Dicyclohexylammonium O , O ’-Diphenyl Phosphate, [(C 6 H 11 ) 2 NH 2 ][(C 6 H 5 O) 2 P(O)(O)]: Spectroscopic Study, Crystal Structure, and Hirshfeld Surface Analysis

: The title salt, [(C 6 H 11 ) 2 NH 2 ][(C 6 H 5 O) 2 P(O)(O)], crystallizes in the chiral space group P 2 1 2 1 2 1 , composed of achiral cation and anion components. The strong charge-assisted N–H . . . O hydrogen bonds build a linear assembly along the a axis, including a non-centrosymmetric C 22 (6) chain graph-set motif. The intra and intermolecular C–H . . . O interactions as well as the C–H . . . π -electron ring interactions also exist in the crystal structure. Fingerprint plots are used for a detailed investigation of intermolecular interactions participating in the crystal packing. The spectroscopic features (IR, 1 H NMR, 13 C{ 1 H} NMR, 31 P{ 1 H} NMR, and mass) are studied. discussed. The synthesis procedure and spectroscopic characterization of the title compound are detailed. A comparison of the cation and anion components of the title salt with the structures including similar components from the CSD is presented.


Introduction
The charge-assisted hydrogen bonds were observed in some cation-anion compounds including phosphorus-oxygen-  [1][2][3][4]. The Cambridge Structural Database (CSD) survey was investigated to compare the hydrogen bond strengths in some phosphate-based classes of salts and neutral closely related structures [4].
The chiral crystal structures from chiral or achiral molecules/components were also studied, and the diversity of hydrogen bond motifs was investigated [5][6][7].
In this article, the chiral crystal structure [(C 6 H 11 ) 2

Structure Description
The title compound crystallizes in the orthorhombic system with chiral space group P212121, and the asymmetric unit is composed of one cation and one anion components (Figure 1). Selected bond distances and angles are given in Table 1. In general, all bond distances are within the characteristic values according to the atoms involved and are in the ranges of similar bonds observed in analogous structures. For example, the phosphorus-oxygen bond lengths of the [P(O)(O)] − segment are 1.469 (2) and 1.459(2) Å, which are slightly more than the typical P=O bond length (1.45 Å) [8].  In the cation, the cyclohexyl rings adopt a chair conformation, and the NH2 unit is situated in the equatorial position with respect to the rings. The large C-N-C angle, of 118.1(2)°, is a result of the steric bulk of the cyclohexyl rings, as has been also observed in the structures with the same cation, typically in [(C6H11)2NH2][C6H5PO2(OH)] (with CSD refcode ZARGOQ and the C-N-C angle of 118.80(10)°) [9].
In the anion, the phosphorus atom has a distorted tetrahedral   In the cation, the cyclohexyl rings adopt a chair conformation, and the NH 2 unit is situated in the equatorial position with respect to the rings. The large C-N-C angle, of 118.1(2) • , is a result of the steric bulk of the cyclohexyl rings, as has been also observed in the structures with the same cation, typically in [(C 6 H 11 ) 2 NH 2 ][C 6 H 5 PO 2 (OH)] (with CSD refcode ZARGOQ and the C-N-C angle of 118.80(10) • ) [9].
In the anion, the phosphorus atom has a distorted tetrahedral (O) 2 [10]. The P-O-C angles of 124.5(2) • and 126.80 (18) • show a few more "s" characters with respect to the sp 2 hybridization. These values in the anion with a (C-O) 2 (O)P(O) core are in accordance with the previously reported P-O-C angles, typically in the (C-O) 2 P(X)(N)-based structures (X = O, S) [3] deposited in the CSD. The similarities and differences of cations and anions in the title structure with the selected related structures in the CSD are compared and discussed in Section 2.2.
In the crystal structure of the title compound, the cations and anions are hydrogen-bonded to each other, through N-H . . . O hydrogen bonds (N1 . . . O1 = 2.806(3) Å and N1 . . . O2 = 2.730(3) Å), building a linear arrangement along the a axis ( Figure 2, Table 2). This assembly includes the non-centrosymmetric C 2 2 (6) graph-set motif. The strength of N-H . . . O hydrogen bonds is a result of the assistance of positive and negative charges in hydrogen bonding interactions.  [3] deposited in the CSD. The similarities and differences of cations and anions in the title structure with the selected related structures in the CSD are compared and discussed in Section 2.2.
In the crystal structure of the title compound, the cations and anions are hydrogen-bonded to each other, through N-H…O hydrogen bonds (N1…O1 = 2.806(3) Å and N1…O2 = 2.730(3) Å), building a linear arrangement along the a axis ( Figure 2, Table 2). This assembly includes the noncentrosymmetric (6) graph-set motif. The strength of N-H…O hydrogen bonds is a result of the assistance of positive and negative charges in hydrogen bonding interactions.
In addition, the crystal packing shows one weak intermolecular C-H…O hydrogen bond (C24…O2 = 3.548(4) Å), and one intramolecular C-H…O hydrogen bond (C12…O4 = 3.139(4) Å) ( Table 2). The C-H…O interactions do not extend the dimensionality of hydrogen bond pattern made by N-H…O hydrogen bonds. Figure 3 indicates a view of crystal packing with the relevant N-H…O and C-H…O hydrogen bonds. This assembly includes an (8) hydrogen-bonded ring motif, made by the cooperation of N1-HN1B…O1 and C24-H24B…O2 hydrogen bonds. The two phenyl rings of the anion also involved in the C-H…π-electron ring interactions, as the acceptors; the geometries are given in Table 2. The C-H…π interactions network is also formed along the a axis ( Figure 4). In all contacts noted, the acceptor sites (O, π) belong to the anion.   the geometries are given in Table 2. The C-H . . . π interactions network is also formed along the a axis ( Figure 4). In all contacts noted, the acceptor sites (O, π) belong to the anion.

Hirshfeld Surface Analysis and Fingerprint Plots
The Hirshfeld surface analysis, which uses three-dimensional (3D) surfaces functions, as well as two-dimensional (2D) fingerprint plots [33,34], is a very useful graphical tool for identification and understanding of intermolecular interactions within a crystal structure. The Hirshfeld surfaces mapped with dnorm and corresponding shape index associated 2D fingerprint plots of the cation and anion of the title structure were generated using the Crystal Explorer software version 3.1 [35], with the structure file in the CIF format as the input.
In the Hirshfeld surfaces of the cation and anion, two large red areas can be seen, which correspond to two intermolecular N-H···O hydrogen bonds, as noted in the crystal structure section. The Hirshfeld surface map is typically represented for the anion and labels 1 and 2 denote to the hydrogen bonds noted (Figure 9); the Hirshfeld surface of the cation represents similar red areas with the hydrogen-bond donor sites, i.e., NH units, within the surface.
Two-dimensional fingerprint plots of the cation and anion are derived from the Hirshfeld surfaces, by plotting the fraction of points on the surface as a function of (de, di), where de and di introduce the distances from a point on the Hirshfeld surface to the nearest atoms outside and inside the surface, respectively. The full fingerprint plots of the cation and anion are given in Figure 10. The full plots were also divided into the figures illustrating different contacts observed in the crystal ( Figure 11).
According to divided fingerprints, the contribution portions of contacts received by the cation are H···H 72.7%, H···O 13.7%, and H···C 13.5%. Similar contacts in the anion have the contribution portions of 54.2%, 22.9%, and 22.8%, respectively. Furthermore, a minor P···H contact is also seen for the anion with the contribution portion of 0.1%. In the fingerprint plots, the H···O contacts develop as one sharp spike, indicating the closest interaction in the crystal. Thus, comparison of the cation and anion moieties of the title compound with the similar structures available in the CSD indicates that the title compound is well-matched with the reported literature.

Hirshfeld Surface Analysis and Fingerprint Plots
The Hirshfeld surface analysis, which uses three-dimensional (3D) surfaces functions, as well as two-dimensional (2D) fingerprint plots [33,34], is a very useful graphical tool for identification and understanding of intermolecular interactions within a crystal structure. The Hirshfeld surfaces mapped with d norm and corresponding shape index associated 2D fingerprint plots of the cation and anion of the title structure were generated using the Crystal Explorer software version 3.1 [35], with the structure file in the CIF format as the input.
In the Hirshfeld surfaces of the cation and anion, two large red areas can be seen, which correspond to two intermolecular N-H···O hydrogen bonds, as noted in the crystal structure section. The Hirshfeld surface map is typically represented for the anion and labels 1 and 2 denote to the hydrogen bonds noted ( Figure 9); the Hirshfeld surface of the cation represents similar red areas with the hydrogen-bond donor sites, i.e., NH units, within the surface.
Two-dimensional fingerprint plots of the cation and anion are derived from the Hirshfeld surfaces, by plotting the fraction of points on the surface as a function of (d e , d i ), where d e and d i introduce the distances from a point on the Hirshfeld surface to the nearest atoms outside and inside the surface, respectively. The full fingerprint plots of the cation and anion are given in Figure 10. The full plots were also divided into the figures illustrating different contacts observed in the crystal (Figure 11).  According to divided fingerprints, the contribution portions of contacts received by the cation are H···H 72.7%, H···O 13.7%, and H···C 13.5%. Similar contacts in the anion have the contribution portions of 54.2%, 22.9%, and 22.8%, respectively. Furthermore, a minor P···H contact is also seen for the anion with the contribution portion of 0.1%. In the fingerprint plots, the H···O contacts develop as one sharp spike, indicating the closest interaction in the crystal.

Spectroscopic Study
In the IR spectrum of the title salt, the intense doublet band with the maxima at 1239 and 1224 cm  [36]. The relatively high negative value is attributed to shielding caused by the negative charge on the oxygen atom. In the 1 H NMR, the signal at 8.80 ppm corresponds to the NH 2 protons, and the downfield chemical shift is due to the hydrogen bonding effect, similar to the one that was reported for a compound exhibiting hydrogen bonding in the X-ray structure [37]. The aliphatic and aromatic protons appear within 1.01 to 2.97 ppm and 7.02 to 7.28 ppm, as expected. In the 13

Spectroscopic Study
In the IR spectrum of the title salt, the intense doublet band with the maxima at 1239 and 1224 cm −1 is assigned to phosphorus-oxygen stretches of the [P=O(O)] − moiety. The broad overlapped bands within 2471 to 3016 cm −1 are assigned to NH stretching frequencies, aliphatic and aromatic CH stretching frequencies, and the overtone of stretching frequencies of the phosphorus-oxygen bonds in the [P=O(O)] − moiety. The broadening of these overlapped bands is related to strong N-H…O hydrogen bonds as were discussed in the X-ray description.  [36]. The relatively high negative value is attributed to shielding caused by the negative charge on the oxygen atom. In the 1 H NMR, the signal at 8.80 ppm corresponds to the NH2 protons, and the downfield chemical shift is due to the hydrogen bonding effect, similar to the one that was reported for a compound exhibiting hydrogen bonding in the X-ray structure [37]. The aliphatic and aromatic protons appear within 1.01 to 2.97 ppm and 7.02 to 7.28 ppm, as expected.
In the 13

Synthesis of [(C 6 H 11 ) 2 NH 2 ][(C 6 H 5 O) 2 P(O)(O)]
General procedure for the preparation of some dicyclohexylammonium di(para-substituted phenyl) phosphates was reported, together with the melting points and elemental analyses of different derivatives such as the title salt, i.e., with the para-substituent H [38]. The synthesis method was based on the reaction of N-methylpyridinium di(para-substituted phenyl phosphates) with HCl and dicyclohexylamine. The title salt reported in this article is the product obtained from hydrolysis in the synthesis process in a different reaction condition, as follows. A solution of dicyclohexylamine (1 mmol) and triethylamine (1 mmol) in acetonitrile was added to a solution of diphenylphosphoryl chloride (1 mmol) in the same solvent (at 273 K) under stirring. After 4 h, the mixture was transferred to a beaker in order to evaporate the solvent at room temperature over the course of a few days. The solid which formed was washed with distilled water and dried. Single crystals (yellow needles) were obtained from a solution of the product in a methanol-acetonitrile

X-ray Data of Crystal Structure
The X-ray data were collected at 293 K with graphite monochromated Mo Kα radiation (0.71073 Å) on a Bruker SMART APEXII area-detector diffractometer. The structure was solved with SHELXS97 [39] by the direct methods algorithm and refined using full-matrix least-squares on F 2 with the SHELXL-2016/6 [40]. All carbon-bound H atoms were placed at calculated positions and were refined on their parent atoms with their U iso set to 1.2U eq . Nitrogen-bound H atoms were located in a difference Fourier map and refined isotropically with their U iso set to 1.2U eq of the carrier N atom.