Arene-perfluoroarene interactions in crystal engineering. 4. Hexa­fluoro­benzene-trans-stilbene (1/1)

In the title complex, C₆F₆·C₁₄H₁₂, nearly parallel mol­ecules of trans-stilbene and librationally disordered hexa­fluoro­benzene form a mixed stack, with each molecule lying on an independent inversion centre. Adjacent stacks pack together in a herring-bone manner.

S1. Comment

While studying arene–perfluoroarene interactions and their possible uses in crystal engineering (Dai et al., 1999; Collings, Batsanov et al., 2001; Collings, Roscoe et al., 2001), we found that arenes and perfluoroarenes of wildly mismatched geometry can be cocrystallized. Trans-stilbene (TSB) is known to form 1:1 complexes with matching perfluorinated species, viz. decafluoro–trans-azabenzene (Bruce et al., 1987) and decafluoro–trans-stilbene (Coates et al., 1998). On the other hand, TSB forms complexes with electron acceptors of rather disparate geometry, e.g. 1:1 complexes with pyromellitic dianhydride (Kodama & Kumakura, 1974) or tetracyanoquinodimethane (Zobel & Ruban, 1983), and 1:2 complexes with 1,2,4,5-tetracyanobenzene (Agostini et al., 1988) or 1,3,5-trinitrobenzene (Bar & Bernstein, 1978). All these are molecular complexes which exhibit no significant charge transfer, and as most arene–perfluoroarene systems behave in the same way, we expected that TSB could also form complexes with geometrically mismatched perfluoroarenes.

Colourless crystals grown from HFB proved to be the 1:1 complex HFB^.TSB, (I). Both the TSB and the HFB molecules have crystallographic C_i symmetry (Fig. 1). The TSB molecule shows no sign of disorder, unlike the structures of TSB itself (Bouwstra et al., 1984) and most of its molecular complexes; these all display the same mode of disorder, namely an overlap of two molecular positions, related by a 180° rotation around the C1···C1' vector. In (I), the TSB molecule is slightly twisted, the planes of the phenyl ring and the olefinic moiety forming a dihedral angle (ϕ) of 7.2 (7)°. Such a conformation is typical for both TSB and its molecular complexes, but contrasts drastically with the twisted conformation observed in the gas phase, where <ϕ²>^1/2 = 31 (5)° (Traettenberg et al., 1975). The bond distances in (I) agree with those seen in pure TSB at 113 K (Hoekstra et al., 1975) or at room temperature, if proper account was taken of the disorder (Bouwstra et al., 1984). Those studies of TSB where the disorder remained unresolved gave spuriously shortened central C═C bond distances (Finder et al., 1974; Bernstein, 1975).

Notwithstanding the low temperature, the HFB molecule shows high atomic displacement parameters, suggesting librational disorder. Attempts to model the disorder by various superpositions of two or three different orientations resulted in unstable refinements if no constraints were applied, or (if severely constrained) converged at much higher R indices than the single-position model. The molecule is probably disordered within one wide flat-bottomed potential well, rather than between separate wells.

The crystal packing of (I) (Fig. 2) comprises mixed stair-like stacks, parallel to the crystallographic a axis. Within each stack, the benzene rings of the HFB and TSB molecules are almost parallel [dihedral angle 3.4 (2)°] and overlap with an average interplanar separation of 3.45 (5) Å. Each HFB molecule is sandwiched between two parallel phenyl rings, and each phenyl ring is sandwiched between a parallel HFB molecule on one side and a phenyl ring inclined by 45.9 (2)° on the other. The latter phenyl ring belongs to a TSB molecule of an adjacent stack, related by the operation of a 2₁ screw axis. These stacks run in the same direction but have different orientations of the molecular planes, making inter-stack dihedral angles of up to 50.9 (2)° (for HFB/HFB). Thus, the packing of (I) can be described as a combination of stacking and herring-bone motifs, in contrast with pure HFB (Boden et al., 1973) and pure TSB, both of which display a purely herring-bone packing, with all molecules making T-fashion (edge-to-face) contacts and with no stacking interactions.

The packing of (I) is relatively loose: the volume per HFB^.TSB unit is larger by 3% than the sum of the molecular volumes in solid TSB at 113 K (249.5 ų; Hoekstra et al., 1975) and in solid HFB at 120 K (147.3 ų; Boden et al., 1973). Such loose packing may explain the disorder of the HFB molecule in (I).

Related literature

For related literature, see: Agostini et al. (1988); Bar & Bernstein (1978); Bernstein (1975); Boden et al. (1973); Bouwstra et al. (1984); Bruce et al. (1987); Coates et al. (1998); Collings, Batsanov, Howard & Marder (2001); Collings, Roscoe, Thomas, Batsanov, Stimson, Howard & Marder (2001); Dai et al. (1999); Finder et al. (1974); Hoekstra et al. (1975); Kodama & Kumakura (1974); Traettenberg et al. (1975); Zobel & Ruban (1983).

S2. Experimental

For the preparation of the title adduct, TSB (0.1 g) was dissolved in HFB (1 ml) with warming. Slow evaporation of the solution at room temperature yielded single crystals of (I).

S3. Refinement

All H atoms were refined and the range of phenyl-ring C—H distances was 0.98 (5)–1.01 (5) Å and C7—H was 1.07 (5) Å.

Computing details

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

Figures

	Fig. 1. The molecules of HFB (solid bonds) and TSB (hollow bonds) in (I), projected onto their mean planes. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) -x, 1 - y, 1 - z.]
	Fig. 2. Crystal packing of (I), with H atoms omitted for clarity.

hexafluorobenzene–trans-stilbene (1/1)

Crystal data

C6F6·C14H12	F(000) = 372
Mr = 366.30	Dx = 1.488 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.401 (3) Å	Cell parameters from 369 reflections
b = 6.118 (2) Å	θ = 10.2–24.2°
c = 12.262 (4) Å	µ = 0.13 mm^−1
β = 107.09 (2)°	T = 120 K
V = 817.5 (4) Å^3	Plate, colourless
Z = 2	0.30 × 0.30 × 0.06 mm

Data collection

SMART 1K CCD area-detector diffractometer	1125 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.049
Graphite monochromator	θmax = 25.4°, θmin = 1.9°
Detector resolution: 8 pixels mm^-1	h = −13→13
ω scans	k = −6→7
4709 measured reflections	l = −14→8
1501 independent 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)] = 0.078	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.207	All H-atom parameters refined
S = 1.11	w = 1/[σ^2(Fo^2) + (0.069P)^2 + 2.177P] where P = (Fo^2 + 2Fc^2)/3
1501 reflections	(Δ/σ)max = 0.001
142 parameters	Δρmax = 0.44 e Å^−3
0 restraints	Δρmin = −0.50 e Å^−3

Special details

Experimental. The data collection nominally covered over a hemisphere of reciprocal space, by a combination of 4 sets of ω scans, each set at different ϕ and/or 2θ angles and each scan (30 sec exposure) covering 0.3° in ω. Crystal to detector distance 4.51 cm. Crystal decay was monitored by repeating 50 initial frames at the end of data collection and comparing 67 duplicate reflections.

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. C(Ph)—H bond distances 0.98 (5) to 1.01 (5), C7—H 1.07 (5) Å.

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

	x	y	z	Uiso*/Ueq
C1	0.3941 (3)	0.4501 (6)	0.5970 (3)	0.0293 (9)
C2	0.3226 (3)	0.2752 (7)	0.6122 (3)	0.0317 (9)
H2	0.315 (4)	0.143 (8)	0.563 (4)	0.046 (12)*
C3	0.2619 (4)	0.2807 (7)	0.6944 (3)	0.0340 (9)
H3	0.210 (4)	0.151 (7)	0.704 (3)	0.038 (11)*
C4	0.2694 (3)	0.4634 (7)	0.7625 (3)	0.0343 (9)
H4	0.226 (4)	0.473 (7)	0.821 (3)	0.037 (11)*
C5	0.3391 (3)	0.6422 (7)	0.7481 (3)	0.0333 (9)
H5	0.343 (4)	0.774 (7)	0.798 (4)	0.041 (12)*
C6	0.4013 (3)	0.6356 (7)	0.6662 (3)	0.0317 (9)
H6	0.455 (4)	0.759 (7)	0.663 (3)	0.031 (10)*
C7	0.4596 (3)	0.4298 (7)	0.5088 (3)	0.0320 (9)
H7	0.443 (4)	0.284 (8)	0.458 (4)	0.052 (13)*
C8	0.0128 (4)	0.3535 (8)	0.4202 (3)	0.0427 (11)
C9	0.0752 (4)	0.5457 (8)	0.4346 (3)	0.0420 (11)
C10	0.0627 (4)	0.6928 (7)	0.5141 (4)	0.0444 (11)
F1	0.0240 (3)	0.2090 (7)	0.3421 (3)	0.1042 (16)
F2	0.1500 (3)	0.5884 (7)	0.3707 (3)	0.0932 (15)
F3	0.1249 (3)	0.8817 (5)	0.5263 (4)	0.0995 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0243 (18)	0.038 (2)	0.0244 (17)	0.0043 (16)	0.0050 (14)	0.0039 (16)
C2	0.030 (2)	0.030 (2)	0.034 (2)	0.0003 (16)	0.0066 (16)	0.0001 (17)
C3	0.031 (2)	0.034 (2)	0.038 (2)	−0.0014 (17)	0.0099 (17)	0.0072 (17)
C4	0.029 (2)	0.047 (2)	0.0269 (18)	0.0037 (18)	0.0085 (16)	0.0045 (18)
C5	0.0267 (19)	0.040 (2)	0.032 (2)	−0.0018 (17)	0.0076 (16)	−0.0089 (18)
C6	0.0257 (19)	0.034 (2)	0.034 (2)	−0.0044 (17)	0.0068 (15)	0.0030 (17)
C7	0.032 (2)	0.035 (2)	0.0277 (18)	−0.0018 (16)	0.0068 (15)	0.0005 (17)
C8	0.034 (2)	0.051 (3)	0.036 (2)	0.015 (2)	−0.0013 (18)	−0.019 (2)
C9	0.026 (2)	0.067 (3)	0.035 (2)	0.009 (2)	0.0132 (17)	0.018 (2)
C10	0.029 (2)	0.023 (2)	0.067 (3)	−0.0051 (17)	−0.008 (2)	0.005 (2)
F1	0.078 (2)	0.138 (3)	0.073 (2)	0.054 (2)	−0.0149 (17)	−0.071 (2)
F2	0.0393 (16)	0.184 (4)	0.0660 (19)	0.022 (2)	0.0308 (14)	0.064 (2)
F3	0.0492 (18)	0.0328 (16)	0.177 (4)	−0.0151 (14)	−0.029 (2)	0.019 (2)

Geometric parameters (Å, º)

C1—C2	1.390 (5)	C6—H6	0.98 (4)
C1—C6	1.405 (5)	C7—C7^i	1.323 (8)
C1—C7	1.490 (5)	C7—H7	1.07 (5)
C2—C3	1.381 (5)	C8—F1	1.337 (5)
C2—H2	1.00 (5)	C8—C9	1.359 (7)
C3—C4	1.383 (6)	C8—C10^ii	1.370 (7)
C3—H3	1.01 (4)	C9—F2	1.342 (5)
C4—C5	1.393 (6)	C9—C10	1.365 (6)
C4—H4	0.99 (4)	C10—F3	1.341 (5)
C5—C6	1.390 (5)	C10—C8^ii	1.370 (7)
C5—H5	1.00 (4)
C2—C1—C6	118.3 (3)	C5—C6—C1	120.5 (4)
C2—C1—C7	118.2 (4)	C5—C6—H6	118 (2)
C6—C1—C7	123.6 (4)	C1—C6—H6	122 (2)
C3—C2—C1	121.2 (4)	C7^i—C7—C1	125.9 (5)
C3—C2—H2	119 (3)	C7^i—C7—H7	117 (2)
C1—C2—H2	120 (3)	C1—C7—H7	117 (2)
C2—C3—C4	120.4 (4)	F1—C8—C9	120.5 (4)
C2—C3—H3	119 (2)	F1—C8—C10^ii	119.6 (5)
C4—C3—H3	120 (2)	C9—C8—C10^ii	119.9 (4)
C3—C4—C5	119.6 (4)	F2—C9—C8	119.4 (4)
C3—C4—H4	122 (2)	F2—C9—C10	120.4 (5)
C5—C4—H4	118 (2)	C8—C9—C10	120.2 (4)
C6—C5—C4	120.0 (4)	F3—C10—C9	119.0 (5)
C6—C5—H5	121 (2)	F3—C10—C8^ii	121.1 (5)
C4—C5—H5	119 (2)	C9—C10—C8^ii	120.0 (4)
C6—C1—C7—C7^i	6.7 (7)

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