Crystal structure and Hirshfeld surface analysis of two imidazo[1,2-a]pyridine derivatives: N-tert-butyl-2-(4-methoxyphenyl)-5-methylimidazo[1,2-a]pyridin-3-amine and N-tert-butyl-2-[4-(dimethylamino)phenyl]imidazo[1,2-a]pyridin-3-amine

In the title imidazo[1,2-a]pyridine derivatives, N-tert-butyl-2-(4-methoxyphenyl)-5-methylimidazo[1,2-a]pyridin-3-amine, (I), and N-tert-butyl-2-[4-(dimethylamino)phenyl]imidazo[1,2-a]pyridin-3-amine, (II), the 4-methoxyphenyl ring in (I) and the 4-(dimethylamino)phenyl ring in (II) are inclined to the mean planes of the respective imidazole rings by 26.69 (9) and 31.35 (10)°.

(I), and 131.1 (2) and 130.4 (2) , respectively, in compound (II)] of the imidazole ring systems are due to the merging of five-and six-membered rings and the strain is taken up by angular distortion rather than by bond length distortion.

Figure 3
A structural overlap view of molecules (I) and (II).

Figure 1
The molecular structure of compound (I), with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. benzene ring and (+) antiperiplanar with the side-chain atoms N1, C16 and C18.

Supramolecular features
In the crystal of (I), molecules are linked by N1-H1AÁ Á ÁN3 i hydrogen bonds (Table 1), forming C(8) chains propagating along the c-axis direction, as shown in Fig. 4. The chains are linked by C-HÁ Á Á interactions, forming layers lying parallel to the ac plane (Fig. 4, Table 1).

Hirshfeld Surface Analysis
Hirshfeld surface analysis was used to quantify the intermolecular contacts of the title compounds, using the software CrystalExplorer17.5 (Turner et al., 2017). The bright-red spots on the Hirshfeld surface mapped over d norm [ Fig. 6(a) and 7(a)], show the presence of N-HÁ Á ÁN and C-HÁ Á Á N interactions with neighbouring molecules. The surfaces mapped over the electrostatic potential are illustrated in Fig. 6 The crystal packing of compound (I) viewed along the b axis, showing the intermolecular N-HÁ Á ÁN hydrogen bonds as dashed lines (Table 1). The C-HÁ Á Á interactions are also represented by cyan dashed lines (Table 1). Table 2 Hydrogen-bond geometry (Å , ) for (II).

Synthesis and crystallization
Compound (I) 5-Methyl-2-aminopyridine (10 mmol) and 4-methoxybenzaldehyde (1 eq.) were solubilized in ethanol. To this solution, tert-butyl isocyanide (1 eq.) and iodine (0.5 mmol %) were added. The reaction mixture was stirred at room temperature overnight. The white precipitate that had formed was filtered off and purified further using silica-gel column chromatography to give a white solid in 60% yield.
Spectroscopic data: NMR spectra were recorded on a Bruker 400 MHz NMR spectrophotometer in CdCl 3 and chemical shifts were recorded in parts per million relative to tetramethylsilane (TMS), used as an internal standard.
Compound ( Crystals of compounds (I) and (II), suitable for X-ray diffraction analysis, were obtained by slow evaporation from ethyl alcohol (EtOH) solution at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds the NH H atoms were located in difference-Fourier maps and freely refined. The C-bound H atoms were included in calculated positions and treated as riding: C-H = 0.93-0.96 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms.      N-tert-butyl-2-(4-methoxyphenyl)-5-methylimidazo[1,2-a]pyridin-3-

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.