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All atoms of the title compound, C5H4Br2N+·Br, lie in a crystallographic mirror plane. The packing within the plane is determined by hydrogen bonds N+—H...Br and C—H...Br, and by Br...Br contacts, but differs from that of the previous polymorph [Freytag & Jones (2001). Z. Naturforsch. Teil B, 56, 889–869], which also lay completely in mirror planes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803007773/bt6266sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803007773/bt6266Isup2.hkl
Contains datablock I

CCDC reference: 214607

Key indicators

  • Single-crystal X-ray study
  • T = 133 K
  • Mean [sigma](C-C) = 0.004 Å
  • R factor = 0.020
  • wR factor = 0.052
  • Data-to-parameter ratio = 22.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
ABSTM_02 Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10 Tmin and Tmax reported: 0.253 0.462 Tmin and Tmax expected: 0.117 0.312 RR = 1.461 Please check that your absorption correction is appropriate. General Notes
ABSTM_02 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 0.676 Tmax scaled 0.312 Tmin scaled 0.171
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

We are interested in secondary bonding contacts (classical and `weak' hydrogen bonds, halogen-halogen contacts) in structures of halopyridinium halides (see Freytag & Jones, 2001, and references therein). In that publication we had already reported the synthesis and structure of the compound 3,5-dibromopyridinium bromide, (I), which crystallized from acetonitrile/methanol/diethyl ether in space group P42/mnm. We have now by chance determined the structure of a second form of the same compound, crystallized from dichloromethane/diethyl ether.

The asymmetric unit, which lies completely in the crystallographic mirror plane y = 0, is presented in Fig. 1. Bond lengths and angles may be regarded as normal, in particular the widened bond angle at the protonated N atom.

The packing within one layer is presented in Fig. 2. A classical N+—H···Br hydrogen bond is observed, as are two `weak' hydrogen bonds of the form C—H···Br (Table 2). Only the shorter of these latter two interactions is shown explicitly in Fig. 2; it has a normalized H···Br distance of only 2.58 Å.

There are also several bromine-bromine contacts. The shortest of these, Br1···Br3(x, y, z − 1) = 3.4752 (5) and Br2···Br3(-x, −y, 1 − z) = 3.5117 Å, involve the anion Br3 and are approximately linear at the central bromine [C—Br···Br = 158.35 (9) and 168.36 (9)°]. Such contacts are thought to be associated with a positive region of charge in the extension of the C—Br vector beyond Br. Two further Br···Br contacts are longer than the double van der Waals radius of 3.7 Å (Bondi, 1964), but may nevertheless be regarded as structurally significant; Br1···Br2(-x, −y, −z) = 3.9011 (5) Å and Br1···Br1(1 − x, −y, −z) = 3.8311 (7) Å. The latter, with C—Br···Br angles equal by symmetry at 119.39 (9)°, is a typical `type I' interaction as classified by Pedireddi et al. (1994); in contrast to type II interactions (one 90° and one 180° angle), these are not thought to represent significant electrostatic interactions, but nevertheless are observed so frequently that some stabilizing effect might be presumed. The former has angles of 101.84 (9) and 136.03 (9)° and lies between types I and II.

The packing of the previous modification differed from the pattern described here in one important respect; the higher symmetry of the layers (4/mmm), in which the N—H bonds of neighbouring rings are exactly antiparallel and `share' two bromides via three-centre hydrogen bonds, thus forming units N+—H(···Br-···)2H—N+. In Fig. 2, the formal conversion of the lower to the higher symmetry form can be seen in terms of the R24(10) ring centred at x = 1/2, z = 1; the pyridine rings to the upper right and lower left of the cell edge should both be rotated anticlockwise.

The distance between the layers is b/2 = 3.419 Å, cf. 3.442 Å in the previous modification; however, the latter has a significantly higher density, 2.631 versus 2.553 Mg m−3, suggesting more efficient packing in its layers. One surmises that the energy balance between the two forms would be very delicate.

Experimental top

During a study of tribromoacetates, small crystals of the title compound were obtained on attempting to crystallize 3,5-dibromopyridinium tribromoacetate from dichloromethane/diethyl ether. Presumably these arose from small quantities of bromine or bromide as a decomposition product.

Refinement top

The acidic H atom was refined freely but with an N—H bond length restraint (DFIX). Other H atoms were included using a riding model with fixed C—H bond lengths of 0.95 Å. Uiso(H) values were fixed at 1.2 times the Ueq of the parent atom.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The formula unit of the title compound in the crystal. Ellipsoids represent 50% probability levels and H-atom radii are arbitrary.
[Figure 2] Fig. 2. Packing diagram of one layer of the title compound (at y = 1/2), projected along the y axis. Secondary interactions are indicated by dashed lines (thick, classical hydrogen bonds and short Br···Br; thin, `weak' hydrogen bonds and long Br···Br).
3,5-Dibromopyridinium bromide top
Crystal data top
C5H4Br2N+·BrF(000) = 584
Mr = 317.82Dx = 2.553 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
a = 11.6270 (8) ÅCell parameters from 4877 reflections
b = 6.8372 (4) Åθ = 3.5–30.5°
c = 10.4344 (6) ŵ = 14.55 mm1
β = 94.574 (4)°T = 133 K
V = 826.85 (9) Å3Prism, colourless
Z = 40.25 × 0.13 × 0.08 mm
Data collection top
Bruker SMART 1000 CCD
diffractometer
1308 independent reflections
Radiation source: fine-focus sealed tube1138 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.030
Detector resolution: 8.192 pixels mm-1θmax = 30.0°, θmin = 2.0°
ω and ϕ scansh = 1616
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
k = 99
Tmin = 0.253, Tmax = 0.462l = 1414
7962 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.020Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.052H atoms treated by a mixture of independent and constrained refinement
S = 1.06 w = 1/[σ2(Fo2) + (0.0338P)2]
where P = (Fo2 + 2Fc2)/3
1308 reflections(Δ/σ)max = 0.001
58 parametersΔρmax = 0.55 e Å3
1 restraintΔρmin = 0.78 e Å3
Crystal data top
C5H4Br2N+·BrV = 826.85 (9) Å3
Mr = 317.82Z = 4
Monoclinic, C2/mMo Kα radiation
a = 11.6270 (8) ŵ = 14.55 mm1
b = 6.8372 (4) ÅT = 133 K
c = 10.4344 (6) Å0.25 × 0.13 × 0.08 mm
β = 94.574 (4)°
Data collection top
Bruker SMART 1000 CCD
diffractometer
1308 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
1138 reflections with I > 2σ(I)
Tmin = 0.253, Tmax = 0.462Rint = 0.030
7962 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0201 restraint
wR(F2) = 0.052H atoms treated by a mixture of independent and constrained refinement
S = 1.06Δρmax = 0.55 e Å3
1308 reflectionsΔρmin = 0.78 e Å3
58 parameters
Special details top

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.

Non-bonded Distances

3.9011 (0.0005) Br1 - Br2_$1 3.5117 (0.0005) Br2 - Br3_$2 3.4752 (0.0005) Br1 - Br3_$4 3.8311 (0.0007) Br1 - Br1_$5 3.9545 (0.0004) Br1 - Br1_$6 3.9545 (0.0004) Br1 - Br1_$7

101.84 (0.09) C3 - Br1 - Br2_$1 136.03 (0.09) Br1 - Br2_$1 - C5_$1 168.36 (0.09) C5 - Br2 - Br3_$2 158.35 (0.09) C3 - Br1 - Br3_$4 119.39 (0.09) C3 - Br1 - Br1_$5 73.42 (0.04) C3 - Br1 - Br1_$6 73.42 (0.04) C3 - Br1 - Br1_$7

Operators for generating equivalent atoms:

$1 − x, −y, −z $2 − x, −y, −z + 1 $3 − x + 1, −y, −z + 1 $4 x, y, z − 1 $5 − x + 1, −y, −z $6 − x + 1/2, y − 1/2, −z $7 − x + 1/2, y + 1/2, −z

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 (Å2) top
xyzUiso*/Ueq
N10.2711 (2)0.00000.3728 (2)0.0210 (5)
H010.318 (3)0.00000.447 (3)0.041 (11)*
C20.3274 (2)0.00000.2649 (3)0.0213 (6)
H20.40930.00000.26870.026*
C30.2623 (3)0.00000.1490 (3)0.0195 (5)
C40.1426 (2)0.00000.1439 (3)0.0209 (6)
H40.09780.00000.06370.025*
C50.0901 (2)0.00000.2585 (3)0.0196 (5)
C60.1582 (3)0.00000.3746 (3)0.0206 (5)
H60.12350.00000.45400.025*
Br10.33492 (3)0.00000.00570 (3)0.02854 (9)
Br20.07127 (2)0.00000.26154 (3)0.02426 (9)
Br30.36075 (2)0.00000.66478 (3)0.02041 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0210 (12)0.0214 (12)0.0196 (12)0.0000.0055 (10)0.000
C20.0163 (13)0.0203 (14)0.0270 (15)0.0000.0001 (11)0.000
C30.0168 (12)0.0225 (14)0.0196 (13)0.0000.0041 (10)0.000
C40.0179 (13)0.0256 (15)0.0188 (13)0.0000.0005 (10)0.000
C50.0165 (12)0.0203 (14)0.0216 (14)0.0000.0001 (10)0.000
C60.0194 (13)0.0212 (14)0.0213 (13)0.0000.0018 (10)0.000
Br10.02211 (15)0.03806 (19)0.02650 (17)0.0000.00851 (12)0.000
Br20.01390 (14)0.02879 (17)0.03013 (17)0.0000.00204 (11)0.000
Br30.01699 (14)0.02412 (16)0.01952 (14)0.0000.00222 (10)0.000
Geometric parameters (Å, º) top
N1—C61.314 (4)C3—Br11.881 (3)
N1—C21.347 (4)C4—C51.386 (4)
N1—H010.912 (19)C4—H40.9500
C2—C31.375 (4)C5—C61.394 (4)
C2—H20.9500C5—Br21.879 (3)
C3—C41.388 (4)C6—H60.9500
C6—N1—C2124.4 (3)C5—C4—C3118.4 (3)
C6—N1—H01121 (3)C5—C4—H4120.8
C2—N1—H01114 (3)C3—C4—H4120.8
N1—C2—C3117.7 (3)C4—C5—C6119.4 (3)
N1—C2—H2121.2C4—C5—Br2121.6 (2)
C3—C2—H2121.2C6—C5—Br2119.0 (2)
C2—C3—C4121.0 (3)N1—C6—C5119.1 (3)
C2—C3—Br1120.1 (2)N1—C6—H6120.4
C4—C3—Br1119.0 (2)C5—C6—H6120.4
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H01···Br30.91 (2)2.29 (2)3.140 (2)156 (4)
C6—H6···Br2i0.953.084.006 (3)166
C2—H2···Br3ii0.952.713.641 (3)168
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z+1.

Experimental details

Crystal data
Chemical formulaC5H4Br2N+·Br
Mr317.82
Crystal system, space groupMonoclinic, C2/m
Temperature (K)133
a, b, c (Å)11.6270 (8), 6.8372 (4), 10.4344 (6)
β (°) 94.574 (4)
V3)826.85 (9)
Z4
Radiation typeMo Kα
µ (mm1)14.55
Crystal size (mm)0.25 × 0.13 × 0.08
Data collection
DiffractometerBruker SMART 1000 CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 1998)
Tmin, Tmax0.253, 0.462
No. of measured, independent and
observed [I > 2σ(I)] reflections
7962, 1308, 1138
Rint0.030
(sin θ/λ)max1)0.704
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.020, 0.052, 1.06
No. of reflections1308
No. of parameters58
No. of restraints1
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.55, 0.78

Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 1998), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP (Siemens, 1994), SHELXL97.

Selected bond angles (º) top
C6—N1—C2124.4 (3)N1—C6—C5119.1 (3)
N1—C2—C3117.7 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H01···Br30.912 (19)2.29 (2)3.140 (2)156 (4)
C6—H6···Br2i0.953.084.006 (3)166
C2—H2···Br3ii0.952.713.641 (3)168
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z+1.
 

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