Redetermination of tetra­methyl tetra­thia­fulvalene-2,3,6,7-tetra­carboxyl­ate

An improved crystal structure of the title compound, C₁₄H₁₂O₈S₄, is reported. The structure, previously solved using the heavy-atom method (R = 7.1%), has now been solved using direct methods. Due to the improved quality of the data set an R value of 2.06% could be achieved. In the crystal, C—H...S and C—H...O contacts link the mol­ecules.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.021
• wR factor = 0.055
• Data-to-parameter ratio = 12.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT480_ALERT_4_C Long H...A H-Bond Reported H5C    ..  O3      ..       2.65 Ang.

Alert level G
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT063_ALERT_4_G Crystal Size Likely too Large for Beam Size ....       0.64 mm
PLAT153_ALERT_1_G The su's on the Cell Axes   are Equal ..........    0.00020 Ang.
PLAT154_ALERT_1_G The su's on the Cell Angles are Equal ..........    0.00100 Deg.
PLAT909_ALERT_3_G Percentage of Observed Data at Theta(Max) still          91 Perc.
PLAT961_ALERT_5_G Dataset Contains no Negative Intensities .......          !

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   1 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   6 ALERT level G = General information/check it is not something unexpected

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

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S1. Comment

Tetrathiafulvalene derivatives are molecules of high importance relating to electroconductive behaviour (Takase et al., 2011).

The present structure of the title compound (TTF) has been refined to an R-value of 2.06% which is clearly better than 7.1% of the previous study reported in 1976 by Belsky and Voet. In particular, this enabled us to refine the positions of hydrogen atoms of the methyl groups with improved accuracy making it possible to find potential hydrogen bonds. In conformity with previous findings, the TTF scaffold is planar and the methoxycarbonyl functions are slightly twisted out of the ring plane [interplanar angles 25.60 (1) and 42.77 (2)°] (Fig. 1).

The refinement shows the molecules being arranged in a layered structure (Fig. 2) stabilized by C—H···O (Desiraju et al., 1999; Katzsch et al., 2011; Fischer et al., 2011) and C—H···S contacts (Mata et al., 2010; Novoa et al., 1995) (Table 1). Two molecules each are associated forming special dimer type species (Fig. 2). In one case, they involve two ester functions [d(C5—H5A···O1) = 2.50 Å] giving rise to a hydrogen bonded ring motif R²₂(10) (Bernstein et al., 1995; Petersen et al., 2007). In the other case, adjacent molecules show hydrogen bonding interactions between ester methyl groups and sulfur atoms [d(C7—H7A···S1) = 2.83 Å] (Saad et al., 2010; Lu et al., 2005). The layers are also connected via C—H···O contacts including a methyl group and a carbonyl function [d(C5—H5C···O3) = 2.65 Å] of superimposed molecules.

Related literature

For the first structure determination of the title compound, see: Belsky & Voet (1976). For a previously reported experimental procedure and physical data, see: Yoneda et al. (1978). For C—H···O hydrogen bonds, see: Desiraju & Steiner (1999); Katzsch et al. (2011); Fischer et al. (2011). For C—H···S hydrogen bonds, see: Mata et al. (2010); Novoa et al. (1995); Lu et al. (2005); Saad et al. (2010). For a description of ring motifs, see: Bernstein et al. (1995); Petersen et al. (2007). For several steps of the synthetic procedure, see: Degani et al. (1986); O'Connor & Jones (1970); Nguyen et al. (2010). For general background to the electroconductive behaviour of tetrathiafulvalene derivatives, see: Takase et al. (2011).

S2. Experimental

The titled tetramethyl tetrathiafulvalene-2,3,6,7-tetracarboxylate was synthesized via a four step reaction sequence: (1) 1,3-Dithiolane-2-thione was prepared from carbon disulfide, sodium sulfide and 1,2-dichloroethane under phase transfer catalyzed condition following literature protocol (I. Degani et al., 1986). (2) Reflux of 1,3-dithiolane-2-thione and dimethyl acetylenedicarboxylate in toluene yielded dimethyl 1,3-dithiole-2-thione-4,5-dicarboxylate (O'Connor & Jones, 1970). (3) This latter compound was treated with mercury(II) acetate in acetic acid/chloroform to obtain dimethyl 1,3-dithiole-2-one-4,5-dicarboxylate (Nguyen et al., 2010). (4) In the final step, the 1,3-dithiol-2-one compound was coupled by a trimethyl phosphite induced reaction according to a literature protocol (Nguyen et al., 2010). For this purpose methyl 1,3-dithiol-2-one-4,5-dicarboxylate (3.00 g, 12.8 mmol) was dissolved in trimethyl phosphite (7.94 g, 64.0 mmol) and stirred for 8 h at 100 °C. After cooling, a fine red precipitate had formed which was filtered and washed with a small amount of cold ethanol to yield 1.62 g (58 %) of the substituted TTF. Physical data of the compound correspond to reported values (Yoneda et al., 1978). Suitable dark red single crystals for X-ray diffraction were grown by slow evaporation from a solution of the title compound in chloroform.

S3. Refinement

H atoms were positioned geometrically and allowed to ride on their parent atoms, with C—H = 0.96 Å, and U_iso=1.5 U_eq (parent atom).

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. Perspective view of the title compound showing thermal ellipsoids at the 50% probability level.
	Fig. 2. Hydrogen-bonds within the layer structure of tetra-substituted TTF.

Tetramethyl tetrathiafulvalene-2,3,6,7-tetracarboxylate

Crystal data

C14H12O8S4	Z = 1
Mr = 436.48	F(000) = 224
Triclinic, P1	Dx = 1.668 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.8666 (2) Å	Cell parameters from 9962 reflections
b = 7.8783 (2) Å	θ = 2.5–45.3°
c = 8.4335 (2) Å	µ = 0.59 mm^−1
α = 100.221 (1)°	T = 100 K
β = 99.255 (1)°	Needle, red
γ = 99.328 (1)°	0.64 × 0.16 × 0.15 mm
V = 434.53 (2) Å^3

Data collection

Bruker APEXII CCD area-detector diffractometer	1534 independent reflections
Radiation source: fine-focus sealed tube	1471 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
phi and ω scans	θmax = 25.0°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −7→8
Tmin = 0.705, Tmax = 0.917	k = −9→9
10884 measured reflections	l = −10→10

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)] = 0.021	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.055	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0273P)^2 + 0.222P] where P = (Fo^2 + 2Fc^2)/3
1534 reflections	(Δ/σ)max = 0.026
120 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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
S1	0.30978 (5)	0.63798 (4)	1.10656 (4)	0.01479 (11)
S2	0.06589 (5)	0.56717 (4)	0.76932 (4)	0.01637 (11)
O1	0.69629 (14)	0.93615 (13)	0.94082 (12)	0.0194 (2)
O2	0.72198 (13)	0.79160 (12)	1.14884 (11)	0.0167 (2)
O3	0.27914 (16)	0.78034 (15)	0.55357 (13)	0.0265 (3)
O4	0.56544 (14)	0.69314 (13)	0.64417 (11)	0.0181 (2)
C1	0.0779 (2)	0.54255 (17)	0.97428 (16)	0.0140 (3)
C2	0.4249 (2)	0.71176 (17)	0.95464 (16)	0.0131 (3)
C3	0.31610 (19)	0.67605 (17)	0.80137 (16)	0.0138 (3)
C4	0.62881 (19)	0.82552 (17)	1.00955 (16)	0.0138 (3)
C5	0.9200 (2)	0.90095 (19)	1.21844 (18)	0.0196 (3)
H5A	1.0006	0.8996	1.1353	0.029*
H5B	0.9840	0.8560	1.3075	0.029*
H5C	0.9061	1.0194	1.2584	0.029*
C6	0.3832 (2)	0.72501 (17)	0.65299 (16)	0.0153 (3)
C7	0.6552 (2)	0.7573 (2)	0.51653 (17)	0.0226 (3)
H7A	0.5790	0.6946	0.4108	0.034*
H7B	0.7911	0.7391	0.5270	0.034*
H7C	0.6548	0.8805	0.5272	0.034*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.01005 (18)	0.02032 (19)	0.01379 (18)	−0.00123 (13)	0.00238 (12)	0.00683 (13)
S2	0.01129 (18)	0.02217 (19)	0.01518 (18)	−0.00117 (13)	0.00129 (13)	0.00788 (13)
O1	0.0162 (5)	0.0197 (5)	0.0233 (5)	−0.0007 (4)	0.0067 (4)	0.0087 (4)
O2	0.0108 (5)	0.0206 (5)	0.0168 (5)	−0.0020 (4)	0.0011 (4)	0.0055 (4)
O3	0.0216 (6)	0.0423 (7)	0.0225 (5)	0.0111 (5)	0.0064 (4)	0.0184 (5)
O4	0.0158 (5)	0.0265 (5)	0.0161 (5)	0.0054 (4)	0.0076 (4)	0.0096 (4)
C1	0.0116 (6)	0.0158 (6)	0.0147 (6)	0.0017 (5)	0.0017 (5)	0.0049 (5)
C2	0.0127 (6)	0.0131 (6)	0.0160 (6)	0.0035 (5)	0.0064 (5)	0.0053 (5)
C3	0.0109 (6)	0.0133 (6)	0.0184 (7)	0.0019 (5)	0.0046 (5)	0.0050 (5)
C4	0.0126 (6)	0.0143 (6)	0.0157 (6)	0.0035 (5)	0.0062 (5)	0.0022 (5)
C5	0.0104 (7)	0.0216 (7)	0.0231 (7)	−0.0023 (5)	0.0002 (5)	0.0024 (6)
C6	0.0154 (7)	0.0147 (6)	0.0152 (7)	0.0009 (5)	0.0032 (5)	0.0032 (5)
C7	0.0188 (7)	0.0342 (8)	0.0176 (7)	0.0022 (6)	0.0087 (6)	0.0110 (6)

Geometric parameters (Å, º)

S1—C2	1.7452 (13)	C1—C1^i	1.343 (3)
S1—C1	1.7570 (13)	C2—C3	1.3419 (19)
S2—C3	1.7468 (13)	C2—C4	1.4882 (18)
S2—C1	1.7636 (13)	C3—C6	1.4921 (18)
O1—C4	1.2022 (16)	C5—H5A	0.9600
O2—C4	1.3363 (16)	C5—H5B	0.9600
O2—C5	1.4559 (16)	C5—H5C	0.9600
O3—C6	1.2007 (17)	C7—H7A	0.9600
O4—C6	1.3263 (16)	C7—H7B	0.9600
O4—C7	1.4487 (16)	C7—H7C	0.9600
C2—S1—C1	94.90 (6)	O2—C5—H5A	109.5
C3—S2—C1	94.65 (6)	O2—C5—H5B	109.5
C4—O2—C5	115.25 (10)	H5A—C5—H5B	109.5
C6—O4—C7	115.57 (11)	O2—C5—H5C	109.5
C1^i—C1—S1	122.42 (14)	H5A—C5—H5C	109.5
C1^i—C1—S2	122.68 (14)	H5B—C5—H5C	109.5
S1—C1—S2	114.90 (7)	O3—C6—O4	125.74 (12)
C3—C2—C4	125.13 (12)	O3—C6—C3	122.87 (12)
C3—C2—S1	117.68 (10)	O4—C6—C3	111.34 (11)
C4—C2—S1	116.86 (10)	O4—C7—H7A	109.5
C2—C3—C6	126.96 (12)	O4—C7—H7B	109.5
C2—C3—S2	117.78 (10)	H7A—C7—H7B	109.5
C6—C3—S2	115.23 (10)	O4—C7—H7C	109.5
O1—C4—O2	125.14 (12)	H7A—C7—H7C	109.5
O1—C4—C2	124.48 (12)	H7B—C7—H7C	109.5
O2—C4—C2	110.33 (11)
C2—S1—C1—C1^i	178.58 (16)	C5—O2—C4—O1	0.21 (18)
C2—S1—C1—S2	−1.44 (8)	C5—O2—C4—C2	−177.38 (10)
C3—S2—C1—C1^i	−177.53 (16)	C3—C2—C4—O1	22.1 (2)
C3—S2—C1—S1	2.49 (8)	S1—C2—C4—O1	−151.10 (11)
C1—S1—C2—C3	−0.67 (11)	C3—C2—C4—O2	−160.29 (12)
C1—S1—C2—C4	173.05 (10)	S1—C2—C4—O2	26.51 (14)
C4—C2—C3—C6	7.2 (2)	C7—O4—C6—O3	10.1 (2)
S1—C2—C3—C6	−179.69 (10)	C7—O4—C6—C3	−172.26 (11)
C4—C2—C3—S2	−170.52 (10)	C2—C3—C6—O3	−137.60 (15)
S1—C2—C3—S2	2.63 (15)	S2—C3—C6—O3	40.13 (17)
C1—S2—C3—C2	−3.06 (11)	C2—C3—C6—O4	44.73 (18)
C1—S2—C3—C6	178.99 (10)	S2—C3—C6—O4	−137.54 (10)

Symmetry code: (i) −x, −y+1, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C7—H7A···S1^ii	0.96	2.83	3.735 (2)	158
C5—H5A···O1^iii	0.96	2.50	3.324 (2)	143
C5—H5C···O3^iv	0.96	2.65	3.481 (2)	145

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