2-Amino-3-methyl­pyridinium acetate

The title compound, C₆H₉N₂⁺·C₂H₃O₂⁻, contains eight- and sixteen-membered hydrogen-bonded rings involving 2-amino-3-methyl­pyridinium and acetate ions. The 2-amino-3-methyl­pyridinium and acetate ions are linked into zigzag chains by C—H...O and N—H...O hydrogen bonds. The dihedral angle between the 2-amino-3-methyl­pyridinium ring and the hydrogen-bonded acetate ion is 6.63 (6)°. The heterocycle is fully protonated, enabling amine–imine tautomerization.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.043
• wR factor = 0.120
• Data-to-parameter ratio = 14.2

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT063_ALERT_3_C Crystal Probably too Large for Beam Size .......       0.64 mm
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C7
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N1     -   H1     ...       1.01 Ang.

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

Hydrogen bonding plays a key role in molecular recognition (Goswami & Ghosh, 1997) and crystal engineering research (Goswami et al., 1998). The design of highly specific solid-state compounds is of considerable significance in organic chemistry due to the important applications of these compounds in the development of new optical, magnetic and electronic systems (Lehn, 1992). 2-Aminopyridine and its derivatives are used in the manufacture of pharmaceuticals, hair dyes and other dyes. The present work is part of a structural study of compound of 2-amino-3-methylpyridinium systems with hydrogen-bond donors and we report here the structure of 2-amino-3-methylpyridinium acetate, (I) (Fig. 1).

In (I), the 2-amino-3-methylpyridinium ions are linked to the acetate ions through N1—H1···O1 and N2—H2A···O2 hydrogen bonds, resulting in the formation of cyclic eight-membered hydrogen-bonded rings (Fig. 1 and Table 2). The eight-membered hydrogen-bonded rings are linked by N2—H2B···O2 and C5—H5···O1 hydrogen bonds forming two-dimensional network. The hydrogen-bonded planes (two-dimensional network) are arranged so that C6—H6···O1 hydrogen bonds form R3⁴₄[16] rings, resulting in a three-dimensional network (Fig. 2).

The 2-aminopyridine–carboxylic acid system has been the subject of theoretical (Inuzuka & Fujimoto, 1990) and spectroscopic (Inuzuka & Fujimoto, 1986) amine–imine tautomerization studies. 2-Aminopyridine and derivatives, like other organic bases, are protonated in acidic solution. The bonding of the H atom to the ring N atom of 2-aminopyridine rather than the amine N atom gives an ion for which an additional resonance structure can be written. As this monocation has more resonance energy (additional ionic resonance) than 2-aminopyridine itself, 2-aminopyridine is a strong base, like amidines (Acheson, 1967).

The present investigation, like our previous work (Büyükgüngör & Odabaşoğlu, 2002, 2003; Odabaşoğlu, Büyükgüngör & Lönnecke, 2003; Odabaşoğlu, Büyükgüngör, Turgut et al., 2003; Büyükgüngör et al., 2004), clearly shows that the positive charge in the 2-aminopyridinium ion is on the amine group. Our investigations also show that the 2-amino-3-methylpyridinium cation is present in the crystal structure in a similar form and the methyl H atoms in the acetate show rotational disorder.

The C1—N2 bond is length approximately equal to that of a C═N double bond (Shanmuga Sundara Raj, Fun, Lu et al., 2000), indicating that atom N2 of the amine group must also be sp2 hybridized. This is also supported by the C1—N2—H2A angle of 117.2 (11)° (Table 1). Similar bond distances and angles have been observed in 2-aminopyridinium succinate succinic acid (Büyükgüngör & Odabaşoğlu, 2002), 2-aminopyridinium adipate monoadipic acid dihydrate (Odabaşoğlu, Büyükgüngör, Turgut et al., 2003), bis(2-aminopyridinium) maleate (Büyükgüngör & Odabaşoğlu, 2003), 2-aminopyridinium fumarate fumaric acid (Büyükgüngör et al., 2004) and in some 2-aminopyridine containing molecules (Yang et al., 1995; Grobelny et al., 1995; Shanmuga Sundara Raj, Fun, Zhao et al., 2000).

S2. Experimental

The title compound was prepared by mixing 3-methyl-2-aminopyridine and acetic acid in a 1:1 molar ratio in water at 353 K. Crystals of (I) were obtained by slow evaporation of the solvent (m.p. 370–372 K).

S3. Refinement

Refined C—H distances are in the range 0.94 (2)–0.98 (2) Å and U_iso values for H atoms are in the range 0.056 (4)–0.097 (7) Ų. The H atoms bounded to C8 were refined as an idealized disordered methyl group (two positions) in their calculated positions, with U_iso(H) = 1.5U_eq of the parent atom.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A view of the molecule of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probalitity level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram of the title compound, showing the hydrogen-bonding scheme (dashed lines).

2-amino-3-methylprydinium acetate

Crystal data

C6H9N2^+·C2H3O2^−	Z = 2
Mr = 168.20	F(000) = 180
Triclinic, P1	Dx = 1.275 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.0451 (8) Å	Cell parameters from 7421 reflections
b = 8.0502 (10) Å	θ = 2.6–28.0°
c = 8.5061 (10) Å	µ = 0.09 mm^−1
α = 65.756 (9)°	T = 296 K
β = 86.505 (9)°	Plate, colorless
γ = 85.326 (9)°	0.64 × 0.49 × 0.24 mm
V = 438.21 (10) Å^3

Data collection

Stoe IPDS-II diffractometer	1646 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.073
Plane graphite monochromator	θmax = 27.7°, θmin = 2.8°
Detector resolution: 6.67 pixels mm^-1	h = −9→8
rotation method scans	k = −10→10
7421 measured reflections	l = −11→11
2054 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.121	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.054P)^2 + 0.0553P] where P = (Fo^2 + 2Fc^2)/3
2054 reflections	(Δ/σ)max < 0.001
145 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.17 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.48331 (16)	0.78843 (16)	0.39524 (15)	0.0413 (3)
C2	0.60971 (17)	0.78674 (17)	0.52011 (16)	0.0451 (3)
C3	0.5650 (2)	0.6853 (2)	0.68885 (18)	0.0561 (3)
C4	0.4028 (2)	0.5851 (2)	0.74037 (18)	0.0591 (4)
C5	0.28844 (19)	0.58748 (18)	0.61765 (17)	0.0513 (3)
C6	0.7862 (2)	0.8901 (2)	0.4611 (2)	0.0581 (4)
C7	0.11314 (18)	0.75965 (17)	0.07288 (16)	0.0472 (3)
C8	−0.0405 (2)	0.7631 (2)	−0.04431 (19)	0.0624 (4)
H8A	−0.1442	0.6951	0.0237	0.094*	0.50
H8B	0.0103	0.7094	−0.1212	0.094*	0.50
H8C	−0.0856	0.8871	−0.1101	0.094*	0.50
H8D	−0.0021	0.8326	−0.1621	0.094*	0.50
H8E	−0.1566	0.8183	−0.0172	0.094*	0.50
H8F	−0.0607	0.6406	−0.0283	0.094*	0.50
N1	0.32929 (14)	0.68791 (14)	0.44885 (13)	0.0453 (3)
N2	0.50971 (18)	0.88402 (17)	0.22719 (14)	0.0557 (3)
O1	0.08560 (14)	0.67309 (15)	0.23200 (12)	0.0630 (3)
O2	0.25814 (16)	0.84162 (18)	0.00586 (13)	0.0722 (4)
H1	0.243 (3)	0.685 (2)	0.360 (2)	0.075 (5)*
H2A	0.427 (3)	0.870 (2)	0.156 (2)	0.070 (5)*
H2B	0.608 (3)	0.958 (2)	0.189 (2)	0.068 (5)*
H3	0.651 (3)	0.687 (3)	0.777 (3)	0.081 (5)*
H4	0.373 (3)	0.516 (3)	0.859 (3)	0.074 (5)*
H5	0.177 (2)	0.521 (2)	0.639 (2)	0.056 (4)*
H6A	0.866 (3)	0.839 (3)	0.386 (3)	0.090 (6)*
H6B	0.754 (3)	1.019 (3)	0.385 (3)	0.097 (7)*
H6C	0.853 (3)	0.883 (3)	0.561 (3)	0.086 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0394 (6)	0.0444 (6)	0.0391 (6)	−0.0094 (4)	−0.0011 (4)	−0.0147 (5)
C2	0.0413 (6)	0.0504 (6)	0.0446 (6)	−0.0094 (5)	−0.0037 (5)	−0.0188 (5)
C3	0.0567 (8)	0.0675 (8)	0.0424 (7)	−0.0149 (6)	−0.0073 (5)	−0.0180 (6)
C4	0.0667 (8)	0.0662 (8)	0.0372 (6)	−0.0212 (7)	0.0028 (6)	−0.0112 (6)
C5	0.0503 (7)	0.0541 (7)	0.0461 (7)	−0.0192 (6)	0.0055 (5)	−0.0149 (5)
C6	0.0457 (7)	0.0741 (10)	0.0558 (8)	−0.0205 (6)	−0.0024 (6)	−0.0246 (7)
C7	0.0470 (6)	0.0517 (7)	0.0429 (6)	−0.0146 (5)	−0.0015 (5)	−0.0171 (5)
C8	0.0567 (8)	0.0774 (9)	0.0524 (8)	−0.0207 (7)	−0.0098 (6)	−0.0215 (7)
N1	0.0427 (5)	0.0500 (5)	0.0412 (6)	−0.0141 (4)	−0.0014 (4)	−0.0148 (4)
N2	0.0543 (6)	0.0680 (7)	0.0388 (6)	−0.0277 (5)	−0.0022 (5)	−0.0111 (5)
O1	0.0552 (6)	0.0829 (7)	0.0426 (5)	−0.0308 (5)	−0.0033 (4)	−0.0121 (5)
O2	0.0661 (6)	0.1001 (8)	0.0442 (5)	−0.0458 (6)	0.0000 (4)	−0.0159 (5)

Geometric parameters (Å, º)

C1—N2	1.3258 (16)	C6—H6C	0.97 (2)
C1—N1	1.3491 (15)	C7—O2	1.2385 (15)
C1—C2	1.4222 (16)	C7—O1	1.2532 (15)
C2—C3	1.3603 (19)	C7—C8	1.5066 (18)
C2—C6	1.4964 (18)	C8—H8A	0.9600
C3—C4	1.396 (2)	C8—H8B	0.9600
C3—H3	1.00 (2)	C8—H8C	0.9600
C4—C5	1.350 (2)	C8—H8D	0.9600
C4—H4	0.95 (2)	C8—H8E	0.9600
C5—N1	1.3536 (16)	C8—H8F	0.9600
C5—H5	0.954 (17)	N1—H1	1.01 (2)
C6—H6A	1.01 (2)	N2—H2A	0.910 (19)
C6—H6B	0.99 (2)	N2—H2B	0.903 (19)
N2—C1—N1	117.94 (10)	H8A—C8—H8B	109.5
N2—C1—C2	123.09 (11)	C7—C8—H8C	109.5
N1—C1—C2	118.97 (10)	H8A—C8—H8C	109.5
C3—C2—C1	117.38 (11)	H8B—C8—H8C	109.5
C3—C2—C6	123.32 (12)	C7—C8—H8D	109.5
C1—C2—C6	119.28 (11)	H8A—C8—H8D	141.1
C2—C3—C4	122.27 (12)	H8B—C8—H8D	56.3
C2—C3—H3	117.7 (12)	H8C—C8—H8D	56.3
C4—C3—H3	120.0 (12)	C7—C8—H8E	109.5
C5—C4—C3	118.51 (12)	H8A—C8—H8E	56.3
C5—C4—H4	120.2 (12)	H8B—C8—H8E	141.1
C3—C4—H4	121.2 (11)	H8C—C8—H8E	56.3
C4—C5—N1	120.39 (12)	H8D—C8—H8E	109.5
C4—C5—H5	125.0 (10)	C7—C8—H8F	109.5
N1—C5—H5	114.6 (10)	H8A—C8—H8F	56.3
C2—C6—H6A	108.2 (12)	H8B—C8—H8F	56.3
C2—C6—H6B	110.8 (13)	H8C—C8—H8F	141.1
H6A—C6—H6B	105.1 (17)	H8D—C8—H8F	109.5
C2—C6—H6C	109.5 (12)	H8E—C8—H8F	109.5
H6A—C6—H6C	113.2 (16)	C1—N1—C5	122.47 (10)
H6B—C6—H6C	109.9 (18)	C1—N1—H1	118.9 (11)
O2—C7—O1	124.41 (12)	C5—N1—H1	118.7 (11)
O2—C7—C8	118.00 (12)	C1—N2—H2A	117.1 (12)
O1—C7—C8	117.58 (12)	C1—N2—H2B	119.5 (11)
C7—C8—H8A	109.5	H2A—N2—H2B	123.4 (16)
C7—C8—H8B	109.5
N2—C1—C2—C3	178.99 (13)	C2—C3—C4—C5	1.0 (3)
N1—C1—C2—C3	−1.30 (19)	C3—C4—C5—N1	−1.2 (2)
N2—C1—C2—C6	−2.9 (2)	N2—C1—N1—C5	−179.15 (12)
N1—C1—C2—C6	176.84 (13)	C2—C1—N1—C5	1.12 (19)
C1—C2—C3—C4	0.3 (2)	C4—C5—N1—C1	0.2 (2)
C6—C2—C3—C4	−177.79 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O2	0.910 (19)	1.890 (19)	2.7992 (15)	179.2 (18)
N2—H2B···O2^i	0.903 (19)	2.026 (18)	2.8426 (16)	149.7 (16)
N1—H1···O1	1.01 (2)	1.64 (2)	2.6390 (14)	173.9 (17)
C5—H5···O1^ii	0.954 (17)	2.424 (17)	3.3566 (16)	165.7 (14)
C6—H6A···O1^iii	1.01 (2)	2.60 (2)	3.605 (2)	172.2 (16)

Symmetry codes: (i) −x+1, −y+2, −z; (ii) −x, −y+1, −z+1; (iii) x+1, y, z.