2,2',5,5'-Tetra­chloro­benzidine

In the crystal structure of the title compound, C₁₂H₈Cl₄N₂, mol­ecules lie on crystallographic twofold axes at the centre of the C-C bonds linking the benzene rings, such that the asymmetric unit consists of a half-mol­ecule. The individual mol­ecules participate in inter­molecular N-H...N, N-H...Cl, C-H...Cl and Cl...Cl [3.4503 (3) Å] inter­actions.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.025
• wR factor = 0.075
• Data-to-parameter ratio = 36.1

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          2
PLAT480_ALERT_4_C Long H...A H-Bond Reported H1B    ..  N1      ..       2.90 Ang.
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600          2

Alert level G
PLAT128_ALERT_4_G Alternate Setting of Space-group C2/c    .......      I2/a

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

   0 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

Benzidines are of great importance in the pigments industry, as their derivatives are employed in the syntheses of a variety of azo-dyes (Schwenecke and Mayer 2005). Furthermore, the presence of two amine functionalities renders this class of molecules attractive to crystal engineers, who may wish to incorporate this class of rigid linear molecule in larger extended networks via hydrogen bonds (Dobrzycki and Wozniak 2008 a, b). During the course of experiments aimed at reacting the title compound with pyrazole-3,5-dicarboxylic acid, a crystalline phase was obtained and shown to be composed solely of 2,2',5,5'-tetrachlorobenzidine. A search of the Cambridge crystallographic structural database showed that this phase has not previously been reported. This molecule packs in monoclinic I2/a, a non-standard setting of C2/c, with one half of the molecule in the asymmetric unit. Very weak hydrogen bonding interactions exist in the structure; the increased lengths are probably due to the bulky chlorine atoms ortho to the amine functionalities.

Related literature

For studies involving the use of benzidines in organic syntheses, see: Schwenecke & Mayer (2005). For studies on 2,2',5,5'-tetrachlorobenzidine in crystal engineering, see: Dobrzycki & Wozniak (2007, 2008). For our studies on related structures, see: Beatty et al. (2002a, 2002b); Ugono et al. (2009).

For related literature, see: .

S2. Experimental

A 20 ml scintillation vial was charged with 52.0 mg (0.30 mmol) of 3,5-pyrazole dicarboxylic acid monohydrate, which was dissolved in 5.0 ml of a 3:2 MeOH:H₂O mixture affording a homogenous solution. To this solution was then added 48.3 mg (0.15 mmol) of 2,2',5,5'-tetrachlorobenzidine. The mixture obtained was filtered and the filtrate was allowed to slowly evaporate to yield colorless single crystals of 2,2',5,5'-tetrachlorobenzidine after a week.

S3. Refinement

All non hydrogen atoms were refined anisotropically. Phenyl hydrogen atoms were placed in calculated positions and treated with a riding model C–H= 0.95 Å, U_iso(H_aryl)= 1.2U_eq(C) for aromatic carbons. The amine hydrogen atoms were also placed in calculated positions and refined using the riding model N–H= 0.88 Å, U_iso(H_amine)= 1.2U_eq(N).

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

Fig. 1. Molecular structure showing 50% probability displacement ellipsoid.

2,2',5,5'-Tetrachlorobenzidine

Crystal data

C12H8Cl4N2	F(000) = 648
Mr = 322.00	Dx = 1.769 Mg m^−3
Monoclinic, I2/a	Melting point = 309–311 K
Hall symbol: -I 2ya	Mo Kα radiation, λ = 0.71073 Å
a = 17.2346 (11) Å	Cell parameters from 5249 reflections
b = 3.8767 (2) Å	θ = 4.5–36.4°
c = 18.1573 (19) Å	µ = 0.96 mm^−1
β = 94.872 (3)°	T = 100 K
V = 1208.77 (16) Å^3	Blocks, colorless
Z = 4	0.23 × 0.22 × 0.14 mm

Data collection

Bruker APEXII CCD diffractometer	2961 independent reflections
Radiation source: fine-focus sealed tube	2595 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
φ and ω scans	θmax = 36.4°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −28→28
Tmin = 0.806, Tmax = 0.879	k = −3→6
11878 measured reflections	l = −30→26

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.025	w = 1/[σ^2(Fo^2) + (0.0404P)^2 + 0.5838P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.075	(Δ/σ)max < 0.001
S = 1.07	Δρmax = 0.62 e Å^−3
2961 reflections	Δρmin = −0.67 e Å^−3
82 parameters

Special details

Experimental. All H atoms were added in their calculated positions and were treated using appropriate riding models.

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
Cl1	0.160889 (12)	0.57866 (5)	0.112011 (11)	0.01179 (5)
Cl2	0.490222 (11)	−0.04833 (5)	0.098542 (11)	0.01279 (6)
N1	0.42631 (4)	0.2547 (2)	0.23242 (4)	0.01399 (13)
H1A	0.4109	0.3405	0.2736	0.017*
H1B	0.4733	0.1666	0.2320	0.017*
C1	0.25315 (5)	0.4094 (2)	0.10312 (5)	0.00977 (13)
C2	0.27558 (5)	0.2934 (2)	0.03511 (4)	0.00940 (12)
C3	0.35064 (5)	0.1556 (2)	0.03688 (4)	0.01012 (13)
H3	0.3688	0.0715	−0.0077	0.012*
C4	0.39925 (5)	0.1373 (2)	0.10113 (5)	0.00990 (13)
C5	0.37670 (5)	0.2584 (2)	0.16844 (4)	0.01036 (13)
C6	0.30195 (5)	0.3964 (2)	0.16774 (5)	0.01065 (13)
H6	0.2842	0.4830	0.2123	0.013*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.00978 (9)	0.01507 (9)	0.01067 (9)	0.00235 (6)	0.00183 (6)	0.00083 (6)
Cl2	0.00832 (9)	0.01894 (10)	0.01088 (10)	0.00207 (6)	−0.00065 (6)	0.00105 (6)
N1	0.0119 (3)	0.0218 (3)	0.0076 (3)	0.0000 (3)	−0.0027 (2)	−0.0006 (2)
C1	0.0089 (3)	0.0118 (3)	0.0086 (3)	0.0002 (2)	0.0006 (2)	0.0005 (2)
C2	0.0084 (3)	0.0118 (3)	0.0079 (3)	−0.0002 (2)	0.0000 (2)	0.0000 (2)
C3	0.0093 (3)	0.0127 (3)	0.0081 (3)	0.0001 (2)	−0.0002 (2)	−0.0006 (2)
C4	0.0076 (3)	0.0130 (3)	0.0088 (3)	0.0001 (2)	−0.0004 (2)	0.0003 (2)
C5	0.0098 (3)	0.0128 (3)	0.0082 (3)	−0.0021 (2)	−0.0009 (2)	0.0005 (2)
C6	0.0110 (3)	0.0135 (3)	0.0074 (3)	−0.0007 (2)	0.0005 (2)	−0.0005 (2)

Geometric parameters (Å, º)

Cl1—C1	1.7402 (8)	C2—C3	1.3974 (11)
Cl2—C4	1.7295 (8)	C2—C2^i	1.4872 (16)
N1—C5	1.3827 (11)	C3—C4	1.3791 (11)
N1—H1A	0.8800	C3—H3	0.9500
N1—H1B	0.8800	C4—C5	1.3948 (12)
C1—C6	1.3854 (12)	C5—C6	1.3940 (12)
C1—C2	1.3993 (12)	C6—H6	0.9500
C5—N1—H1A	120.0	C2—C3—H3	118.9
C5—N1—H1B	120.0	C3—C4—C5	121.97 (7)
H1A—N1—H1B	120.0	C3—C4—Cl2	119.03 (6)
C6—C1—C2	122.84 (8)	C5—C4—Cl2	118.98 (6)
C6—C1—Cl1	115.40 (6)	N1—C5—C6	121.10 (8)
C2—C1—Cl1	121.75 (6)	N1—C5—C4	122.30 (8)
C3—C2—C1	115.29 (7)	C6—C5—C4	116.56 (7)
C3—C2—C2^i	120.00 (8)	C1—C6—C5	121.05 (8)
C1—C2—C2^i	124.63 (8)	C1—C6—H6	119.5
C4—C3—C2	122.26 (8)	C5—C6—H6	119.5
C4—C3—H3	118.9
C6—C1—C2—C3	1.26 (12)	C3—C4—C5—N1	−177.11 (8)
Cl1—C1—C2—C3	−178.33 (6)	Cl2—C4—C5—N1	4.10 (11)
C6—C1—C2—C2^i	178.20 (6)	C3—C4—C5—C6	0.59 (12)
Cl1—C1—C2—C2^i	−1.39 (9)	Cl2—C4—C5—C6	−178.20 (6)
C1—C2—C3—C4	−0.36 (12)	C2—C1—C6—C5	−1.26 (12)
C2^i—C2—C3—C4	−177.46 (6)	Cl1—C1—C6—C5	178.35 (6)
C2—C3—C4—C5	−0.56 (13)	N1—C5—C6—C1	178.02 (8)
C2—C3—C4—Cl2	178.23 (6)	C4—C5—C6—C1	0.29 (12)

Symmetry code: (i) −x+1/2, y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Cl2^ii	0.88	2.79	3.3650 (8)	124
C3—H3···Cl1^iii	0.95	2.71	3.5013 (9)	141
N1—H1B···N1^ii	0.88	2.90	3.2159 (12)	103

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