Crystal structure of 4-methylsulfanyl-2-(2H-tetrazol-2-yl)pyrimidine

The title compound, C6H6N6S, crystallized with two independent molecules (A and B) in the asymmetric unit. The conformation of the two molecules differs slightly. While the tetrazole ring is inclined to the pyrimidene ring by 5.48 (7) and 4.24 (7)° in molecules A and B, respectively, the N—C—S—C torsion angles of the thiomethyl groups differ by ca 180°. In the crystal, the A and B molecules are linked via a C—H⋯N hydrogen bond. They stack along the b-axis direction forming columns within which there are weak π–π interactions present [shortest inter-centroid distance = 3.6933 (13) Å].


S1. Comment
4-tetrazolylpyrimidines are well reported scaffolds in many bioactive entities. Besides synthetic chemistry, tetrazolyl substituted aromatic systems are also of high interest for example, in metal-ligand research (Kim et al., 2008;Stoessel et al., 2010), drug development (Pasternak et al., 2012;Biswas et al., 2015) and polymer discovery (Yu et al., 2008;Sengupta et al., 2010). Thus, the knowledge of the three dimensional structure of these moieties is of crucial importance for the rational design in these fields of research. Recently, we have reported a novel method to synthesize such compounds (Thomann et al., 2014). We have reported the synthesis of 4-(methylthio)-2-(1H-tetrazol-1-yl)pyrimidine (1).
Interestingly, when scaling up the reaction, another product was found in small amounts. NMR analytical characterization revealed the compound to be the 2-tetrazolyl regioisomer (2). To determine unequivocally proof of the structure of this compound, we determined its crystal structure.
The title compound (2), crystallized with two independent molecules (A and B) in the asymmetric unit ( Fig. 1). Interestingly, the two molecules differ in their conformation. While the tetrazole moieties are arranged similarly, with the tetrazole ring is inclined to the pyrimidene ring by 5.48 (7) and 4.24 (7) ° in molecules A and B, respectively, the thiomethyl groups have a difference of the torsion angle about the C ar ···S bond of ca 180° [for example, torsion angle N5-C4-S1-C6 = 0.89 (12) °, compared to torsion angle N11-C10-S2-C12 = −176.78 (10) °] indicating higher rotational freedom than the tetrazoles (Fig. 1). The latter finding is of importance for computational chemists in medicinal chemistry, as the polarized hydrogen at atom C5 of the tetrazole ring is able to form non-classical hydrogen bonds.
Therefore, the results from the crystal structure may favour this conformational isomer for in silico predictions.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were located in a difference Fourier map and freely refined.

Figure 1
The molecular structure of the two independent molecules (A and B) of the title compound (2), with atom labelling.
Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The crystal packing of the two independent molecules (A black; B red) of the title compound (2), viewed along the a axis.
Hydrogen bonds are shown as dashed lines (see Table 1).