Polymorph β of 1H-benzimidazole

A second ortho­rhom­bic polymorph (β) of 1H-benzimidazole, C₇H₆N₂, metastable at room temperature, has been obtained. It has a melting point of 431 K and a crystal density of 1.27 Mg m⁻³. At room temperature, the crystals transform into the well known ortho­rhom­bic α form, with a melting point of 445 K. In both polymorphs, benzimidazole mol­ecules are connected into polymeric chains via N—H...N hydrogen bonds. However, the mode of aromatic ring inter­actions differs significantly in the two crystalline forms. In the α form, the mol­ecules show edge-to-face inter­actions, whereas in the new β form, a sandwich–herringbone arrangement of the aromatic mol­ecules is observed.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.053
• wR factor = 0.116
• Data-to-parameter ratio = 12.4

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Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2004); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Stereochemical Workstation Operation Manual (Siemens, 1989) and Mercury (Version 1.3; Bruno et al., 2002); software used to prepare material for publication: SHELXL97.

1H-benzimidazole

Crystal data

C7H6N2	Dx = 1.271 Mg m^−3
Mr = 118.14	Melting point = 431–432 K
Orthorhombic, Pccn	Mo Kα radiation, λ = 0.71073 Å
a = 9.7257 (11) Å	Cell parameters from 2816 reflections
b = 16.6879 (17) Å	θ = 4–25°
c = 7.6056 (11) Å	µ = 0.08 mm^−1
V = 1234.4 (3) Å^3	T = 295 K
Z = 8	Needle, colourless
F(000) = 496	0.6 × 0.2 × 0.02 mm

Data collection

Kuma KM4 CCD κ geometry diffractometer	887 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.028
Graphite monochromator	θmax = 25.0°, θmin = 4.2°
ω scans	h = −11→9
4312 measured reflections	k = −19→14
1091 independent reflections	l = −9→9

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.116	H-atom parameters constrained
S = 1.17	w = 1/[σ^2(Fo^2) + (0.0569P)^2] where P = (Fo^2 + 2Fc^2)/3
1091 reflections	(Δ/σ)max < 0.001
88 parameters	Δρmax = 0.11 e Å^−3
0 restraints	Δρmin = −0.17 e Å^−3

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	0.85139 (16)	0.47227 (8)	0.19758 (18)	0.0516 (5)
H1	0.7676	0.4887	0.1995	0.068 (6)*
C2	0.95811 (19)	0.50402 (13)	0.2859 (2)	0.0553 (5)
H2	0.9494	0.5484	0.3590	0.063 (6)*
N3	1.07556 (15)	0.46717 (9)	0.26031 (18)	0.0559 (5)
C4	1.1264 (2)	0.34826 (11)	0.0648 (2)	0.0597 (6)
H4	1.2198	0.3455	0.0904	0.074 (6)*
C5	1.0668 (2)	0.29575 (12)	−0.0519 (3)	0.0666 (6)
H5	1.1210	0.2571	−0.1061	0.077 (6)*
C6	0.9266 (2)	0.29926 (12)	−0.0908 (3)	0.0652 (6)
H6	0.8898	0.2633	−0.1714	0.077 (6)*
C7	0.8420 (2)	0.35477 (11)	−0.0127 (2)	0.0594 (6)
H7	0.7482	0.3564	−0.0366	0.063 (6)*
C8	0.90272 (17)	0.40831 (10)	0.1034 (2)	0.0441 (5)
C9	1.04281 (17)	0.40549 (10)	0.1431 (2)	0.0457 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0376 (10)	0.0607 (10)	0.0566 (9)	0.0025 (8)	0.0029 (7)	0.0033 (8)
C2	0.0533 (13)	0.0633 (13)	0.0493 (10)	0.0002 (10)	0.0039 (9)	−0.0035 (10)
N3	0.0441 (10)	0.0676 (11)	0.0559 (9)	−0.0002 (8)	−0.0025 (7)	−0.0068 (8)
C4	0.0465 (13)	0.0631 (13)	0.0695 (12)	0.0054 (9)	0.0008 (10)	−0.0016 (11)
C5	0.0692 (15)	0.0547 (13)	0.0759 (13)	0.0053 (11)	0.0066 (11)	−0.0059 (11)
C6	0.0742 (15)	0.0525 (13)	0.0688 (12)	−0.0090 (11)	−0.0079 (11)	−0.0062 (10)
C7	0.0497 (13)	0.0564 (12)	0.0721 (12)	−0.0076 (10)	−0.0090 (10)	0.0053 (10)
C8	0.0407 (11)	0.0456 (11)	0.0460 (9)	−0.0020 (8)	0.0029 (8)	0.0083 (8)
C9	0.0416 (12)	0.0493 (11)	0.0461 (9)	−0.0036 (8)	0.0026 (8)	0.0047 (9)

Geometric parameters (Å, º)

N1—C2	1.345 (2)	C4—H4	0.9300
N1—C8	1.3791 (19)	C5—C6	1.396 (3)
N1—H1	0.8600	C5—H5	0.9300
C2—N3	1.312 (2)	C6—C7	1.374 (3)
C2—H2	0.9300	C6—H6	0.9300
N3—C9	1.398 (2)	C7—C8	1.388 (2)
C4—C5	1.376 (2)	C7—H7	0.9300
C4—C9	1.389 (2)	C8—C9	1.396 (2)
C2—N1—C8	106.55 (15)	C7—C6—C5	121.44 (19)
C2—N1—H1	126.7	C7—C6—H6	119.3
C8—N1—H1	126.7	C5—C6—H6	119.3
N3—C2—N1	114.41 (17)	C6—C7—C8	116.97 (18)
N3—C2—H2	122.8	C6—C7—H7	121.5
N1—C2—H2	122.8	C8—C7—H7	121.5
C2—N3—C9	103.96 (15)	N1—C8—C7	132.41 (17)
C5—C4—C9	117.90 (18)	N1—C8—C9	105.48 (14)
C5—C4—H4	121.0	C7—C8—C9	122.09 (16)
C9—C4—H4	121.0	C4—C9—C8	120.11 (16)
C4—C5—C6	121.47 (19)	C4—C9—N3	130.27 (16)
C4—C5—H5	119.3	C8—C9—N3	109.60 (14)
C6—C5—H5	119.3

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···N3^i	0.86	2.03	2.884 (2)	172

Symmetry code: (i) x−1/2, −y+1, −z+1/2.