The charge-transfer complex trans-STB-TCNQF₄

In the crystal structure of the title charge-transfer complex, namely trans-stilbene-2,2'-(2,3,5,6-tetra­fluoro­benzene-1,4-diyl­idene)­propane­di­nitrile (1/1) (trans-STB-TCNQF₄), C₁₄H₁₂·C₁₂F₄N₄, the planar STB and TCNQF₄ mol­ecules are stacked alternately. The structure is not isostructural with that of STB-TCNQ. No anomaly was found in the displacement parameters of any atoms, while the bond length of the central C=C moiety was shorter than the corresponding bond in ethyl­ene. This suggests that the central C=C moiety of the STB mol­ecule vibrates with a large amplitude, similar to the case in free STB and STB-TCNQ.

S1. Comment

The dynamic co-operation between molecular (atomic) dynamics and change in electronic state is of current interest (Mitani et al., 1988; Nakasuji et al., 1991). Although most studies in the field have been performed on systems with hydrogen bonds, recently, the authors have demonstrated the interplay in a high-Tc organic superconductor, i.e. κ-(BEDT-TTF)₂Cu[N(CN)₂]Br [BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene; Saito et al., 1999; Akutsu et al., 2000]. As another approach, the authors have shown that reorientation of the molecule involved in the charge transfer (CT) occurs in the crystalline lattice of the CT complex trans-stilbene–TCNQ (STB-TCNQ, where TCNQ is 7,7,8,8-tetracyano-p-quinodimethane; Saito et al., 2000). We report here the crystal structure of STB–TCNQF₄ (TCNQF₄ is 7,7,8,8-tetracyano-2,3,5,6-tetrafluoro-p-quinodimethane), (I), which is a halogenated derivative of STB–TCNQ.

A view of the two molecules in the asymmetric unit is shown in Fig. 1 and the packing is shown in Fig. 2. The STB molecule lies about an inversion center at (0, 0, 0) and the TCNQF₄ molecule lies about an inversion center at (1/2, 0, 0) at room temperature, and these are ordered in space group P2₁/n, in contrast to what was found in the structure of STB—TCNQ in space group C2/m (Zobel & Ruban, 1983). Thus, the crystal structure of the present complex is not isostructural with that of STB–TCNQ. Molecules of STB and TCNQF₄ stack alternately to form a column along the a direction. The STB and TCNQF₄ molecules overlap with a slip of half the molecular length (Fig. 2). This is different from the exact overlapping and ring-over-ring arrangement in STB–TCNQ. In STB–TCNQF₄ the interplanar angle between the unique ring of the STB molecule and that of the TCNQF₄ is 5.59 (11)°. The separations of the ring centroids from the plane of the adjacent overlapped rings are 3.255 (unique STB ring plane centroid to TCNQF₄ plane) and 3.355 Å (TCNQF₄ centroid to unique STB ring plane). No unusual displacement parameters were found for any atoms.

The central C═C bond length in the STB molecule is 1.315 (4) Å, which is equal to the corresponding length in STB–TCNQ [1.318 (6) Å; Zobel & Ruban, 1983] within experimental error. The angle of the central Ph—C═C moiety is 126.9 (2)°. While the bond length suggests a localization of electron density on the central C═C moiety, the Ph—C═C angle indicates delocalization on the central C═C moiety. Since the degree of CT of (I) was estimated to be ca 0.2 e by IR measurement, the central C═C bond in (I) should be longer than the bond of 1.337 (6) Å in ethylene (International Tables for X-ray Crystallography, Vol. III, 1968). Short central C═C bonds have been widely observed in the structural results of free STB and its derivatives (Finder et al., 1974; Bernstein, 1975; Bouwstra et al., 1984). Ogawa et al. (1992) proposed a possible cause for this anomalously short C═C bond, i.e. that molecules oscillate in a shallow potential with a large amplitude while maintaining the orientation of the phenyl rings. The existance of this type of molecular vibration in STB was supported by a lattice dynamical calculation (Saito & Ikemoto, 1996). The observed short C═C bond implies that the STB molecule vibrates in the assumed manner with a large amplitude, as proposed by Ogawa et al. (1992), even in (I).

Related literature

For related literature, see: Akutsu et al. (2000); Bernstein (1975); Bouwstra et al. (1984); Finder et al. (1974); Mitani et al. (1988); Nakasuji et al. (1991); Ogawa et al. (1992); Saito & Ikemoto (1996); Saito et al. (1999, 2000); Zobel & Ruban (1983).

S2. Experimental

Crystals of STB–TCNQF₄ were prepared by slow cooling of a concentrated acetone solution containing STB and TCNQF₄. The complex was obtained as needle-like dark-green crystals. The molar ratio was found to be 1:1 by chemical analysis, i.e. the complex was STB–TCNQF₄. Crystals were slightly air sensitive.

S3. Refinement

H atoms were treated as riding atoms with a C—H distance of 0.93 Å.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1995); program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: TEXSAN and SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: TEXSAN.

Figures

	Fig. 1. The two molecules in the asymmetric unit of the STB–TCNQF4 complex. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view showing the molecular arrangement in the unit cell of the STB–TCNQF4 complex.

trans-stilbene - 2,2'-(2,3,5,6-tetrafluorobenzene-1,4-diylidene)- propanedinitrile (1/1)

Crystal data

C14H12·C12F4N4	F(000) = 464.00
Mr = 456.40	Dx = 1.481 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 9.555 (2) Å	Cell parameters from 25 reflections
b = 6.287 (2) Å	θ = 29.4–30.0°
c = 17.295 (2) Å	µ = 0.12 mm^−1
β = 99.99 (1)°	T = 293 K
V = 1023.2 (4) Å^3	Needle, green
Z = 2	0.2 × 0.2 × 0.2 mm

Data collection

Rigaku AFC-7R diffractometer	Rint = 0.015
Radiation source: Rigaku rotating anode	θmax = 27.5°, θmin = 2.7°
Graphite monochromator	h = −12→0
ω–2θ scans	k = 0→8
2716 measured reflections	l = −21→22
2347 independent reflections	3 standard reflections every 150 reflections
1463 reflections with I > 2σ(I)	intensity decay: 1.6%

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)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.124	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0513P)^2 + 0.1154P] where P = (Fo^2 + 2Fc^2)/3
2347 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.18 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
C1	0.15683 (17)	0.0100 (3)	0.08790 (10)	0.0385 (4)
C2	0.20911 (19)	0.1646 (3)	0.14274 (11)	0.0459 (5)
H2	0.1620	0.2942	0.1424	0.055*
C3	0.3302 (2)	0.1288 (4)	0.19781 (11)	0.0494 (5)
H3	0.3639	0.2341	0.2341	0.059*
C4	0.40076 (19)	−0.0623 (3)	0.19906 (11)	0.0461 (5)
H4	0.4829	−0.0854	0.2356	0.055*
C5	0.34932 (19)	−0.2197 (3)	0.14593 (11)	0.0449 (5)
H5	0.3961	−0.3497	0.1473	0.054*
C6	0.22822 (19)	−0.1845 (3)	0.09053 (10)	0.0414 (4)
H6	0.1943	−0.2911	0.0549	0.050*
C7	0.02950 (17)	0.0600 (3)	0.02951 (10)	0.0414 (4)
H7	−0.0137	0.1904	0.0350	0.050*
F1	0.60329 (11)	0.27403 (16)	0.11706 (6)	0.0465 (3)
F2	0.62162 (10)	−0.38391 (16)	−0.01573 (6)	0.0451 (3)
N1	0.8412 (2)	0.0810 (3)	0.23756 (11)	0.0657 (5)
N2	0.88659 (19)	−0.4638 (3)	0.10582 (12)	0.0641 (5)
C10	0.62444 (15)	−0.0618 (3)	0.05665 (9)	0.0309 (3)
C11	0.55158 (16)	0.1375 (3)	0.06035 (9)	0.0324 (4)
C12	0.56340 (17)	−0.1935 (3)	−0.00834 (10)	0.0327 (4)
C13	0.74051 (17)	−0.1224 (3)	0.11100 (10)	0.0357 (4)
C14	0.79472 (18)	−0.0020 (3)	0.17994 (11)	0.0439 (4)
C15	0.81832 (18)	−0.3151 (3)	0.10589 (11)	0.0421 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0306 (8)	0.0492 (11)	0.0366 (9)	0.0022 (8)	0.0081 (7)	0.0036 (8)
C2	0.0421 (10)	0.0524 (11)	0.0438 (10)	0.0083 (9)	0.0094 (8)	−0.0034 (9)
C3	0.0448 (10)	0.0637 (13)	0.0396 (10)	−0.0017 (10)	0.0075 (8)	−0.0094 (9)
C4	0.0365 (9)	0.0644 (13)	0.0364 (9)	0.0025 (9)	0.0037 (7)	0.0078 (9)
C5	0.0402 (10)	0.0489 (11)	0.0462 (10)	0.0080 (8)	0.0090 (8)	0.0093 (9)
C6	0.0398 (9)	0.0448 (10)	0.0387 (9)	−0.0013 (8)	0.0045 (7)	−0.0014 (8)
C7	0.0348 (9)	0.0452 (10)	0.0446 (10)	0.0081 (8)	0.0081 (7)	0.0015 (8)
F1	0.0478 (6)	0.0415 (6)	0.0454 (6)	−0.0012 (5)	−0.0053 (5)	−0.0122 (5)
F2	0.0459 (6)	0.0360 (6)	0.0510 (6)	0.0106 (4)	0.0015 (5)	−0.0057 (5)
N1	0.0689 (12)	0.0644 (12)	0.0538 (10)	−0.0085 (10)	−0.0174 (9)	−0.0017 (9)
N2	0.0546 (10)	0.0612 (12)	0.0734 (13)	0.0212 (9)	0.0026 (9)	0.0085 (10)
C10	0.0273 (7)	0.0343 (9)	0.0312 (8)	−0.0019 (7)	0.0059 (6)	0.0032 (7)
C11	0.0332 (8)	0.0316 (8)	0.0317 (8)	−0.0038 (7)	0.0040 (6)	−0.0042 (7)
C12	0.0324 (8)	0.0296 (8)	0.0369 (8)	0.0030 (7)	0.0085 (7)	−0.0010 (7)
C13	0.0302 (8)	0.0378 (9)	0.0381 (9)	−0.0005 (7)	0.0037 (6)	0.0036 (7)
C14	0.0383 (9)	0.0453 (11)	0.0436 (10)	−0.0019 (8)	−0.0055 (8)	0.0061 (8)
C15	0.0344 (9)	0.0469 (11)	0.0427 (10)	0.0033 (8)	0.0004 (7)	0.0064 (8)

Geometric parameters (Å, º)

C1—C2	1.389 (3)	C7—H7	0.93
C1—C6	1.397 (3)	F1—C11	1.3324 (17)
C1—C7	1.474 (2)	F2—C12	1.3356 (18)
C2—C3	1.383 (3)	N1—C14	1.144 (2)
C2—H2	0.93	N2—C15	1.140 (2)
C3—C4	1.376 (3)	C10—C13	1.377 (2)
C3—H3	0.93	C10—C12	1.436 (2)
C4—C5	1.382 (3)	C10—C11	1.440 (2)
C4—H4	0.93	C11—C12^ii	1.341 (2)
C5—C6	1.386 (2)	C12—C11^ii	1.341 (2)
C5—H5	0.93	C13—C14	1.431 (3)
C6—H6	0.93	C13—C15	1.432 (3)
C7—C7^i	1.315 (4)
C2—C1—C6	118.33 (15)	C7^i—C7—C1	126.9 (2)
C2—C1—C7	118.34 (17)	C7^i—C7—H7	116.5
C6—C1—C7	123.32 (16)	C1—C7—H7	116.5
C3—C2—C1	120.98 (18)	C13—C10—C12	123.00 (15)
C3—C2—H2	119.5	C13—C10—C11	123.25 (15)
C1—C2—H2	119.5	C12—C10—C11	113.74 (13)
C4—C3—C2	120.14 (18)	F1—C11—C12^ii	118.74 (15)
C4—C3—H3	119.9	F1—C11—C10	118.22 (13)
C2—C3—H3	119.9	C12^ii—C11—C10	123.02 (14)
C3—C4—C5	119.87 (16)	F2—C12—C11^ii	118.53 (15)
C3—C4—H4	120.1	F2—C12—C10	118.19 (14)
C5—C4—H4	120.1	C11^ii—C12—C10	123.24 (15)
C4—C5—C6	120.22 (18)	C10—C13—C14	123.69 (16)
C4—C5—H5	119.9	C10—C13—C15	123.84 (16)
C6—C5—H5	119.9	C14—C13—C15	112.46 (14)
C5—C6—C1	120.43 (17)	N1—C14—C13	175.2 (2)
C5—C6—H6	119.8	N2—C15—C13	175.5 (2)
C1—C6—H6	119.8
C6—C1—C2—C3	1.1 (3)	C12—C10—C11—F1	−177.68 (13)
C7—C1—C2—C3	−178.47 (17)	C13—C10—C11—C12^ii	−178.37 (16)
C1—C2—C3—C4	−0.1 (3)	C12—C10—C11—C12^ii	0.7 (3)
C2—C3—C4—C5	−1.0 (3)	C13—C10—C12—F2	0.6 (2)
C3—C4—C5—C6	1.1 (3)	C11—C10—C12—F2	−178.46 (13)
C4—C5—C6—C1	−0.1 (3)	C13—C10—C12—C11^ii	178.37 (16)
C2—C1—C6—C5	−1.0 (3)	C11—C10—C12—C11^ii	−0.7 (3)
C7—C1—C6—C5	178.56 (17)	C12—C10—C13—C14	−174.10 (16)
C2—C1—C7—C7^i	175.4 (2)	C11—C10—C13—C14	4.8 (3)
C6—C1—C7—C7^i	−4.2 (4)	C12—C10—C13—C15	4.3 (3)
C13—C10—C11—F1	3.3 (2)	C11—C10—C13—C15	−176.74 (16)

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