Crystal structure of potassium hydrogen bis((E)-2-{4-[3-(thiophen-3-yl)acryloyl]phenoxy}acetate)

The title compound, C30H23KO8S2, contains one molecule of (E)-2-{4-[3-(thiophen-3-yl)acryloyl]phenoxy}acetic acid and one molecule of its potassium salt in the asymmetric unit. The distorted KO6 octahedra share edges, resulting in chains running in the [010] direction.

The synthesis and spectroscopic data of (E)-2-{4-[3-(thiophen-3-yl)acryloyl]phenoxy}acetic acid are described. Crystallization from an ethanol-water mixture resulted in the title compound, C 30 H 23 KO 8 S 2 or [K(C 15 H 11 O 4 S)(C 15 H 12 O 4 S)] n , containing one molecule of the acid and one molecule of the potassium salt in the asymmetric unit. Both molecules share the H atom between their carboxyl groups and a potassium ion. The C C bonds display an E configuration. The thiophene and phenyl rings in the two molecules are inclined by 43.3 (2) and 22.7 (2) . The potassium ion is octahedrally coordinated by six O atoms. This distorted octahedron shares on opposite sides two oxygen atoms with inversion-related octahedra, resulting in chains of octahedra running in the [010] direction, which form ladder-like chains by C-HÁ Á Á interactions. A Hirshfeld surface analysis indicates that the highest contributions to the surface contacts arise from interactions in which H atoms are involved, with the most important contribution being from HÁ Á ÁH (31.6 and 31.9% for the two molecules) interactions.

Chemical context
Over the last two decades, water-soluble polythiophenes and their derivatives have been of particular importance among conjugated polyelectrolytes owing to a unique combination of high conductivity, environmental stability and structural versatility, allowing derivatization of the -conjugated backbone in view of numerous technological applications Chayer et al., 1997;Wang et al., 2013). Many regioregular polythiophenes with pendant carboxylic acid functionality have been studied (Ewbank et al., 2004;McCullough et al., 1997;Wu et al., 2015;Janá ky et al., 2010). The increased alkyl side-chain length allows for increased coplanarity of the main-chain thiophene rings to advance regioregular polythiophene backbones (Vu Quoc et al., 2019a). A lot of synthetic research has been conducted with a view to increasing the side-chain length of thiophene rings (Vu Quoc et al., 2020). Crystal studies of thiophene monomers have also been reported (Vu Quoc et al., 2017, 2018, 2019b. (E)-2-{4-[3-(thiophen-3-yl)acryloyl]phenoxy}acetic acid are reported. This compound is considered to be a good monomer for the synthesis of water-soluble polythiophene-based conjugated polyelectrolytes. A single-crystal structure determination indicates that after crystallization, crystals were obtained containing one molecule of the acid and one molecule of the potassium salt in the asymmetric unit.

Structural commentary
The title compound crystallizes in the triclinic space group P1 as a complex formed between the acid and the potassium salt of the acid, as illustrated in Fig. 1. In the following discussion, molecule A includes atoms S1-O20 and molecule B atoms S21-O40. Both molecules share hydrogen atom H19 between their carboxyl groups and a potassium ion, K41. Atom H19 is involved in hydrogen-bonding interactions with atoms O39 and O40 (Table 1). The dihedral angle between the thiophene and phenyl rings is 43.3 (2) for molecule A and 22.7 (2) for molecule B. The C C bonds display an E configuration, resulting in short intramolecular C6-H6Á Á ÁO9 and C26-H26Á Á ÁO29 interactions (Table 1). The terminal thiophene groups are involved in intense thermal motion. Fig. 2 shows an overlay diagram of the two molecules A and B [r.m.s. deviation 0.5622 Å as calculated using Mercury (Macrae et al., 2020)]. The largest differences are caused by the different orientation of the phenyl groups.

Supramolecular features
In the crystal packing, the potassium ion K41 interacts with six molecules of which two occur in the carboxylic acid form  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Overlay diagram of the two molecules A (green) and B (blue), comprising the asymmetric unit. H atoms are hidden for clarity (Mercury; Macrae et al., 2020).

Figure 1
The molecular structure of the title compound, showing the atomlabelling scheme and displacement ellipsoids at the 30% probability level.

Figure 4
Potassium atom K41 is surrounded by six different molecules. The six KÁ Á ÁO interactions participating in the distorted octahedral coordination are shown in turquoise, the two longer ones in yellow.

Table 2
Percentage contributions of interatomic contacts to the Hirshfeld surfaces of the two molecules.

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed using CrystalExplorer (Turner et al., 2017). The Hirshfeld surfaces of molecules A and B mapped over d norm are given in Fig. 7a and b, respectively. The relative distributions from the different interatomic contacts to the Hirshfeld surfaces are presented in Table 2. The bright-red spots at atoms O19, H19 and O39 are indicative of the O19-H19Á Á ÁO39 hydrogen bond between the molecules. The additional faint-red spots near atoms O16, O19, O20, O36, O39 and O40 concern the KÁ Á ÁO interactions in the crystal structure. It should be noted that the Hirshfeld surfaces are almost identical for the two molecules. The same is true for the fingerprint plots ( Fig. 7c and d). The sharp tips at d e + d i ' 1.4 Å arise from the O19-H19Á Á ÁO39 hydrogen bond. The principal contribution to the Hirshfeld surfaces involves HÁ Á ÁH contacts at 31.6 and 31.9% for molecules A and B, respectively. These are followed by CÁ Á ÁH/HÁ Á ÁC (21.1 and 20.0%) OÁ Á ÁH/HÁ Á ÁO (17.4 and 17.3%) and SÁ Á ÁH/HÁ Á ÁS (8.8 and 9.9%) contacts.

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.42, last update February 2021; Groom et al., 2016) for the fragment R 1 -CH CH-C( O)-p-C 6 H 4 -R 2 gave 619 hits (with C atoms double-bond acyclic). For only 33 cases (5.3%), the double bond has the Z configuration (Fig. 8a). The histogram of the dihedral angle between the planes of the double bond and the phenyl ring shows values between 0.0 and 86.2 (Fig. 8b). A search with thiophene as R 1 resulted in only four hits (CSD refcodes XOLJUG, XOLKAN, XOLKER and XOLKIV; Vu Quoc et al., 2019c) displaying the E configuration and dihedral angles in the range 6.7 to 15.8 (smaller than in the title compound). Only one structure was found for which R 2 is the same as in the title compound (OCH 2 COOH; CSD refcode TAMJID; Abdul Ajees et al., 2017)     The Hirshfeld surfaces of molecules (a) A and (b) B mapped over d norm in the colour ranges À1.0475 to 1.0150 and À1.1101 to 1.0300 a.u., respectively, together with the full two-dimensional fingerprint plots for molecules (c) A and (d) B.
bonds to the carboxyl groups of two neighbouring molecules and in addition to a carbonyl of a third neighbouring enone moiety.
A mixture of ethyl 2-(4-acetylphenoxy)acetate (5 mmol), 3thiophenecarbaldehyde (5 mmol) and 50 mL of ethanol was stirred in ice-cold water for 20 minutes. Then, 5 mL of 50% KOH solution was added dropwise to the reaction mixture, which was then stirred continuously for 5 h. At the end of the reaction, water was added to the reaction mixture and stirring was continued until all solids in the mixture were dissolved. Concentrated HCl was slowly added to the obtained solution until the solution changed from brown to yellow. The solution was then heated until crystals appeared. The solid then began to crystallize when the solution temperature started to decrease. The crystallized solid was filtered off, washed thoroughly with water and recrystallized from an ethanol-water mixture to give 2-

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atom H19 was located from a difference electron-density map and refined freely with an U iso (H) value of 1.5U eq of the parent atom O19. The other H atoms were placed in idealized positions and included as riding contributions with an U iso (H) values of 1.2U eq of the parent atom, with C-H distances of 0.93 (aromatic) and 0.97 Å (CH 2 ). In the final cycles of refinement, 12 outliers with |error/e.s.d.| > 5.0 were omitted.

Potassium hydrogen bis((E)-2-{4-[3-(thiophen-3-yl)acryloyl]phenoxy}acetate)
Crystal data 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.