cis-Bis(2,2'-bipyridyl-N,N')dichlorosilicon diiodide

The crystal and molecular structure of the title compound, C₂₀H₁₆Cl₂N₄Si²⁺·2I^-, has been determined at 173 K. To our knowledge, this is the first crystal structure of a silicon tetrahalide complex with a bidentate base as a ligand. The two chloro ligands are cis relative to each other. The Si-N bonds trans to a chloro ligand are longer than the Si-N bonds trans to an Si-N bond. This feature is observed for the majority of M(bipy)₂Cl₂ (M = metal and bipy = 2,2'-bipyridyl) complexes, but it does not hold for all structures retrieved from the Cambridge Structural Database. The two pyridyl rings of each bipyridyl unit are nearly coplanar, whereas the bipyridyl units are almost perpendicular to each other. The two I^- ions are more than 5 Å from the silicon centre. As a result, the compound can definitely be described as ionic. The crystal packing is stabilized by short C-H...I contacts.

S1. Comment

In recent years coordination compounds of silicon have been the subject of many structural (Hensen et al., 1983; Tandura et al., 1986), spectroscopic (Helmer et al., 1983; Bassindale & Stout, 1984), reactivity (Chuit et al., 1993) and ab initio studies (Damrauer et al., 1988; Arshadi et al., 1996). A subset of that class of compounds, the complexes between siliconhalides and tertiary aromatic nitrogen bases, are of fundamental interest concerning Lewis acid-base interactions. However, little information is available about the molecular structure of complexes containing a bidentate nitrogen base. Cationic bis-2,2'-bipyridyl-silicon complexes have been described by Kummer & Seshadri (1977), Kummer et al. (1977) and Sawitzki et al. (1978). The cation has been characterized spectroscopically with IR and NMR techniques and an octahedral structure was proposed for the complex with the chlorine ligands cis to each other.

In order to determine unambiguously the nature of the silicon complex and its precise geometry we have synthesized the title compound, (I), and present here the first crystal structure of a silicontetrahalide complex containing a bidentate nitrogen base. \sch

The silicon atom in the title compound is in fact virtually octahedrally co-ordinated (Table 1). The two chloro ligands are arranged cis with respect to each other. The two Si—Cl bonds are rather short compared with similar ionic complexes (Hensen et al., 2000), where these bonds are in the range from 2.184 (1) to 2.207 (1) Å. The Si—N bond lengths are in the usual range, but they are significantly different from each other. The Si—N bonds trans to a Si—Cl bond are longer than the Si—N bonds trans to an Si—N bond. This feature could also be observed when the central atom of the complex is replaced by Ga (Restivo & Palenik, 1972), Al (Bellavance et al., 1977), Mo (Hey et al., 1983), Fe (Figgis, Reynolds & Lehner, 1983; Figgis, Patrick et al., 1983), Ni (Hipler et al., 1998) and Mn (Lumme & Lindell, 1988; McCann et al., 1998). In the Re complex (Helberg et al., 1996) all four Si—N bonds are of equal length. In the Co complex (Krämer & Strähle, 1986) in one bipyridyl unit the Si—N bond trans to a Cl ligand is longer than the Si—N bond trans to an Si—N bond, but in the other bipyridyl unit the inverse situation is found. In the Rh complex (Lahuerta et al., 1991) the Si—N bonds trans to a Cl ligand are shorter than the Si—N bonds trans to an Si—N bond. In the Ru^III complex the Si—N bonds show the same relation as in the title compound, but in the Ru^II complex the situation is inverse (Eggleston et al., 1985). As a result of that, there is a strong tendency of the Si—N bond trans to the chloro ligand to be longer than the Si—N bond trans to an Si—N bond, but this feature is not encountered in all the structures retrieved from the Cambridge Structural Database (Version 5.18, October 1999; Allen & Kennard, 1983), a fact which might be attributed to the different electronic configuration of the central atom. It is interesting to note that in all but one Me(bipy)₂Hal₂ complexes retrieved from the database the halogen ligands are chlorine atoms. The only exception is bis-(2,2'-bipyridine)-cis-di-iodo-calcium (Skelton et al., 1996).

The N—Si—N bond angles between two N atoms of the same bipyridyl unit are rather small due to steric strain. This fact is also observed in the previously mentioned bis-bipyridyl complexes.

Both N—C—C—N torsion angles of the bipyridyl units are very small [3.0 (3)°] indicating that the two pyridyl rings of each bipyridyl unit are nearly coplanar. The dihedral angle between the two bipyridyl units is 85.47 (5)°. The distances between Si1 and the two iodine ions [Si1···I1(2 - x, 1 - y, 1 - z) 5.130 (1) and Si1···I2(x - 1,y,z) 5.677 (1) Å] demonstrate the ionic character of the title compound. Both iodine ions show short contacts to aromatic H atoms (Table 2).

S2. Experimental

The title compound was prepared according to Kummer et al. (1977) from SiCl₂I₂ with 2,2'-bipyridine in chloroform and dried in vacuo. An elemental analysis revealed that the red brown powder still contained one equivalent of chloroform. The crystal structure analysis, however, clearly showed that there is no solvent in the crystal. A ²⁹Si NMR spectrum of the title compound in deuterated methanol showed one single signal at -161.0 p.p.m.. Kummer & Seshadri (1977) had found for [SiCl₂bipy₂]Cl₂ a value of -161.1 p.p.m.. Thus, the different anions do not show any effect on the chemical shift of the silicon atom. Recrystallization of the title compound in warm methanol yielded dark red crystals, which seemed not to be very susceptible to hydrolysis.

S3. Refinement

All H atoms were located by difference Fourier synthesis refined with fixed individual displacement parameters [U(H) = 1.2 U_eq(C)] using a riding model with C—H = 0.95 Å.

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 in SHELXTL-Plus (Sheldrick, 1991).

Figures

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

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Crystal data

C20H16Cl2N4Si^2+·2I^−	F(000) = 1272
Mr = 665.16	Dx = 1.957 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.831 (2) Å	Cell parameters from 8192 reflections
b = 14.927 (3) Å	θ = 0–25°
c = 12.929 (3) Å	µ = 3.09 mm^−1
β = 98.63 (3)°	T = 173 K
V = 2257.4 (8) Å^3	Block, dark red
Z = 4	0.50 × 0.45 × 0.40 mm

Data collection

Siemens CCD three-circle diffractometer	6809 independent reflections
Radiation source: fine-focus sealed tube	5513 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
ω scans	θmax = 31.9°, θmin = 1.7°
Absorption correction: empirical (SADABS; Sheldrick, 1996)	h = −15→16
Tmin = 0.240, Tmax = 0.290	k = −20→22
47312 measured reflections	l = −17→17

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)] = 0.029	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.060	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0208P)^2 + 2.551P] where P = (Fo^2 + 2Fc^2)/3
6809 reflections	(Δ/σ)max = 0.004
262 parameters	Δρmax = 0.59 e Å^−3
0 restraints	Δρmin = −0.82 e Å^−3

Special details

Experimental. ;

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.

The data collection nominally covered a sphere of reciprocal space, by a combination of seven sets of exposures; each set had a different ϕ angle for the crystal and each exposure covered 0.3° in ω. The crystal-to-detector distance was 4.5 cm. Coverage of the unique set is 100% complete to at least 26.4° 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
I1	0.915812 (14)	0.666289 (11)	0.378287 (12)	0.03081 (5)
I2	1.391391 (16)	0.657641 (12)	0.921795 (14)	0.03722 (5)
Si1	0.75504 (5)	0.51796 (4)	0.72980 (4)	0.01859 (11)
Cl1	0.92615 (5)	0.56316 (4)	0.72435 (4)	0.02584 (11)
Cl2	0.67761 (5)	0.64305 (4)	0.67566 (5)	0.02775 (12)
N1	0.77425 (16)	0.54887 (13)	0.87562 (14)	0.0221 (4)
C1	0.7514 (2)	0.62950 (17)	0.9155 (2)	0.0303 (5)
H1	0.7136	0.6739	0.8703	0.036*
C2	0.7822 (2)	0.64867 (19)	1.0211 (2)	0.0358 (6)
H2	0.7658	0.7057	1.0478	0.043*
C3	0.8367 (2)	0.5846 (2)	1.0868 (2)	0.0362 (6)
H3	0.8586	0.5971	1.1591	0.043*
C4	0.8592 (2)	0.50160 (19)	1.04657 (18)	0.0319 (5)
H4	0.8959	0.4564	1.0912	0.038*
C5	0.82781 (18)	0.48514 (16)	0.94089 (17)	0.0227 (4)
N2	0.81398 (15)	0.40292 (12)	0.78324 (14)	0.0196 (4)
C6	0.84761 (19)	0.40127 (16)	0.88897 (17)	0.0226 (4)
C7	0.8959 (2)	0.32494 (18)	0.9383 (2)	0.0304 (5)
H7	0.9201	0.3249	1.0118	0.037*
C8	0.9086 (2)	0.24894 (18)	0.8803 (2)	0.0322 (5)
H8	0.9425	0.1965	0.9130	0.039*
C9	0.8717 (2)	0.25039 (16)	0.7744 (2)	0.0301 (5)
H9	0.8775	0.1982	0.7336	0.036*
C10	0.8258 (2)	0.32825 (15)	0.72749 (19)	0.0255 (5)
H10	0.8020	0.3290	0.6540	0.031*
N3	0.60578 (15)	0.46645 (12)	0.73474 (14)	0.0203 (4)
C11	0.5478 (2)	0.46822 (17)	0.81668 (19)	0.0281 (5)
H11	0.5782	0.5008	0.8776	0.034*
C12	0.4447 (2)	0.42357 (19)	0.8142 (2)	0.0348 (6)
H12	0.4054	0.4254	0.8730	0.042*
C13	0.3998 (2)	0.37653 (18)	0.7261 (2)	0.0357 (6)
H13	0.3299	0.3448	0.7239	0.043*
C14	0.4578 (2)	0.37590 (17)	0.6408 (2)	0.0316 (5)
H14	0.4274	0.3446	0.5788	0.038*
C15	0.56019 (19)	0.42127 (15)	0.64667 (18)	0.0232 (4)
N4	0.73035 (16)	0.47222 (12)	0.58981 (14)	0.0209 (4)
C16	0.63004 (19)	0.42671 (14)	0.56289 (18)	0.0229 (4)
C17	0.6016 (2)	0.38905 (16)	0.46479 (19)	0.0301 (5)
H17	0.5330	0.3555	0.4482	0.036*
C18	0.6740 (2)	0.40060 (17)	0.39074 (19)	0.0348 (6)
H18	0.6554	0.3755	0.3228	0.042*
C19	0.7734 (2)	0.44910 (17)	0.41731 (19)	0.0327 (6)
H19	0.8231	0.4588	0.3671	0.039*
C20	0.8006 (2)	0.48383 (16)	0.51791 (18)	0.0275 (5)
H20	0.8698	0.5162	0.5362	0.033*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.03052 (8)	0.03602 (9)	0.02469 (8)	−0.00595 (7)	0.00018 (6)	−0.00469 (6)
I2	0.04448 (11)	0.03173 (9)	0.03463 (10)	0.00009 (7)	0.00326 (7)	0.00019 (7)
Si1	0.0182 (3)	0.0206 (3)	0.0160 (3)	−0.0012 (2)	−0.0007 (2)	0.0005 (2)
Cl1	0.0221 (3)	0.0311 (3)	0.0240 (3)	−0.0072 (2)	0.0021 (2)	0.0008 (2)
Cl2	0.0315 (3)	0.0215 (2)	0.0279 (3)	0.0018 (2)	−0.0033 (2)	0.0015 (2)
N1	0.0214 (9)	0.0270 (9)	0.0176 (9)	−0.0035 (7)	0.0026 (7)	−0.0029 (7)
C1	0.0329 (13)	0.0304 (12)	0.0279 (12)	−0.0026 (10)	0.0052 (10)	−0.0056 (10)
C2	0.0397 (15)	0.0400 (15)	0.0303 (13)	−0.0107 (12)	0.0134 (11)	−0.0143 (11)
C3	0.0338 (14)	0.0548 (17)	0.0207 (12)	−0.0169 (12)	0.0059 (10)	−0.0090 (11)
C4	0.0290 (12)	0.0470 (15)	0.0181 (11)	−0.0071 (11)	−0.0012 (9)	0.0019 (10)
C5	0.0179 (10)	0.0305 (11)	0.0194 (10)	−0.0053 (9)	0.0018 (8)	0.0008 (9)
N2	0.0157 (8)	0.0229 (9)	0.0196 (9)	−0.0005 (7)	0.0003 (7)	0.0027 (7)
C6	0.0181 (10)	0.0308 (12)	0.0183 (10)	−0.0027 (9)	0.0006 (8)	0.0042 (9)
C7	0.0294 (12)	0.0363 (13)	0.0235 (11)	0.0004 (10)	−0.0026 (9)	0.0094 (10)
C8	0.0288 (12)	0.0316 (13)	0.0343 (13)	0.0040 (10)	−0.0016 (10)	0.0122 (10)
C9	0.0297 (13)	0.0244 (11)	0.0350 (13)	0.0049 (9)	0.0010 (10)	0.0028 (10)
C10	0.0254 (11)	0.0261 (11)	0.0239 (11)	0.0023 (9)	0.0002 (9)	0.0005 (9)
N3	0.0167 (8)	0.0216 (9)	0.0217 (9)	0.0001 (7)	−0.0003 (7)	0.0008 (7)
C11	0.0233 (11)	0.0346 (13)	0.0266 (12)	−0.0022 (10)	0.0049 (9)	−0.0014 (10)
C12	0.0219 (12)	0.0419 (15)	0.0419 (15)	−0.0020 (10)	0.0094 (11)	0.0035 (12)
C13	0.0204 (11)	0.0313 (13)	0.0547 (17)	−0.0046 (10)	0.0032 (11)	0.0011 (12)
C14	0.0244 (12)	0.0274 (12)	0.0402 (14)	−0.0026 (10)	−0.0045 (10)	−0.0035 (11)
C15	0.0202 (10)	0.0197 (10)	0.0274 (11)	0.0018 (8)	−0.0043 (8)	−0.0006 (8)
N4	0.0240 (9)	0.0204 (9)	0.0168 (8)	0.0015 (7)	−0.0016 (7)	0.0031 (7)
C16	0.0238 (11)	0.0188 (10)	0.0234 (11)	0.0015 (8)	−0.0051 (8)	0.0012 (8)
C17	0.0327 (13)	0.0260 (12)	0.0278 (12)	0.0008 (10)	−0.0081 (10)	−0.0042 (9)
C18	0.0513 (16)	0.0298 (13)	0.0202 (11)	0.0087 (11)	−0.0051 (11)	−0.0047 (10)
C19	0.0478 (16)	0.0292 (12)	0.0218 (12)	0.0044 (11)	0.0071 (11)	0.0016 (10)
C20	0.0345 (13)	0.0267 (11)	0.0214 (11)	−0.0025 (10)	0.0046 (9)	0.0026 (9)

Geometric parameters (Å, º)

Si1—N4	1.9155 (19)	C7—C8	1.381 (4)
Si1—N1	1.9209 (19)	C8—C9	1.373 (4)
Si1—N3	1.9359 (19)	C9—C10	1.384 (3)
Si1—N2	1.9411 (19)	N3—C11	1.346 (3)
Si1—Cl1	2.1450 (9)	N3—C15	1.363 (3)
Si1—Cl2	2.1502 (9)	C11—C12	1.386 (3)
N1—C1	1.352 (3)	C12—C13	1.375 (4)
N1—C5	1.363 (3)	C13—C14	1.384 (4)
C1—C2	1.390 (4)	C14—C15	1.380 (3)
C2—C3	1.373 (4)	C15—C16	1.460 (3)
C3—C4	1.385 (4)	N4—C20	1.348 (3)
C4—C5	1.383 (3)	N4—C16	1.366 (3)
C5—C6	1.456 (3)	C16—C17	1.382 (3)
N2—C10	1.346 (3)	C17—C18	1.388 (4)
N2—C6	1.365 (3)	C18—C19	1.379 (4)
C6—C7	1.386 (3)	C19—C20	1.392 (3)
N4—Si1—N1	172.65 (9)	N2—C6—C7	120.9 (2)
N4—Si1—N3	83.05 (9)	N2—C6—C5	113.77 (19)
N1—Si1—N3	92.13 (9)	C7—C6—C5	125.3 (2)
N4—Si1—N2	90.95 (8)	C8—C7—C6	119.7 (2)
N1—Si1—N2	83.10 (8)	C9—C8—C7	119.0 (2)
N3—Si1—N2	85.27 (8)	C8—C9—C10	119.7 (2)
N4—Si1—Cl1	95.27 (7)	N2—C10—C9	121.7 (2)
N1—Si1—Cl1	89.06 (7)	C11—N3—C15	118.9 (2)
N3—Si1—Cl1	174.93 (6)	C11—N3—Si1	126.39 (16)
N2—Si1—Cl1	89.98 (6)	C15—N3—Si1	114.68 (16)
N4—Si1—Cl2	90.28 (6)	N3—C11—C12	121.5 (2)
N1—Si1—Cl2	95.33 (7)	C13—C12—C11	119.6 (3)
N3—Si1—Cl2	90.54 (6)	C12—C13—C14	119.2 (2)
N2—Si1—Cl2	175.46 (6)	C15—C14—C13	119.2 (2)
Cl1—Si1—Cl2	94.26 (3)	N3—C15—C14	121.5 (2)
C1—N1—C5	119.1 (2)	N3—C15—C16	113.28 (19)
C1—N1—Si1	125.92 (17)	C14—C15—C16	125.2 (2)
C5—N1—Si1	114.55 (15)	C20—N4—C16	119.3 (2)
N1—C1—C2	121.3 (3)	C20—N4—Si1	125.70 (16)
C3—C2—C1	119.6 (3)	C16—N4—Si1	114.92 (16)
C2—C3—C4	119.3 (2)	N4—C16—C17	121.2 (2)
C5—C4—C3	119.5 (2)	N4—C16—C15	113.92 (19)
N1—C5—C4	121.2 (2)	C17—C16—C15	124.8 (2)
N1—C5—C6	114.00 (19)	C16—C17—C18	119.5 (2)
C4—C5—C6	124.8 (2)	C19—C18—C17	119.0 (2)
C10—N2—C6	118.89 (19)	C18—C19—C20	119.8 (2)
C10—N2—Si1	127.05 (15)	N4—C20—C19	121.1 (2)
C6—N2—Si1	114.05 (15)
N4—Si1—N1—C1	−144.8 (6)	N4—Si1—N3—C11	−179.6 (2)
N3—Si1—N1—C1	−96.0 (2)	N1—Si1—N3—C11	6.0 (2)
N2—Si1—N1—C1	179.1 (2)	N2—Si1—N3—C11	88.9 (2)
Cl1—Si1—N1—C1	89.0 (2)	Cl1—Si1—N3—C11	109.5 (7)
Cl2—Si1—N1—C1	−5.2 (2)	Cl2—Si1—N3—C11	−89.36 (19)
N4—Si1—N1—C5	43.0 (7)	N4—Si1—N3—C15	3.43 (15)
N3—Si1—N1—C5	91.80 (16)	N1—Si1—N3—C15	−171.00 (16)
N2—Si1—N1—C5	6.82 (16)	N2—Si1—N3—C15	−88.11 (16)
Cl1—Si1—N1—C5	−83.27 (15)	Cl1—Si1—N3—C15	−67.5 (8)
Cl2—Si1—N1—C5	−177.46 (15)	Cl2—Si1—N3—C15	93.65 (15)
C5—N1—C1—C2	0.5 (4)	C15—N3—C11—C12	1.6 (3)
Si1—N1—C1—C2	−171.45 (19)	Si1—N3—C11—C12	−175.33 (19)
N1—C1—C2—C3	−0.2 (4)	N3—C11—C12—C13	−0.3 (4)
C1—C2—C3—C4	−0.5 (4)	C11—C12—C13—C14	−1.0 (4)
C2—C3—C4—C5	0.8 (4)	C12—C13—C14—C15	1.1 (4)
C1—N1—C5—C4	−0.1 (3)	C11—N3—C15—C14	−1.5 (3)
Si1—N1—C5—C4	172.70 (18)	Si1—N3—C15—C14	175.73 (18)
C1—N1—C5—C6	180.0 (2)	C11—N3—C15—C16	178.4 (2)
Si1—N1—C5—C6	−7.2 (2)	Si1—N3—C15—C16	−4.4 (2)
C3—C4—C5—N1	−0.5 (4)	C13—C14—C15—N3	0.2 (4)
C3—C4—C5—C6	179.4 (2)	C13—C14—C15—C16	−179.7 (2)
N4—Si1—N2—C10	0.3 (2)	N1—Si1—N4—C20	−134.6 (6)
N1—Si1—N2—C10	176.0 (2)	N3—Si1—N4—C20	176.1 (2)
N3—Si1—N2—C10	83.3 (2)	N2—Si1—N4—C20	−98.77 (19)
Cl1—Si1—N2—C10	−94.95 (19)	Cl1—Si1—N4—C20	−8.71 (19)
Cl2—Si1—N2—C10	106.0 (8)	Cl2—Si1—N4—C20	85.59 (19)
N4—Si1—N2—C6	179.25 (16)	N1—Si1—N4—C16	47.5 (7)
N1—Si1—N2—C6	−5.08 (15)	N3—Si1—N4—C16	−1.72 (15)
N3—Si1—N2—C6	−97.81 (16)	N2—Si1—N4—C16	83.40 (16)
Cl1—Si1—N2—C6	83.97 (15)	Cl1—Si1—N4—C16	173.46 (14)
Cl2—Si1—N2—C6	−75.1 (8)	Cl2—Si1—N4—C16	−92.23 (15)
C10—N2—C6—C7	1.7 (3)	C20—N4—C16—C17	2.8 (3)
Si1—N2—C6—C7	−177.36 (18)	Si1—N4—C16—C17	−179.18 (17)
C10—N2—C6—C5	−178.46 (19)	C20—N4—C16—C15	−178.1 (2)
Si1—N2—C6—C5	2.5 (2)	Si1—N4—C16—C15	−0.2 (2)
N1—C5—C6—N2	3.0 (3)	N3—C15—C16—N4	3.0 (3)
C4—C5—C6—N2	−176.9 (2)	C14—C15—C16—N4	−177.1 (2)
N1—C5—C6—C7	−177.1 (2)	N3—C15—C16—C17	−178.1 (2)
C4—C5—C6—C7	3.0 (4)	C14—C15—C16—C17	1.8 (4)
N2—C6—C7—C8	−1.0 (4)	N4—C16—C17—C18	−2.6 (3)
C5—C6—C7—C8	179.1 (2)	C15—C16—C17—C18	178.5 (2)
C6—C7—C8—C9	−0.8 (4)	C16—C17—C18—C19	0.4 (4)
C7—C8—C9—C10	2.0 (4)	C17—C18—C19—C20	1.4 (4)
C6—N2—C10—C9	−0.4 (3)	C16—N4—C20—C19	−1.0 (3)
Si1—N2—C10—C9	178.44 (18)	Si1—N4—C20—C19	−178.71 (18)
C8—C9—C10—N2	−1.4 (4)	C18—C19—C20—N4	−1.1 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···I1^i	0.95	3.00	3.938 (3)	171
C13—H13···I1^ii	0.95	3.01	3.829 (3)	145
C8—H8···I1^iii	0.95	2.99	3.693 (3)	132
C11—H11···I2^iv	0.95	3.33	3.745 (3)	109
C18—H18···I2^v	0.95	3.17	4.093 (3)	165

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