Crystal structure of a second triclinic polymorph of 2-methyl­pyridinium picrate

Jeganathan Gomathi; Doraisamyraja Kalaivani

doi:10.1107/S205698901501912X

. 2015 Oct 17;71(Pt 11):o848–o849. doi: 10.1107/S205698901501912X

Crystal structure of a second triclinic polymorph of 2-methylpyridinium picrate

Jeganathan Gomathi ^a, Doraisamyraja Kalaivani ^a,^*

PMCID: PMC4645006 PMID: 26594559

Abstract

The title molecular salt, C₆H₈N⁺·C₆H₂N₃O₇ ⁻ (systematic name: 2-methylpyridinium 2,4,6-trinitrophenolate), crystallizes with two cations and two anions in the asymmetric unit. In the crystal, the cations are linked to the anions via bifurcated N—H⋯(O,O) hydrogen bonds, generating R ₁ ²(6) graph-set motifs. Numerous C—H⋯O hydrogen bonds are observed between these cation–anion pairs, which result in a three-dimensional network. In addition, weak aromatic π–π stacking between the 2-methylpyridinium rings [inter-centroid distance = 3.8334 (19) Å] and very weak stacking [inter-centroid distance = 4.0281 (16) Å] between inversion-related pairs of picrate anions is observed. The title salt is a second triclinic polymorph of the structure (also with Z′ = 2) reported earlier [Anita et al. (2006). Acta Cryst. C62, o567–o570; Chan et al. (2014 ▸). CrystEngComm, 16, 4508–4538]. In the title compound, the cations and anions display a chequerboard arrangement when viewed down [100], whereas in the first polymorph, (010) layers of alternating cations and anions are apparent in a [100] view. It is interesting that the unit-cell lengths are almost identical for the two polymorphs, although the inter-axial angles are quite different.

Keywords: crystal structure; polymorphism; 2-methylpyridinium picrate; 3-methylpyridinium picrate; 2,4,6-trinitrophenolate

Related literature

For the first triclinic polymorph of 2-methylpyridinium picrate, see: Anitha et al. (2006 ▸); Chan et al. (2014 ▸). For the crystal structure of the isomeric 3-methylpyridinium picrate, see: Gomathi & Kalaivani (2015 ▸). graphic file with name e-71-0o848-scheme1.jpg

Experimental

Crystal data

C₆H₈N⁺·C₆H₂N₃O₇ ⁻
M _r = 322.24
Triclinic,
a = 8.1524 (4) Å
b = 11.8809 (6) Å
c = 14.6377 (9) Å
α = 102.077 (3)°
β = 90.001 (3)°
γ = 100.692 (3)°
V = 1361.21 (13) Å³
Z = 4
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 296 K
0.35 × 0.35 × 0.30 mm

Data collection

Bruker Kappa APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ▸) T _min = 0.952, T _max = 0.969
25854 measured reflections
4789 independent reflections
3165 reflections with I > 2σ(I)
R _int = 0.034

Refinement

R[F ² > 2σ(F ²)] = 0.052
wR(F ²) = 0.159
S = 1.06
4789 reflections
423 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.35 e Å⁻³
Δρ_min = −0.27 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▸); cell refinement: SAINT (Bruker, 2004 ▸); data reduction: SAINT; 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.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S205698901501912X/hb7512sup1.cif

e-71-0o848-sup1.cif^{(798.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901501912X/hb7512Isup2.hkl

e-71-0o848-Isup2.hkl^{(381.2KB, hkl)}

Click here for additional data file.^{(5.5KB, cml)}

Supporting information file. DOI: 10.1107/S205698901501912X/hb7512Isup3.cml

Click here for additional data file.^{(1.3MB, tif)}

ORTEP . DOI: 10.1107/S205698901501912X/hb7512fig1.tif

ORTEP view of the title molecular salt with displacement ellipsoids drawn at 40% probability.

Click here for additional data file.^{(1.2MB, tif)}

. DOI: 10.1107/S205698901501912X/hb7512fig2.tif

A partial view of the crystal packing diagram of the title molecular salt (hydrogen bonds and π–π stacking are shown as dotted lines).

CCDC reference: 1417625

Additional supporting information: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (, ).

DHA	DH	HA	D A	DHA
N7H7AO9	0.95(4)	2.28(4)	2.813(4)	114(3)
N7H7AO14	0.95(4)	1.76(4)	2.678(3)	160(3)
N8H8AO1	0.94(4)	2.35(4)	2.894(4)	117(3)
N8H8AO7	0.94(4)	1.76(4)	2.660(3)	158(4)
C5H5O2ⁱ	0.93	2.50	3.423(4)	170
C9H9O8ⁱⁱ	0.93	2.45	3.365(3)	167
C14H14O10ⁱⁱⁱ	0.93	2.54	3.456(4)	167
C17H17O3	0.93	2.34	3.078(4)	136
C18H18BO12ⁱ	0.96	2.64	3.488(5)	148
C20H20O13^iv	0.93	2.55	3.247(4)	132
C23H23O8ⁱⁱ	0.93	2.63	3.394(4)	140
C23H23O11	0.93	2.36	3.122(4)	139

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

The authors are thankful to UGC, New Delhi, for financial support and the SAIF, IIT Madras, Chennai, for the data collection.

supplementary crystallographic information

S1. Comment

Previous attempt in our laboratories to synthesize carbon-bonded anionic sigma complex with two heterocyclic moieties (substituted imidazole and pyridine) from the ethanolic solution containing 2-chloro-1,3,5-trinitrobenzene, hydantoin and 3-methylpyridine yielded 3-methylpyridinium picrate, a triclinic polymorph (Gomathi & Kalaivani, 2015). In the present work, a similar attempt with 2-methylpyridine instead of 3-methylpyridine in the reaction mixture, yielded 2-methylpyridinium picrate which crystallizes in the triclinic system with space group P1. Fig. 1 & 2 depict ORTEP and packing view of title molecular salt of present investigation respectively. Anita et al. (Anitha et al., 2006) have synthesized 2-methylpyridinium picrate by slow evaporation of the aqueous solution containing pyridoxine and picric acid in a 1:1 stoichiometric ratio at room temperature. They isolated instead of the expected picric acid complex with pyridoxine, crystals of 2-methylpyridinium picrate. Another group (Chan et al., 2014) has prepared 2-methylpyridinium picrate by adding picric acid to liquid 2-methylpyridine without other organic solvents. 2-Methylpyridinium picrate synthesized by both the groups also crystallize in the triclinic system with space group P1. The unit cell parameters of 2-methylpyridinium picrate of both the groups are nearly similar. However, 2-methypyridinium picrate reported in this article differs in the inter-axial bond angles noticeably. In addition to this observation, no disorder is observed in the title molecule, whereas, 2-methylpyridinium picrate reported by Anita et al. one of the oxygen atoms of the nitro group of picrate anion is disordered, with occupancy factors of 0.71 and 0.29. The dihedral angles between the planes of phenyl ring of picrate anions and that of 2-methylpyridinium cations of two molecules present in the asymmetric unit are greater than 80 ° [dihedral angle between (i) planes constituting C1-C2-C3-C4-C5-C6 and N7-C13-C14-C15-C16-C17, 85.54 (11)°; (ii) C1-C2-C3-C4-C5-C6 and N8-C19-C20-C21-C22-C23, 87.60 (11)°; (iii) C7-C8-C9-C10-C11-C12 and N7-C13-C14-C15-C16-C17, 80.60 (11)°; (iv) C7-C8-C9-C10-C11-C12 and N8-C19-C20-C21-C22-C23, 82.49 (10)°], which unambigously reflects the absence of π-bonding between the aromatic rings of anion and cation and supports the fact that the main contributing factor of the formation of the product is proton-transfer reaction. Protonation of the nitrogen atom is further evidenced from the values of the C-N bond distances. N-H···O hydrogen bonding is noticed between the cation and anion parts of two molecules of asymmetric unit and the bifurcation at N-H forming N-H···O hydrogen bonds with the oxygen atoms of phenolate and nitro group results in R₁²(6) ring motif and this sort of linkage is highly responsible for the stability of the molecule. Along with this ring motif, other ring motifs such as R²₂(7), R³₃(13) and R⁴₃(19) are also stabilizing the crystal system. The nitro group involved in forming R₁²(6) ring motif bends only slightly from the plane of the aromatic ring to which it is attached [dihedral angles, 21.68 (16)° and 24.16 (12)°], whereas, the other nitro group lying on the other side of C-O^- bond twists from the ring remarkably [dihedral angles, 79.94 (12)° and 53.29 (15)°]. This kind of twisting may probably reduce the strain due to overcrowding around C-O^-. The plane of the nitro group para with respect to C-O^- lies almost in the plane of the phenyl ring [dihedral angles, 5.02 (19)° and 3.08 (29)°].

S2. Experimental

2-Chloro-1,3,5-trinitrobenzene [2.56 g (0.01 mol)] was dissolved in 30 ml of rectified spirit and mixed with hydantoin [1.00 g (0.01 mol)] in 20 ml of the same solvent. After mixing of these two solutions, 3 ml of 2-methylpyridine (0.03 mol) was added and the solution was heated to 318 K. The solution was stirred at this temperature with the help of magnetic stirrer for 5 h. The solution was cooled to room temperature and then filtered carefully. The clear maroon-red colour solution obtained was allowed to evaporate slowly maintaining the temperature at 293 K. After a period of six weeks, maroon-red coloured crystals formed from the solution. The crystals were filtered, powdered and washed with 30 ml of dry ether and recrystallized from rectified spirit. Instead of the expected carbon-bonded anionic sigma complex with hydantoin, crystals of 2-methylpyridinium picrate were obtained (yield: 70%; m.p.: 423 K).