Hydrogen-bonding patterns in 2,2-bis(4-methylphenyl)hexafluoropropane pyridinium and ethylenediammonium salt crystals

The crystal structures of two salt crystals of 2,2-bis(4-methylphenyl)hexafluoropropane (Bmphfp) with amines, namely, dipyridinium 4,4′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)dibenzoate 4,4′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)dibenzoic acid, 2C5H6N+·C17H8F6O42−·C17H10F6O4, (1), and a monohydrated ethylenediammonium salt ethane-1,2-diaminium 4,4′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)dibenzoate monohydrate, C2H10N22+·C17H8F6O42−·H2O, (2), are reported. Compounds1and2crystallize, respectively, in space groupP21/cwithZ′ = 2 and in space groupPbcawithZ′ = 1. The crystals of compound1contain neutral and anionic Bmphfp molecules, and form a one-dimensional hydrogen-bonded chain motif. The crystals of compound2contain anionic Bmphfp molecules, which form a complex three-dimensional hydrogen-bonded network with the ethylenediamine and water molecules.


Chemical context
In recent years, porous organic frameworks have been researched extensively because of their structural versatility and potential applications in gas storage and separation and as catalysts and chemical sensors (He et al., 2011). Hydrogenbonded organic frameworks (HOFs), which are constructed via intermolecular hydrogen bonds, are being actively investigated for such applications (Hisaki et al., 2018). HOFs are basically flexible to allow solution-based fabrication/reassembly and dynamic structural conversion as compared to covalent organic frameworks (COFs) (Miyano et al., 2016). Several multiple-carboxylic acids are reported to create HOFs via carboxylic dimers (Bassanetti et al., 2016;Hisaki, 2020). 2,2-Bis(4-methylphenyl)hexafluoropropane (Bmphfp) is a Vshaped di-carboxylic acid forming a one-dimensional hydrogen-bonded chain in the crystal structure (Tang et al., 2010). The HOFs based on carboxylic acids can be modified or rebuilt by salt formation with various organic bases (Galcera et al., 2012).

Figure 1
Molecular structures of (a) compound 1, and (b) compound 2. Displacement ellipsoids are drawn at the 50% probability level.
hydrogen bonds with three surrounding ethylenediammonium cations (Fig. 3a). Therefore, five of the six hydrogen-atom donors of the ethylenediammonium cations are connected to Bmphfp molecules, resulting in a complex three-dimensional hydrogen-bonding network. The water molecule is linked to both Bmphfp and ethylenediamine molecules via two O-HÁ Á ÁO and one N-HÁ Á ÁO hydrogen bonds. Thus, the water molecules are highly stabilized by these intermolecular interactions in the crystal structure (Fig. 3b). Weak C-HÁ Á ÁF and FÁ Á ÁF interactions are observed between Bmphfp molecules, resulting interatomic distances of 3.493 (1) Å (CÁ Á ÁF) and 2.890 (1) Å (FÁ Á ÁF), respectively. In compound 2, the Bmphfp molecules do not form a discrete 1-D hydrogen bond chain motif as observed in compound 1 because the one carboxyl group is terminated by an ethylenediamine molecule.

Hirshfeld surface analysis
Hirshfeld surfaces (McKinnon et al., 2007) and their associated two-dimensional fingerprint plots (Spackman & McKinnon, 2002) were calculated using CrystalExplorer17 (Turner et al., 2017). The d norm surface of the Bmphfp molecules in compounds 1 and 2 are shown in Fig. 4a There is no significant difference in the contact contributions of each of the molecules (Tables 4 and 5). However, in the fingerprint plots, molecule B has no contribution from contacts with a long interatomic distance (highlighted by the red circle in Fig. 4a) compared to molecule A. Thus, molecule B is more closely packed with the surrounding molecules in the crystal than molecule A. This may be due to the difference in the ionic state between neutral molecule A and anionic molecule B. Compound 1 (molecule A and B) has strong hydrogen-bonding interactions, with similar but slightly weaker interactions for compound 2. The contributions to the Hirshfeld surface for 2 are listed in Table 6. Hirshfeld surface mapped over d norm of (a) Bmphfp molecule A and (b) Bmphfp molecule B in compound 1, and (c) the Bmphfp molecule in compound 2. Two-dimensional fingerprint plots of these Bmphfp molecules are shown in (d)-(f), respectively.

Synthesis and crystallization
The reagents 2,2-bis(4-methylphenyl)hexafluoropropane, pyridine and ethylenediamine were purchased from TCI Co., Ltd. (Japan). 2,2-Bis(4-methylphenyl)hexafluoropropane (2.5 mmol, 0.083 g) was dissolved in methanol 10 mL. The Bmphfp solution was mixed into 5 mL of a 1.0 M pyridine methanol solution under stirring. After slow evaporation, colourless plate-like crystals of compound 1 were obtained. When the Bmphfp solution was mixed into 5 ml of a 1.0 M ethylenediamine methanol solution under stirring, colourless needle-like crystals of compound 2 were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 7    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.