2-Aminopyridinium benzoate

Cyclic eight-membered hydrogen-bonded rings exist in the title compound, C₅H₇N₂⁺·C₇H₅O₂⁻, involving the 2-amino­pyridinium and benzoate ions. Each benzoate ion has two intramolecular hydrogen bonds. 2-Amino­pyridinium benzoate ion pairs are linked by N—H...O hydrogen bonds, with an N...O distance of 2.8619 (14) Å.

S1. Comment

The present work is part of a structural study of complexes of 2-aminopyridinium systems with hydrogen-bond donors, and we report here on the structure of 2-aminopyridinium benzoate, (I). A similar series of complexes formed from 2-aminopyridine and carboxylates has been reported previously (Büyükgüngör & Odabaşoǧlu, 2002; Odabaşoǧlu et al., 2002). 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 structures is of considerable significance in organic chemistry, due to their important applications in the development of new optical, magnetic and electronic systems (Ballardini et al., 1994, Lehn, 1992). \sch

A view of the hydrogen-bonded structure of (I) and its numbering scheme are shown in Fig. 1. The complex owes its formation to hydrogen bonds between atoms O1 and O2 of the benzoate ion and atoms H13 and H14 of the 2-aminopyridinium ion, respectively. There is an eight-membered ring in the structure. This ring is formed as a result of the O1···H13 and O2···H14 hydrogen bonds. In addition to these hydrogen bonds, there is an intramolecular N—H···O hydrogen bond connecting units of (I). The hydrogen-bond distances in (I) are shorter than in 2-aminopyridinium salicylate [O1···N1 2.699 (4) and O2···N2 2.868 (16) Å; Gellert & Hsu, 1988].

2-Aminopyridine is protonated in acidic solutions. The bonding of the H atom to the ring N atom of 2-aminopyridine, but not to the amino N atom, gives an ion for which an additional resonance structure can be written (Acheson, 1967). The present investigation, like our previous work (Büyükgüngör & Odabaşoǧlu, 2002; Odabaşoǧlu et al., 2002), clearly shows that the positive charge in the 2-aminopyridinium ion is on the amino group.

The phenyl and pyridine rings of (I) display an almost coplanar configuration, with a dihedral angle of 8.4 (2)°. The C1—N2 bond is 1.3332 (15) Å, and this value is approximately equal to that of the C═N double bond (Shanmuga Sundara Raj, Fun, Lu et al., 2000), indicating that atom N2 of the amino group must also be sp² hybridized. This is also supported by the C1—N2—H14 angle of 120.3 (9)° and by the fact that atoms C1, N2, H14 and H15 lie almost in the pyridine plane, with a maximum deviation of 0.09 (1) Å for atom H15. Similar bond distances and angles have been observed in 2-aminopyridinium succinate-succinic acid (Büyükgüngör & Odabaşoǧlu, 2002) and 2-aminopyridinium adipate monoadipic acid dihydrate (Odabaşoǧlu et al., 2002), 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 2-aminopyridine and benzoic acid in a 1:1 molar ratio in ethanol (95%) at 353 K, and crystals of (I) were obtained by slow evaporation of the solvent.

S3. Refinement

C—H distances were refined in the range 0.950 (13)–0.997 (13) Å, and U_iso values for H atoms are in the range 0.041 (3)–0.066 (5) Ų.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: WinGX (Farrugia, 1997).

Figures

	Fig. 1. A view of the two moieties of (I), with the atom-numbering scheme and 50% probability displacement ellipsoids. H atoms are shown as small spheres of arbitrary radii and hydrogen bonds are indicated by dashed lines.
	Fig. 2. A packing diagram for (I), viewed along the b axis. The a axis is to the right and the c axis is upwards.

2-aminopyridinium benzoate

Crystal data

C5H7N2^+·C7H5O2^−	Dx = 1.322 Mg m^−3
Mr = 216.24	Melting point: 422 K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 986 reflections
a = 12.2129 (17) Å	θ = 2.8–26.6°
b = 11.5137 (16) Å	µ = 0.09 mm^−1
c = 15.456 (2) Å	T = 208 K
V = 2173.4 (5) Å^3	Prism, colourless
Z = 8	0.40 × 0.30 × 0.15 mm
F(000) = 912

Data collection

Bruker SMART CCD area-detector diffractometer	2650 independent reflections
Radiation source: fine-focus sealed tube	1664 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.065
ω scans	θmax = 28.8°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Blessing, 1995)	h = −16→16
Tmin = 0.964, Tmax = 0.986	k = −14→14
13050 measured reflections	l = −12→20

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.036	All H-atom parameters refined
wR(F^2) = 0.088	w = 1/[σ^2(Fo^2) + (0.0498P)^2
S = 0.89	(Δ/σ)max < 0.001
2650 reflections	Δρmax = 0.16 e Å^−3
194 parameters	Δρmin = −0.17 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0145 (12)

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
O1	0.62593 (6)	0.44911 (7)	0.43041 (5)	0.0395 (2)
O2	0.59058 (6)	0.62265 (7)	0.37343 (6)	0.0434 (2)
N1	0.79645 (8)	0.54400 (8)	0.51018 (6)	0.0339 (2)
N2	0.77734 (9)	0.72376 (9)	0.44664 (7)	0.0454 (3)
C1	0.83142 (9)	0.65460 (9)	0.50104 (7)	0.0347 (3)
C2	0.92242 (10)	0.69101 (11)	0.54985 (8)	0.0403 (3)
C3	0.97307 (11)	0.61424 (12)	0.60330 (8)	0.0470 (3)
C4	0.93678 (11)	0.49911 (12)	0.60993 (9)	0.0469 (3)
C5	0.84824 (10)	0.46769 (11)	0.56311 (8)	0.0404 (3)
C6	0.56793 (9)	0.51828 (9)	0.38525 (7)	0.0318 (3)
C7	0.46694 (8)	0.47050 (9)	0.34263 (7)	0.0314 (3)
C8	0.39861 (9)	0.54416 (11)	0.29612 (7)	0.0383 (3)
C9	0.30646 (10)	0.50147 (12)	0.25465 (8)	0.0452 (3)
C10	0.28187 (11)	0.38443 (12)	0.25919 (8)	0.0468 (3)
C11	0.34884 (11)	0.31044 (12)	0.30488 (8)	0.0485 (3)
C12	0.44105 (10)	0.35311 (11)	0.34684 (8)	0.0414 (3)
H2	0.9492 (10)	0.7692 (12)	0.5447 (8)	0.051 (4)*
H3	1.0352 (12)	0.6391 (12)	0.6366 (9)	0.056 (4)*
H4	0.9739 (12)	0.4426 (12)	0.6463 (9)	0.058 (4)*
H5	0.8176 (9)	0.3896 (11)	0.5635 (7)	0.041 (3)*
H8	0.4200 (10)	0.6262 (11)	0.2927 (8)	0.048 (3)*
H9	0.2577 (11)	0.5554 (11)	0.2221 (8)	0.050 (3)*
H10	0.2168 (11)	0.3553 (11)	0.2308 (9)	0.055 (4)*
H11	0.3348 (11)	0.2293 (12)	0.3066 (9)	0.065 (4)*
H12	0.4882 (10)	0.3020 (11)	0.3794 (8)	0.043 (3)*
H13	0.7320 (11)	0.5165 (11)	0.4779 (8)	0.050 (4)*
H14	0.7146 (12)	0.6967 (12)	0.4178 (9)	0.060 (4)*
H15	0.8064 (12)	0.7968 (14)	0.4374 (9)	0.066 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0373 (4)	0.0321 (4)	0.0490 (5)	0.0018 (3)	−0.0114 (4)	0.0017 (4)
O2	0.0378 (5)	0.0297 (4)	0.0626 (6)	−0.0010 (3)	−0.0045 (4)	0.0037 (4)
N1	0.0334 (5)	0.0324 (5)	0.0358 (6)	−0.0051 (4)	−0.0031 (4)	−0.0019 (4)
N2	0.0464 (6)	0.0316 (6)	0.0582 (7)	−0.0067 (5)	−0.0083 (5)	0.0045 (5)
C1	0.0351 (6)	0.0332 (6)	0.0358 (6)	−0.0033 (5)	0.0054 (5)	−0.0055 (5)
C2	0.0388 (6)	0.0419 (7)	0.0402 (7)	−0.0097 (5)	0.0032 (6)	−0.0086 (6)
C3	0.0389 (7)	0.0624 (9)	0.0396 (7)	−0.0080 (6)	−0.0046 (6)	−0.0111 (6)
C4	0.0473 (7)	0.0530 (8)	0.0406 (7)	0.0000 (6)	−0.0086 (6)	0.0005 (6)
C5	0.0454 (7)	0.0383 (7)	0.0375 (7)	−0.0021 (6)	−0.0022 (6)	0.0012 (5)
C6	0.0291 (6)	0.0324 (6)	0.0339 (6)	0.0031 (5)	0.0044 (5)	−0.0021 (5)
C7	0.0292 (5)	0.0365 (6)	0.0285 (6)	0.0012 (5)	0.0032 (5)	−0.0009 (5)
C8	0.0379 (6)	0.0413 (7)	0.0356 (7)	0.0065 (5)	0.0011 (5)	−0.0010 (5)
C9	0.0393 (7)	0.0575 (9)	0.0387 (7)	0.0100 (6)	−0.0074 (6)	−0.0041 (6)
C10	0.0381 (7)	0.0660 (9)	0.0364 (7)	−0.0064 (6)	−0.0057 (6)	−0.0060 (6)
C11	0.0538 (8)	0.0486 (8)	0.0430 (8)	−0.0147 (6)	−0.0071 (6)	0.0021 (6)
C12	0.0442 (7)	0.0407 (7)	0.0391 (7)	−0.0046 (6)	−0.0080 (6)	0.0046 (6)

Geometric parameters (Å, º)

O1—C6	1.2740 (13)	C4—H4	0.973 (15)
O2—C6	1.2466 (13)	C5—H5	0.974 (12)
N1—C1	1.3505 (14)	C6—C7	1.5027 (15)
N1—C5	1.3570 (15)	C7—C12	1.3896 (16)
N1—H13	0.985 (14)	C7—C8	1.3902 (15)
N2—C1	1.3332 (15)	C8—C9	1.3853 (17)
N2—H14	0.940 (15)	C8—H8	0.982 (12)
N2—H15	0.924 (16)	C9—C10	1.3824 (19)
C1—C2	1.4071 (16)	C9—H9	0.997 (13)
C2—C3	1.3589 (19)	C10—C11	1.3761 (19)
C2—H2	0.961 (14)	C10—H10	0.968 (13)
C3—C4	1.4014 (19)	C11—C12	1.3893 (18)
C3—H3	0.961 (14)	C11—H11	0.950 (13)
C4—C5	1.3505 (18)	C12—H12	0.964 (13)
C1—N1—C5	121.74 (10)	O2—C6—O1	124.02 (10)
C1—N1—H13	120.2 (8)	O2—C6—C7	118.09 (10)
C5—N1—H13	118.0 (8)	O1—C6—C7	117.88 (10)
C1—N2—H14	120.3 (9)	C12—C7—C8	118.76 (10)
C1—N2—H15	116.8 (9)	C12—C7—C6	121.49 (10)
H14—N2—H15	122.9 (12)	C8—C7—C6	119.74 (10)
N2—C1—N1	118.19 (10)	C9—C8—C7	120.70 (12)
N2—C1—C2	123.47 (11)	C9—C8—H8	122.2 (7)
N1—C1—C2	118.34 (11)	C7—C8—H8	117.0 (7)
C3—C2—C1	119.45 (12)	C10—C9—C8	119.92 (12)
C3—C2—H2	120.3 (8)	C10—C9—H9	120.2 (7)
C1—C2—H2	120.2 (8)	C8—C9—H9	119.9 (7)
C2—C3—C4	121.04 (12)	C11—C10—C9	120.03 (12)
C2—C3—H3	119.4 (8)	C11—C10—H10	120.4 (8)
C4—C3—H3	119.5 (8)	C9—C10—H10	119.6 (8)
C5—C4—C3	117.87 (13)	C10—C11—C12	120.17 (13)
C5—C4—H4	120.3 (8)	C10—C11—H11	121.1 (9)
C3—C4—H4	121.8 (8)	C12—C11—H11	118.7 (9)
C4—C5—N1	121.52 (12)	C11—C12—C7	120.43 (12)
C4—C5—H5	123.5 (7)	C11—C12—H12	120.7 (7)
N1—C5—H5	115.0 (7)	C7—C12—H12	118.8 (7)
C5—N1—C1—N2	178.83 (11)	O2—C6—C7—C8	−3.84 (16)
C5—N1—C1—C2	−1.63 (16)	O1—C6—C7—C8	177.02 (10)
N2—C1—C2—C3	−179.53 (12)	C12—C7—C8—C9	−0.05 (17)
N1—C1—C2—C3	0.96 (16)	C6—C7—C8—C9	178.49 (10)
C1—C2—C3—C4	0.64 (19)	C7—C8—C9—C10	−0.12 (18)
C2—C3—C4—C5	−1.6 (2)	C8—C9—C10—C11	0.02 (19)
C3—C4—C5—N1	0.95 (19)	C9—C10—C11—C12	0.3 (2)
C1—N1—C5—C4	0.67 (18)	C10—C11—C12—C7	−0.4 (2)
O2—C6—C7—C12	174.66 (10)	C8—C7—C12—C11	0.33 (17)
O1—C6—C7—C12	−4.48 (16)	C6—C7—C12—C11	−178.19 (11)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H13···O1	0.985 (14)	1.678 (14)	2.6552 (12)	170.9 (12)
N2—H14···O2	0.940 (15)	1.868 (16)	2.7996 (14)	170.6 (13)
N2—H15···O1^i	0.924 (16)	1.942 (16)	2.8619 (14)	173.9 (13)

Symmetry code: (i) −x+3/2, y+1/2, z.