The structures of eleven (4-phenyl)piperazinium salts containing organic anions

Eleven (4-phenyl)piperazinium salts containing organic anions have been prepared and structurally characterized.

Eleven (4-phenyl)piperazinium salts containing organic anions have been prepared and structurally characterized, namely, 4-phenylpiperazin-1-ium 4-fluorobenzoate monohydrate, C 10  , 12. Compounds 1 and 3-12 are all 1:1 salts with the acid proton transferred to the phenylpiperaizine basic N atom (the secondary amine) with the exception of 3 where there is disorder in the proton position with it being 68% attached to the base and 32% attached to the acid. Of the structures with similar stoichiometries only 3 and 9 are isomorphous. The 4-phenyl substituent in all cases occupies an equatorial position except for 12 where it is in an axial position. The crystal chosen for structure 7 was refined as a nonmerohedral twin. There is disorder in 5, 6, 10 and 11. For both 5 and 6, a nitro group is disordered and was modeled with two equivalent orientations with occupancies of 0.62 (3)/0.38 (3) and 0.690 (11)/0.310 (11), respectively. For 6, 10 and 11, this disorder is associated with the phenyl ring of the phenylpiperazinium cation with occupancies of 0.687 (10)/0.313 (10), 0.51 (7)/0.49 (7) and 0.611 (13)/389 (13), respectively. For all salts, the packing is dominated by the N-HÁ Á ÁO hydrogen bonds formed by the cation and anion. In addition, several structures contain C-HÁ Á Á (1, 3, 4, 8, 9, 10, and 12) and aromaticstacking interactions (6 and 8) and one structure (5) contains a -NO 2 Á Á Á interaction. For all structures, the Hirshfeld surface fingerprint plots show the expected prominent spikes as a result of the N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds.

Structural commentary
Compounds 1 and 3-12 (Figs. 1-11) are all 1:1 molecular salts with the acid proton transferred to the secondary N atom of The molecular structure of 3 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 1
The molecular structure of 1 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 3
The molecular structure of 4 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 4
The molecular structure of 5 with hydrogen bonds shown as dashed lines and disorder of the nitro group indicated. Atomic displacement parameters are at the 30% probability level.
the phenylpiperaizine base with the exception of 3 where there is disorder in the proton position with it being 68% attached to the base and 32% attached to the acid. Compounds 1, 3 and 9 crystallize as mono-hydrates but the remaining crystals are solvent free. In compounds 1, 3, 4, 5 and 9, the anions are all benzoate ions or p-substituted benzoates but only 3 and 9 are isomorphous. Compounds 6, 7 and 8 contain picrate or nitrated benzoate anions while 10 contains a tosylate anion and 11 and 12 contain hydrogen tartarate and hydrogen fumarate mono-anions. Apart from the disorder in the acidic proton position mentioned above, there is disorder in 5, 6, 10 and 11. For 5 this disorder is confined to the nitro substituent on the benzoate anion, which is disordered over two orientations with occupancies of 0.62 (3)/0.38 (2). For 6, 10 and 11 the disorder is associated with the phenyl ring of the phenylpiperazinium cation, with occupancies of 0.687 (10)/ 0.313 (10), 0.51 (7)/0.49 (7) and 0.611 (13) The molecular structure of 6 with hydrogen bonds shown as dashed lines and disorder of the phenyl ring and one nitro group indicated. Atomic displacement parameters are at the 30% probability level.

Figure 6
The molecular structure of 7 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 7
The molecular structure of 8 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 8
The molecular structure of 9 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level.

Figure 9
The molecular structure of 10 with hydrogen bonds shown as dashed lines and disorder of the phenyl rings indicated. Atomic displacement parameters are at the 30% probability level.

Figure 11
The molecular structure of 12 with hydrogen bonds shown as dashed lines. Atomic displacement parameters are at the 30% probability level. Note the axial conformation of the phenyl ring.

Figure 10
The molecular structure of 11 with hydrogen bonds shown as dashed lines and disorder of the phenyl ring indicated. Atomic displacement parameters are at the 30% probability level.
tively. This is a common feature of this moiety as shown in a recent study (Kiran Kumar et al., 2019a) of 12 salts of the 4-methoxyphenylpiperazinium cation, of which four were found to contain similar disorder of the phenyl ring. For the structures containing benzoate or p-substituted benzoate anions, the C-O distances fall into two groups. In one group (3,5), these distances are the same within experimental error at 2.246 (4) Å , while in the second group (1, 4, and 9) these are substantially different and average 2.235 (4) and 2.255 (4) Å .
For the structures containing the 3,5-dinitrosalicylic (6), 3,5dinitrobenzoate (7) and 2,3,5-trinitrophenolate ions (8), some interesting patterns emerge. In the anion of compound 6, the carboxyl group is unionized, with C-O distances of 1.211 (4) and 1.309 (4) Å and it is the phenolic H atom that has been lost (Fig. 5). The C12-O3 distance, 1.283 (4) Å , is closer to that normally found in ketones than to that typical of phenols or phenolates (Allen et al., 1987). In addition, the C11-C12 and C12-C13 distances, 1.428 (4) and 1.449 (5) Å , respectively, are significantly larger than the other C-C distances in this ring, which lie in the rather narrow range 1.370 (4)-1.398 (4) Å , but the C-N and N-O distances of the nitro substituents are all typical of their types. These observations indicate that the negative charge in this anion is delocalized over the five atoms C11, C13, C14, C15 and C16, but without any significant delocalization onto the nitro groups, as has been observed in trinitrophenolate (picrate) anions (Kavitha et al., 2006;Sagar et al., 2017;Shaibah et al., 2017a,b). The carboxylate anion in 7 contains similar C-O distances [C17-O1 = 1.251 (14); C17-O2 = 1.256 (14) Å ]. Structure 8 contains a picrate anion. Here the situation is similar to that of 6 in that the C-O distance is even shorter at 1.244 (3) Å and in the phenyl ring the C-C bonds are not equal with C11-C12 and C11-C16 being 1.443 (3) and 1.445 (3) Å , respectively, while the remaining C-C bonds range from 1.360 (3) to 1.386 (3) Å . For the nitro groups the C-N distances range from 1.441 (3) to 1.456 (3) Å , indicating that the negative charge in this anion is also delocalized over the five atoms C11, C13, C14, C15 and C16, but without any significant delocalization onto the nitro groups.
Structure 10 contains the tosylate anion. There are two formula units in the asymmetric unit and in both anions the S-O distances are almost equal within experimental error ranging from 1.448 (12) to 1.462 (11) Å and 1.430 (13) to 1.473 (11) Å . Structures 11 and 12 contain the mono-anions of the di-carboxylic acids tartaric acid and fumaric acid. For both structures the metrical parameters of both cation and anion are in the normal range for such species. It notable that in 1 and 3-11, the phenyl substituent occupies an equatorial position in the piperazinium cation, but for 12 this substituent occupies an axial position.

Figure 15
Packing diagram for 4 viewed along the c axis showing how the R 8 8 (24) rings pack in the a-axis direction.

Figure 14
Partial packing diagram for 4 showing the R 8 8 (24) ring with a topology analogous to the seam of a tennis ball involving N-HÁ Á ÁO hydrogen bonds.

Figure 19
Packing diagram for 7 showing how the R 4 4 (22) rings shown in the previous figure are linked in the [111] direction by C 2 2 (6) chains also involving N-HÁ Á ÁO hydrogen bonds involving the phenylpiperazinium cation and carboxylate group of the 3,5-dinitrobenzoate anion and weak C-HÁ Á ÁO interactions.

Figure 20
Partial packing diagram for 8 showing the C 2 2 (8) chains made up of N-HÁ Á ÁO hydrogen bonds involving the phenylpiperazinium cation and a nitro group of the picrate anion. Hydrogen-bonding interactions are shown by dashed lines.
Structure 11 has a complicated packing arrangement as in addition to the phenylpiperazinium NH 2 group, the flexible tartarate anion contains four OH groups and there is a water Packing diagram for 8 viewed along the b axis showing how the picrate anions forminteractions in the a-axis direction.

Figure 22
Partial packing diagram for 8 showing one of the C-HÁ Á Á interactions involving the phenyl ring of the phenylpiperazinium cation.

Figure 23
Partial packing diagram for 9 showing one of the two anti-parallel C 2 2 (6) chains linked by N-HÁ Á ÁO hydrogen bonds and C-HÁ Á ÁO interactions propagating in the a-axis direction.

Figure 24
Packing diagram for 9 viewed along the c-axis direction showing the two anti-parallel C 2 2 (6) chains linked by N-HÁ Á ÁO and C-HÁ Á ÁO interactions involving the water oxygen atom, which combine to form ribbons in the a-axis direction. molecule of crystallization. Multiple N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bonding interactions combine to form a three-dimensional array (Fig. 26).
The Hirshfeld surface fingerprint plots for 1 and 3-12 generated using CrystalExplorer are available in the supporting information. All of them show the distinctive 'pincer spikes' associated with the N-HÁ Á ÁO and/or O-HÁ Á ÁO hydrogen bonds (Spackman et al., 2021).

Figure 26
Packing diagram for 11 viewed along the a axis where multiple N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds involving the phenylpiperazinium NH 2 group, the tartarate anion and water molecule of crystallization combine to form a three-dimensional network.

Figure 27
Packing diagram for 12 viewed along the c-axis direction showing the two C 1 1 (7) chains propagating in the b-axis direction involving the fumarate anions and composed of O-HÁ Á ÁO hydrogen bonds which are in turn cross-linked by both N-HÁ Á ÁO hydrogen bonds and C-HÁ Á ÁO interactions.

4-Phenylpiperazin-1-ium 4-fluorobenzoate monohydrate (1)
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.

4-Phenylpiperazin-1-ium 4-bromobenzoate monohydrate (3)
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.

4-Phenylpiperazin-1-ium 4-nitrobenzoate (5)
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.18 e Å −3 Δρ min = −0.20 e Å −3 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. ( (

4-Phenylpiperazin-1-ium 2-hydroxy-4,6-dinitrophenolate (7)
Crystal data  195P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.30 e Å −3 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. Refinement. Refined as a 2-component twin.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters
178 (   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.