2-Amino-6-methyl­pyridinium 4-methyl­benzene­sulfonate

K Syed Suresh Babu; M Dhavamurthy; M NizamMohideen; G Peramaiyan; R Mohan

doi:10.1107/S1600536814008587

. 2014 Apr 26;70(Pt 5):o600–o601. doi: 10.1107/S1600536814008587

2-Amino-6-methylpyridinium 4-methylbenzenesulfonate

K Syed Suresh Babu ^a,^b, M Dhavamurthy ^a, M NizamMohideen ^b,^*, G Peramaiyan ^a, R Mohan ^a,^*

PMCID: PMC4011207 PMID: 24860395

Abstract

In the asymmetric unit of the title salt, C₆H₉N₂ ⁺·C₇H₇O₃S⁻, there are two independent 2-amino-6-methylpyridinium cations and two independent 4-methylbenzenesulfonate anions. Both cations are protonated at their pyridine N atoms and their geometries reveal amine–imine tautomerism. In the 4-methylbenzenesulfonate anions, the carboxylate groups are twisted out of the benzene ring planes by 88.4 (1) and 86.2 (2)°. In the crystal, the sulfonate O atoms of an anion interact with the protonated N atoms and the 2-amino groups of a cation via a pair of N—H⋯O hydrogen bonds, forming an R ₂ ²(8) ring motif. These motifs are connected via N—H⋯O hydrogen bonds, forming chains running along the a-axis direction. Within the chains there are weak C—H⋯O hydrogen bonds present. In addition, aromatic π–π stacking interactions [centroid–centroid distances = 3.771 (2), 3.599 (2), 3.599 (2) and 3.497 (2) Å] involving neighbouring chains are also observed.

Related literature

For crystal structures of related pyridine derivatives and their applications, see: Babu et al. (2014 ▶); Rajkumar et al. (2014 ▶); Jin et al. (2005 ▶). For unprotonated aminopyridine derivatives, see: Anderson et al. (2005 ▶). For the structure of amino-methylpyridinium, see: Nahringbauer & Kvick (1977 ▶). For details of sulfonates, see: Onoda et al. (2001 ▶); Baskar Raj et al. (2003 ▶). For applications of benzenesulfonic acid, see: Wang & Wei (2007 ▶). For simple organic–inorganic salts containing strong intermolecular hydrogen bonds, see: Sethuram et al. (2013a ▶,b ▶); Shihabuddeen Syed et al. (2013 ▶); Showrilu et al. (2013 ▶); Huq et al. (2013 ▶). For bond-length data, see: Allen et al. (1987 ▶). For studies on the tautomeric forms of 2-aminopyridine systems, see: Ishikawa et al. (2002 ▶). For graph-set analysis, see: Etter (1990 ▶); Bernstein et al. (1995 ▶). graphic file with name e-70-0o600-scheme1.jpg

Experimental

Crystal data

C₆H₉N₂ ⁺·C₇H₇O₃S⁻
M _r = 280.35
Triclinic,
a = 7.5343 (2) Å
b = 13.6212 (5) Å
c = 13.9887 (5) Å
α = 106.307 (2)°
β = 97.946 (1)°
γ = 92.103 (2)°
V = 1360.31 (8) Å³
Z = 4
Mo Kα radiation
μ = 0.24 mm⁻¹
T = 293 K
0.35 × 0.25 × 0.20 mm

Data collection

Bruker Kappa APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2004 ▶) T _min = 0.920, T _max = 0.953
32534 measured reflections
6237 independent reflections
4709 reflections with I > 2σ(I)
R _int = 0.026

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.119
S = 1.06
6237 reflections
372 parameters
6 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.37 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: APEX2 and SAINT (Bruker, 2004 ▶); data reduction: SAINT and XPREP (Bruker, 2004 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012 ▶) and Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: WinGX (Farrugia, 2012 ▶) and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536814008587/su2726sup1.cif

e-70-0o600-sup1.cif^{(33.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814008587/su2726Isup2.hkl

e-70-0o600-Isup2.hkl^{(299.1KB, hkl)}

Click here for additional data file.^{(5.3KB, cml)}

Supporting information file. DOI: 10.1107/S1600536814008587/su2726Isup3.cml

CCDC reference: 997539

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O2	0.90 (1)	1.88 (1)	2.772 (2)	171 (2)
N2—H2A⋯O3ⁱ	0.87 (1)	2.01 (1)	2.880 (2)	174 (2)
N2—H2B⋯O1	0.88 (1)	2.07 (1)	2.919 (2)	162 (2)
N3—H3A⋯O5	0.89 (1)	1.90 (1)	2.789 (2)	174 (2)
N4—H4A⋯O4ⁱⁱ	0.88 (1)	2.02 (1)	2.882 (2)	167 (2)
N4—H4B⋯O6	0.88 (1)	2.04 (1)	2.883 (2)	162 (2)
C22—H22⋯O5ⁱⁱ	0.93	2.58	3.455 (2)	157

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

Acknowledgments

The authors are thankful to the SAIF, IIT Madras, for the data collection.

supplementary crystallographic information

1. Introduction

2-Aminopyridine and its derivatives play an important role in heterocyclic chemistry. Pyridine heterocycles and their derivatives are present in many large molecules having photo-chemical, electro-chemical and catalytic applications (Babu et al., 2014). Simple organic-inorganic salts containing strong intermolecular hydrogen bonds have attracted an attention as materials which display ferroelectric-paraelectric phase transitions (Sethuram, et al., 2013a,b; Huq et al., 2013; Shihabuddeen Syed et al., 2013; Showrilu et al., 2013). Hydrogen-bonding patterns involving sulfonate groups in biological systems and metal complexes are of current interest (Onoda et al., 2001). Such interactions can be utilized for designing supramolecular architectures (Baskar Raj et al., 2003). Benzenesulfonic acid, is a particularly strong organic acid which is capable of protonating N-containing heterocycles and other Lewis bases (Wang & Wei, 2007). We have recently reported the crystal structures of 2-amino-6-methylpyridinium 2,2,2-trichloroacetate (Babu et al., 2014) and 2-Amino-5-nitropyridinium hydrogen oxalate (Rajkumar et al., 2014). In continuation of our studies of pyridinium derivatives, the crystal structure determination of the title compound has been undertaken.

2. Comment / Result and Discussion

The asymmetric unit of title salt, Fig. 1, consists of two crystallographically independent protonated 2-amino-6-methylpyridinium cation and two crystallographically independent 4-methyl benzenesulfonate anions. The normal probability plot analyses (International Tables for X-ray Crystallography, 1974, Vol. IV, pp. 293–309) for both bond lengths and angles show that the differences between the two symmetry independent molecules are of a statistical nature. All bond lengths (Allen et al., 1987) and angles are within normal ranges and comparable with those in closely related structures (Babu et al., 2014; Rajkumar et al., 2014). A proton transfer from the carboxyl group of p-toluenesulfonic acid to atom N1 and N3 of 2-amino-6-methyl pyridine resulted in the formation of a salt. This protonation lead to the widening of the C8—N1—C12 and C21—N3—C25 angles of the pyridine rings to 124.0 (2) ° and 123.8 (2) °, compared to 115.3 (2) ° in the unprotonated aminopyridine (Anderson et al., 2005). This type of protonation is observed in various aminopyridine acid complexes (Babu et al., 2014; Rajkumar et al., 2014).

In the cation, the N2—C8 [1.325 (2) Å] N4—C21 bonds [1.325 (2) Å] is shorter than the N1—C8 [1.347 (2) Å], N1—C12 [1.360 (2) Å], N3—C21[1.352 (2) Å] and N3—C25[1.362 (2) Å] bonds, and the C8—C9 [1.406 (3) Å], C10—C11 [1.398 (3) Å], C21—C22 [1.405 (3) Å] and C23—C24 [1.401 (3) Å] bonds are significantly longer than C9—C10 [1.357 (3) Å], C11—C12 [1.356 (3) Å]. C22—C23 [1.357 (3) Å] and C24—C25 [1.353 (3) Å] bonds, are similar to those in the amino-methylprydinium cation (Babu et al., 2014; Rajkumar et al., 2014). In contrast, in the solid state structure of amino-methylpyridinium, the N—C bond out of ring is clearly longer than that in the ring (Nahringbauer et al., 1977). The geometrical features of the amino-methylpyridinium cation (N1/N2/C1/C6 and N3/N4/C9—C13) resemble those observed in other 2-aminopyridinium structures (Babu et al., 2014; Rajkumar et al., 2014) that are believed to be involved in amine-imine tautomerism (Ishikawa et al., 2002). Similar features are also provided by cation amino-methylpyridinium (N3/N4/C7/C12). However, previous study show that a pyridinium cation always possesses an expanded angle of C—N—C in comparison with the parent pyridine (Jin et al., 2005).

The examination of pyridinium rings shows that these units are planar with mean deviation of -0.006 (2) and 0.005 (2) Å for atoms C8 and C21, from the mean planes defined by the six constituent atoms. The dihedral angle between the 2-amino-6-methylpyridinium cation and 4-methylbenzenesulfonate anion group is 88.4 (2) and 86.2 (2)° for the both molecules, respectively. In both the molecules, the protonated 2-amino-6-methylpyridinium cation is essentially planar, with maximum deviations of -0.012 (2) for atom C13 and -0.006 (2) Å for atom C25.

3. Hydrogen bonding interaction / Intermolecular N—H···O and C—H···O interaction

In the crystal (Fig. 2), the protonated atoms (N1 and N3) and a nitrogen atom of the 2-amino groups (N2 and N4) of the 2-amino-6-methylpyridinium cations are hydrogen bonded to the carboxylate oxygen atoms (O1, O2, O3 and O4) of the sulfonate groups of the p-toluenesulfonate anions via a pair of intermolecular N—H···O hydrogen bonds (Table 1), forming a ring motif with a graph-set notation of R²₂(8) [Etter, 1990; Bernstein et al., 1995]. The sulfonate group mimics the carboxylate anion's mode of association, which is more commonly seen when binding with 2-aminopyrimidines. It is well known that sulfonates imitate carboxylates in forming such bidentate motifs (Baskar Raj et al., 2003).

Furthermore, these motifs are connected via N—H···O hydrogen bonds (Fig. 2 and Table 1), involving the 2-amino group of the 2-amino-6-methyl pyridinium cation and atoms O3 and O4 of an anion, to form a supramolecular chains along the a axis direction. Weak C—H···O hydrogen bonds, involving a pyridine group of the cation and an O atom of a sulfonate anion, within the chains are also observed (Fig. 2 and Table 1).

4. Aromatic interaction

In addition, the cations of neighbouring chains are linked through aromatic π-π interactions with centroid distances Cg1···Cg1ⁱⁱⁱ = 3.771 (2), Cg1···Cg2^iv = 3.599 (2), Cg2···Cg1^v = 3.599 (2) and Cg2···Cg2^vi = 3.497 (2) Å [symmetry codes are as in Table 1 and (iii) = -x+1,-y+1,-z+2; (iv) = x, y, z+ (v) = x, y, z+1; (vi) = -x+1, -y, -z; Cg1 and Cg2 are the centroids of the N1/C8—C12 and N3/C21—C25 rings, respectively].

5. Uses

The identification of such supramolecular patterns will help us design and construct preferred hydrogen bonding patterns of drug like molecules.

6. Synthesis and crystallization

Crystals of the title compound were obtained by slow evaporation of a 1:1 equimolar mixture of 2-amino-6-methylpyridine and benzenesulfonic acid in methanol at room temperature.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. N-bound H atoms were located in a difference Fourier map and refined with distance restraints: N—H = 0.88 (1) and 0.90 (1) Å for NH₂ and NH H atoms, respectively. The C-bound H atoms were positioned geometrically and refined using a riding model: 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. A rotating group model was used for the methyl group.