Co-crystal structure, Hirshfeld surface analysis and DFT studies of 3,4-ethylenedioxythiophene solvated bis[1,3-bis(pentafluorophenyl)propane-1,3-dionato]copper(II)

The title complex, Cu(L)2 or [Cu(C15HF10O2)2], comprising one copper ion and two fully fluorinated ligands (L −), was crystallized with 3,4-ethylenedioxythiophene (EDOT, C6H6O2S) as a guest molecule to give in a dichloromethane solution a unique co-crystal, Cu(L)2·3C6H6O2S.


Chemical context
3,4-Ethylenedioxythiophene, EDOT, is a familiar reagent for polythiophene or oligothiophene organic-active materials such as organic conductive macromolecules and optoelectronic materials. The corresponding poly-3,4-ethylenedioxythiophene, PEDOT, is one of the typical organic conductive materials with a high conductivity, environmental stability, mechanical strength and visible light transmittance, thus showing wide ranges of applications (Skotheim et al., 1998;Groenendaal et al., 2000;Kirchmeyer & Reuter, 2005). The affinity as a guest molecule and the corresponding intermolecular interactions in co-crystals of EDOT are crucial issues for chemists in order to understand the molecular recognition and supramolecular association events (Storsberg et al., 2000). The crystal packing and the relative intermolecular interactions are estimated by the oxygen and sulfur atoms for coordination bonds and molecular stacking of theinteractions for the five-membered hetero-conjugated aromatic ring. On the other hand, molecular crystals of fully fluorinated coordination complexes have been studied as hosts, showing flexible and responsive crystal-packing structures depending on the guest molecules. Typically, the copper complex, Cu(L) 2 , produces unique co-crystals abundantly taken into benzene derivatives after crystallization and ISSN 2056-9890 reversibly encapsulates their vapors , while the corresponding single crystals of Cu(dbm) 2 (dbm = dibenzoylmethane) showed no interaction with the guest molecules. The driving forces of the molecular recognition estimated a metalÁ Á Á interaction (Hunter, 1994;Ma & Dougherty, 1997) induced by improvement of the cationic properties of the central metal as a result of the fluorinewithdrawing nature and arene-perfluoroarene interaction (Williams, 1993(Williams, , 2017Hori, 2012) induced by the exact opposite quadrupole moment between the pentafluorophenyl ring of the complex and the aromatic ring of the guest molecule.
In this study, we examined the encapsulation of 3,4-ethylenedioxythiophene for the title complex, Cu(L) 2 , indicating a new guest-encapsulated crystal, Cu(L) 2 Á3EDOT (I), as shown in the Scheme. The crystal of (I) was prepared by previously reported protocols (Hori & Arii, 2007). Typically, Cu(L) 2 and an excess amount of EDOT in CH 2 Cl 2 (or AcOEt) were slowly evaporated to yield green block-shaped crystals. The driving forces and the detailed weak intermolecular inter-actions were investigated by Hirshfeld surface analysis and DFT calculations. Using the same procedure, the corresponding compound Pd(L) 2 ÁnEDOT was not obtained, then Pd(L) 2 was separately crystallized, showing different metal characteristics and affinity for EDOT. The electrostatic potential of the metal ions is also discussed.

Figure 2
Views of part of the crystal structure of (I): (a) 1:1 alternating linear structure with EDOT-1 and Cu(L) 2 , (b) EDOT-2A and EDOT-3 in the void spaces of the linear chain with the (c) head-to-tail and (d) head-tohead arrangements in the crystal. Color scheme: C, gray; H, white; Cu, orange; F, light green; O, red; S, yellow.

Figure 1
The molecular structure of (I) at 100 K, showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level. The minor EDOT-2B component is omitted.
1.32 (1) Å for EDOT-2A, and 1.361 (6) and 1.365 (6) Å for EDOT-3. EDOT-2A has a large variation in the distance because of the structural disorder, while the analysis was performed without restricting the binding distance of the carbon-to-carbon bonds. For comparison of the molecular recognitions of Cu(L) 2 , negative quadrupole moments of the molecules, e.g., benzene and carbon dioxide, are reversibly recognized in the crystals, because of the positive quadrupole moments of the pentaflurophenyl groups (Hori et al. , 2017. Thus, the crystal structure of (I) indicates the possibility that the butadiene moiety, C C-C C, in EDOT also has a negative surface and interacts in the crystal of Cu(L) 2 through electrostatic interactions.

DFT calculations
The DFT calculations were performed to obtain quantitative values for the surface potential and intermolecular interactions. The electrostatic potentials of Cu(L) 2 and EDOT in (I) range from À135.79 to +162.31 kJ mol À1 , as shown in Fig. 5. The highest electrostatic potential, in which the electron-poor region is shown in blue, is on the Cu atom, the edge of the ketonato hydrogen, the central part of the pentafluorophenyl rings in Cu(L) 2 , and the aromatic and aliphatic hydrogen atoms of EDOT. The lowest electrostatic potential, shown in red, is around the oxygen atoms of Cu(L) 2 and EDOT. The highest electrostatic potentials of the centers of the pentafluorophenyl rings A-D are approximately +97, +90, +91, +83 kJ mol À1 , respectively, which is almost the same as the independently calculated value for Cu(L) 2 (+97 kJ mol À1 for the pentafluorophenyl ring), which was calculated using the currently reported crystal structure (Crowder et al., 2019). The lowest electrostatic potentials of the five-membered rings of EDOT are À77, À63, and À63 kJ mol À1 for EDOT-1, 2A and 3, respectively, indicating the electron distribution is slightly lower than that calculated independently for EDOT (À81 kJ mol À1 ) and used to estimate the intermolecular interactions of Cu(L) 2 and EDOT. The electrostatic potential maps of the EDOT molecules are shown in Fig. 5c. The lefthand structure, optimized and calculated for an independent molecule, clearly indicates that the EDOT-2A has more positive surfaces. The lowest electrostatic potentials of the oxygen atoms are À117 and À118 kJ mol À1 for EDOT (calculated from the refined structure of a single component), À85 and À121 kJ mol À1 for EDOT-1, À109 and À63 kJ mol À1 for EDOT-2A, and À102 and À113 kJ mol À1 for EDOT-3. (a) Structure and (b) the energy potential maps of Cu(L) 2 with the surrounding EDOT molecules and (c) the energy potential maps of independent EDOT and each solvated EDOT molecule in (I). The color of the potential is shown between À120 kJ mol À1 (red) to +120 kJ mol À1 (blue).  actions of the oxygen atoms; one oxygen in EDOT-1 is an electron donor for the coordination bond with decreasing electron density (À85 kJ mol À1 ) and one oxygen in EDOT-2A is an electron donor for the hydrogen bond with decreasing electron density (À63 kJ mol À1 ). The highest electrostatic potential of the surface of the aliphatic H atoms is +162 kJ mol À1 in EDOT-2A and the values of each EDOT are +116, +112, and +123 kJ mol À1 for EDOT (calculated), EDOT-1, and EDOT-3, respectively. The lowest electrostatic potential on sulfur is À32 kJ mol À1 in EDOT-2A and the values of each EDOT are À79, À65, and À48 kJ mol À1 for EDOT (calculated), EDOT-1, and EDOT-3, respectively. These results show the outflowing of the surface electrons due to the formation of the co-crystal and the corresponding intermolecular interactions.

Synthesis
To a solution of Cu(L) 2 (15 mg, 17 mmol) in chloroform (2 ml) was added an excess amount of EDOT. The solution was evaporated slowly to give green crystals of Cu(L) 2 Á3EDOT (I), which were separated by filtration and characterized by crystallographic and thermogravimetric (TG) analyses.

Thermogravimetric studies
In the TG analysis for (I), the weight loss indicates an approximate one-step elimination (Fig. 6); the total elimination of EDOT was found to be 33.6%, which is almost the same as the calculated value of 33.0% around 50-130 C. The release curve is gentle, and the coordinated EDOT and solvated EDOT are gradually separated from the crystals without being distinguished, confirming the weak coordination bond due to the Jahn-Teller effect of the Cu ion. In the complex, the positive electrostatic potential on the copper (+206.41 kJ mol À1 ) in the independent crystal of Cu(L) 2 was higher than that of the corresponding non-fluorinated complex, +116.71 kJ mol À1 for Cu(dbm) 2 (Kusakawa et al., 2020) due to the substitution of the pentafluorophenyl groups, indicating that the present EDOT recognition was induced. For the same procedure, Pd(L) 2 and EDOT were combined to give brown needle-shaped crystals, which are clearly characterized as Pd(L) 2 as a single component  and no guest release was observed by the brown crystals of Pd(L) 2 ; the electrostatic potentials on the metal center of Pd(L) 2 and Pd(dbm) 2 are À1.0 and À73 kJ mol À1 , respectively (Kusakawa et al., 2020).
In summary, we have discussed the crystal structure and the intermolecular interactions for three EDOT molecules inserted in (I), in which guest recognition is induced by the flexible orientations and positive electrostatic potentials of the pentafluorophenyl groups and the enhanced positive potential on the copper ion of the fluorinated complex, Cu(L) 2 . The crystal structure clearly suggests that the alternate coordination polymer between the metal center of Cu(L) 2 and the oxygen atom of EDOT-1 was obtained along the a axis through the weak coordination bond and the close stacking between the pentafluorophenyl group of Cu(L) 2 and the aromatic moiety of EDOT-2 and EDOT-3 was obtained through the arene-perfluoroarene interactions.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in geometrically idealized positions and refined as riding with C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic. TG curves of (I) showing the one-step elimination; the scan rate was 5.0 C min À1 .

Bis[1,3-bis(pentafluorophenyl)propane-1,3-dionato]copper(II) 3,4-ethylenedioxythiophene trisolvate
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.