N-[2-(2,2-Dimethylpropanamido)pyrimidin-4-yl]-2,2-dimethylpropanamide n-hexane 0.25-solvate hemihydrate

The asymmetric unit of the title compound, C14H22N4O2·0.25C6H14·0.5H2O, contains two independent molecules of 2,4-bis(pivaloylamino)pyrimidine (M) with similar conformations, one water molecule and one-half n-hexane solvent molecule situated on an inversion center. In one independent M molecule, one of the two tert-butyl groups is rotationally disordered between two orientations in a 3:2 ratio. The n-hexane solvent molecule is disordered between two conformations in the same ratio. The water molecule bridges two independent M molecules via O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds into a 2M·H2O unit, and these units are further linked by N—H⋯N hydrogen bonds into chains running in the [010] direction. Weak C—H⋯O interactions are observed between the adjacent chains.

The asymmetric unit of the title compound, C 14 H 22 N 4 O 2 Á-0.25C 6 H 14 Á0.5H 2 O, contains two independent molecules of 2,4bis(pivaloylamino)pyrimidine (M) with similar conformations, one water molecule and one-half n-hexane solvent molecule situated on an inversion center. In one independent M molecule, one of the two tert-butyl groups is rotationally disordered between two orientations in a 3:2 ratio. The n-hexane solvent molecule is disordered between two conformations in the same ratio. The water molecule bridges two independent M molecules via O-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds into a 2MÁH 2 O unit, and these units are further linked by N-HÁ Á ÁN hydrogen bonds into chains running in the [010] direction. Weak C-HÁ Á ÁO interactions are observed between the adjacent chains.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
The 2,4-bis(pivaloylamino)pyrimidine is able to form various rotamers in solution (Ośmiałowski et al., 2012). The high flexibility of this molecule with respect to the related pyridine derivatives is caused by the presence of two nitrogen atoms within the aromatic ring. This was confirmed by studies of association of such derivatives with various supramolecular counterparts (Ośmiałowski et al., 2010;2012). In the crystal structure of the related pyridine derivative (2,6-bis(pivaloylamino)pyridine) a weak N-H···O═C interaction was found, which further links the molecules into chain motif (Crane, 2003).
The 2,4-bis(pivaloylamino)pyrimidine was crystallized from n-hexane as hemisolvate monohydrate. In the asymmetric unit there are two independent molecules of the title compound ( Figure 1). Water molecule interacts with these molecules via O-H···O, N-H···O and O-H···N intermolecular hydrogen bonds (Table 1) thereby joins them into hydrogenbonded dimer ( Figure 2). It is worth mentioning that water molecule incorporated between two subjected molecules forces those to adopt the Z,E,Z,Z conformation (Ośmiałowski et al., 2012), in which the electron repulsion between heterocyclic nitrogen atoms (N1, N1A) and carbonyl oxygen atoms (O8, O8A) are observed.
Furthermore, each independent molecule forms an intermolecular N-H···N hydrogen bond (Table 1), thus producing infinite chain of dimers running parallel to the [010] direction. Two centrosymmetrically related chains interact each other via weak C-H···O interactions ( Table 1).
The partially disordered n-hexane solvent molecule lies on the inversion centre. In the crystal lattice it is surrounded by the terminal t-butyl groups. This arrangement precludes any significant intermolecular interactions with other molecules in crystal.

Experimental
The title compound was synthesized according to the method of Ośmiałowski et al. (2012). Crystals suitable for X-ray measurements were obtained by crystallization from n-hexane.

Refinement
All non-hydrogen atoms were refined anisotropically. One t-butyl group (atoms C16, C17, C18) of molecule 1 as well as some atoms of hexane solvent molecule (C20 and all H-atoms) were refined as disordered over two sets of sites with occupancies fixed at 0.60:0.40. The C-C bond distances within the disordered t-butyl group as well as the C-C distances between disordered atoms within hexane moiety (pairs: C19-C20/C19-C20 and C21-C20/C21-C20A, respectively) were restrained to be approximately equal. Moreover, the U ij components of atoms in two t-butyl groups in molecule 1 were restrained to be similar. Additionally, the ADPs of the C16B atom were restrained to be approximately isotropic.

Figure 1
Two independent molecules M in (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.