)-1.9805 (12) Å) and two O atoms from two water molecular adopting a planar arrangement (d(Cu-O) = 1.9621 (12)-1.9719 (12) Å). The Cu(II) center is displaced out of the N 2 O 2 plane by 0.028 (2)Å in the direction of one of perchlorate ligand with d(Cu-O9) = 2.3287 (12) Å. The O atom of the second perchlorate group occupies a sixth coordination site at a longer distance of 2.5058 (12) Å, completing the overall (4 + 1 + 1) type coordination. O9 is situated slightly off the axial direct of the square pyramid, nevertheless it is close enough to the Cu atom (Hathaway, 1973). The bipyridine rings of the 2,2'-bipyridine ligand are twisted relative to each other at 2.2 (8)°.
The crystal structure can be described as alternating layers of polyhedral (ClO 4 tetrahedrals and CuN 2 O 4 octahedrals) perpendicular to c axis (Fig. 2).
The crystal packing in (I) is governed by classical hydrogen bond,viz. water molecules and perchlorate (Table 1, Fig. 3). All water H atoms are involved in these hydrogen bonds In the crystal, the components of the structure are linked via intermolecular O-H···O hydrogen bonds to form a two-dimensional layers parallel to (001) plane (Fig. 3). Additional stabilization within these layers is provided by π-π [3.7848 (9)Å to 4.4231 (9) Å] stacking interactions. These interaction bonds link the molecules within the layers and also link the layers together and reinforcing the cohesion of the structure.
The combination of these hydrogen bonds generates an alternating centrosymmetric rings in two-dimensional network which can be described by the graph-set motif R 4 2 (12) and R 4 4 (16) (Bernstein et al. 1995;Etter et al., 1990).

Experimental
The title compound was prepared by adding a methanol solution (10 ml) of copper (II) acetate monohydrate (0.1 mmol) to a methanol solution (10 ml) of 2,2'-bipyridine (0.1 mmol) and (1 ml) the perchloric acid. The mixture was stirred for about 2 h at 323 K and filtered. The filtrate was slowly evaporated at room temperature to yield blue crystals of (I) suitable for X-ray analysis.