A neutral complex of an azino-DTDAF compound with TCNQ

In the crystal structure of the title 1:1 complex, ethyl 2-{[5-(ethoxy­carbonyl)-2,3-dihydro-3,4-di­methyl-1,3-thia­zol-2-yl­idene]­hydrazono}-2,3-di­hydro-3,4-di­methyl-1,3-thia­zole-5-carboxyl­ate-7,7,8,8-tetra­cyano-p-quinodi­methane (1/1), C₁₆H₂₂N₄O₄S₂·C₁₂H₄N₄, the planar donor and tetra­cyano-p-quinodi­methane (TCNQ) mol­ecules are each located on inversion centres and are stacked alternately. The bond lengths indicate that, in this complex, the donor and acceptor are neutral, as confirmed by IR investigation.

S1. Comment

Extended dithiadiazafulvalenes (DTDAF) which possess an azino spacer group between the two thiazole rings are interesting candidates for the synthesis of molecular materials (Barlow et al., 1976). Indeed, the insertion of an azino spacer group induces a wider difference between the two oxidation potentials of the donor than for DTDAF alone (Hünig et al., 1974). Therefore, the window of potential stability of the cation radical species is increased. In the course of our study on azino-DTDAF compounds and their ability to form complexes with various organic acceptors, we prepared the title complex, (III). \sch

The azino-DTDAF derivative, (II), was prepared using the thiazolium salt, (I), as the starting material (Bellec et al., 1999). This salt reacts in a basic medium with hydrazine monohydrate to afford (III). The strategy used is outlined in the Scheme (Hünig et al., 1964). The title complex, (III), was obtained by mixing a solution of the donor (II) with a solution of TCNQ.

The crystal structure determination of (III) reveals a stoichiometry of one donor molecule for one TCNQ molecule (Fig. 1). Both molecules possess crystallographic C_i symmetry. The planar donor and TCNQ molecules form infinite alternating stacks along the b axis, wherein the planes of the donor and the acceptor are parallel, with an interplanar separation of b/2 (3.41 Å) (Fig. 2). Interestingly, within the stacks, the long axis of the TCNQ is perpendicular to that of the donor.

No short intermolecular contacts, either within or between the stacks, are observed. The bond distances of the TCNQ in (III) are essentially the same as in crystals of pure TCNQ (Long et al., 1965).

Using the empirical formula of Kistenmacher (Kistenmacher et al., 1982), which correlates bond lengths with the formal charge of the TCNQ in various charge-transfer salts, we found no charge transfer on TCNQ in (III). Therefore, complex (III) is neutral. This was confirmed by the nitrile stretching absorption band in the FT—IR spectra, ν_CN = 2218 cm^-1, which is close to the value for neutral TCNQ (ν_CN = 2224 cm^-1). This neutral complex finds its origin in the difference between the redox potential of the donor and the acceptor. Indeed, the azino-DTDAF derivative (II) oxidizes at E₁ = 0.48 V, far above the reduction potential of TCNQ (E₁ = 0.20 V versus SCE).

S2. Experimental

The synthesis of (II) was carried out according to the method of Hünig et al. (1964). To a solution of 5-(ethoxycarbonyl)-2-(ethylthio)-3,4-dimethyl-1,3-thiazolium tetrafluoroborate, (I) (1.00 g, 3 mmol), in acetonitrile (5 ml) and ethanol (5 ml), hydrazine hydrate (0.073 ml, 1.5 mmol) and triethylamine (0.84 ml, 6 mmol) were added. The mixture was strirred under an inert athmosphere at room temperature for 1 h. The yellow precipitate which formed was filtered off, washed with ethanol and recrystallized from acetonitrile to give donor (II) in 70% yield [m.p. 535 K]. Spectroscopic analysis: ¹H NMR (200 MHz, CDCl₃, δ, p.p.m.): 1.33 (t, 6H), 2.53 (s, 6H), 3.40 (s, 6H), 4.25 (q, 4H); elemental analysis, found (calculated): C 48.30 (48.23), H 5.57 (5.56), N 14.09 (14.06), S 16.21 (16.09)%. Cyclic voltammetry measurements were carried out in Bu₄NPF₆ as the supporting electrolyte at room temperature in CH₂Cl₂, versus SCE (please define). The title complex was prepared by mixing a hot acetonitrile solution of TCNQ (0.042 g, 0.2 mmol) with a hot dichloromethane solution of (II) (0.04 g, 0.1 mmol). Dark purple crystals of (III), suitable for X-ray diffraction studies, were obtained by slow evaporation of the solution at room temperature.

S3. Refinement

H atoms were introduced at calculated positions, with C—H = 0.93–0.97 Å, included in structure factor calculations and refined using a riding model.

Computing details

Data collection: EXPOSE in IPDS (Stoe, 1999); cell refinement: SELECT and CELL in IPDS; data reduction: INTEGRATE in IPDS; program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing details.

Figures

	Fig. 1. A view of (III) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented as small spheres of arbitrary radii.
	Fig. 2. The crystal packing of (III) viewed along the b axis. H atoms have been omitted for clarity.

(III)

Crystal data

C16H22N4O4S2·C12H4N4	F(000) = 628
Mr = 602.70	Dx = 1.361 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 20.960 (4) Å	Cell parameters from 4723 reflections
b = 6.8198 (14) Å	θ = 2.1–25.9°
c = 11.730 (2) Å	µ = 0.23 mm^−1
β = 118.67 (3)°	T = 293 K
V = 1471.2 (5) Å^3	Parallelepiped, dark purple
Z = 2	0.3 × 0.3 × 0.3 mm

Data collection

Stoe IPDS area-detector diffractometer	1135 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.036
Graphite monochromator	θmax = 26.1°, θmin = 2.2°
Detector resolution: 6.66 pixels mm^-1	h = −25→25
rotation, ϕ increment 2° scans	k = −7→7
7171 measured reflections	l = −14→14
1526 independent reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.041	H-atom parameters constrained
wR(F^2) = 0.108	w = 1/[σ^2(Fo^2) + (0.073P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.97	(Δ/σ)max < 0.001
1526 reflections	Δρmax = 0.26 e Å^−3
128 parameters	Δρmin = −0.25 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.039 (5)

Special details

Experimental. Data were collected with an area detector (Stoe IPDS) with a crystal-to-plate distance of 70 mm (θ_max = 26.11°) and with a ϕ increment of 2°.

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	Occ. (<1)
S1	0.93046 (4)	0.0000	0.14076 (6)	0.0438 (3)
N1	0.84242 (12)	0.0000	−0.1060 (2)	0.0436 (6)
N2	0.96518 (12)	0.0000	−0.0549 (2)	0.0450 (6)
O1	0.74318 (12)	0.0000	0.1450 (2)	0.0732 (8)
O2	0.86127 (12)	0.0000	0.2948 (2)	0.0628 (6)
C1	0.91603 (14)	0.0000	−0.0187 (2)	0.0397 (6)
C2	0.81787 (18)	0.0000	−0.2451 (3)	0.0654 (9)
H2A	0.8593	0.0000	−0.2595	0.098*
H2B	0.7891	0.1149	−0.2838	0.098*	0.50
H2C	0.7891	−0.1149	−0.2838	0.098*	0.50
C3	0.79813 (15)	0.0000	−0.0492 (3)	0.0436 (6)
C4	0.71770 (17)	0.0000	−0.1329 (3)	0.0621 (8)
H4A	0.7061	0.0000	−0.2226	0.093*
H4B	0.6976	0.1149	−0.1149	0.093*	0.50
H4C	0.6976	−0.1149	−0.1149	0.093*	0.50
C5	0.83581 (15)	0.0000	0.0817 (3)	0.0440 (7)
C6	0.80676 (17)	0.0000	0.1731 (3)	0.0514 (7)
C7	0.8427 (2)	0.0000	0.3991 (3)	0.0826 (12)
H7A	0.8143	−0.1155	0.3936	0.099*	0.50
H7B	0.8143	0.1155	0.3936	0.099*	0.50
C8	0.9117 (3)	0.0000	0.5219 (4)	0.1019 (16)
H8A	0.9017	0.0000	0.5937	0.153*
H8B	0.9392	0.1149	0.5260	0.153*	0.50
H8C	0.9392	−0.1149	0.5260	0.153*	0.50
N3	0.67704 (19)	0.0000	0.4391 (3)	0.0955 (12)
N4	0.44881 (17)	0.0000	0.3475 (3)	0.0851 (11)
C9	0.54219 (16)	0.0000	0.2641 (3)	0.0503 (7)
C10	0.61769 (19)	0.0000	0.3622 (3)	0.0631 (9)
C11	0.49044 (17)	0.0000	0.3110 (3)	0.0592 (9)
C12	0.57484 (15)	0.0000	0.0888 (3)	0.0448 (7)
H12	0.6241	0.0000	0.1488	0.054*
C13	0.52179 (14)	0.0000	0.1345 (2)	0.0427 (6)
C14	0.55422 (14)	0.0000	−0.0378 (2)	0.0452 (7)
H14	0.5894	0.0000	−0.0645	0.054*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0422 (4)	0.0556 (5)	0.0404 (4)	0.000	0.0253 (3)	0.000
N1	0.0432 (12)	0.0513 (15)	0.0407 (11)	0.000	0.0237 (10)	0.000
N2	0.0438 (12)	0.0552 (17)	0.0441 (11)	0.000	0.0275 (10)	0.000
O1	0.0549 (14)	0.104 (2)	0.0822 (16)	0.000	0.0498 (13)	0.000
O2	0.0639 (14)	0.0871 (18)	0.0558 (13)	0.000	0.0437 (11)	0.000
C1	0.0444 (15)	0.0368 (16)	0.0438 (13)	0.000	0.0258 (12)	0.000
C2	0.0582 (19)	0.092 (3)	0.0418 (15)	0.000	0.0205 (14)	0.000
C3	0.0421 (14)	0.0397 (17)	0.0567 (15)	0.000	0.0300 (12)	0.000
C4	0.0437 (16)	0.066 (2)	0.074 (2)	0.000	0.0262 (15)	0.000
C5	0.0438 (15)	0.0461 (18)	0.0542 (16)	0.000	0.0332 (13)	0.000
C6	0.0585 (18)	0.051 (2)	0.0620 (18)	0.000	0.0429 (15)	0.000
C7	0.090 (3)	0.117 (4)	0.068 (2)	0.000	0.060 (2)	0.000
C8	0.106 (4)	0.156 (5)	0.061 (2)	0.000	0.054 (2)	0.000
N3	0.0587 (19)	0.154 (4)	0.0551 (16)	0.000	0.0121 (16)	0.000
N4	0.0633 (19)	0.147 (3)	0.0493 (15)	0.000	0.0304 (15)	0.000
C9	0.0470 (16)	0.057 (2)	0.0446 (14)	0.000	0.0201 (12)	0.000
C10	0.056 (2)	0.085 (3)	0.0447 (15)	0.000	0.0213 (15)	0.000
C11	0.0523 (18)	0.085 (3)	0.0372 (13)	0.000	0.0187 (13)	0.000
C12	0.0354 (13)	0.0496 (19)	0.0467 (14)	0.000	0.0176 (11)	0.000
C13	0.0437 (15)	0.0406 (17)	0.0438 (13)	0.000	0.0211 (12)	0.000
C14	0.0389 (14)	0.0496 (18)	0.0475 (15)	0.000	0.0212 (12)	0.000

Geometric parameters (Å, º)

S1—C1	1.746 (2)	C5—C6	1.465 (4)
S1—C5	1.760 (3)	C7—C8	1.473 (6)
N1—C3	1.378 (3)	C7—H7A	0.9700
N1—C1	1.383 (3)	C7—H7B	0.9700
N1—C2	1.457 (4)	C8—H8A	0.9600
N2—C1	1.289 (3)	C8—H8B	0.9600
N2—N2^i	1.410 (5)	C8—H8C	0.9600
O1—C6	1.209 (4)	N3—C10	1.133 (4)
O2—C6	1.333 (4)	N4—C11	1.142 (4)
O2—C7	1.451 (3)	C9—C13	1.367 (4)
C2—H2A	0.9600	C9—C11	1.433 (4)
C2—H2B	0.9600	C9—C10	1.443 (4)
C2—H2C	0.9600	C12—C14	1.332 (4)
C3—C5	1.349 (4)	C12—C13	1.448 (4)
C3—C4	1.489 (4)	C12—H12	0.9300
C4—H4A	0.9600	C13—C14^ii	1.446 (4)
C4—H4B	0.9600	C14—C13^ii	1.446 (4)
C4—H4C	0.9600	C14—H14	0.9300
C1—S1—C5	89.73 (12)	O1—C6—C5	126.2 (3)
C3—N1—C1	114.4 (2)	O2—C6—C5	109.8 (2)
C3—N1—C2	125.7 (2)	O2—C7—C8	106.8 (3)
C1—N1—C2	119.9 (2)	O2—C7—H7A	110.4
C1—N2—N2^i	109.8 (2)	C8—C7—H7A	110.4
C6—O2—C7	117.6 (3)	O2—C7—H7B	110.4
N2—C1—N1	122.7 (2)	C8—C7—H7B	110.4
N2—C1—S1	126.7 (2)	H7A—C7—H7B	108.6
N1—C1—S1	110.59 (18)	C7—C8—H8A	109.5
N1—C2—H2A	109.5	C7—C8—H8B	109.5
N1—C2—H2B	109.5	H8A—C8—H8B	109.5
H2A—C2—H2B	109.5	C7—C8—H8C	109.5
N1—C2—H2C	109.5	H8A—C8—H8C	109.5
H2A—C2—H2C	109.5	H8B—C8—H8C	109.5
H2B—C2—H2C	109.5	C13—C9—C11	122.4 (3)
C5—C3—N1	112.8 (2)	C13—C9—C10	121.7 (3)
C5—C3—C4	127.5 (2)	C11—C9—C10	115.9 (3)
N1—C3—C4	119.6 (2)	N3—C10—C9	179.9 (4)
C3—C4—H4A	109.5	N4—C11—C9	179.5 (3)
C3—C4—H4B	109.5	C14—C12—C13	121.1 (2)
H4A—C4—H4B	109.5	C14—C12—H12	119.5
C3—C4—H4C	109.5	C13—C12—H12	119.5
H4A—C4—H4C	109.5	C9—C13—C14^ii	120.8 (2)
H4B—C4—H4C	109.5	C9—C13—C12	121.7 (2)
C3—C5—C6	127.7 (3)	C14^ii—C13—C12	117.5 (2)
C3—C5—S1	112.43 (18)	C12—C14—C13^ii	121.4 (3)
C6—C5—S1	119.9 (2)	C12—C14—H14	119.3
O1—C6—O2	124.0 (3)	C13^ii—C14—H14	119.3

Symmetry codes: (i) −x+2, −y, −z; (ii) −x+1, −y, −z.