p-Phenyl­enedimethanaminium dibromide

In the title salt, C₈H₁₄N₂²⁺·2Br⁻, the cation has a crystallographically imposed centre of symmetry. The compound is isostructural with the chloride analogue. In the crystal structure, the cations and anions are connected via N—H...Br hydrogen bonds, forming layers parallel to the bc plane.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.034
• wR factor = 0.084
• Data-to-parameter ratio = 21.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              Br
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600          9

Alert level G
PLAT154_ALERT_1_G The su's on the Cell Angles are Equal  (x 10000)       3000 Deg.
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT764_ALERT_4_G Overcomplete CIF Bond List Detected (Rep/Expd) .       1.20 Ratio

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   4 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
   1 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

At present, much attention in ferroelectric material field is focused on developing ferroelectric pure organic or inorganic compounds (Haertling, 1999; Homes et al., 2001). Recently we have reported the synthesis of a variety of compounds (Fu et al., 2009; Hang et al., 2009), which have potential piezoelectric and ferroelectric properties. In order to develop new materials of this kind, we investigated the physical properties of the title compound. Its dielectric constant as a function of temperature (93-440 K) indicates that the permittivity is basically temperature-independent (dielectric constant ranging from 3.2 to 4.4), suggesting that this compound should be not a real ferroelectrics or that no distinct phase transition occurred within the measured temperature range. Herein, we report the synthesis and crystal structure of the title compound (Fig. 1).

The cation of the title compound possesses crystallographically imposed centre of symmetry. The compound is isostructural to the chloride analogue (Arkenbout et al., 2007). Bond lengths and angles are within their normal ranges. In the crystal packing (Fig. 2), cations and anions are connected via intermolecular N—H···Br hydrogen bonds (Table 1) to form layers parallel to the bc plane. Contrary to what observed in the chloride salt, the separation between the centroids of stacked aromatic rings (4.446 (2) Å) suggests that no π···π stacking interactions are present.

Related literature

For the synthesis, structures and properties of ferroelectric pure organic or inorganic compounds, see: Haertling (1999); Homes et al. (2001); Fu et al. (2009); Hang et al. (2009). For the structure of the isostructural chloride salt, see: Arkenbout et al. (2007).

S2. Experimental

Hydrobromic acid (4.05 g, 40%) was added slowly to a solution of 1,4-phenylenedimethanamine (2.72 g, 0.02 mol) in methanol. After several days, colourless prismatic crystals of the title compound suitable for X-ray analysis were obtained on slow evaporation of the solvent.

S3. Refinement

H atoms were positioned geometrically and refined using a riding model, with C—H = 0.93-0.97 Å, N—H = 0.89 Å, and with U_iso(H) = 1.2_eq(C, N).

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL/PC (Sheldrick, 2008); software used to prepare material for publication: SHELXTL/PC (Sheldrick, 2008).

Figures

	Fig. 1. The structure of the title compound showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Atoms labelled with the suffix A are related by the symmetry code (1-x, 1-y, 1-z).
	Fig. 2. Crystal packing of the title compound approximately viewed along the b axis, showing the hydrogen bondings network.

p-Phenylenedimethanaminium dibromide

Crystal data

C8H14N2^2+·2Br^−	Z = 1
Mr = 298.01	F(000) = 146
Triclinic, P1	Dx = 1.861 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 4.4462 (9) Å	Cell parameters from 1213 reflections
b = 6.0331 (12) Å	θ = 2.6–27.5°
c = 10.347 (2) Å	µ = 7.58 mm^−1
α = 101.90 (3)°	T = 293 K
β = 99.79 (3)°	Prism, colorless
γ = 94.29 (3)°	0.20 × 0.20 × 0.20 mm
V = 265.89 (9) Å^3

Data collection

Rigaku Mercury2 diffractometer	1213 independent reflections
Radiation source: fine-focus sealed tube	1107 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
Detector resolution: 13.6612 pixels mm^-1	θmax = 27.5°, θmin = 3.5°
CCD_Profile_fitting scans	h = −5→5
Absorption correction: multi-scan (CrystalClear; Rigaku, 2005)	k = −7→7
Tmin = 0.837, Tmax = 1.000	l = −13→13
2767 measured reflections

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)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.084	w = 1/[σ^2(Fo^2) + (0.0314P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
1213 reflections	Δρmax = 0.59 e Å^−3
56 parameters	Δρmin = −0.68 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.102 (8)

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
N1	0.5050 (7)	0.6880 (4)	0.8667 (3)	0.0352 (6)
H1A	0.4270	0.7394	0.9393	0.042*
H1B	0.6628	0.7845	0.8646	0.042*
H1C	0.5668	0.5525	0.8698	0.042*
C2	0.2679 (7)	0.6652 (6)	0.7437 (3)	0.0354 (8)
H2D	0.1943	0.8121	0.7417	0.042*
H2E	0.0952	0.5593	0.7466	0.042*
C5	0.3474 (8)	0.3493 (5)	0.5579 (3)	0.0345 (7)
H5A	0.2447	0.2476	0.5965	0.041*
C7	0.3911 (7)	0.5816 (5)	0.6174 (3)	0.0293 (7)
C10	0.4567 (8)	0.2702 (6)	0.4418 (3)	0.0353 (8)
H10A	0.4276	0.1150	0.4028	0.042*
Br1	−0.14338 (7)	0.20342 (5)	0.87105 (3)	0.03667 (19)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0523 (17)	0.0363 (15)	0.0199 (14)	0.0134 (12)	0.0156 (11)	0.0027 (12)
C2	0.0390 (17)	0.0412 (19)	0.0265 (17)	0.0107 (14)	0.0140 (13)	0.0005 (15)
C5	0.0451 (18)	0.0314 (17)	0.0300 (19)	0.0020 (13)	0.0145 (14)	0.0088 (15)
C7	0.0343 (16)	0.0345 (17)	0.0197 (16)	0.0071 (12)	0.0074 (12)	0.0040 (14)
C10	0.055 (2)	0.0265 (16)	0.0249 (18)	0.0067 (14)	0.0131 (15)	0.0013 (14)
Br1	0.0478 (3)	0.0329 (3)	0.0303 (3)	0.00763 (15)	0.01254 (16)	0.00384 (18)

Geometric parameters (Å, º)

N1—C2	1.483 (4)	C5—C10	1.380 (4)
N1—H1A	0.8880	C5—C7	1.394 (4)
N1—H1B	0.8839	C5—H5A	0.9300
N1—H1C	0.8865	C7—C10^i	1.382 (5)
C2—C7	1.509 (4)	C10—C7^i	1.382 (5)
C2—H2D	0.9700	C10—H10A	0.9300
C2—H2E	0.9700
C2—N1—H1A	109.9	H2D—C2—H2E	107.9
C2—N1—H1B	109.6	C10—C5—C7	120.0 (3)
H1A—N1—H1B	109.3	C10—C5—H5A	120.0
C2—N1—H1C	109.0	C7—C5—H5A	120.0
H1A—N1—H1C	109.4	C10^i—C7—C5	119.1 (3)
H1B—N1—H1C	109.6	C10^i—C7—C2	121.7 (3)
N1—C2—C7	111.9 (2)	C5—C7—C2	119.3 (3)
N1—C2—H2D	109.2	C5—C10—C7^i	120.9 (3)
C7—C2—H2D	109.2	C5—C10—H10A	119.5
N1—C2—H2E	109.2	C7^i—C10—H10A	119.5
C7—C2—H2E	109.2

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Br1^ii	0.89	2.49	3.359 (3)	167
N1—H1B···Br1^iii	0.88	2.59	3.363 (3)	146
N1—H1C···Br1^iv	0.89	2.55	3.422 (3)	167

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