Crystal-structure studies of 4-phenylpiperazin-1-ium 4-ethoxybenzoate monohydrate, 4-phenylpiperazin-1-ium 4-methoxybenzoate monohydrate, 4-phenylpiperazin-1-ium 4-methylbenzoate monohydrate and 4-phenylpiperazin-1-ium trifluoroacetate 0.12-hydrate

Four novel piperazinium salts are reported, and based on 1-phenylpiperazinium as a common cation in the asymmetric units that include additionally water molecules, and different P-substituent benzoate anions or a trifluoroacetate anion. They are hydrated and there are three crystallized as 1:1 salts while the fourth is a 2:2 salt. Their crystal packing depends on strong ribbons or sheets stabilized by hydrogen bonds of type N—H⋯O and O—H⋯O and other interactions as C—H⋯O, C—H⋯π and C—H⋯F in the trifluoroacetate-based one.


Chemical context
Piperazines are among the most important building blocks in today's drug discovery efforts and are found in biologically active compounds across a number of different therapeutic areas (Brockunier et al., 2004;Bogatcheva et al., 2006). For a review on the current pharmacological and toxicological information for piperazine derivative, see Elliott (2011). Various pharmacological properties of phenylpiperazines and their derivatives have been discussed by several authors (Cohen et al., 1982;Conrado et al., 2010;Neves et al., 2003;Hanano et al., 2000). The design and synthesis of phenylpiperazine derivatives as potent anticancer agents for prostate cancer have been described (Demirci et al., 2019). Many pharmaceutical compounds are derived from 1-phenylpiperazine, viz., oxypertine, trazodone, nefazodone, etc.

Figure 3
The independent components of compound (III) showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Supramolecular features
In the crystal structure of (I), the cation pairs are connected across two water molecules by C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming an R 4 2 (10) ring motif in which the anions and cations are linked through the water molecules by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming ribbons along the a-axis direction (Table 1, Fig. 5a). In addition, a set of C-HÁ Á Á interactions, through the benzene rings of the anions and the cations, connect the molecules together in ribbons along the a-axis direction (Table 1, Fig. 5b). The C-HÁ Á ÁO, N-HÁ Á ÁO, O-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions together form a three-dimensional network, contributing to the stabilization of the crystal structure.
In the crystal structure of (II), the cations, the anions and the water molecules are connected by C-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming ribbons along the aaxis direction (Table 2, Fig. 6a). Furthermore, the cations interact via C--HÁ Á Á interactions through the benzene ring of the anion, forming ribbons along the b-axis direction ( Table 2  The independent components of compound (IV) showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 30% probability level. (Atom splitting is omitted for clarity.) Table 1 Hydrogen-bond geometry (Å , ) for (I).

D-HÁ
three-dimensional network, contributing to the stabilization of the crystal structure.
In the crystal structure of (III), the cations, the anions and the water molecules are connected by C-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming ribbons along the aaxis direction (Table 3, Fig. 7). There are no C-HÁ Á Á interactions orstacking interactions. The crystal structure is stabilized by C-HÁ Á ÁO, N-HÁ Á ÁO, O-HÁ Á ÁO hydrogen bonds and van der Waals interactions between the ribbons, which run along the a-axis direction.
These sheets further interact to maintain the crystal structure by linking through the oxygen atoms of water molecules and by van der Waals interactions. As shown in Table 4, the main interactions in the structure of (IV) involve the oxygen atoms  Table 2 Hydrogen-bond geometry (Å , ) for (II).

Figure 6
Parts of the crystal structure of compound (II) showing (a) the formation of hydrogen-bonded ribbons parallel to [010] and (b) a general view of the C-HÁ Á Á interactions parallel to [010]. Hydrogen bonds and C-HÁ Á Á interactions are drawn as dashed lines. Table 4 Hydrogen-bond geometry (Å , ) for (IV).

Figure 7
Part of the crystal structure of compound (III) showing the formation of a hydrogen-bonded chain of rings parallel to [001]. Hydrogen bonds are drawn as dashed lines.
of carboxylate groups, while the 0.12 fraction of the water molecule contributes with one interaction of the type C-HÁ Á ÁO and it is weak in comparison to the other oxygen-based ones.

Refinement
Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = 0.054 wR(F 2 ) = 0.124 S = 1.08 3424 reflections 244 parameters 2 restraints 0 constraints Primary atom site location: structure-invariant direct methods Secondary atom site location: structureinvariant direct methods Hydrogen site location: mixed H atoms treated by a mixture of independent and constrained refinement (17) 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.

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.

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.