Crystal structure and biological evaluation of 4-methylmorpholin-4-ium 1,3-dimethyl-2,6-dioxo-5-(2,4,6-trinitrophenyl)-1,2,3,6-tetrahydropyrimidin-4-olate

In the crystal of title molecular salt, the protonated N atom of the 4-methylmorpholin-4-ium cation forms a hydrogen bond with a carbonyl O atom of the barbiturate anion. This N—H⋯O hydrogen bond contributes to the good stability of the reported salt, which exhibits noticeable anticonvulsant and hypnotic activity.


Structural commentary
The molecular structure of the title molecular salt is depicted in Fig. 1. The protonated nitrogen atom of the N-methylmorpholinium cation forms a hydrogen bond with the carbonyl group O atom of the 1,3-dimethyl-5-(2,4,6-trinitrophenyl) barbiturate anion (Table 1 and Fig. 2). This N-HÁ Á ÁO hydrogen bond may well be the driving force for the formation of the title molecular salt. All the bond lengths and bond angles are normal and comparable with those observed in related barbiturates (Gunaseelan & Doraisamyraja, 2014;Vaduganathan & Doraisamyraja, 2014). The six-membered morpholin-4-ium ring has a chair conformation. In the anion, the 1,3-dimethyl barbituric acid ring and the symmetrically substituted trinitrophenyl ring, linked via the C4-C7 bond, are not co-planar but subtend an angle of 44.88 (7) . The planes of the nitro groups substituted in the aromatic ring ortho with respect to the ring junction of the anion deviate to a greater extent than that of the para nitro group [dihedral angles of 42.66 (10) and 45.44 (9 ) for the ortho nitro groups and 12.5 (8) for the para nitro group]. Thus the para nitro group is more involved in delocalizing the charge of the anion than the ortho nitro groups, which imparts a red colour for the title molecular salt.

Supramolecular features
In the crystal, in addition to the N-HÁ Á ÁO hydrogen bond linking the cation and anion, there are a number of C-HÁ Á ÁO hydrogen bonds present, leading to the formation of a threedimensional network, enclosing two sizable R 2 2 (11) and R 2 2 (10) ring motifs (Table 1 and Fig. 2).

Figure 2
A view along the b axis of the crystal packing of the title molecular salt. Hydrogen bonds are shown as dotted lines (see Table 1 for details). method on albino rats (Misra et al., 1973;Kulkarni, 1999). The therapeutic dose (100 mg kg À1 ) induces hypnosis in albino mice (Dewas, 1953) and the molecular salt is non-cytotoxic on human embryonic kidney cell-HEK 293 (Mosmann, 1983).

Synthesis and crystallization
1-Chloro-2,4,6-trinitrobenzene (TNCB: 2.5 g, 0.01 mol) dissolved in 30 ml of absolute ethanol was mixed with 1,3dimethylbarbituric acid (1.6 g, 0.01 mol) in 30 ml of absolute ethanol. After mixing these two solutions, 3 ml of N-methylmorpholine (0.03 mol) was added and the mixture was shaken vigorously for 6 to 7 h. The solution was filtered and the filtrate was kept at room temperature. After a period of four weeks, dark shiny maroon-red-coloured crystals formed from the solution. The crystals were filtered and washed with 30 ml of dry ether and recrystallized from absolute ethanol (yield: 70%; m.p.: 483 K).

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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.