Poly[diaquadi-μ-hydroxido-κ4 O:O-dinitrato-κ4 O:O′-bis[3-(pyridin-4-yl-κN)-5-(pyridin-3-yl)-1,2,4-oxadiazole]dicopper(II)]

The title compound, [Cu2(NO3)2(OH)2(C12H8N4O)2(H2O)2]n, consists of a neutral polymeric CuII complex in which each CuII atom has a distorted octahedral geometry defined by a pyridyl N atom from a 3-(pyridin-3-yl)-5-(pyridin-4-yl)-1,2,4-oxadiazole ligand and five O atoms from a water molecule, two nitrates and two hydroxides. Two CuII ions are bridged by two hydroxide anions resulting in a Cu2O2 loop, located across an inversion center and connected by the nitrate anions into a broad two-dimensional polymeric structure parallel to (100). In the crystal, there are O—H⋯O hydrogen bonds between the coodinated water molecule and the nitrate and hydroxide, and between the hydroxide and the nitrate. Intermolecular π–π interactions are present between pyridine rings in adjacent two-dimensional structures, with a centroid–centroid distance of 3.582 (2) Å.

The title compound, [Cu 2 (NO 3 ) 2 (OH) 2 (C 12 H 8 N 4 O) 2 (H 2 O) 2 ] n , consists of a neutral polymeric Cu II complex in which each Cu II atom has a distorted octahedral geometry defined by a pyridyl N atom from a 3-(pyridin-3-yl)-5-(pyridin-4-yl)-1,2,4oxadiazole ligand and five O atoms from a water molecule, two nitrates and two hydroxides. Two Cu II ions are bridged by two hydroxide anions resulting in a Cu 2 O 2 loop, located across an inversion center and connected by the nitrate anions into a broad two-dimensional polymeric structure parallel to (100). In the crystal, there are O-HÁ Á ÁO hydrogen bonds between the coodinated water molecule and the nitrate and hydroxide, and between the hydroxide and the nitrate. Intermolecularinteractions are present between pyridine rings in adjacent two-dimensional structures, with a centroid-centroid distance of 3.582 (2) Å .

Related literature
For the preparation of the ligand, see: Chiou & Shine (1989). For a related structure, see: Sarkar et al. (2008).
In the structure, each Cu II ion has a distorted octahedral geometry defined by a pyridyl N atom from a 3-(pyridin-3yl)-5-(pyridin-4-yl)-1,2,4-oxadiazole ligand and five O atoms from a water molecule, two nitrates, and two hydroxides( Fig.1). For each Cu II center, the equatorial sites are occupied by a water molecule, a pyridyl N atom, and two hydroxides, the apical sites being occupied by two oxygen atoms of nitrate anions. The equatorial bond distances are in the range 1.945 (2)-1.999 (2) Å while the axial bond distances are 2.431 (2) and 2.716 (2) Å. Neighbouring Cu II ions are connected by two hydroxide anions into Cu 2 O 2 loops with a Cu···Cu distance of 2.956 (1) Å. Similar Cu 2 O 2 structure can be constructed by acetates (Sarkar et al. 2008). The result is the formation of centrosymmetric dimeric units, further connected by the nitrate anions to form broad two-dimensional structures parallel to (100).
In the crystal, there are O-H···O hydrogen bonds between the coodinated water molecule and the nitrate or hydroxide, and between the hydroxide and the nitrate. The details are listed in Table 1. There are also intermolecular π-π interactions between pyridine rings in neighboring two-dimensional structures, with a centroid-centroid distance of 3.582 (2)Å (Fig 2).

Refinement
H atoms bonded to O atoms were located in a difference map and refined with distance restraints of O-H = 0.86 (2) Å.
Other H atoms were positioned geometrically and refined using a riding model with C-H = 0.93(aromatic) and C-H = 0.96(CH 3 ) Å. All H atoms were refined with U iso (H) = 1.2 (1.5 for methyl groups) timesU eq (C).

Figure 2
Packing view of the complex down the a axis, showing the two-dimensional structures in projection. O-H···O hydrogen bonds are shown in dashed lines. Note interdigitation of the aromatic groups in neighbouring two-dimensional structures, leading to π-π interactions.