The unexpected but predictable tetrazole packing in flexible 1-benzyl-1H-tetrazole

The crystal structure of 1-benzyl-1H-tetrazole, C8H8N4, was undertaken to study the geometry and intermolecular interactions of the (1-substituted) 1H-tetrazole moiety. It crystallizes in the monoclinic space group P21 with unit cell dimensions a = 7.6843(5), b = 5.5794(4), c = 9.4459(7) Å, ß = 100.949(4)°, V = 397.61(5) Å3, Z = 2, density (calculated) = 1.338 gcm-3. The packing of the molecules in the crystal structure is dominated by a number of weak intermolecular hydrogen bonds of the type CHN and CHC. This results in segregated infinite S-shaped layers of phenyl and tetrazole rings where each tetrazole ring is coordinated by six others. There are no pp interactions. A group developing crystal structure prediction methods for highly flexible molecules was challenged to predict this Z' = 1 crystal structure from the chemical diagram. The experimental structure was found, having essentially the same lattice energy (?Elatt 0.1 kJmol-1) as the most stable computationally generated structure, which had the expected pp interaction and no segregation of tetrazole rings. The successful crystal structure prediction confirms that the intra and intermolecular interactions of the tetrazole group can be adequately represented by single molecule ab initio-based methods, which represent the electrostatic effects of the lone pairs and p electron density. The predicted structure provided a starting model, which was easily refined in SHELXL-97, providing indisputable proof that it is an accurate reproduction of the crystal structure.