Bis[2-(3-pyridinio)benzimidazolium] di-μ-chloro-bis­[trichloro­cadmium(II)]

The title compound, (C₁₂H₁₁N₃)₂[Cd₂Cl₈], consists of two discrete 2-(3-pyridinio)benzimidazolium cations and one [Cd₂Cl₈]⁴⁻ anion. The dimeric [Cd₂Cl₈]⁴⁻ anion lies about an inversion centre and consists of two distorted [CdCl₅] trigonal bipyramids which share a common edge. The two Cd atoms are each coordinated by two μ-Cl atoms and three terminal Cl atoms, with a Cd...Cd separation of 3.9853 (6) Å. The packing displays two-dimensional hydrogen-bonded sheets, which are further linked by C—H...Cl contacts and π–π stacking inter­actions to yield a three-dimensional network.

S1. Comment

Crystal engineering of inorganic–organic hybrid materials is based on a modular approach, where discrete building blocks are constructed into extended networks. In the search for reliable strategies for crystal synthesis by design, a key goal is the identification and exploitation of robust synthons to control the relative orientation of the molecular component of the solid. Among the usual interactions found to assemble the molecular crystal, hydrogen-bonding interactions have attracted the most attention. In the case of transition metal chloride complexes, the M—Cl moieties (M is a transition metal) can act as good hydrogen-bond acceptors (Gillon et al., 2000; Lewis & Orpen, 1998; Luque et al., 2002). We report here the title complex salt, (I), composed of a novel [Cd₂Cl₈]⁴⁻ anion and two protonated 2-(3-pyridyl)benzimidazole cations, in which the N—H···Cl hydrogen bonds and π–π stacking interactions aggregate the anions and cations into a three-dimensional network.

As shown in Fig. 1, compound (I) is composed of two 2-(3-pyridinio)benzimidazolium cations and a novel [Cd₂Cl₈]⁴⁻ anion which lies about an inversion centre, chosen for convenience to be (1/2, 1/2, 1/2). In the unique cation, the pyridyl ring is rotated out of the benzimidazyl ring plane with a dihedral angle of 12.9 (2)°. The dimeric [Cd₂Cl₈]⁴⁻ anion can best be described as consisting of two distorted trigonal bipyramids, [CdCl₅], which share a common edge. The bridging Cl1 atom is axial to one Cd atom and equatorial to the other. The Cd1—Cl1—Cd1ⁱ—Cl1ⁱ ring (see Table 1 for symmetry code) is strictly planar because of the inversion centre. In the [CdCl₅] moiety, atoms Cl1, Cl3 and Cl4 are equatorial, while Cl2 and Cl1ⁱ are axial. Atom Cd1 and these three equatorial atoms are almost coplanar, with atom Cd1 being 0.1305 (8) Å from the Cl1/Cl3/Cl4 plane and displaced toward the axial atom Cl2. According to the different classes of Cd—Cl bond lengths, a logical sequence is apparent: Cd—Cl(axial,bridging) 2.7498 (12) Å > Cd—Cl(axial,terminal) 2.6573 (13) Å > Cd—Cl(equatorial,bridging) 2.5483 (12) Å > Cd—Cl(equatorial,terminal) 2.4605 (11) and 2.4325 (13) Å (Table 1). There is clearly no Cd—Cd bond in the dimer, the Cd···Cd distance of 3.9853 (6) Å being longer than the value of 3.53 Å found for the Cd···Cd distance in the dimeric [Cd₂Cl₆]²⁻ anion (Bart et al., 1980).

The dimeric [Cd₂Cl₈]⁴⁻ anion of (I) exhibits a new coordination geometry, although it has been studied as part of a larger Cd–Ni compound (Chesnut et al., 1999) which had terminal Cl atoms bonded to Ni atoms. Other dimeric Cd anions, such as [Cd₂Cl₆]²⁻ (Bart et al., 1980), have been described, but the Cd atoms have distorted tetrahedral geometry. In some polymeric structures (Charles et al., 1984; Puget et al., 1991; Doudin & Chapuis, 1992), the Cd centre generally displays octahedral coordination.

In the crystal lattice of (I), there are hydrogen-bonding and π–π stacking interactions. There are both N—H···Cl and C—H···Cl interactions between the 2-(3-pyridinio)benzimidazolium cations and the dimeric [Cd₂Cl₈]⁴⁻ anions (Table 2). The N—H···Cl interactions generate a sheet structure, as shown in Fig. 2. In addition, there are π–π stacking interactions between adjacent aromatic and pyridine rings, as shown in Fig. 3. The centroid···centroid separation of rings N11/C12–C16(x, y, z) and C4–C9(x, 1/2 − y, z − 1/2) is 3.592 (6) Å, and the shortest atom···atom separation is 3.345 (7) Å between atoms C14(x, y, z) and C8(x, 1/2 − y, z − 1/2). These interactions, and the C—H···Cl interactions involving atoms C12 and C16 (Table 2), serve to generate a three-dimensional network.

S2. Experimental

2-(3-Pyridyl)benzimidazole was synthesized according to the literature method of Alcalde et al. (1992). An aqueous solution (20 ml) of 2-(3-pyridyl)benzimidazole (1.6 mmol), CdCl₂ (1.2 mmol) and HCl (0.2 ml) was continuously stirred for about 30 min, and the solution was then allowed to stand at room temperature for several days, to give colourless crystals of (I) (yield 81%). Analysis calculated for C₂₄H₂₂Cd₂N₆Cl₈: C 31.92, H 2.46, N 9.31%; found: C 32.12, H 2.71, N 9.37%. IR (KBr, ν, cm⁻¹): 3468 (s), 1625 (s), 1526 (s), 1378 (s), 1261 (m), 1114 (m), 876 (s), 811 (s), 765 (m), 666 (m), 527 (m), 488 (m).

S3. Refinement

All H atoms were visible in difference maps and were treated as riding atoms, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1994); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997) in WinGX (version 1.70.01; Farrugia, 1999); molecular graphics: SHELXL97 and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The structure of (I), showing the [Cd2Cl8]^2− anion and the two inversion-related cations. Displacement ellipsoids are at the 30% probability level. [Symmetry code: (i) 1 − x, 1 − y, 1 − z.]
	Fig. 2. A view showing part of the hydrogen-bonded sheet in the crystal structure of (I). Atoms labelled with a dollar ($), asterisk (*) or hash (#) are at the symmetry positions (1 − x, 1 − y, 1 − z), (2 − x, y − 1/2, 1/2 − z) and (1 − x, 1/2 − y, z − 1/2), respectively.
	Fig. 3. A view showing the π–π overlap in the two cations of (I). Atoms labelled with an ampersand (&) are at the symmetry position (x, 1/2 − y, z − 1/2).

Bis[2-(3-pyridinio)benzimidazolium] di-µ-chloro-bis[trichlorocadmium(II)]

Crystal data

(C12N3H11)2[Cd2Cl8]	F(000) = 880
Mr = 902.88	Dx = 2.029 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3960 reflections
a = 7.5295 (5) Å	θ = 3.1–25.0°
b = 15.8570 (13) Å	µ = 2.19 mm^−1
c = 12.3755 (9) Å	T = 293 K
β = 90.457 (6)°	Prism, colourless
V = 1477.53 (19) Å^3	0.20 × 0.15 × 0.06 mm
Z = 2

Data collection

Siemens SMART CCD area-detector diffractometer	2593 independent reflections
Radiation source: fine-focus sealed tube	2209 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.058
ω scans	θmax = 25.0°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→8
Tmin = 0.643, Tmax = 0.880	k = −15→18
9164 measured reflections	l = −14→14

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)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.091	H-atom parameters constrained
S = 1.16	w = 1/[σ^2(Fo^2) + (0.0262P)^2 + 2.7025P] where P = (Fo^2 + 2Fc^2)/3
2593 reflections	(Δ/σ)max = 0.001
181 parameters	Δρmax = 0.74 e Å^−3
0 restraints	Δρmin = −0.58 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
Cd1	0.57513 (5)	0.50178 (2)	0.34599 (3)	0.01288 (13)
Cl1	0.72097 (15)	0.47411 (8)	0.52910 (9)	0.0147 (3)
Cl2	0.88392 (17)	0.45816 (8)	0.25981 (10)	0.0196 (3)
Cl3	0.40480 (16)	0.39105 (8)	0.25211 (9)	0.0174 (3)
Cl4	0.58697 (16)	0.65098 (8)	0.30089 (10)	0.0188 (3)
N1	0.8397 (5)	0.2605 (3)	0.2625 (3)	0.0125 (9)
H1	0.8324	0.3137	0.2498	0.015*
N3	0.9056 (5)	0.1280 (3)	0.2445 (3)	0.0136 (9)
H3	0.9485	0.0821	0.2185	0.016*
N11	1.1689 (5)	0.1751 (3)	−0.0532 (3)	0.0150 (9)
H11	1.2004	0.1339	−0.0939	0.018*
C2	0.9237 (6)	0.2039 (3)	0.2001 (4)	0.0118 (10)
C4	0.8076 (6)	0.1337 (3)	0.3386 (4)	0.0129 (10)
C5	0.7542 (7)	0.0733 (3)	0.4122 (4)	0.0183 (11)
H5	0.7813	0.0165	0.4033	0.022*
C6	0.6581 (7)	0.1022 (3)	0.4997 (4)	0.0186 (11)
H6	0.6182	0.0636	0.5508	0.022*
C7	0.6192 (6)	0.1885 (3)	0.5134 (4)	0.0161 (11)
H7	0.5570	0.2056	0.5742	0.019*
C8	0.6709 (6)	0.2484 (3)	0.4391 (4)	0.0147 (11)
H8	0.6433	0.3051	0.4475	0.018*
C9	0.7667 (6)	0.2192 (3)	0.3506 (4)	0.0126 (10)
C12	1.0755 (6)	0.1582 (3)	0.0352 (4)	0.0147 (11)
H12	1.0461	0.1028	0.0519	0.018*
C13	1.0224 (6)	0.2232 (3)	0.1020 (4)	0.0120 (10)
C14	1.0692 (6)	0.3056 (3)	0.0743 (4)	0.0148 (11)
H14	1.0355	0.3505	0.1179	0.018*
C15	1.1656 (6)	0.3200 (3)	−0.0181 (4)	0.0180 (11)
H15	1.1966	0.3747	−0.0374	0.022*
C16	1.2156 (6)	0.2531 (3)	−0.0815 (4)	0.0164 (11)
H16	1.2816	0.2622	−0.1436	0.020*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0152 (2)	0.0106 (2)	0.0129 (2)	−0.00084 (14)	0.00075 (14)	0.00002 (14)
Cl1	0.0142 (6)	0.0161 (6)	0.0139 (6)	0.0011 (5)	0.0005 (5)	0.0015 (5)
Cl2	0.0198 (6)	0.0124 (6)	0.0268 (7)	−0.0032 (5)	0.0086 (5)	−0.0058 (5)
Cl3	0.0219 (7)	0.0162 (6)	0.0140 (6)	−0.0055 (5)	0.0032 (5)	−0.0029 (5)
Cl4	0.0197 (7)	0.0133 (6)	0.0232 (7)	−0.0019 (5)	−0.0022 (5)	0.0060 (5)
N1	0.015 (2)	0.008 (2)	0.015 (2)	0.0016 (17)	0.0016 (17)	0.0000 (17)
N3	0.016 (2)	0.010 (2)	0.014 (2)	0.0034 (17)	0.0008 (17)	−0.0032 (17)
N11	0.013 (2)	0.018 (2)	0.014 (2)	0.0036 (18)	0.0003 (17)	−0.0035 (18)
C2	0.012 (2)	0.014 (3)	0.009 (2)	−0.001 (2)	−0.0017 (19)	−0.004 (2)
C4	0.011 (2)	0.014 (3)	0.013 (2)	−0.001 (2)	−0.0017 (19)	−0.004 (2)
C5	0.024 (3)	0.012 (3)	0.019 (3)	0.002 (2)	−0.003 (2)	0.000 (2)
C6	0.021 (3)	0.021 (3)	0.014 (2)	−0.004 (2)	0.000 (2)	0.003 (2)
C7	0.013 (3)	0.023 (3)	0.012 (2)	0.000 (2)	0.004 (2)	−0.004 (2)
C8	0.015 (3)	0.014 (3)	0.015 (3)	0.003 (2)	−0.002 (2)	−0.005 (2)
C9	0.013 (3)	0.013 (3)	0.011 (2)	−0.001 (2)	−0.0028 (19)	−0.001 (2)
C12	0.012 (3)	0.014 (3)	0.019 (3)	−0.002 (2)	−0.001 (2)	0.000 (2)
C13	0.009 (2)	0.015 (3)	0.012 (2)	0.000 (2)	−0.0040 (19)	0.002 (2)
C14	0.013 (2)	0.015 (3)	0.016 (3)	0.000 (2)	−0.003 (2)	−0.003 (2)
C15	0.015 (3)	0.016 (3)	0.022 (3)	−0.005 (2)	−0.002 (2)	0.005 (2)
C16	0.015 (3)	0.021 (3)	0.013 (3)	−0.002 (2)	0.000 (2)	0.002 (2)

Geometric parameters (Å, º)

Cd1—Cl4	2.4325 (13)	C4—C9	1.398 (7)
Cd1—Cl3	2.4605 (12)	C5—C6	1.386 (7)
Cd1—Cl1	2.5483 (12)	C5—H5	0.93
Cd1—Cl2	2.6573 (13)	C6—C7	1.411 (7)
Cd1—Cl1^i	2.7498 (12)	C6—H6	0.93
Cl1—Cd1^i	2.7498 (12)	C7—C8	1.380 (7)
N1—C2	1.345 (6)	C7—H7	0.93
N1—C9	1.389 (6)	C8—C9	1.395 (7)
N1—H1	0.8598	C8—H8	0.93
N3—C2	1.330 (6)	C12—C13	1.382 (7)
N3—C4	1.386 (6)	C12—H12	0.93
N3—H3	0.8598	C13—C14	1.397 (7)
N11—C12	1.332 (6)	C14—C15	1.378 (7)
N11—C16	1.333 (7)	C14—H14	0.93
N11—H11	0.8595	C15—C16	1.374 (7)
C2—C13	1.461 (6)	C15—H15	0.93
C4—C5	1.385 (7)	C16—H16	0.93
Cl4—Cd1—Cl3	127.27 (4)	C6—C5—H5	121.9
Cl4—Cd1—Cl1	110.80 (4)	C5—C6—C7	121.6 (5)
Cl3—Cd1—Cl1	121.09 (4)	C5—C6—H6	119.2
Cl4—Cd1—Cl2	97.31 (4)	C7—C6—H6	119.2
Cl3—Cd1—Cl2	94.54 (4)	C8—C7—C6	121.9 (4)
Cl1—Cd1—Cl2	86.55 (4)	C8—C7—H7	119.1
Cl4—Cd1—Cl1^i	91.44 (4)	C6—C7—H7	119.1
Cl3—Cd1—Cl1^i	86.72 (4)	C7—C8—C9	116.5 (5)
Cl1—Cd1—Cl1^i	82.51 (4)	C7—C8—H8	121.8
Cl2—Cd1—Cl1^i	167.89 (4)	C9—C8—H8	121.8
Cd1—Cl1—Cd1^i	97.49 (4)	N1—C9—C8	132.1 (5)
C2—N1—C9	109.1 (4)	N1—C9—C4	106.5 (4)
C2—N1—H1	125.4	C8—C9—C4	121.4 (5)
C9—N1—H1	125.5	N11—C12—C13	119.9 (5)
C2—N3—C4	110.1 (4)	N11—C12—H12	120.0
C2—N3—H3	124.9	C13—C12—H12	120.0
C4—N3—H3	125.0	C12—C13—C14	118.3 (4)
C12—N11—C16	122.9 (4)	C12—C13—C2	119.5 (5)
C12—N11—H11	118.6	C14—C13—C2	122.1 (4)
C16—N11—H11	118.5	C15—C14—C13	119.7 (5)
N3—C2—N1	108.5 (4)	C15—C14—H14	120.2
N3—C2—C13	125.9 (4)	C13—C14—H14	120.2
N1—C2—C13	125.6 (5)	C16—C15—C14	119.6 (5)
C5—C4—N3	131.8 (5)	C16—C15—H15	120.2
C5—C4—C9	122.4 (4)	C14—C15—H15	120.2
N3—C4—C9	105.8 (4)	N11—C16—C15	119.5 (4)
C4—C5—C6	116.2 (5)	N11—C16—H16	120.2
C4—C5—H5	121.9	C15—C16—H16	120.2
Cl4—Cd1—Cl1—Cd1^i	88.69 (5)	C7—C8—C9—C4	0.0 (7)
Cl3—Cd1—Cl1—Cd1^i	−81.56 (5)	C5—C4—C9—N1	−179.6 (4)
Cl2—Cd1—Cl1—Cd1^i	−174.79 (4)	N3—C4—C9—N1	0.8 (5)
Cl1^i—Cd1—Cl1—Cd1^i	0.0	C5—C4—C9—C8	0.9 (7)
C4—N3—C2—N1	0.0 (5)	N3—C4—C9—C8	−178.7 (4)
C4—N3—C2—C13	178.3 (4)	C16—N11—C12—C13	0.2 (7)
C9—N1—C2—N3	0.6 (5)	N11—C12—C13—C14	0.0 (7)
C9—N1—C2—C13	−177.7 (4)	N11—C12—C13—C2	−178.6 (4)
C2—N3—C4—C5	180.0 (5)	N3—C2—C13—C12	13.4 (7)
C2—N3—C4—C9	−0.5 (5)	N1—C2—C13—C12	−168.5 (5)
N3—C4—C5—C6	179.0 (5)	N3—C2—C13—C14	−165.1 (5)
C9—C4—C5—C6	−0.5 (7)	N1—C2—C13—C14	13.0 (7)
C4—C5—C6—C7	−0.8 (7)	C12—C13—C14—C15	0.2 (7)
C5—C6—C7—C8	1.6 (8)	C2—C13—C14—C15	178.7 (4)
C6—C7—C8—C9	−1.2 (7)	C13—C14—C15—C16	−0.4 (7)
C2—N1—C9—C8	178.6 (5)	C12—N11—C16—C15	−0.5 (7)
C2—N1—C9—C4	−0.9 (5)	C14—C15—C16—N11	0.6 (7)
C7—C8—C9—N1	−179.4 (5)

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—H1···Cl2	0.86	2.33	3.152 (4)	161
N3—H3···Cl2^ii	0.86	2.35	3.126 (4)	150
N11—H11···Cl1^ii	0.86	2.72	3.306 (4)	127
N11—H11···Cl3^iii	0.86	2.49	3.182 (4)	138
C12—H12···Cl1^iv	0.93	2.75	3.396 (5)	128
C14—H14···Cl2	0.93	2.71	3.623 (5)	168
C16—H16···Cl4^v	0.93	2.59	3.458 (5)	156

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