The addition-reaction product of 1,1,1,4,4,4-hexa­chloro-1,4-disila­butane with N-methyl­imidazole

The product of the addition reaction of 1,1,1,4,4,4-hexa­chloro-1,4-disila­butane with N-methyl­imidazole is μ-ethyl­ene-C¹:C²-bis­[di­chloro­tris(1-methyl­imidazole-N³)­silicon(IV)] dichloride, C₂₆H₄₀Cl₄N₁₂Si₂²⁺·2Cl⁻. Two of the six Cl atoms are replaced by aromatic nitro­gen bases and the coordination sphere of silicon is extended from four to six. The mol­ecule is located on a crystallographic centre of inversion. The environment around the Si atom can be described as a slightly distorted octahedron with the Cl atoms occupying axial positions and the three N-methyl­imidazole ligands and the ethyl­ene bridge in the equatorial plane.

S1. Comment

In recent years the extension of the coordination sphere of silicon in complexes with organic nitrogen bases has been the subject of numerous studies (Bechstein et al., 1990; Chuit et al., 1993; Kane et al., 1998; Hensen, Kettner et al., 1998; Hensen, Mayr-Stein, Stumpf et al., 2000). Several complexes of silicon halides are already known, but little is known about adducts of compounds containing more than one silicon centre. We present in this work the product of the addition reaction of 1,1,1,4,4,4-hexachloro-1,4-disilabutane with N-methylimidazole: µ-ethylene-C¹:C²-bis[dichlorotris(1-methylimidazole-N³)silicon(IV)] dichloride, (I). \sch

Only two of the six chlorine atoms are replaced by aromatic nitrogen bases, but the coordination sphere of silicon is extended from four to six. The reaction product is a dication (located on a crystallographic centre of inversion) crystallizing with two chloride ions. Compared with other hexacoordinated complexes of halogen silanes with tertiary nitrogen bases, the current product shows a remarkable new feature: it bears two silicon centres that both carry a formal charge of +1. In contrast, until now only neutral addition complexes, e.g. dichlorosilanebispyridine (Hensen, Stumpf et al., 1998), tetrachlorobis(4-methylpyridine)silicon (Hensen, Mayr-Stein, Spangenberg & Bolte et al., 2000), tetrachlorobis(3,4-bismethylpyridine)silicon (Hensen, Mayr-Stein, Spangenberg, Bolte & Rühl et al., 2000), or dicationic complexes, e.g. SiHCl(N-methylimidazole)₄]²⁺ (Hensen, Kettner et al. 1998), SiCl₂(N-methylimidazole)₄]²⁺ with different counter ions and solvent molecules (Hensen, Stumpf et al., 2000), bis(2,2'-bipyridyl-N,N')dichlorosilicon (Hensen, Mayr-Stein, Rühl & Bolte et al., 2000), were obtained. The current structure is the first example of a hexacoordinated silicon centre where only one halogen atom is removed from the coordination sphere of the starting material, thus the ratio of removed halogen ligands to newly added base ligands of 1:3 is observed for the first time. The silicon centres appear in a nearly ideal octahedral environment, where the two remaining chlorine ligands occupy axial positions. The three N-methylimidazole groups and the ethylene bridge lie in the equatorial plane. There are only minor deviations from perfect octahedral coordination: all bond angles involving C1 are bigger than 90°; whereas the two Si—N bonds trans to each other are of nearly the same length the Si—N bond trans to C1 is slightly shorter than the other two; the two Si—Cl bonds differ by approximately 0.05 Å. Compared with the free Lewis acid 1,1,1,4,4,4-hexachloro-1,4-disilabutane (Mitzel et al., 1997) in which the Si—Cl bond lengths range from 2.0225 (6) to 2.0283 (6) Å, those in the current structure are considerably longer. For comparison, a search of the Cambridge Crystallographic Database (Version 5.19, April 2000; Allen & Kennard, 1983) yielded 39 Si—Cl fragments (hexacoordinated Si, monocoordinated Cl) with a mean Si—Cl bond length of 2.20 (5) Å. Furthermore, it is remarkable that the Si—C—C angle is widened to nearly 120°, a fact that can be attributed to the bulky substituents at the silicon centres. The C—C bond length, on the other hand, shows a normal value. The crystal packing is stabilized by short contacts between the Cl⁻ ion and various H atoms (Table 2).

S2. Experimental

To 1,1,1,4,4,4-hexachloro-1,4-disilabutane (5 ml) in chloroform (25 ml) N-methylimidazole was added and the reaction was monitored by measuring the temperature. After approximately 2 h, the precipitated solid was isolated, washed and dried. Crystals of (I) were obtained by subliming the powder in an evacuated glass ampoule for several days at 315 K.

S3. Refinement

All H atoms were located by difference Fourier synthesis refined with fixed individual displacement parameters [U(H) = 1.5 U_eq(C_methyl) or U(H) = 1.2 U_eq(C)] using a riding model with C—H(aromatic) = 0.95, C—H(secondary) = 0.99 or C—H(methyl) = 0.98 Å, respectively. The methyl groups were allowed to rotate about their local threefold axis.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1996).

Figures

Fig. 1. Perspective view of (I) with the atom numbering; displacement ellipsoids are at the 50% probability level.

(I)

Crystal data

C26H40Cl4N12Si2^2+·2Cl^−	F(000) = 820
Mr = 789.58	Dx = 1.452 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 13.8976 (1) Å	Cell parameters from 5816 reflections
b = 7.5553 (1) Å	θ = 1.0–25.0°
c = 17.3704 (2) Å	µ = 0.58 mm^−1
β = 97.947 (1)°	T = 133 K
V = 1806.39 (3) Å^3	Block, colourless
Z = 2	0.30 × 0.20 × 0.20 mm

Data collection

Siemens CCD three circle diffractometer	3679 independent reflections
Radiation source: fine-focus sealed tube	2894 reflections with I > 2σ(I)
Highly oriented graphite crystal monochromator	Rint = 0.057
ω scans	θmax = 26.4°, θmin = 1.8°
Absorption correction: empirical SADABS (Sheldrick,1996)	h = −17→17
Tmin = 0.84, Tmax = 0.90	k = −9→9
22213 measured reflections	l = −21→21

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)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.085	H-atom parameters constrained
S = 1.08	Calculated w = 1/[σ^2(Fo^2) + (0.0273P)^2 + 1.7731P] where P = (Fo^2 + 2Fc^2)/3
3679 reflections	(Δ/σ)max = 0.002
211 parameters	Δρmax = 0.34 e Å^−3
0 restraints	Δρmin = −0.29 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. Coverage of the unique set is 100% complete to at least 25.0° in θ. Crystal decay was monitored by repeating the initial frames at the end of data collection and analyzing the duplicate reflections.

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

	x	y	z	Uiso*/Ueq
Si1	0.84087 (5)	0.38063 (9)	0.50006 (4)	0.01560 (15)
Cl1	0.92492 (4)	0.14794 (8)	0.55269 (3)	0.02066 (14)
Cl2	0.74196 (4)	0.60133 (7)	0.44516 (3)	0.01875 (14)
C1	0.95282 (16)	0.4996 (3)	0.47145 (14)	0.0201 (5)
H1A	0.9674	0.4461	0.4223	0.024*
H1B	0.9344	0.6244	0.4600	0.024*
N11	0.85095 (13)	0.5002 (3)	0.60054 (11)	0.0167 (4)
C12	0.84753 (18)	0.6741 (3)	0.61186 (14)	0.0206 (5)
H12	0.8362	0.7594	0.5714	0.025*
N13	0.86209 (15)	0.7128 (3)	0.68765 (11)	0.0231 (5)
C13	0.8624 (2)	0.8914 (4)	0.72107 (16)	0.0362 (7)
H13A	0.8385	0.9763	0.6802	0.054*
H13B	0.9288	0.9232	0.7434	0.054*
H13C	0.8202	0.8939	0.7618	0.054*
C14	0.87626 (19)	0.5561 (3)	0.72759 (15)	0.0264 (6)
H14	0.8887	0.5421	0.7824	0.032*
C15	0.86903 (18)	0.4257 (3)	0.67401 (14)	0.0231 (6)
H15	0.8753	0.3027	0.6849	0.028*
N21	0.81128 (14)	0.2478 (3)	0.40312 (11)	0.0189 (4)
C22	0.72472 (18)	0.2332 (3)	0.36007 (13)	0.0198 (5)
H22	0.6667	0.2861	0.3723	0.024*
N23	0.73072 (15)	0.1339 (3)	0.29721 (12)	0.0243 (5)
C23	0.6487 (2)	0.0874 (4)	0.23813 (15)	0.0343 (7)
H23A	0.5890	0.1399	0.2520	0.051*
H23B	0.6418	−0.0416	0.2354	0.051*
H23C	0.6606	0.1329	0.1875	0.051*
C24	0.82645 (19)	0.0812 (4)	0.29999 (15)	0.0282 (6)
H24	0.8527	0.0099	0.2629	0.034*
C25	0.87520 (19)	0.1506 (3)	0.36549 (14)	0.0244 (6)
H25	0.9425	0.1353	0.3830	0.029*
N31	0.72537 (14)	0.2692 (3)	0.52886 (11)	0.0165 (4)
C32	0.64996 (16)	0.3474 (3)	0.55490 (13)	0.0182 (5)
H32	0.6438	0.4712	0.5626	0.022*
N33	0.58432 (14)	0.2262 (3)	0.56864 (11)	0.0190 (4)
C33	0.48716 (18)	0.2626 (4)	0.58895 (16)	0.0274 (6)
H33A	0.4871	0.3783	0.6145	0.041*
H33B	0.4697	0.1706	0.6243	0.041*
H33C	0.4397	0.2632	0.5416	0.041*
C34	0.61760 (18)	0.0619 (3)	0.54997 (14)	0.0209 (5)
H34	0.5859	−0.0485	0.5539	0.025*
C35	0.70426 (17)	0.0893 (3)	0.52498 (14)	0.0196 (5)
H35	0.7443	0.0000	0.5076	0.024*
Cl3	0.47226 (5)	0.28993 (8)	0.35530 (4)	0.02731 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si1	0.0144 (3)	0.0158 (3)	0.0166 (3)	0.0018 (3)	0.0024 (3)	0.0015 (3)
Cl1	0.0185 (3)	0.0187 (3)	0.0248 (3)	0.0045 (2)	0.0028 (2)	0.0033 (2)
Cl2	0.0166 (3)	0.0179 (3)	0.0215 (3)	0.0024 (2)	0.0017 (2)	0.0025 (2)
C1	0.0170 (12)	0.0236 (13)	0.0196 (12)	−0.0011 (10)	0.0025 (10)	0.0013 (10)
N11	0.0140 (10)	0.0182 (10)	0.0181 (10)	0.0006 (8)	0.0026 (8)	0.0015 (8)
C12	0.0231 (13)	0.0194 (13)	0.0192 (12)	0.0010 (11)	0.0031 (10)	0.0022 (10)
N13	0.0290 (12)	0.0199 (11)	0.0208 (11)	−0.0007 (9)	0.0054 (9)	−0.0020 (9)
C13	0.061 (2)	0.0209 (14)	0.0278 (15)	0.0001 (14)	0.0107 (14)	−0.0063 (12)
C14	0.0357 (16)	0.0255 (14)	0.0178 (13)	−0.0011 (12)	0.0029 (11)	0.0045 (11)
C15	0.0290 (14)	0.0206 (13)	0.0196 (12)	−0.0004 (11)	0.0031 (11)	0.0022 (10)
N21	0.0194 (11)	0.0171 (10)	0.0208 (10)	0.0020 (8)	0.0050 (9)	−0.0001 (8)
C22	0.0192 (13)	0.0208 (13)	0.0201 (12)	−0.0021 (10)	0.0045 (10)	−0.0006 (10)
N23	0.0256 (12)	0.0244 (12)	0.0232 (11)	−0.0047 (10)	0.0050 (9)	−0.0049 (9)
C23	0.0326 (16)	0.0430 (18)	0.0272 (15)	−0.0093 (14)	0.0046 (12)	−0.0127 (13)
C24	0.0297 (15)	0.0276 (15)	0.0292 (15)	0.0036 (12)	0.0113 (12)	−0.0079 (12)
C25	0.0223 (13)	0.0251 (14)	0.0269 (14)	0.0038 (11)	0.0074 (11)	−0.0006 (11)
N31	0.0163 (10)	0.0156 (10)	0.0175 (10)	0.0007 (8)	0.0026 (8)	0.0006 (8)
C32	0.0175 (12)	0.0172 (12)	0.0197 (12)	0.0012 (10)	0.0024 (10)	−0.0010 (10)
N33	0.0159 (10)	0.0206 (11)	0.0202 (10)	−0.0009 (9)	0.0014 (8)	−0.0014 (9)
C33	0.0185 (13)	0.0275 (15)	0.0378 (15)	−0.0021 (11)	0.0097 (12)	−0.0048 (12)
C34	0.0232 (13)	0.0162 (12)	0.0224 (13)	−0.0009 (10)	0.0001 (10)	0.0007 (10)
C35	0.0199 (13)	0.0150 (12)	0.0236 (13)	0.0016 (10)	0.0019 (10)	0.0002 (10)
Cl3	0.0312 (4)	0.0204 (3)	0.0307 (3)	−0.0022 (3)	0.0058 (3)	0.0001 (3)

Geometric parameters (Å, º)

Si1—C1	1.921 (2)	N21—C22	1.330 (3)
Si1—N31	1.938 (2)	N21—C25	1.384 (3)
Si1—N11	1.953 (2)	C22—N23	1.337 (3)
Si1—N21	1.954 (2)	N23—C24	1.383 (3)
Si1—Cl1	2.2351 (9)	N23—C23	1.467 (3)
Si1—Cl2	2.2840 (8)	C24—C25	1.347 (4)
C1—C1^i	1.531 (5)	N31—C32	1.335 (3)
N11—C12	1.330 (3)	N31—C35	1.390 (3)
N11—C15	1.386 (3)	C32—N33	1.337 (3)
C12—N13	1.336 (3)	N33—C34	1.379 (3)
N13—C14	1.372 (3)	N33—C33	1.468 (3)
N13—C13	1.469 (3)	C34—C35	1.351 (3)
C14—C15	1.349 (4)
C1—Si1—N31	177.81 (10)	C14—N13—C13	126.9 (2)
C1—Si1—N11	93.10 (9)	C15—C14—N13	106.8 (2)
N31—Si1—N11	85.97 (8)	C14—C15—N11	109.0 (2)
C1—Si1—N21	95.67 (10)	C22—N21—C25	106.3 (2)
N31—Si1—N21	85.20 (8)	C22—N21—Si1	126.38 (16)
N11—Si1—N21	171.10 (9)	C25—N21—Si1	127.36 (17)
C1—Si1—Cl1	94.45 (8)	N21—C22—N23	110.6 (2)
N31—Si1—Cl1	87.56 (6)	C22—N23—C24	107.5 (2)
N11—Si1—Cl1	91.68 (6)	C22—N23—C23	125.1 (2)
N21—Si1—Cl1	89.11 (6)	C24—N23—C23	127.3 (2)
C1—Si1—Cl2	90.73 (8)	C25—C24—N23	106.6 (2)
N31—Si1—Cl2	87.29 (6)	C24—C25—N21	108.9 (2)
N11—Si1—Cl2	90.01 (6)	C32—N31—C35	106.17 (19)
N21—Si1—Cl2	88.41 (6)	C32—N31—Si1	127.75 (16)
Cl1—Si1—Cl2	174.46 (4)	C35—N31—Si1	126.07 (16)
C1^i—C1—Si1	119.1 (2)	N31—C32—N33	110.2 (2)
C12—N11—C15	105.7 (2)	C32—N33—C34	108.4 (2)
C12—N11—Si1	126.11 (16)	C32—N33—C33	126.0 (2)
C15—N11—Si1	128.08 (16)	C34—N33—C33	125.1 (2)
N11—C12—N13	111.0 (2)	C35—C34—N33	106.3 (2)
C12—N13—C14	107.5 (2)	C34—C35—N31	109.0 (2)
C12—N13—C13	125.6 (2)
N31—Si1—C1—C1^i	115 (2)	N11—Si1—N21—C25	−141.6 (5)
N11—Si1—C1—C1^i	50.4 (3)	Cl1—Si1—N21—C25	−46.4 (2)
N21—Si1—C1—C1^i	−131.1 (3)	Cl2—Si1—N21—C25	138.5 (2)
Cl1—Si1—C1—C1^i	−41.5 (3)	C25—N21—C22—N23	−0.6 (3)
Cl2—Si1—C1—C1^i	140.4 (3)	Si1—N21—C22—N23	179.44 (16)
C1—Si1—N11—C12	59.5 (2)	N21—C22—N23—C24	0.1 (3)
N31—Si1—N11—C12	−118.5 (2)	N21—C22—N23—C23	178.6 (2)
N21—Si1—N11—C12	−110.9 (6)	C22—N23—C24—C25	0.4 (3)
Cl1—Si1—N11—C12	154.09 (19)	C23—N23—C24—C25	−178.0 (2)
Cl2—Si1—N11—C12	−31.2 (2)	N23—C24—C25—N21	−0.7 (3)
C1—Si1—N11—C15	−116.0 (2)	C22—N21—C25—C24	0.8 (3)
N31—Si1—N11—C15	66.0 (2)	Si1—N21—C25—C24	−179.20 (18)
N21—Si1—N11—C15	73.6 (6)	C1—Si1—N31—C32	−15 (3)
Cl1—Si1—N11—C15	−21.5 (2)	N11—Si1—N31—C32	50.5 (2)
Cl2—Si1—N11—C15	153.3 (2)	N21—Si1—N31—C32	−128.3 (2)
C15—N11—C12—N13	−0.1 (3)	Cl1—Si1—N31—C32	142.37 (19)
Si1—N11—C12—N13	−176.50 (16)	Cl2—Si1—N31—C32	−39.69 (19)
N11—C12—N13—C14	0.4 (3)	C1—Si1—N31—C35	164 (2)
N11—C12—N13—C13	−179.5 (2)	N11—Si1—N31—C35	−130.7 (2)
C12—N13—C14—C15	−0.4 (3)	N21—Si1—N31—C35	50.51 (19)
C13—N13—C14—C15	179.5 (3)	Cl1—Si1—N31—C35	−38.81 (19)
N13—C14—C15—N11	0.4 (3)	Cl2—Si1—N31—C35	139.13 (19)
C12—N11—C15—C14	−0.1 (3)	C35—N31—C32—N33	1.1 (3)
Si1—N11—C15—C14	176.12 (18)	Si1—N31—C32—N33	−179.90 (15)
C1—Si1—N21—C22	−132.1 (2)	N31—C32—N33—C34	−0.7 (3)
N31—Si1—N21—C22	45.9 (2)	N31—C32—N33—C33	−172.4 (2)
N11—Si1—N21—C22	38.3 (7)	C32—N33—C34—C35	0.0 (3)
Cl1—Si1—N21—C22	133.6 (2)	C33—N33—C34—C35	171.8 (2)
Cl2—Si1—N21—C22	−41.5 (2)	N33—C34—C35—N31	0.6 (3)
C1—Si1—N21—C25	48.0 (2)	C32—N31—C35—C34	−1.1 (3)
N31—Si1—N21—C25	−134.0 (2)	Si1—N31—C35—C34	179.89 (16)

Symmetry code: (i) −x+2, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C34—H34···Cl3^ii	0.95	2.61	3.450 (3)	147
C33—H33A···Cl3^iii	0.98	2.61	3.540 (3)	159
C22—H22···Cl3	0.95	2.68	3.524 (3)	149

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