(S)-1-(2-Ammonio-3-methyl­butyl)-1,2-dihydro­pyridin-2-iminium dibromide

In the title compound, C₁₀H₁₉N₃²⁺·2Br⁻, the plane of the three butyl C atoms nearest to the pyridine ring is almost perpendicular to the ring [dihedral angle = 84.80 (2)°]. The N atom of the ammonium group is displaced by 1.150 (8) Å from the plane of these three C atoms. The iminium N atom lies on the opposite side of this plane. The crystal structure is stabilized by hydrogen bonds between the N and Br atoms, as well as by inter­molecular C—H...Br inter­actions.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.010 Å
• R factor = 0.041
• wR factor = 0.092
• Data-to-parameter ratio = 15.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.31
PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?
PLAT341_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...         10
PLAT480_ALERT_4_C Long H...A H-Bond Reported H3     ..  BR1     ..       3.02 Ang.
PLAT480_ALERT_4_C Long H...A H-Bond Reported H6A    ..  BR1     ..       2.96 Ang.

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.313
            Tmax scaled      0.313 Tmin scaled      0.119
REFLT03_ALERT_4_G  WARNING: Large fraction of Friedel related reflns may
                     be needed to determine absolute structure
           From the CIF: _diffrn_reflns_theta_max           26.99
           From the CIF: _reflns_number_total               2307
           Count of symmetry unique reflns         1611
           Completeness (_total/calc)            143.20%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       696
           Fraction of Friedel pairs measured     0.432
           Are heavy atom types Z>Si present        yes
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT791_ALERT_1_G Confirm the Absolute Configuration of C7     ...          S
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          3

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

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   5 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Ionic liquids, specially functional ionic liquids, have received growing attention recently due to their tuneable features for various chemical tasks. (S. Luo, et al., 2006). The title compound, readily synthesized from commercially available L-valine and 2-aminopyridine, might have potential utilities in some specific chemical tasks, when it is converted into a kind of functional ionic liquid by neutralization with sodium hydroxide. The structure of (S)-1-(2-ammonio-3-methylbutyl)pyridin-2(1H)-iminium dibromide is shown in Fig. 1.

The crystal is built of doubly protonated cations and bromide anions. The protonation of the amines is appropriate like in the scheme, for the C1—N2 bond distance reveals its double bond property. The dihedral angle between the plane of three alkyl carbons C6/C7/C8 and the pyridine ring is 84.80 (2) °, which means the two planes are approximately perpendicular to one another. The atom N3 of the ammonium group bonded to the alkyl chain is displaced from the plane of three carbons C6/C7/C8 by 1.150 (8) Å. The iminium N2 lies on the opposite side of this plane. The crystal structure is stablized by hydrogen-bonds between the atoms N and Br as well as by intermolecular C—H—Br interactions. The molecular packing of the title compound showing H-bridge interactions between cationic-anionic groups is shown in Fig. 2.

Related literature

For the synthesis of (S)-1-bromo-3-methylbutan-2-amine hydrobromide, see: Xu et al. (2006). For related literature, see: Luo et al. (2006).

S2. Experimental

The title compound was synthesized by treating 2-aminopyridine (0.94 g,10 mmol) with (S)-1-bromo-3-methylbutan-2-amine hydrobromide (2.47 g,10 mmol) in MeCN (30 ml) under stirring at 353 K for 24 h (yield 81%). The compound (S)-1-bromo-3-methylbutan-2-amine hydrobromide was obtained from commercially available L-valine by reduction with NaBH₄ and subsequent bromination with PBr₃ (Xu et al., 2006). Suitable crystals of the title compound were obtained by slow evaporation of an ethanol solution at room temperature.

S3. Refinement

All carbon-bonded H atoms were placed in calculated positions with C—H = 0.93 Å (aromatic), C—H = 0.98 Å (sp), C—H = 0.93 Å (sp2), C—H = 0.96 Å(sp3) and refined using a riding model, with U_iso(H)=1.2_eq(C). N-bound H atoms were located in a difference map and refined with an N—H distance restraint of 0.86 (3) Å.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SMART (Bruker, 2001); data reduction: SAINT-Plus (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The asymmetric unit of the title compound with the atomic labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The molecular packing of the title compound showing H-bridge interactions between cationic-anionic groups.

(S)-1-(2-Ammonio-3-methylbutyl)-1,2-dihydropyridin-2-iminium dibromide

Crystal data

C10H19N3^2+·2Br^−	F(000) = 340
Mr = 341.10	Dx = 1.607 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 5.9311 (11) Å	Cell parameters from 1818 reflections
b = 12.456 (2) Å	θ = 5.4–53.4°
c = 9.6807 (18) Å	µ = 5.73 mm^−1
β = 99.733 (3)°	T = 293 K
V = 704.9 (2) Å^3	Prismatic, colorless
Z = 2	0.45 × 0.34 × 0.20 mm

Data collection

Bruker SMART APEX CCD diffractometer	2307 independent reflections
Radiation source: fine-focus sealed tube	2054 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
ϕ and ω scans	θmax = 27.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −7→7
Tmin = 0.381, Tmax = 1.000	k = −12→15
4117 measured reflections	l = −12→12

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)] = 0.041	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0533P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.99	(Δ/σ)max < 0.001
2307 reflections	Δρmax = 0.91 e Å^−3
147 parameters	Δρmin = −0.71 e Å^−3
3 restraints	Absolute structure: Flack (1983), 696 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.06 (2)

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

	x	y	z	Uiso*/Ueq
Br1	1.02019 (11)	0.21057 (4)	0.84434 (6)	0.03666 (18)
Br2	0.61945 (10)	0.78903 (5)	0.54550 (7)	0.03742 (19)
N1	0.7631 (8)	0.4733 (4)	0.2958 (5)	0.0269 (11)
N2	0.4665 (11)	0.5923 (5)	0.3096 (7)	0.0398 (14)
N3	0.9054 (9)	0.3672 (4)	0.5746 (5)	0.0291 (11)
H3A	0.7799	0.3302	0.5406	0.044*
H3B	0.9481	0.3518	0.6651	0.044*
H3C	1.0172	0.3496	0.5280	0.044*
C1	0.5506 (11)	0.5110 (5)	0.2454 (6)	0.0295 (14)
C2	0.4223 (13)	0.4609 (6)	0.1291 (7)	0.0404 (17)
H2	0.2766	0.4863	0.0937	0.048*
C3	0.5050 (15)	0.3772 (7)	0.0677 (7)	0.052 (2)
H3	0.4149	0.3427	−0.0072	0.062*
C4	0.7331 (15)	0.3408 (7)	0.1176 (8)	0.052 (2)
H4	0.7975	0.2856	0.0725	0.062*
C5	0.8497 (13)	0.3880 (6)	0.2301 (7)	0.0378 (16)
H5	0.9953	0.3628	0.2661	0.045*
C6	0.9101 (11)	0.5224 (6)	0.4176 (7)	0.0314 (14)
H6A	0.8922	0.5998	0.4119	0.038*
H6B	1.0686	0.5060	0.4131	0.038*
C7	0.8569 (10)	0.4843 (5)	0.5581 (6)	0.0274 (13)
H7	0.6928	0.4945	0.5567	0.033*
C8	0.9855 (11)	0.5495 (6)	0.6818 (7)	0.0369 (16)
H8	0.9549	0.6256	0.6605	0.044*
C9	0.8975 (15)	0.5251 (8)	0.8154 (7)	0.057 (2)
H9A	0.9414	0.4535	0.8456	0.086*
H9B	0.7338	0.5309	0.7994	0.086*
H9C	0.9614	0.5753	0.8867	0.086*
C10	1.2447 (12)	0.5333 (8)	0.6994 (8)	0.057 (2)
H10A	1.3194	0.5787	0.7734	0.086*
H10B	1.2962	0.5514	0.6135	0.086*
H10C	1.2809	0.4596	0.7224	0.086*
H2A	0.355 (12)	0.623 (8)	0.260 (9)	0.09 (4)*
H2B	0.525 (13)	0.636 (6)	0.371 (7)	0.06 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0508 (4)	0.0348 (4)	0.0231 (3)	−0.0033 (3)	0.0026 (3)	−0.0009 (3)
Br2	0.0309 (3)	0.0355 (4)	0.0448 (4)	0.0023 (3)	0.0033 (3)	−0.0065 (3)
N1	0.033 (3)	0.025 (3)	0.024 (3)	0.001 (2)	0.007 (2)	0.004 (2)
N2	0.040 (4)	0.035 (4)	0.041 (4)	0.006 (3)	−0.002 (3)	−0.003 (3)
N3	0.032 (3)	0.029 (3)	0.026 (3)	−0.004 (2)	0.004 (2)	0.003 (2)
C1	0.041 (4)	0.028 (4)	0.018 (3)	−0.001 (3)	0.002 (3)	0.006 (3)
C2	0.042 (4)	0.051 (5)	0.025 (3)	−0.004 (3)	−0.005 (3)	0.006 (3)
C3	0.074 (5)	0.054 (5)	0.025 (4)	−0.011 (4)	−0.002 (4)	−0.012 (4)
C4	0.077 (6)	0.049 (5)	0.032 (4)	0.006 (4)	0.014 (4)	−0.010 (3)
C5	0.051 (4)	0.038 (4)	0.026 (4)	0.009 (3)	0.012 (3)	0.003 (3)
C6	0.031 (3)	0.032 (4)	0.028 (3)	−0.003 (3)	−0.004 (3)	0.001 (3)
C7	0.021 (3)	0.030 (3)	0.029 (3)	0.001 (2)	−0.001 (2)	0.003 (3)
C8	0.046 (4)	0.030 (4)	0.031 (4)	0.002 (3)	−0.004 (3)	−0.006 (3)
C9	0.066 (5)	0.077 (6)	0.025 (4)	0.014 (5)	−0.003 (4)	−0.015 (4)
C10	0.035 (4)	0.088 (7)	0.043 (5)	−0.016 (4)	−0.008 (3)	−0.014 (5)

Geometric parameters (Å, º)

Br1—H3B	2.4578	C4—C5	1.325 (10)
Br2—H2B	2.55 (7)	C4—H4	0.9300
N1—C1	1.356 (8)	C5—H5	0.9300
N1—C5	1.380 (8)	C6—C7	1.523 (9)
N1—C6	1.476 (8)	C6—H6A	0.9700
N2—C1	1.329 (9)	C6—H6B	0.9700
N2—H2A	0.84 (8)	C7—C8	1.538 (9)
N2—H2B	0.84 (7)	C7—H7	0.9800
N3—C7	1.490 (8)	C8—C9	1.506 (11)
N3—H3A	0.8900	C8—C10	1.531 (10)
N3—H3B	0.8900	C8—H8	0.9800
N3—H3C	0.8900	C9—H9A	0.9600
C1—C2	1.396 (9)	C9—H9B	0.9600
C2—C3	1.334 (11)	C9—H9C	0.9600
C2—H2	0.9300	C10—H10A	0.9600
C3—C4	1.431 (11)	C10—H10B	0.9600
C3—H3	0.9300	C10—H10C	0.9600
C1—N1—C5	119.8 (6)	C7—C6—H6A	108.8
C1—N1—C6	122.1 (5)	N1—C6—H6B	108.8
C5—N1—C6	118.2 (5)	C7—C6—H6B	108.8
C1—N2—H2A	114 (7)	H6A—C6—H6B	107.7
C1—N2—H2B	133 (6)	N3—C7—C6	109.6 (5)
H2A—N2—H2B	107 (9)	N3—C7—C8	111.9 (5)
C7—N3—H3A	109.5	C6—C7—C8	112.3 (6)
C7—N3—H3B	109.5	N3—C7—H7	107.6
H3A—N3—H3B	109.5	C6—C7—H7	107.6
C7—N3—H3C	109.5	C8—C7—H7	107.6
H3A—N3—H3C	109.5	C9—C8—C10	111.4 (6)
H3B—N3—H3C	109.5	C9—C8—C7	111.3 (6)
N2—C1—N1	119.7 (6)	C10—C8—C7	111.9 (6)
N2—C1—C2	121.4 (7)	C9—C8—H8	107.3
N1—C1—C2	118.8 (7)	C10—C8—H8	107.3
C3—C2—C1	121.2 (7)	C7—C8—H8	107.3
C3—C2—H2	119.4	C8—C9—H9A	109.5
C1—C2—H2	119.4	C8—C9—H9B	109.5
C2—C3—C4	119.7 (7)	H9A—C9—H9B	109.5
C2—C3—H3	120.2	C8—C9—H9C	109.5
C4—C3—H3	120.2	H9A—C9—H9C	109.5
C5—C4—C3	117.9 (7)	H9B—C9—H9C	109.5
C5—C4—H4	121.0	C8—C10—H10A	109.5
C3—C4—H4	121.0	C8—C10—H10B	109.5
C4—C5—N1	122.5 (7)	H10A—C10—H10B	109.5
C4—C5—H5	118.7	C8—C10—H10C	109.5
N1—C5—H5	118.7	H10A—C10—H10C	109.5
N1—C6—C7	113.7 (5)	H10B—C10—H10C	109.5
N1—C6—H6A	108.8
C5—N1—C1—N2	179.3 (6)	C6—N1—C5—C4	−178.0 (7)
C6—N1—C1—N2	−2.4 (9)	C1—N1—C6—C7	82.3 (7)
C5—N1—C1—C2	1.2 (8)	C5—N1—C6—C7	−99.4 (7)
C6—N1—C1—C2	179.5 (6)	N1—C6—C7—N3	64.0 (7)
N2—C1—C2—C3	−177.9 (7)	N1—C6—C7—C8	−170.9 (5)
N1—C1—C2—C3	0.2 (10)	N3—C7—C8—C9	−67.1 (7)
C1—C2—C3—C4	−2.8 (11)	C6—C7—C8—C9	169.2 (6)
C2—C3—C4—C5	4.2 (11)	N3—C7—C8—C10	58.3 (8)
C3—C4—C5—N1	−3.0 (11)	C6—C7—C8—C10	−65.5 (8)
C1—N1—C5—C4	0.3 (10)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2B···Br2	0.84 (7)	2.55 (7)	3.368 (7)	167 (8)
N2—H2A···Br1^i	0.84 (8)	2.53 (8)	3.357 (6)	168 (10)
N3—H3C···Br2^ii	0.89	2.50	3.369 (5)	166
N3—H3B···Br1	0.89	2.46	3.238 (5)	147
N3—H3A···Br2^iii	0.89	2.43	3.281 (5)	160
C3—H3···Br1^iv	0.93	3.02	3.892 (8)	157
C4—H4···Br1^v	0.93	2.91	3.748 (8)	150
C6—H6A···Br1^vi	0.97	2.96	3.528 (7)	119
C5—H5···Br2^ii	0.93	2.83	3.721 (7)	162
C8—H8···Br2	0.98	2.93	3.793 (7)	147

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