Triethylammonium 2,4-dinitrophenylbarbiturate

In the title molecular salt [systematic name: triethylammonium 5-(2,4-dinitrophenyl)-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate], C6H16N+·C10H5N4O7 −, the cation and anion are linked by an N—H⋯O hydrogen bond. In the crystal, inversion-related barbiturate rings are centrosymmetrically connected through pairs of N—H⋯O hydrogen bonds, forming R 2 2(8)R 2 2(8) ring motifs.


Related literature
For further information on the anticonvulsant properties of the title compound and general background, see: Kalaivani et al. (2008). For a related structure, see: Craven (1964). For data on hydrogen-bond motifs in organic crystals, see: Allen et al.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
We have recently prepared the title compound, (I), which has anticonvulsant activity (Kalaivani et al., 2008). We now report its crystal structure.
ORTEP view of the title compound is shown in Fig. 1. The presence of the leaving group (chlorine atom) para with respect to the nitrogroup of the starting molecule (1 -chloro -2,4 -dinitrobenzene) facilitates the formation of the title compound in the presence of barbituric acid and triethylamine. Absence of chlorine atom, as indicated by the qualitative test on the synthesized barbirutrate has been supported by the crystallographic data. The title molecule is coloured red and it has been attributed to the delocalization of negative charge (Kalaivani et al., 2008) which has also been substantiated by the bond angles and bond lengths of single-crystal X-ray data of 2,4-dinitrophenyl and barbiturate rings. The bond angles and bond lengths of barbiturate residue of the title molecule are compatible with that of barbiturate ion (Craven, 1964), evidencing the delocalization of negative charge in the barbiturate ring.
Presence of double bond (delocalized) between C3 and C5 atoms fixes the configuration of the molecule as depicted in Fig. 1. The N5-H5···O2 hydrogen bond between the asymmetric units is the main driving force for the orientation of the triethylammonium cation (Fig. 2). Two inversion related barbiturate anions interact through a pair of N-H···O=C hydrogen bonds involving N1-H1 atoms and the carbonyl oxygen atom (O1) forming a R 2 2 (8) ring motif. The same ring motif is also due to a pair of N-H···O hydrogen bonds involving N2-H2 atoms and the carbonyl oxygen atom (O3). This motif is one of the 24 most frequently observed bimolecular cyclic hydrogen-bonded motifs in organic crystal structures (Allen et al., 1998). The hydrogen bonds observed in the title molecule are mainly responsible for its stability. The high solubility of the title drug molecule in water (4 g cc -1 at 298 K) is due to the positively charged triethylammonium cation and negatively charged 2,4-dinitrophenylbarbiturate anion of the asymmetric unit.

Experimental
The title compound was prepared as described previously (Kalaivani et al., 2008) and recrystallized from absolute ethanol to yield maroon blocks of (I).

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. Fig. 1. The molecular structure of (I) showing 50% displacement ellipsoids.