Crystal structure of ethylenedioxytetrathiafulvalene-4,5-bis(thiolbenzoic acid) 0.25-hydrate

In the crystal of the title compound, the benzoic acid molecules are linked by O—H⋯O hydrogen bonds, forming inversion dimers with (8) motifs. The dimers are linked further via weak C—H⋯O hydrogen bonds, and S⋯S and S⋯C contact interactions into a layer structure.


Chemical context
Tetrathiafulvalene (TTF) and its derivatives have received much attention in recent years due to their unique electrical properties and synthetic versatility (Canvert et al., 2009;Xiao et al., 2012). Among them, bis(ethylenedioxy)-TTF (BEDO-TTF) derivatives have afforded two-dimensional stable metallic CT complexes resulting from its self-assembling nature in partially oxidized states (Horiuchi et al., 1996). Ethylenedioxy-TTF (EDO-TTF) is a noted electron-donor molecule, and (EDO-TTF) 2 PF 6 shows a metal-insulator thermal transition at near room temperature (Ota et al., 2002). There are also many reports that peripheral arylation of TTF could afford photochemically active organic materials. Recently, Shao's group reported a method to introduce aryls to TTF through the sulfur atom (Sun et al., 2013;Zhang et al., 2015). Our group has also reported a donor molecule, EDO-TTF-pyridine (Xiao et al., 2012). To obtain more insight into this system, we report here the synthesis and crystal structure of the title compound.

Structural commentary
The asymmetric unit of the title compound contains one benzoic acid molecule and a quarter molecule of solvent water ISSN 2056-9890 ( Fig. 1). The TTF core adopts a boat conformation, as usually observed in neutral TTF derivatives. The central plane A (S1/ S2/C5/C6/S3/S4) and the adjacent planes B (S3/S4/C7/C8/S5/ S6) and C (S1/S2/C3/C4/O1/O2) are almost planar with r.m.s. deviations of 0.0233, 0.0274 and 0.0105 Å , respectively. The dihedral angles between planes A and B and A and C are 31.24 (4) and 26.83 (6) , respectively. Plane B makes dihedral angles of 85.88 (11) and 82.03 (15) , respectively, with the benzene C9-C14 and C16-C21 rings. These benzene rings are approximately parallel, subtending a dihedral angle of 11.82 (14) . All bond lengths and angles in the TTF fragment are within the range of the values for a neutral TTF molecule (Zhang et al., 2015).

Figure 2
A view of the inversion dimer of the title compound with two R 2 2 (8) hydrogen-bond motifs. O-HÁ Á ÁO hydrogen bonds are shown as dotted lines.

Figure 3
A view of the crystal packing of the title compound, showing O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, and SÁ Á ÁS and SÁ Á ÁC interactions.

Figure 1
The molecular structure of the title compound, showing the atomnumbering scheme. Displacement ellipsoids are drawn at the 50% probability level. A, B and C indicate mean planes defined by six atoms.
al. (2000) has a similar structure to the title compound. Both structures include O-HÁ Á ÁO hydrogen bonds between carboxyl groups with R 2 2 (8) ring motifs.

Synthesis and crystallization
The title compound was prepared according to the reaction scheme shown in Fig. 4.
Finally, compound 1 was obtained by hydrolysis reaction of compound 2: A 50 ml flask was charged with compound 2 (260 mg, 0.50 mmol) under an N 2 atmosphere. Degassed methanol (6 ml) and THF (6 ml) were added to generate a suspension. In a separate flask, sodium hydroxide (230 mg, 5.8 mmol) was dissolved in degassed water (4 ml). The sodium hydroxide solution was added to compound 2 and the reaction was heated to reflux for 8 h. The reaction was then cooled to room temperature and the volatiles were removed in vacuo. Hydrochloric acid (1 mol l À1 , 15 ml) was added to afford a maroon precipitate, which was collected by filtration and washed with water (50 ml). The product was collected and dried under high vacuum for 12 h to afford 1 as a maroon solid (179 mg, 0.35 mmol, 70% yield

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Carboxyl H atoms were located in a difference-Fourier map and refined with O-H = 0.85 (2) Å , and with U iso (H) = 1.2U eq (O). H atoms bonded to C and O(water) atoms were positioned geometrically and included in the refinement in the riding-model approximation (C-H = 0.93 or 0.97 Å , and O-H = 0.85 Å ) with U iso (H) = 1.2U eq (C or O). In the refinement, the occupancy of the lattice water molecule was fixed at 0.25, which was estimated from the results of element analysis and gave acceptable displacement parameters for the water O atom. Synthesis of the title compound. Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT-Plus (Bruker, 2014); data reduction: SAINT-Plus (Bruker, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.