Crystal structure of bis(3,5-diisopropyl-1 H -pyrazol- 4-ammonium) tetra ﬂ uoroterephthalate, 2 [C 9 H 18 N 3 ][C 8 F 4 O 4 ]

2[C 9 H 18 N 3 ][C 8 F 4 O 4 ], monoclinic, I 2/ a (no. 15), a = 10.2282(4) Å, b = 11.9366(5) Å, c = 24.5548(12) Å, β = 98.948(4) ° , V = 2961.4(2) Å 3 , Z = 4, R gt ( F ) = 0.0456, w R ref ( F 2 ) = 0.1217, T = 178 K.

The molecular structure is shown in the figure.Table 1 contains crystallographic data and Table 2 contains the list of the atoms including atomic coordinates and displacement parameters.

Experimental details
The C-bound H atoms were geometrically placed (C-H = 0.98-1.00Å) and refined as riding with U iso (H) = 1.2-1.5Ueq (C).The N-bound H atoms were located in a difference Fourier map and refined with pyrazolyl-N-H = 0.88 ± 0.01 Å and ammonium-N-H = 0.91 ± 0.01 Å with U iso (H) = 1.2 and 1.5U eq (N), respectively.Owing to poor agreement, one reflection, i.e. (1 1 0), being affected by the beam-stop, was omitted from the final cycles of refinement.

Comment
Covalent organic frameworks (COFs) are a new class of materials having two-or three-dimensional architectures resulting from the reactions between organic precursors being characterised by strong covalent bonds between the original precursors to afford porous and stable crystalline materials [5].Recent interest has focussed upon in the construction of COFs through imine-C=N bond formation through the reaction of an aromatic amine with a carbonyl compound, such as an aldehyde, and by imide C-N bond formation by the reaction of an aromatic amine with a carbonyl compound, such as a carboxylic acid or an acid anhydride [6].With this in mind, recent reports have described the crystal structures of products obtained from the reactions of 4-amino-3,5-diisopropyl-1-pyrazole (L 1 HpzNH 2 ) [7] and of 4-amino-3,5-dimethyl-1-pyrazole (L 0 HpzNH 2 ) [8] with benzene-1,4-dicarboxaldehyde (terephthalaldehyde) [9,10].These studies were complemented by the structure determination of the product of the reaction between L 0 HpzNH 2 with tetrafluoroterephthalic acid, through imide-C-N bond formation, motivated by the desire to improve solubility in normal organic solvents [11].However, the obtained product proved to be a salt, i.e. {(4-ammonium-3,5-dimethyl-1-pyrazole)} 2 -(tetrafluoroterephthalate) [11]; this salt is later referred to as "(II)".Herein, the structure of title compound was obtained by the reaction of the more electron-donating isopropyl substituted precursor, L 1 HpzNH 2 , with tetrafluoroterephthalic acid in anhydrous tetrahydrofuran solution.However, this reaction, too, resulted in a salt, (I).
The IR spectrum of (I) features a new characteristic absorption band at 3239 cm −1 , assigned to N-H stretching.Further, the sharp N-H 2 stretching band of the L 1 HpzNH 2 precursor, at 3374 cm −1 , disappeared [7].In addition, new C=O stretching bands, at 1624 and 1606 cm −1 , are clearly shifted from the C=O stretching band, at 1700 cm −1 , of tetrafluoroterephthalic acid.The observed bands in the IR spectrum of (I) very closely resemble those of the previously reported salt, {(4-ammonium-3,5-dimethyl-1-pyrazole)} 2 (tetrafluoroterephthalate), i.e. 3197 s ν(N-H), 1639 s and 1607 cm −1 s ν(C=O) [11].The expected signals in 1 H NMR spectrum of (I) were observed at 1.29 ppm (methyl-H) and 3.07 ppm (methine-H), the latter of which are shifted downfield compound to those of L 1 HpzNH 2 at 2.97 ppm.A detailed determination of the structural details of (I) in the solid-state was achieved through X-ray crystallography.The molecular structures of the constituents of salt (I) are shown in the upper view of the figure (50 % displacement ellipsoids; unlabelled atoms are related by the symmetry operation 0.5 − x, 1.5 − y, 0.5 − z).The H1n and H2n atoms are statistically disordered over the N1 and N2 atoms.The asymmetric-unit comprises a 4-ammonium-3,5-diisopropyl-1-pyrazole cation, in a general position, and half a 2,3,5,6tetrafluorobenzene-1,4-dicarboxylate dianion, as this is located about an inversion centre.
The dianion deviates from planarity with the carboxylate residues being splayed with respect to the phenyl ring as the dihedral angle between the respective least-squares planes is 55.99(8)°.This result contrasts the near perpendicular relationship observed in (II), i.e. 83.14(6)° [11].
A complementary analysis of the molecular packing to the above was achieved through the calculation of the Hirshfeld surfaces as well as of the full and delineated two-dimensional fingerprint plots employing Crystal Explorer 21 [12] and standard procedures [13].The calculations were based on the two-molecule aggregate shown in the upper view of the figure, i.e. with the full di-anion, the most prominent contacts in the crystal of (I) are H⋯H [40.When compared to the comparable analysis conducted on the three-molecule aggregate in the non-isostructural methyl analogue (II) [11], several trends are apparent.First and foremost amongst these trends is the greater contribution of H⋯H contacts in the crystal of (I) cf.(II) [23.5 %], an observation correlated with the greater number of hydrogen atoms in the cation.While, to a first approximation, the contributions from the H⋯O/O⋯H and H⋯F/F⋯H contacts in (I) and (II) [i.e.23.8 and 19.8 %, respectively] are the same, there is a greater range and more significant contributions from other surface contacts in (II), reflecting, for example, the presence of π⋯π interactions.
8 %] followed by H⋯O/O⋯H [21.7 %] and H⋯F/F⋯H [20.3 %].Significant contributions to the surface contacts are also made by H⋯C/C⋯H [8.0 %] and O⋯F/F⋯O [4.3 %] with smaller contributions from H⋯N/N⋯H [2.9 %] and F⋯F [1.0 %].When the calculations were performed on the individual components of (I), rather different contributions are evident, as anticipated.The cation has significantly greater contributions to the Hirshfeld surface from H⋯H contacts, at 62.7 %, compared to (I), with concomitantly diminished contributions from H⋯O/O⋯H [12.9 %] and H⋯F/F⋯H [11.2 %].Small increases are seen in H⋯C/C⋯H [8.7 %] and H⋯N/N⋯H [4.5 %] contacts.Lacking hydrogen atoms, the di-anion has a vastly different spread of contributors to the surface contacts, with the most prominent being H⋯O/O⋯H [36.4 %] and H⋯F/F⋯H [34.7 %] followed by H⋯C/C⋯C [16.6 %] and O⋯F/F⋯O [8.4 %] contacts.Smaller contributions are made by F⋯F [2.0 %] and C⋯O/O⋯C [1.9 %] contacts.

Table  :
Data collection and handling.

Table  :
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å  ).