3,3′-Dimethyl-1,1′-methyl­ene­di­imid­azolium tetrachloro­cobaltate(II)

The title compound, (C₉H₁₄N₄)[CoCl₄], a methyl­ene-bridged bis-imidazolium salt containing a tetrachloro­cobaltate anion, is one of the first examples where an alkyl-bridged bis-imidazolium compound could be structurally characterized. Short C—H...Cl contacts between the imidazolium C—H bonds and the Cl atoms of the counter-anion build up a three-dimensional network and indicate that the C—H bonds are strongly polarized.

S1. Comment

Metal complexes of N-heterocyclic carbenes (NHC) have been shown to be extremely versatile and stable catalysts for a wide range of reactions (Herrmann, 2002). In particular, chelating NHC complexes have proved to have enhanced thermal stability, leading to remarkable catalytic properties. For instance, bridged palladium triscarbene complexes have been successfully applied in various catalytic reactions (e.g. C—C coupling reactions; Herrmann et al., 1995, 1998), and in particular to C—H activation (Muehlhofer, Strassner & Herrmann, 2002). A convenient synthesis of bridged NHC complexes is the conversion of basic metal precursors, such as palladium(II) acetate, with a bridged imidazolium salt (Herrmann et al., 1998). Here, we report the structural characterization of a methylene-bridged imidazolium salt with a tetrachlorocobaltate counteranion, (I). Previously, only a few reports of solid-state structures of imidazolium salts containing transition metal–halide anions have been published (Dullius et al., 1998; Ortwerth et al., 1998; Hasan et al., 1999, 2001), including the related 1-ethyl-3-methylimidazolium tetrachlorocobaltate (Hitchcock et al., 1993). They all show short contacts between imidazolium H atoms and the halide atoms of the anion, due to ionic interactions.

The structure of (I) is depicted in Fig. 1, and selected geometric parameters are given in Table 1. For steric reasons, the N—CH—N unit in the two imidazole moieties points in opposite directions. The N1—C1 and N2—C1 (and N3—C6 and N4—C6) bonds are almost identical, which indicates delocalization within these bonds. The dihedral angle between the imidazole rings is 72.97 (9)°. The Co atom of the counteranion is surrounded by four Cl⁻ ions in a tetrahedral fashion, with bond lengths ranging from 2.2680 (7) to 2.2907 (7) Å. As previously observed for analogous compounds, several short contacts are formed between C—H bonds and the Cl⁻ of the anion. In the case of (I), they are established by imidazolium ring H atoms, as well as by both H atoms of the methylene bridge and one H atom of the methyl group (bond distances in Table 2). This shows a possible polarization of all C—H bonds adjacent to an N atom in an imidazolium salt, and not only of the central C—H bond in the N—CH—N unit, which is deprotonated during the formation of metal–NHC complexes.

From the Co-editor: Please check important changes in the following paragraph. As can be seen from Fig. 2 and Table 2, the most acidic H atoms take part in C—H···Cl contacts, which build up a bilayer structure parallel to the ab plane. Contacts such as C2—H21···Cl3^iv [symmetry code: (iv) 1/2 − x, y − 1/2, 1/2 − z], which are longer but still within the sum of the relevant van der Waals radii (2.95 Å; Reference?), connect these layers into a three-dimensional network.

From the Co-editor: Please provide a reference for the source of the van der Waals radii.

S2. Experimental

The title compound was prepared by reaction of 1,1'-dimethyl-3,3'-methylenediimidazolium dibromide (Muehlhofer, Strassner, Herdtweck & Herrmann, 2002) with cobalt(II) chloride hexahydrate in refluxing tetrahydrofuran/ethanol (2:1) for 10 h. The resulting light-blue precipitate was isolated by filtration and washed with tetrahydrofuran (yield 73%). Elemental analysis revealed a formulation of a 1:1 mixture of the tetrachloro- and corresponding tetrabromocobaltate compounds. Analysis calculated for C₉H₁₄Br₂Cl₂CoN₄: C 23.10, H 3.02, N 11.97%; found: C 23.15, H 3.01, N 11.98%. Crystals of (I) could be obtained selectively by slow diffusion of tetrahydrofuran into a solution of the product in dimethylsulfoxide.

S3. Refinement

From the Co-editor: Please check corrected text below. One methyl group is disordered over two sets of positions, with occupancies of 0.61 (3) and 0.39 (3). Methyl H atoms were located from difference Fourier syntheses and refined as part of rigid rotating groups, with C—H = 0.98 Å and U_iso(H) = 1.5U_eq(C). Other H atoms were placed in calculated positions and refined using a riding model, with methylene and aromatic C—H distances of 0.99 and 0.95 Å, respectively, and U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: KappaCCD Server Software (Nonius, 2001); cell refinement: DENZO (Nonius, 2001); data reduction: DENZO; program(s) used to solve structure: SIR92 (Altomare, 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1998); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: PLATON.

Figures

	Fig. 1. A perspective view of (I), showing the atom-numbering scheme and the disorder in the C9 methyl group (dashed lines). Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A stereo view of the unit cell of (I), showing the hydrogen-bonding network.

3,3'-Dimethyl-1,1'-methylenediimidazolium tetrachlorocobaltate(II)

Crystal data

(C9H14N4)[CoCl4]	F(000) = 1528
Mr = 378.97	Dx = 1.623 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 3026 reflections
a = 15.2885 (1) Å	θ = 1.5–25.2°
b = 7.1995 (1) Å	µ = 1.78 mm^−1
c = 28.2539 (3) Å	T = 173 K
β = 94.0770 (4)°	Plate, light blue
V = 3102.02 (6) Å^3	0.38 × 0.20 × 0.05 mm
Z = 8

Data collection

Nonius KappaCCD area-detector diffractometer	2784 independent reflections
Radiation source: NONIUS FR591 rotating anode	2509 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.044
Detector resolution: 18 pixels mm^-1	θmax = 25.2°, θmin = 1.5°
ϕ and ω rotation scans	h = −18→18
Absorption correction: multi-scan (DENZO; Nonius, 2001)	k = −8→8
Tmin = 0.562, Tmax = 0.916	l = −33→33
32195 measured reflections

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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.067	H-atom parameters constrained
S = 1.05	Weighting scheme based on measured s.u.'s w = 1/[σ^2(Fo^2) + (Fo^2) + (0.029P)^2 + 4.883P] where P = (Fo^2 + 2Fc^2)/3
2784 reflections	(Δ/σ)max < 0.001
166 parameters	Δρmax = 0.31 e Å^−3
0 restraints	Δρmin = −0.28 e Å^−3

Special details

Experimental. Diffractometer operator E. Herdtweck scanspeed 2 x 40 s per film repetition 1 dx 40 992 films measured in 8 data sets set 1: phi-scan with delta_phi = 1.0 set 2 to 8: omega-scans with delta_omega = 1.0

Refinement. The crystal was fixed in a capillary with perfluorinated ether and transferred to the diffractometer. Preliminary examination and data collection were carried out on an area detecting system (Nonius, MACH3, κ-CCD) at the window of a rotating anode (Nonius, FR951) and graphite monochromated Mo K_α radiation (λ = 0.71073 Å). Eight data sets were measured in rotation scan modus with Δϕ / Δω = 1.0°. Raw data were corrected for Lorentz, polarization, and, arising from the scaling procedure, for latent decay and absorption effects. The structure was solved by a combination of direct methods and difference Fourier syntheses. All non-hydrogen atoms were refined with anisotropic displacement parameters.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
N1	0.16816 (12)	0.5446 (3)	0.20446 (6)	0.0304 (6)
N2	0.12457 (12)	0.7854 (3)	0.16470 (6)	0.0294 (6)
N3	0.06209 (12)	0.8651 (3)	0.08664 (7)	0.0294 (6)
N4	−0.04959 (12)	0.7799 (3)	0.04123 (7)	0.0316 (6)
C1	0.18091 (15)	0.6450 (3)	0.16677 (8)	0.0305 (7)
C2	0.10120 (17)	0.6210 (4)	0.22733 (9)	0.0474 (9)
C3	0.07359 (18)	0.7708 (4)	0.20265 (9)	0.0513 (10)
C4	0.2162 (2)	0.3761 (4)	0.21968 (11)	0.0534 (10)
C5	0.11583 (16)	0.9289 (3)	0.12812 (9)	0.0373 (8)
C6	−0.02461 (15)	0.8422 (3)	0.08418 (8)	0.0302 (7)
C7	0.02299 (17)	0.7633 (4)	0.01542 (8)	0.0381 (8)
C8	0.09285 (16)	0.8151 (3)	0.04368 (8)	0.0369 (8)
C9	−0.13979 (17)	0.7331 (4)	0.02414 (10)	0.0452 (9)
Co	0.40632 (2)	0.82778 (4)	0.12818 (1)	0.0302 (1)
Cl1	0.54288 (4)	0.87927 (8)	0.10327 (2)	0.0319 (2)
Cl2	0.31724 (4)	0.69706 (9)	0.06859 (2)	0.0369 (2)
Cl3	0.33625 (4)	1.08951 (8)	0.14925 (2)	0.0396 (2)
Cl4	0.41672 (4)	0.62947 (9)	0.19100 (2)	0.0454 (2)
H11	0.22350	0.62110	0.14460	0.0370*
H21	0.07840	0.57610	0.25560	0.0570*
H31	0.02740	0.85180	0.21000	0.0620*
H41	0.23280	0.38350	0.25380	0.0800*
H42	0.26910	0.36510	0.20220	0.0800*
H43	0.17880	0.26720	0.21320	0.0800*
H51	0.08880	1.04100	0.14120	0.0450*
H52	0.17470	0.96350	0.11860	0.0450*
H61	−0.06200	0.86640	0.10890	0.0360*
H71	0.02350	0.72270	−0.01650	0.0460*
H81	0.15220	0.81700	0.03570	0.0440*
H91	−0.14560	0.74030	−0.01060	0.0680*	0.61 (3)
H92	−0.18050	0.82100	0.03740	0.0680*	0.61 (3)
H93	−0.15350	0.60680	0.03420	0.0680*	0.61 (3)
H94	−0.17410	0.70510	0.05130	0.0680*	0.39 (3)
H95	−0.13920	0.62440	0.00330	0.0680*	0.39 (3)
H96	−0.16620	0.83860	0.00650	0.0680*	0.39 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0310 (10)	0.0342 (10)	0.0261 (10)	0.0020 (8)	0.0036 (8)	0.0012 (8)
N2	0.0273 (10)	0.0339 (11)	0.0263 (10)	0.0015 (8)	−0.0028 (8)	−0.0008 (8)
N3	0.0272 (10)	0.0317 (10)	0.0290 (10)	0.0003 (8)	−0.0003 (8)	0.0053 (8)
N4	0.0315 (10)	0.0332 (10)	0.0292 (10)	0.0018 (8)	−0.0040 (8)	0.0020 (8)
C1	0.0291 (12)	0.0314 (12)	0.0317 (12)	0.0008 (10)	0.0064 (10)	−0.0020 (10)
C2	0.0389 (15)	0.074 (2)	0.0303 (13)	0.0199 (14)	0.0105 (11)	0.0097 (13)
C3	0.0425 (15)	0.079 (2)	0.0335 (14)	0.0303 (15)	0.0106 (12)	0.0062 (14)
C4	0.067 (2)	0.0413 (15)	0.0534 (18)	0.0176 (14)	0.0153 (15)	0.0138 (13)
C5	0.0360 (14)	0.0336 (13)	0.0404 (14)	−0.0029 (11)	−0.0106 (11)	0.0054 (11)
C6	0.0293 (12)	0.0320 (12)	0.0295 (12)	−0.0002 (10)	0.0028 (10)	0.0010 (9)
C7	0.0438 (15)	0.0444 (14)	0.0267 (12)	0.0068 (12)	0.0071 (11)	0.0019 (11)
C8	0.0313 (13)	0.0468 (15)	0.0334 (13)	0.0062 (11)	0.0075 (10)	0.0086 (11)
C9	0.0375 (15)	0.0505 (16)	0.0455 (15)	−0.0057 (12)	−0.0108 (12)	−0.0032 (13)
Co	0.0299 (2)	0.0333 (2)	0.0274 (2)	0.0024 (1)	0.0019 (1)	−0.0016 (1)
Cl1	0.0280 (3)	0.0334 (3)	0.0343 (3)	−0.0028 (2)	0.0018 (2)	−0.0004 (2)
Cl2	0.0283 (3)	0.0509 (4)	0.0315 (3)	−0.0004 (3)	0.0023 (2)	−0.0093 (3)
Cl3	0.0387 (3)	0.0367 (3)	0.0443 (3)	0.0039 (3)	0.0087 (3)	−0.0084 (3)
Cl4	0.0487 (4)	0.0520 (4)	0.0366 (3)	0.0167 (3)	0.0099 (3)	0.0152 (3)

Geometric parameters (Å, º)

Co—Cl1	2.2805 (7)	C1—H11	0.95
Co—Cl2	2.2911 (7)	C2—H21	0.95
Co—Cl3	2.2679 (7)	C3—H31	0.95
Co—Cl4	2.2746 (7)	C4—H43	0.98
N1—C4	1.467 (4)	C4—H41	0.98
N1—C1	1.313 (3)	C4—H42	0.98
N1—C2	1.365 (3)	C5—H52	0.99
N2—C5	1.461 (3)	C5—H51	0.99
N2—C3	1.374 (3)	C6—H61	0.95
N2—C1	1.327 (3)	C7—H71	0.95
N3—C6	1.333 (3)	C8—H81	0.95
N3—C8	1.380 (3)	C9—H95	0.98
N3—C5	1.457 (3)	C9—H96	0.98
N4—C6	1.324 (3)	C9—H94	0.98
N4—C7	1.376 (3)	C9—H91	0.98
N4—C9	1.468 (3)	C9—H92	0.98
C2—C3	1.336 (4)	C9—H93	0.98
C7—C8	1.340 (3)
Co···C1	3.915 (2)	C6···Cl3^vi	3.431 (2)
Co···C6^i	3.882 (2)	C6···Cl1^vi	3.519 (2)
Co···H11	3.2289	C6···Co^ix	3.882 (2)
Co···H61^i	3.4063	C6···Cl2^ix	3.524 (2)
Co···H71^ii	3.4236	C7···C7^xi	3.575 (4)
Co···H93^iii	3.4025	C7···Cl2^ii	3.536 (3)
Cl1···C1^iii	3.285 (2)	C7···Cl1^ii	3.582 (2)
Cl1···C5^i	3.484 (2)	C8···Cl2	3.556 (3)
Cl1···C6^iii	3.519 (2)	C8···Cl2^ii	3.547 (2)
Cl1···C7^ii	3.582 (2)	C9···Cl2^ix	3.645 (3)
Cl2···C8	3.556 (3)	C9···C9^xii	3.553 (4)
Cl2···C6^i	3.524 (2)	C1···H41^iv	3.0503
Cl2···C7^ii	3.536 (3)	C2···H21^viii	2.8399
Cl2···C1	3.606 (2)	C3···H21^viii	3.0242
Cl2···C9^i	3.645 (3)	C3···H31^viii	3.0589
Cl2···C8^ii	3.547 (2)	C9···H96^xii	3.0739
Cl3···C6^iii	3.431 (2)	H11···Co	3.2289
Cl3···C2^iv	3.557 (3)	H11···H42	2.5239
Cl3···C5	3.573 (3)	H11···Cl2	2.7208
Cl3···C4^v	3.479 (3)	H11···Cl4	3.1461
Cl4···C3^i	3.524 (3)	H21···C2^viii	2.8399
Cl4···C1	3.623 (2)	H21···C3^viii	3.0242
Cl1···H51^i	2.7323	H21···H21^viii	2.3956
Cl1···H71^ii	2.6880	H21···Cl3^vii	2.9052
Cl2···H11	2.7208	H31···C3^viii	3.0589
Cl2···H81^ii	3.0177	H31···H31^viii	2.4658
Cl2···H81	2.7645	H31···Cl4^ix	2.6493
Cl2···H96^i	3.1409	H41···C1^vii	3.0503
Cl2···H93^iii	3.1477	H42···Cl4	2.9863
Cl2···H92^i	2.8482	H42···Cl3^x	2.7290
Cl2···H71^ii	2.9896	H42···H11	2.5239
Cl3···H52	2.7146	H51···Cl1^ix	2.7323
Cl3···H94^iii	2.8834	H51···Cl4^ix	3.1358
Cl3···H61^iii	2.8188	H52···Cl3	2.7146
Cl3···H21^iv	2.9053	H52···H81	2.5695
Cl3···H42^v	2.7290	H61···H94	2.5569
Cl4···H11	3.1461	H61···Co^ix	3.4063
Cl4···H42	2.9863	H61···Cl4^ix	3.0300
Cl4···H61^i	3.0300	H61···Cl3^vi	2.8188
Cl4···H31^i	2.6493	H71···Cl1^ii	2.6880
Cl4···H51^i	3.1358	H71···Co^ii	3.4236
C1···Co	3.915 (2)	H71···Cl2^ii	2.9896
C1···Cl2	3.606 (2)	H81···H52	2.5695
C1···Cl4	3.623 (2)	H81···Cl2	2.7645
C1···Cl1^vi	3.285 (2)	H81···Cl2^ii	3.0177
C2···Cl3^vii	3.557 (3)	H92···Cl2^ix	2.8482
C2···C2^viii	3.432 (4)	H93···Co^vi	3.4025
C2···C4^iv	3.580 (4)	H93···Cl2^vi	3.1477
C3···Cl4^ix	3.524 (3)	H94···H61	2.5569
C4···C2^vii	3.580 (4)	H94···Cl3^vi	2.8834
C4···Cl3^x	3.479 (3)	H96···Cl2^ix	3.1409
C5···Cl1^ix	3.484 (2)	H96···C9^xii	3.0739
C5···Cl3	3.573 (3)
Cl1—Co—Cl2	110.45 (2)	C2—C3—H31	126.40
Cl1—Co—Cl3	113.94 (2)	N1—C4—H41	109.42
Cl1—Co—Cl4	109.15 (2)	H41—C4—H43	109.51
Cl2—Co—Cl3	105.49 (2)	H42—C4—H43	109.42
Cl2—Co—Cl4	108.69 (2)	H41—C4—H42	109.54
Cl3—Co—Cl4	108.95 (2)	N1—C4—H42	109.45
C1—N1—C2	108.8 (2)	N1—C4—H43	109.49
C1—N1—C4	126.4 (2)	N2—C5—H51	109.39
C2—N1—C4	124.9 (2)	N3—C5—H52	109.42
C1—N2—C3	108.1 (2)	N2—C5—H52	109.34
C1—N2—C5	126.62 (19)	N3—C5—H51	109.31
C3—N2—C5	125.3 (2)	H51—C5—H52	107.95
C5—N3—C8	125.57 (19)	N4—C6—H61	125.92
C5—N3—C6	125.7 (2)	N3—C6—H61	125.98
C6—N3—C8	108.76 (19)	N4—C7—H71	126.31
C6—N4—C7	108.92 (19)	C8—C7—H71	126.31
C6—N4—C9	125.6 (2)	N3—C8—H81	126.55
C7—N4—C9	125.5 (2)	C7—C8—H81	126.62
N1—C1—N2	108.8 (2)	N4—C9—H94	109.40
N1—C2—C3	107.3 (2)	N4—C9—H95	109.42
N2—C3—C2	107.1 (2)	H92—C9—H93	109.48
N2—C5—N3	111.36 (18)	H94—C9—H95	109.53
N3—C6—N4	108.1 (2)	H94—C9—H96	109.48
N4—C7—C8	107.4 (2)	H95—C9—H96	109.55
N3—C8—C7	106.8 (2)	N4—C9—H96	109.45
N1—C1—H11	125.65	H91—C9—H92	109.48
N2—C1—H11	125.58	H91—C9—H93	109.48
C3—C2—H21	126.29	N4—C9—H91	109.47
N1—C2—H21	126.38	N4—C9—H92	109.47
N2—C3—H31	126.54	N4—C9—H93	109.45
C2—N1—C1—N2	0.5 (3)	C8—N3—C5—N2	−105.8 (3)
C4—N1—C1—N2	179.6 (2)	C5—N3—C6—N4	−179.0 (2)
C1—N1—C2—C3	−0.1 (3)	C8—N3—C6—N4	−0.1 (3)
C4—N1—C2—C3	−179.2 (2)	C5—N3—C8—C7	179.3 (2)
C3—N2—C1—N1	−0.7 (3)	C6—N3—C8—C7	0.5 (3)
C5—N2—C1—N1	−179.2 (2)	C7—N4—C6—N3	−0.3 (3)
C1—N2—C3—C2	0.6 (3)	C9—N4—C6—N3	178.8 (2)
C5—N2—C3—C2	179.2 (2)	C6—N4—C7—C8	0.6 (3)
C1—N2—C5—N3	82.7 (3)	C9—N4—C7—C8	−178.5 (2)
C3—N2—C5—N3	−95.6 (3)	N1—C2—C3—N2	−0.3 (3)
C6—N3—C5—N2	72.9 (3)	N4—C7—C8—N3	−0.6 (3)

Symmetry codes: (i) x+1/2, y−1/2, z; (ii) −x+1/2, −y+3/2, −z; (iii) x+1/2, y+1/2, z; (iv) −x+1/2, y+1/2, −z+1/2; (v) x, y+1, z; (vi) x−1/2, y−1/2, z; (vii) −x+1/2, y−1/2, −z+1/2; (viii) −x, y, −z+1/2; (ix) x−1/2, y+1/2, z; (x) x, y−1, z; (xi) −x, −y+2, −z; (xii) −x−1/2, −y+3/2, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C6—H61···Cl3^vi	0.95	2.82	3.431 (2)	123
C1—H11···Cl2	0.95	2.72	3.606 (2)	155
C2—H21···Cl3^vii	0.95	2.91	3.557 (3)	127
C3—H31···Cl4^ix	0.95	2.65	3.524 (3)	153
C4—H42···Cl3^x	0.98	2.73	3.479 (3)	134
C5—H51···Cl1^ix	0.99	2.73	3.484 (2)	133
C5—H52···Cl3	0.99	2.71	3.573 (3)	145
C7—H71···Cl1^ii	0.95	2.69	3.582 (2)	157
C8—H81···Cl2	0.95	2.76	3.556 (3)	141

Symmetry codes: (ii) −x+1/2, −y+3/2, −z; (vi) x−1/2, y−1/2, z; (vii) −x+1/2, y−1/2, −z+1/2; (ix) x−1/2, y+1/2, z; (x) x, y−1, z.