trans-Dichloro­tetra­benzimidazole­cadmium(II) tetra­benzimidazole: a three-dimensional supra­molecular structure built from C—H...π, N—H...Cl and N—H...N hydrogen bonds

The title compound, [CdCl₂(C₇H₆N₂)₄]·4C₇H₆N₂, consists of a Cd(Bzim)₄Cl₂ complex (Bzim is benzimidazole) lying on a fourfold rotation axis in the space group P4nc, and four benzimidazole mol­ecules which are linked to the coordinated benzimidazole unit by N—H...N hydrogen bonds. One N—H...Cl and three C—H...π hydrogen bonds link these units into a three-dimensional supra­molecular structure.

S1. Comment

Benzimidazole is a very important group which has been applied in the drug design of antitumour agents (Arrowsmith et al., 2002; Hay et al., 2003), and its metal complexes are reported to have the activities of the superoxide dismutase (SOD) enzyme (Nishida et al., 1991; Kwak et al., 1999; Liao et al., 2001; Qin et al., 2005) and nuclease (Liu et al., 2004). Because of our interest in these areas, the title compound, (I), was synthesized and we report its crystal structure here.

Compound (I) (Fig. 1) consists of a Cd(Bzim)₄Cl₂ complex and four free benzimidazole molecules, lying around a fourfold rotation axis in space group P4nc. In the complex, four N atoms from four benzimidazole ligands and two Cl⁻ counter-anions coordinate to Cd²⁺, giving rise to an octahedron with four N atoms in the equatorial plane and two Cl⁻ anions occupying the apical positions. It is interesting that the four benzimidazole ligands coordinated to Cd surround the Cd atom like a flower, similar to the structure in the complex [Ni₂(Bzim)₈Cl₃](Cl)·4C₃H₆O (Drew et al., 1968). Each benzimidazole ligand is inclined to the equatorial plane of the octahedron at an angle of 41.19 (6)°. Associated with the asymmetric arrangement of benzimidazole ligands along the axial direction, the two Cd—Cl1 distances differ significantly (Table 1). The four free benzimidazole molecules are hydrogen-bonded to the four coordinated benzimidazole ligands by N2—H···N3 bonding, with a dihedral angle between the hydrogen-bonded benzimidazole ligands of 82.69 (8)°. Therefore, the whole structure of (I) is like a flower with double-layer foliage, forming a fourfold axially symmetric molecule.

Three C—H···π and one N—H···Cl hydrogen bonds (Table 2) link the complexes into ladders along [001]. The two C—H···π interactions of C1—H···Cg1ⁱⁱ [Cg1 is the centroid of the C9–C14 ring; symmetry code: (ii) 3/2 − y, 3/2 − x, 1/2 + z] and C8—H···Cg2ⁱⁱ (Cg2 is the centroid of the C2–C7 ring) link neighbouring hydrogen-bonded benimidazole pairs to form a zigzag double chain in the c direction. The third C—H···π interaction is between C6—H and the centroid of the five-membered ring N3/C8/N4/C10/C9 at the symmetry position (3/2 − x, y − 1/2, z − 1/2). All hydrogen bonds involve the uncoordinated benzimidazole. Therefore, in the crystal structure of compound (I), the free benzimidazoles are actually stabilized outside the complex by five hydrogen bonds. As the complex is a fourfold axially symmetric molecule and neighbouring molecules have the same interactions in four directions, so every molecule of (I) indeed connects eight neighbouring ones at the apical position of a cube, building the compound into a three-dimensional structure.

Compared with another space group (I4₁/a) of the same crystal system (Glidewell et al., 2005), similar large void spaces were examined using PLATON (Spek, 2003). In the three-dimensional structure of (I), there are channels parallel to [001] (Fig. 3) and these account in total for 193.1 ų per unit cell, i.e. some 7.1% of the total volume. The channels lie along the twofold axes, with an average cross-sectional area of ca 10.4 Ų and an average diameter of ca 3.64 Å. The reflection data were subjected to the SQUEEZE routine in PLATON before the final refinement, and this suggested the presence of only 2.2 electrons per unit cell within the voids.

S2. Experimental

The compound was synthesized under hydrothermal conditions. A mixture of V₂O₅, CdCl₂·2.5H₂O, 1,2-di(1H-benzo[d]imidazol-2-yl)ethane-1,2-diol, imidazole and distilled water in a molar ratio of 1:1:2:2:720 was heated from 293 to 448 K in 2 h in a 25 ml stainless-steel reactor with a Teflon liner, and the temperature was kept constant at 448 K for 92 h. Yellow crystals of (I) were obtained from the filtrate at room temperature over several days.

S3. Refinement

H atoms attached to C and N atoms of (I) were placed in geometrically idealized positions, with C—H = 0.93 and N—H = 0.86 Å, and refined with U_iso(H) = 1.2U_eq(C,N). The correct orientation of the structure relative to the polar axis direction was established using the Flack parameter (Flack 1983). Examination of the refined structure using PLATON (Spek, 2003) revealed the presence of void spaces having a total volume of 193.1 ų per unit cell, arranged into four channels along the c axis direction. There was a low residual electron density of 0.54 e Å⁻³ located 0.94 Å from Cd1.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC (Sheldrick, 1999); software used to prepare material for publication: SHELXTL/PC.

Figures

	Fig. 1. The structure of (I), with displacement ellipsoids drawn at the 30% probability level. H atoms are shown as small spheres of arbitrary radii and dotted lines indicate hydrogen bonds. [Symmetry codes: (i) 1 − x, 1 − y, z; (ii) 1 − y, x, z; (iii) y, 1 − x, z.]
	Fig. 2. The edge-to-face C—H···π (dashed lines) and N—H···Cl (dotted lines) hydrogen bonding in (I). H atoms not involved the hydrogen bonding shown in the figure have been omitted for clarity. Cg1 is the centroid of the C9–C14 ring, Cg2 is the centroid of the C2–C7 ring and Cg3 is the centroid of the N3/C8/N4/C10/C9 ring. [Symmetry codes: (i) 1 − y, x, z; (ii) 1/2 + x, 1/2 − y, −1/2 + z; (iii) y, 1 − x, −1 + z; (iv) 1/2 − y, 3/2 − x, −1/2 + z].
	Fig. 3. An ab projection of the crystal structure of (I), showing the [001] channels.

trans-Dichlorotetrabenzimidazolecadmium(II) tetrabenzimidazole

Crystal data

[CdCl2(C7H6N2)4]·4C7H6N2	Dx = 1.384 Mg m^−3
Mr = 1128.40	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4nc	Cell parameters from 4359 reflections
Hall symbol: P 4 -2n	θ = 2.4–25.4°
a = 17.0805 (18) Å	µ = 0.56 mm^−1
c = 9.2818 (15) Å	T = 298 K
V = 2707.9 (6) Å^3	Block, yellow
Z = 2	0.40 × 0.30 × 0.20 mm
F(000) = 1156

Data collection

Bruker SMART 1K CCD area-detector diffractometer	2379 independent reflections
Radiation source: fine-focus sealed tube	2088 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ω scans	θmax = 25.0°, θmin = 1.7°
Absorption correction: multi-scan (SADABS: Sheldrick, 2000)	h = −18→20
Tmin = 0.808, Tmax = 0.897	k = −20→12
12444 measured reflections	l = −11→10

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)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0519P)^2 + 0.1395P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
2379 reflections	Δρmax = 0.54 e Å^−3
172 parameters	Δρmin = −0.42 e Å^−3
1 restraint	Absolute structure: Flack (1983), with how many Friedel pairs?
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.01 (4)

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
Cd1	0.5000	0.5000	0.50007 (7)	0.03843 (16)
Cl1	0.5000	0.5000	0.1979 (3)	0.0441 (7)
Cl2	0.5000	0.5000	0.7851 (3)	0.0474 (8)
N1	0.61932 (14)	0.56926 (14)	0.4937 (4)	0.0372 (6)
N2	0.69740 (17)	0.67076 (16)	0.5320 (4)	0.0486 (9)
H2	0.7140	0.7144	0.5666	0.058*
C1	0.6295 (2)	0.6364 (2)	0.5635 (4)	0.0446 (9)
H1	0.5931	0.6572	0.6274	0.054*
C2	0.68658 (17)	0.56028 (19)	0.4120 (4)	0.0369 (7)
C3	0.73562 (19)	0.62441 (19)	0.4364 (4)	0.0437 (8)
C4	0.8063 (2)	0.6321 (3)	0.3654 (5)	0.0662 (13)
H4	0.8383	0.6755	0.3799	0.079*
C5	0.8273 (2)	0.5739 (3)	0.2739 (6)	0.0716 (13)
H5	0.8749	0.5775	0.2256	0.086*
C6	0.7793 (5)	0.5082 (2)	0.2495 (6)	0.0589 (16)
H6	0.7957	0.4691	0.1866	0.071*
C7	0.7086 (2)	0.5016 (2)	0.3182 (5)	0.0475 (9)
H7	0.6762	0.4587	0.3019	0.057*
N3	0.76878 (19)	0.82070 (18)	0.5324 (4)	0.0585 (9)
N4	0.85570 (17)	0.91533 (18)	0.5041 (6)	0.0637 (8)
H4A	0.8982	0.9415	0.5161	0.076*
C8	0.8369 (2)	0.8480 (2)	0.5687 (5)	0.0606 (11)
H8	0.8698	0.8229	0.6339	0.073*
C9	0.7403 (2)	0.8748 (2)	0.4354 (5)	0.0545 (10)
C10	0.7943 (2)	0.9352 (2)	0.4158 (5)	0.0532 (9)
C11	0.7809 (3)	0.9976 (2)	0.3264 (6)	0.0679 (14)
H11	0.8173	1.0378	0.3169	0.081*
C12	0.7122 (7)	0.9983 (3)	0.2523 (8)	0.088 (3)
H12	0.7010	1.0398	0.1908	0.106*
C13	0.6579 (3)	0.9369 (4)	0.2675 (8)	0.1022 (19)
H13	0.6117	0.9379	0.2143	0.123*
C14	0.6715 (3)	0.8764 (3)	0.3583 (6)	0.095 (2)
H14	0.6349	0.8364	0.3684	0.114*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.03005 (17)	0.03005 (17)	0.0552 (3)	0.000	0.000	0.000
Cl1	0.0423 (11)	0.0423 (11)	0.0478 (13)	0.000	0.000	0.000
Cl2	0.0464 (11)	0.0464 (11)	0.0495 (12)	0.000	0.000	0.000
N1	0.0330 (12)	0.0356 (13)	0.0429 (15)	−0.0012 (10)	−0.0062 (16)	0.0023 (17)
N2	0.0463 (15)	0.0360 (15)	0.064 (2)	−0.0094 (13)	−0.0012 (16)	−0.0104 (15)
C1	0.0392 (19)	0.043 (2)	0.051 (2)	0.0030 (17)	0.0093 (16)	−0.0030 (17)
C2	0.0329 (17)	0.0370 (17)	0.0407 (19)	0.0033 (14)	−0.0037 (16)	0.0035 (16)
C3	0.0371 (18)	0.0391 (18)	0.055 (2)	−0.0058 (15)	−0.0022 (17)	0.0027 (17)
C4	0.048 (2)	0.066 (3)	0.084 (3)	−0.019 (2)	0.015 (2)	−0.006 (2)
C5	0.042 (2)	0.083 (3)	0.091 (4)	−0.008 (2)	0.023 (2)	−0.001 (3)
C6	0.059 (4)	0.054 (3)	0.064 (4)	0.007 (2)	0.008 (3)	−0.009 (2)
C7	0.045 (2)	0.044 (2)	0.054 (2)	0.0018 (17)	0.0023 (19)	0.0052 (17)
N3	0.0583 (19)	0.0472 (18)	0.070 (3)	−0.0142 (15)	−0.0114 (18)	0.0030 (18)
N4	0.0448 (16)	0.0532 (18)	0.093 (2)	−0.0126 (14)	0.006 (3)	−0.011 (2)
C8	0.061 (3)	0.051 (2)	0.069 (3)	−0.002 (2)	−0.005 (2)	−0.009 (2)
C9	0.059 (2)	0.045 (2)	0.059 (2)	−0.0111 (19)	−0.013 (2)	−0.015 (2)
C10	0.057 (2)	0.044 (2)	0.059 (2)	−0.0039 (19)	0.016 (2)	−0.011 (2)
C11	0.075 (4)	0.045 (2)	0.083 (3)	−0.001 (2)	0.031 (3)	0.000 (2)
C12	0.109 (8)	0.077 (5)	0.080 (5)	0.033 (4)	0.019 (4)	0.013 (3)
C13	0.092 (4)	0.096 (5)	0.119 (5)	0.004 (4)	−0.041 (4)	0.001 (4)
C14	0.095 (4)	0.065 (3)	0.125 (5)	−0.024 (3)	−0.047 (3)	0.017 (3)

Geometric parameters (Å, º)

Cd1—N1^i	2.357 (2)	C6—C7	1.370 (9)
Cd1—N1	2.357 (2)	C6—H6	0.9300
Cd1—N1^ii	2.357 (2)	C7—H7	0.9300
Cd1—N1^iii	2.357 (2)	N3—C8	1.299 (5)
Cd1—Cl2	2.645 (3)	N3—C9	1.380 (5)
Cd1—Cl1	2.804 (3)	N4—C8	1.336 (6)
N1—C1	1.328 (5)	N4—C10	1.373 (5)
N1—C2	1.385 (4)	N4—H4A	0.8601
N2—C1	1.333 (5)	C8—H8	0.9300
N2—C3	1.357 (5)	C9—C14	1.376 (6)
N2—H2	0.8600	C9—C10	1.396 (5)
C1—H1	0.9300	C10—C11	1.370 (6)
C2—C7	1.380 (5)	C11—C12	1.361 (12)
C2—C3	1.397 (4)	C11—H11	0.9300
C3—C4	1.382 (5)	C12—C13	1.408 (10)
C4—C5	1.356 (6)	C12—H12	0.9300
C4—H4	0.9300	C13—C14	1.353 (7)
C5—C6	1.408 (7)	C13—H13	0.9300
C5—H5	0.9300	C14—H14	0.9300
N1^i—Cd1—N1	177.13 (19)	C4—C5—H5	118.9
N1^i—Cd1—N1^ii	89.964 (5)	C6—C5—H5	118.9
N1—Cd1—N1^ii	89.964 (6)	C7—C6—C5	120.3 (5)
N1^i—Cd1—N1^iii	89.964 (6)	C7—C6—H6	119.9
N1—Cd1—N1^iii	89.964 (5)	C5—C6—H6	119.9
N1^ii—Cd1—N1^iii	177.13 (19)	C6—C7—C2	118.3 (4)
N1^i—Cd1—Cl2	91.44 (10)	C6—C7—H7	120.9
N1—Cd1—Cl2	91.44 (10)	C2—C7—H7	120.9
N1^ii—Cd1—Cl2	91.44 (10)	C8—N3—C9	104.2 (3)
N1^iii—Cd1—Cl2	91.44 (10)	C8—N4—C10	107.3 (3)
N1^i—Cd1—Cl1	88.56 (10)	C8—N4—H4A	126.3
N1—Cd1—Cl1	88.56 (10)	C10—N4—H4A	126.4
N1^ii—Cd1—Cl1	88.56 (10)	N3—C8—N4	114.0 (4)
N1^iii—Cd1—Cl1	88.56 (10)	N3—C8—H8	123.0
Cl2—Cd1—Cl1	180.000 (1)	N4—C8—H8	123.0
C1—N1—C2	104.7 (3)	C14—C9—N3	130.8 (4)
C1—N1—Cd1	122.3 (2)	C14—C9—C10	118.9 (4)
C2—N1—Cd1	132.5 (2)	N3—C9—C10	110.3 (3)
C1—N2—C3	107.8 (3)	C11—C10—N4	132.9 (4)
C1—N2—H2	126.0	C11—C10—C9	122.9 (4)
C3—N2—H2	126.2	N4—C10—C9	104.1 (3)
N1—C1—N2	112.8 (3)	C12—C11—C10	117.1 (5)
N1—C1—H1	123.6	C12—C11—H11	121.4
N2—C1—H1	123.6	C10—C11—H11	121.4
C7—C2—N1	130.7 (3)	C11—C12—C13	120.8 (6)
C7—C2—C3	120.6 (3)	C11—C12—H12	119.6
N1—C2—C3	108.8 (3)	C13—C12—H12	119.6
N2—C3—C4	132.6 (3)	C14—C13—C12	121.2 (6)
N2—C3—C2	106.0 (3)	C14—C13—H13	119.4
C4—C3—C2	121.4 (4)	C12—C13—H13	119.4
C5—C4—C3	117.4 (4)	C13—C14—C9	119.0 (5)
C5—C4—H4	121.3	C13—C14—H14	120.5
C3—C4—H4	121.3	C9—C14—H14	120.5
C4—C5—C6	122.1 (5)
N1^ii—Cd1—N1—C1	−145.1 (2)	C3—C4—C5—C6	0.6 (8)
N1^iii—Cd1—N1—C1	37.8 (4)	C4—C5—C6—C7	0.6 (9)
Cl2—Cd1—N1—C1	−53.7 (3)	C5—C6—C7—C2	−0.7 (8)
Cl1—Cd1—N1—C1	126.3 (3)	N1—C2—C7—C6	179.3 (4)
N1^ii—Cd1—N1—C2	44.6 (4)	C3—C2—C7—C6	−0.3 (6)
N1^iii—Cd1—N1—C2	−132.5 (2)	C9—N3—C8—N4	0.0 (5)
Cl2—Cd1—N1—C2	136.0 (3)	C10—N4—C8—N3	−0.1 (5)
Cl1—Cd1—N1—C2	−44.0 (3)	C8—N3—C9—C14	178.4 (5)
C2—N1—C1—N2	0.3 (4)	C8—N3—C9—C10	0.0 (5)
Cd1—N1—C1—N2	−172.3 (2)	C8—N4—C10—C11	179.0 (5)
C3—N2—C1—N1	−0.3 (4)	C8—N4—C10—C9	0.1 (4)
C1—N1—C2—C7	−179.9 (4)	C14—C9—C10—C11	2.2 (6)
Cd1—N1—C2—C7	−8.4 (6)	N3—C9—C10—C11	−179.2 (4)
C1—N1—C2—C3	−0.2 (4)	C14—C9—C10—N4	−178.7 (4)
Cd1—N1—C2—C3	171.3 (2)	N3—C9—C10—N4	−0.1 (4)
C1—N2—C3—C4	178.1 (4)	N4—C10—C11—C12	179.6 (5)
C1—N2—C3—C2	0.1 (4)	C9—C10—C11—C12	−1.6 (7)
C7—C2—C3—N2	179.8 (3)	C10—C11—C12—C13	−0.2 (9)
N1—C2—C3—N2	0.1 (4)	C11—C12—C13—C14	1.4 (10)
C7—C2—C3—C4	1.6 (6)	C12—C13—C14—C9	−0.8 (10)
N1—C2—C3—C4	−178.2 (4)	N3—C9—C14—C13	−179.2 (5)
N2—C3—C4—C5	−179.3 (4)	C10—C9—C14—C13	−1.0 (8)
C2—C3—C4—C5	−1.7 (6)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···N3	0.86	2.07	2.836 (4)	149
N4—H4A···Cl1^iv	0.86	2.62	3.377 (4)	147
C1—H1···Cg1^v	0.93	2.87	3.675 (4)	146
C8—H8···Cg2^v	0.93	2.61	3.525 (5)	167
C6—H6···Cg3^vi	0.93	2.88	3.527 (6)	128

Symmetry codes: (iv) −x+3/2, y+1/2, z+1/2; (v) −y+3/2, −x+3/2, z+1/2; (vi) −x+3/2, y−1/2, z−1/2.