5,5′-(p-Phenylene)di-1H-tetrazole

Crystals of the title organic compound, C8H6N8, were generated in situ through the [2 + 3]-cycloaddition reaction involving the precursor 1,4-dicyanobenzene and azide in water with Zn2+ as Lewis acid. The asymmetric unit consists of one half-molecule, and a twofold axis of symmetry passes through the centre of the benzene ring. There is an intermolecular N—H⋯N hydrogen bond. The molecules are assembled into a three-dimensional supramolecular framework by π–π stacking interactions, with a perpendicular distance of 3.256 Å [centroid–centroid = 3.9731 (8) Å] between two tetrazole ring planes, and 3.382 Å between the benzene ring and tetrazole ring planes [centroid–centroid = 3.5010 (9) Å].

Crystals of the title organic compound, C 8 H 6 N 8 , were generated in situ through the [2 + 3]-cycloaddition reaction involving the precursor 1,4-dicyanobenzene and azide in water with Zn 2+ as Lewis acid. The asymmetric unit consists of one half-molecule, and a twofold axis of symmetry passes through the centre of the benzene ring. There is an intermolecular N-HÁ Á ÁN hydrogen bond. The molecules are assembled into a three-dimensional supramolecular framework bystacking interactions, with a perpendicular distance of 3.256 Å [centroid-centroid = 3.9731 (8) Å ] between two tetrazole ring planes, and 3.382 Å between the benzene ring and tetrazole ring planes [centroid-centroid = 3.5010 (9) Å ].

Comment
Owing to the efforts of Sharpless and Demko in the past years, the preparation of 5-substituted tetrazolate ligands has now become a safe and convenient procedure (Demko et al., 2001). Recently, Metzger and Furmeier reported that 5-substituted tetrazolates can also be synthesized from nitriles in toluene (Furmeier et al., 2003), and Xiong et al. reported several coordination polymers obtained from the reaction of the tetrazoles generated in situ with a variety of 5-substituted groups under hydrothermal conditions (Xiong et al., 2002). However, the coordination polymers containing the ligands synthesized in situ from the precursor ligands containing two-cyano groups have rarely been reported Wang et al., 2005). Herein we report the title compound (I).
The supramolecular structure is stabilized by aromatic π-π-stacking interactions.

Experimental
A mixture of ZnCl 2 (1.5 mmol), 1,4-dicyanobenzene (1 mmol) and azide (3 mmol) in 15 ml H 2 O was heated at 160oC for three days in a sealed 25 ml Teflon-Lined stainless steel vessel under autogenous pressure. After the reaction mixture was slowly cooled down to room temperature, colorless prismlike crystals were produced, which were collected by filtration and washed with distilled water and dried in air.

Refinement
H atoms were placed in idealized positions, with with C-H distances of 0.93 Å, N-H distances of 0.86 Å, and allowed to ride on their respective parent C atoms with the constraint U iso (H) = 1.2U eq (C).