2-Amino-1-(4-nitro­benzyl)pyridinium bromide

In the title compound, C₁₂H₁₂N₃O₂⁺·Br⁻, the pyridine and benzene rings make a dihedral angle of 85.0 (1)°. In the solid state, N—H...Br hydrogen bonds link two cations and two anions into a centrosymmetric cluster.

Key indicators

• Single-crystal X-ray study
• T = 273 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.032
• wR factor = 0.085
• Data-to-parameter ratio = 13.4

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S1. Comment

Pyridinium compounds show biological activities, such as antibacterial and antifungal (Akkurt et al., 2005) properties. In continuation of our work on the study of pyridinium derivatives, the structure determination of the title compound, (I), has been undertaken.

A view of the cation and anion of (I), with the atom-labelling scheme, is shown in Fig. 1. The bond lengths and angles in the pyridinium ring are normal (Allen et al., 1987) and comparable with those reported for related structures (Sundar et al., 2004a,b; 2005). The C1–N2 bond length [1.330 (3) Å] is intermediate between typical C—N single- and double-bond distances, indicating significant conjugation. The dihedral angle between the pyridine rings of two adjacent molecules related by the symmetry operator (1 − x, y, 1/2 − z) is 7.31 (2)°, with a separation distance of 3.803 (2) Å. This indicates the presence of some π–π stacking interaction. The sum of the bond angles around atom N3 is close to 360° (Table 1), indicating the absence of an sp³ lone pair. The dihedral angle between the least-squares planes of the pyridine and benzene rings is 85.0 (1)°. The NO₂ moiety is slightly twisted from the plane of the benzene ring by 12.1 (4)°. This may be due to the intramolecular short contact between atoms O1 and H11 (2.45 Å), which is less than the sum of their van der Waals radii (2.72 Å; Reference for vdW radii?).

In order to understand the packing effect on the molecules, an energy minimization of the cation of (I) was carried out using the program WINMOPAC (Version 7.21; Shchepin & Litvinov, 1998). A least-squares fit of the cation of (I) with its energy-minimized counterpart gives an r.m.s. deviation of 0.45 Å (Fig. 2). The conformations of the molecule in the crystal and the free molecule are significantly different only in the orientation of the benzene ring. This is evident from the increase of the non-bonded distance of O1···H11 from 2.45 Å (the molecule in the crystal) to 3.22 Å (energy-minimized molecule). In the energy-minimized molecule, the rotation about the N3—C10 bond has obviously reduced the strain that was observed in the molecules of the crystal.

In the solid state, the crystal packing is stabilized by N—H···Br hydrogen bonds (Table 2), which link two cations and two anions into centrosymmetric clusters (Fig. 3).

S2. Experimental

A solution of 2-aminopyridine (1.15 g, 0.5 mol) and p-nitrobenzyl bromide (2.7 g, 0.5 mol) in dry acetone was refluxed for 2 h. After cooling to room temperature (303 K), the solid which separated was filtered off and washed with dry acetone to give the stable salt, (I) (yield 2.35 g, 61%; m.p. 517–519 K), which was recrystallized from ethanol–water (9:1 v/v).

S3. Refinement

All H atoms were placed in geometrically calculated positions and refined as riding, with C—H = 0.93–0.98 Å and N—H = 0.86 Å, and with U_iso(H) = 1.2U_eq of the parent atom.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: DIRDIF99 (Beurskens et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and PARST (Nardelli, 1995).

Figures

	Fig. 1. A view of the cation and anion of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown by circles of arbitrary radii.
	Fig. 2. Superimposed fit of the cation of (I) (red) and its energy-minimized counterpart (green).
	Fig. 3. The crystal packing, viewed along the a axis and showing N—H···Br hydrogen-bonded (dashed lines) clusters.

2-Amino-1-(4-nitrobenzyl)pyridinium bromide

Crystal data

C12H12O2N3^+·Br^−	Dx = 1.658 Mg m^−3
Mr = 310.16	Melting point: 518 K
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2ab	Cell parameters from 6556 reflections
a = 8.0505 (6) Å	θ = 2.7–26.6°
b = 14.0971 (10) Å	µ = 3.31 mm^−1
c = 21.8990 (15) Å	T = 273 K
V = 2485.3 (3) Å^3	Block, colourless
Z = 8	0.10 × 0.10 × 0.09 mm
F(000) = 1248

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1899 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.041
Graphite monochromator	θmax = 25.0°, θmin = 1.9°
ω scans	h = −9→9
16442 measured reflections	k = −16→16
2203 independent reflections	l = −26→26

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.032	H-atom parameters constrained
wR(F^2) = 0.085	w = 1/[σ^2(Fo^2) + (0.0323P)^2 + 2.4183P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
2203 reflections	Δρmax = 0.43 e Å^−3
164 parameters	Δρmin = −0.47 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: 0.0062 (5)

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
Br1	1.01693 (4)	−0.09384 (2)	0.105125 (15)	0.05078 (16)
C1	0.6431 (3)	0.09972 (17)	0.03121 (12)	0.0345 (6)
C2	0.5791 (4)	0.14921 (19)	−0.01942 (12)	0.0408 (6)
H2	0.6504	0.1700	−0.0500	0.049*
C3	0.4136 (4)	0.1667 (2)	−0.02373 (13)	0.0466 (7)
H3	0.3720	0.1997	−0.0572	0.056*
C4	0.3060 (4)	0.1354 (2)	0.02168 (15)	0.0508 (8)
H4	0.1927	0.1474	0.0190	0.061*
C5	0.3683 (4)	0.0876 (2)	0.06956 (14)	0.0456 (7)
H5	0.2967	0.0661	0.0999	0.055*
C6	0.5944 (4)	0.01860 (19)	0.12924 (11)	0.0394 (6)
H6A	0.6813	−0.0252	0.1172	0.047*
H6B	0.5035	−0.0183	0.1460	0.047*
C7	0.6608 (3)	0.08365 (17)	0.17824 (11)	0.0333 (6)
C8	0.7423 (4)	0.0422 (2)	0.22713 (12)	0.0424 (6)
H8	0.7529	−0.0234	0.2287	0.051*
C9	0.8079 (4)	0.0966 (2)	0.27336 (13)	0.0438 (7)
H9	0.8619	0.0687	0.3063	0.053*
C10	0.7912 (3)	0.1934 (2)	0.26936 (12)	0.0403 (7)
C11	0.7089 (4)	0.2367 (2)	0.22200 (13)	0.0439 (7)
H11	0.6978	0.3023	0.2208	0.053*
C12	0.6430 (4)	0.18091 (19)	0.17625 (12)	0.0403 (6)
H12	0.5863	0.2090	0.1440	0.048*
N1	0.5351 (3)	0.06982 (16)	0.07470 (10)	0.0355 (5)
N2	0.8053 (3)	0.08377 (17)	0.03638 (11)	0.0441 (6)
H2A	0.8433	0.0541	0.0677	0.053*
H2B	0.8721	0.1032	0.0084	0.053*
N3	0.8684 (3)	0.2529 (2)	0.31648 (12)	0.0568 (7)
O1	0.8792 (4)	0.3374 (2)	0.30749 (12)	0.0800 (8)
O2	0.9211 (4)	0.2134 (2)	0.36222 (11)	0.0787 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0479 (2)	0.0596 (2)	0.0448 (2)	0.00445 (14)	0.00594 (13)	0.01166 (14)
C1	0.0395 (14)	0.0344 (13)	0.0295 (13)	−0.0054 (11)	0.0001 (11)	−0.0055 (11)
C2	0.0516 (17)	0.0406 (15)	0.0301 (14)	−0.0005 (13)	−0.0016 (13)	0.0007 (11)
C3	0.0562 (18)	0.0428 (16)	0.0407 (16)	0.0062 (14)	−0.0117 (14)	−0.0060 (13)
C4	0.0389 (16)	0.0561 (18)	0.0574 (19)	0.0038 (14)	−0.0090 (15)	−0.0160 (16)
C5	0.0397 (16)	0.0547 (18)	0.0423 (17)	−0.0069 (13)	0.0065 (13)	−0.0109 (14)
C6	0.0520 (16)	0.0367 (14)	0.0296 (13)	−0.0078 (12)	0.0043 (13)	0.0017 (11)
C7	0.0374 (14)	0.0368 (14)	0.0256 (12)	−0.0031 (11)	0.0058 (11)	0.0000 (10)
C8	0.0542 (17)	0.0396 (14)	0.0333 (14)	0.0049 (13)	0.0043 (13)	0.0020 (12)
C9	0.0436 (16)	0.0622 (19)	0.0257 (13)	0.0064 (14)	0.0027 (12)	0.0024 (13)
C10	0.0358 (15)	0.0570 (17)	0.0280 (13)	−0.0061 (13)	0.0048 (11)	−0.0117 (13)
C11	0.0525 (17)	0.0372 (14)	0.0419 (15)	−0.0039 (13)	0.0026 (14)	−0.0051 (13)
C12	0.0479 (16)	0.0397 (15)	0.0331 (14)	−0.0006 (12)	−0.0046 (12)	0.0010 (12)
N1	0.0390 (12)	0.0404 (12)	0.0271 (11)	−0.0075 (10)	−0.0003 (9)	−0.0041 (9)
N2	0.0389 (13)	0.0564 (15)	0.0370 (13)	−0.0039 (11)	0.0006 (10)	0.0086 (11)
N3	0.0460 (15)	0.087 (2)	0.0375 (15)	−0.0143 (14)	0.0080 (12)	−0.0219 (15)
O1	0.095 (2)	0.0741 (18)	0.0704 (17)	−0.0275 (16)	−0.0020 (15)	−0.0289 (14)
O2	0.0804 (18)	0.119 (2)	0.0369 (13)	−0.0151 (17)	−0.0124 (13)	−0.0173 (14)

Geometric parameters (Å, º)

C1—N2	1.330 (3)	C7—C12	1.379 (4)
C1—N1	1.357 (3)	C7—C8	1.385 (4)
C1—C2	1.408 (4)	C8—C9	1.375 (4)
C2—C3	1.359 (4)	C8—H8	0.9300
C2—H2	0.9300	C9—C10	1.374 (4)
C3—C4	1.390 (4)	C9—H9	0.9300
C3—H3	0.9300	C10—C11	1.374 (4)
C4—C5	1.343 (4)	C10—N3	1.468 (4)
C4—H4	0.9300	C11—C12	1.380 (4)
C5—N1	1.370 (4)	C11—H11	0.9300
C5—H5	0.9300	C12—H12	0.9300
C6—N1	1.475 (3)	N2—H2A	0.8600
C6—C7	1.509 (4)	N2—H2B	0.8600
C6—H6A	0.9700	N3—O1	1.211 (4)
C6—H6B	0.9700	N3—O2	1.222 (4)
N2—C1—N1	121.1 (2)	C9—C8—C7	121.1 (3)
N2—C1—C2	120.7 (3)	C9—C8—H8	119.5
N1—C1—C2	118.2 (2)	C7—C8—H8	119.5
C3—C2—C1	120.2 (3)	C10—C9—C8	118.0 (3)
C3—C2—H2	119.9	C10—C9—H9	121.0
C1—C2—H2	119.9	C8—C9—H9	121.0
C2—C3—C4	120.2 (3)	C11—C10—C9	122.5 (3)
C2—C3—H3	119.9	C11—C10—N3	118.8 (3)
C4—C3—H3	119.9	C9—C10—N3	118.8 (3)
C5—C4—C3	119.0 (3)	C10—C11—C12	118.7 (3)
C5—C4—H4	120.5	C10—C11—H11	120.6
C3—C4—H4	120.5	C12—C11—H11	120.6
C4—C5—N1	121.4 (3)	C7—C12—C11	120.2 (3)
C4—C5—H5	119.3	C7—C12—H12	119.9
N1—C5—H5	119.3	C11—C12—H12	119.9
N1—C6—C7	113.1 (2)	C1—N1—C5	120.9 (2)
N1—C6—H6A	109.0	C1—N1—C6	120.9 (2)
C7—C6—H6A	109.0	C5—N1—C6	118.2 (2)
N1—C6—H6B	109.0	C1—N2—H2A	120.0
C7—C6—H6B	109.0	C1—N2—H2B	120.0
H6A—C6—H6B	107.8	H2A—N2—H2B	120.0
C12—C7—C8	119.5 (2)	O1—N3—O2	123.8 (3)
C12—C7—C6	123.0 (2)	O1—N3—C10	118.6 (3)
C8—C7—C6	117.5 (2)	O2—N3—C10	117.6 (3)
N2—C1—C2—C3	−178.8 (2)	C6—C7—C12—C11	−178.9 (3)
N1—C1—C2—C3	0.5 (4)	C10—C11—C12—C7	−0.4 (4)
C1—C2—C3—C4	−0.3 (4)	N2—C1—N1—C5	179.1 (2)
C2—C3—C4—C5	−0.2 (4)	C2—C1—N1—C5	−0.2 (4)
C3—C4—C5—N1	0.5 (4)	N2—C1—N1—C6	0.0 (4)
N1—C6—C7—C12	9.9 (4)	C2—C1—N1—C6	−179.3 (2)
N1—C6—C7—C8	−170.4 (2)	C4—C5—N1—C1	−0.3 (4)
C12—C7—C8—C9	−0.9 (4)	C4—C5—N1—C6	178.8 (3)
C6—C7—C8—C9	179.4 (3)	C7—C6—N1—C1	81.4 (3)
C7—C8—C9—C10	−0.5 (4)	C7—C6—N1—C5	−97.7 (3)
C8—C9—C10—C11	1.5 (4)	C11—C10—N3—O1	−11.1 (4)
C8—C9—C10—N3	−176.6 (2)	C9—C10—N3—O1	167.1 (3)
C9—C10—C11—C12	−1.1 (4)	C11—C10—N3—O2	170.3 (3)
N3—C10—C11—C12	177.1 (2)	C9—C10—N3—O2	−11.5 (4)
C8—C7—C12—C11	1.3 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···Br1	0.86	2.64	3.382 (2)	145
N2—H2B···Br1^i	0.86	2.65	3.416 (2)	150

Symmetry code: (i) −x+2, −y, −z.