6-Amino-2-(pivaloylamino)pyridinium benzoate

In the crystal structure of the title salt, C10H16N3O+·C7H5O2 −, the cations and anions are linked to each other via N—H⋯O hydrogen bonds, forming infinite chains running along [010]. The crystal structure also features C—H⋯O and π–π stacking interactions, which assemble the chains into supramolecular layers parallel to (100). The π–π stacking interactions are observed between the pyridine rings of inversion-related cations with a centroid–centroid distance of 3.867 (2) Å.

In the crystal structure of the title salt, C 10 H 16 N 3 O + ÁC 7 H 5 O 2 À , the cations and anions are linked to each other via N-HÁ Á ÁO hydrogen bonds, forming infinite chains running along [010]. The crystal structure also features C-HÁ Á ÁO andstacking interactions, which assemble the chains into supramolecular layers parallel to (100). Thestacking interactions are observed between the pyridine rings of inversionrelated cations with a centroid-centroid distance of 3.867 (2) Å .

Comment
Co-crystallization is used in the pharmaceutical industry to improve the shelf life of drugs (Vishweshwar et al., 2006;Lemmerer, 2012). It is also used in many fields of chemistry, including material science. It is known that 2-acylaminopyridine forms co-crystals with acids, while in 2-aminopyridine acid complexes proton transfer takes place, yielding salts (Aakeröy et al., 2010;2006). The current report deals with the competition between formation of a salt and co-crystal. It is worth pointing out that the 2-acylamino moiety prefers to form co-crystals, while the 6-amino moiety prefers salt formation. In 2-pivaloylamino pyridine, both groups are present in the same molecule. Moreover, the increased acidity of NH in the -NHCO-group, in general, increases the hydrogen bonding donation ability of the NH proton. On the other hand, we used the sterically demanding pivaloyl group to hinder the efficient NH···O═C interaction of the -NHCO-tBu part of the title molecule. Thus the interacting acid is pushed to transfer the proton to the heterocyclic nitrogen and to form a salt with 2-pivaloylamino-6-aminopyridine. It is worth noting that the NH 2 group attached to C6 of the pyridine ring causes an increase of electron density at the ring nitrogen. More systematic studies on co-crystallization of 2-acylaminopyridine with benzoic acids are in progress. For the steric effects in hydrogen bonded compounds, refer to our previous publications (Ośmiałowski et al., 2012a,b;2010a,b).
As illustrated in Figure 1, the asymmetric unit of the title salt, (I), contains one protonated 2-pivaloylamino-6-aminopyridine cation and one benzoate anion, both located in general positions.
The geometric parameters of the 2-pivaloylamino-6-aminopyridine cation are in good agreement with those found for the related structures (Ośmiałowski et al., 2010a,b). In the benzoate anion the C-O distances, 1.268 (3) Å and 1.253 (3) Å, clearly indicate the delocalization of the negative charge within the carboxylate group.

Experimental
For the synthesis of the title compound, equimolar ammounts of 2-pivaloylamino-6-aminopyridine and benzoic acid were mixed in methanol. The solution was left for a couple of days for slow evaporation and produced single crystals. The parent 2-pivaloylamino-6-aminopyridine was prepared according to a literature procedure (Ośmiałowski et al., 2010a).