Crystal structure of 1,10-phenanthrolinium 3-hydroxy-2,4,6-trinitrophenolate

The 1,10-phenanthrolinium cation and 3-hydroxy-2,4,6-trinitrophenolate anion are held together through an N—H⋯O hydrogen bond. In the crystal, cation–anion pairs are connected by C—H⋯O hydrogen bonds, forming a chain structure along [101]. Spectroscopic data also support the formation of a molecular salt. Sensitivity tests and thermal testing indicate that it is an insensitive high energy density material (IHEDM).


Structural commentary
The molecular structure of the title molecular salt is depicted in Fig. 1. The acidic hydrogen atom of the phenolic group in styphnic acid protonates the nitrogen atom of 1,10-phenanthroline, making it a cation. An S(6) ring motif is formed in the anion by an intramolecular O-HÁ Á ÁO hydrogen bond (Table 1). Of the three nitro groups present in the anion, the plane of the one which is involved in the intramolecular hydrogen bond deviates only slightly from the plane of benzene ring [dihedral angle 3.94 (8) ] to which it is attached. The nitro group flanked between the C-O À group and the O-H group deviates to a greater extent [dihedral angle 78.62 (1) ] than the remaining nitro group which is oriented between the C-H and C-O À groups [dihedral angle 15.27 (7) ].

Supramolecular features
In the crystal, the C-O À (acceptor) group of the phenolate anion and the N-H (donor) of the cation form an N-HÁ Á ÁO hydrogen bond (Table 1 and

Synthesis and crystallization
Equimolar solutions of each of styphnic acid (2.45 g, 0.01 mol, 40 mL) and 1,10-phenanthroline monohydrate (1.98 g, 0.01 mol, 30 mL) in ethanol were mixed and shaken well for 3 h. On standing at 298 K for two h, the mixture yielded a yellow solid which was ground, washed well with dry ether and recrystallized from a ethanol-water mixture. Shining yellow single crystals were obtained from the mother liquor by slow evaporation (m.p. 395 K, yield 80%). Although the monoprotonated salt is obtained in good yield, several attempts to 784 Muthulakshmi and Kalaivani C 12 H 9 N 2 + ÁC 6 H 2 N 3 O 8 À Acta Cryst. (2015). E71, 783-785 research communications Figure 1 A view of the molecular structure of the title molecular salt, with the atom labelling. Displacement ellipsoids are drawn at the 40% probability level. The N-HÁ Á ÁO hydrogen bond is shown as a dashed line. Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) x À 1 2 ; Ày þ 1 2 ; z À 1 2 .

Figure 2
The crystal packing of the title molecular salt viewed along the a axis. Hydrogen bonds are shown as dotted lines.

Figure 3
The crystal packing of the title molecular salt viewed along the b axis. Hydrogen bonds are shown as dotted lines.
prepare the diprotonated salt from styphnic acid and 1,10phenanthroline by mixing them in different concentrations in solvents of different polarity were not successful. The title molecular salt is produced due to a proton-transfer reaction in which one of the two phenolic group hydrogen atoms is transferred to one of the tertiary nitrogen atoms of 1,10phenanthroline. This type of interaction is also evidenced by the spectroscopic data

Sensitivity testing and thermal studies
The title molecular salt has three nitro groups attached to the benzene ring and hence it was subjected to sensitivity testing (impact sensitivity and friction sensitivity) and thermal studies (TGA/DTA). The molecular salt is insensitive towards impact and friction (Meyer et al., 2007). The activation energy for the decomposition of the title molecular salt was determined from TGA/DTA curves obtained at four different heating rates (5, 10, 15 and 20 K min À1 ) applying Ozawa and Kissinger methods (Kissinger, 1957;Ozawa, 1965). The activation energy determined was 459 kJ mol À1 from the Ozawa plot and 478 kcal mol À1 from the Kissinger plot. The sensitivity tests and thermal studies indicate that this molecular salt is an insensitive high-energy-density material (IHEDM).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-and O-bound H atoms were positioned geometrically with C-H = 0.93 Å and O-H = 0.82 Å , and were refined as riding with U iso (H) = 1.2U eq (C) and 1.5U eq (O). The N-bound H atom was located in a difference Fourier map and refined freely [N-H = 0.94 (2) Å ]. Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015). 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.