Crystal structures of 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium benzoate and 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium picrate

In each of the title compounds, the cation is conformationally chiral, exhibiting conformational disorder, while two of the nitro groups in the picrate anion also exhibit disorder. In the benzoate salt, the ions are linked into a chain of rings by N—H⋯O hydrogen bonds, whole in the picrate salt, the hydrogen-bonded four-ion aggregate contains four different types of ring.


Structural commentary
Compound (I) consists of a reduced benzothiazolium cation in which protonation has occurred exclusively at atom N13, and a benzoate anion and the two ions within the selected asymmetric unit are linked by two fairly short and nearly linear N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (8) motif ( Fig. 1 and Table 1). In the cation, the six-membered ring is disordered over two sets of atomic sites with occupancies 0.721 (5) and 0.279 (5), and each disorder component adopts a half-chair conformation (Fig. 2). The ring-puckering parameters calculated for the atom sequence (Cx3A,Cx4,Cx5,Cx6,Cx7,Cx7A), where x = 1 for the major conformer and x = 2 for the minor form, of Q = 0.452 (5) Å , = 47.3 (8) and ' = 146.1 (10) when x = 1, with corresponding values Q = 0.453 (13) Å , = 138.5 (19) and ' = 340 (3) when x = 2. For an idealized halfchair form the puckering angles are = 50.8 and ' = (60k + 30) , where k represents an integer. In each of (I) and (II), in fact, the cation exhibits no internal symmetry and hence is conformationally chiral: in each case the space group confirms the presence of equal numbers of the two conformational enantiomers. In the benzoate anion in (I), the carboxyl group makes a dihedral angle of 10.5 (2) with the aryl ring, and the two C-O distances are identical within experimental uncertainty, 1.252 (3) and 1.255 (3) Å , consistent with the complete transfer of a proton from the acid component to atom N13, as deduced from difference maps and confirmed by the refinement.

Figure 2
The disordered cation in compound (I), showing the approximately enantiomorphic nature of the two disorder components. For the sake of clarity the H atoms and most of the atom labels have been omitted: the major form is drawn as solid lines and the minor form as broken lines.

Figure 1
The independent ionic components of compound (I), showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 30% probability level, and the two N-HÁ Á ÁO hydrogen bonds within the selected asymmetric unit are shown as dashed lines.
In both compounds the bond distances C12-N12 and C12-N13 are nearly identical, 1.329 (6) and 1.323 (3) Å respectively in (I) and 1.312 (3) and 1.336 (9) Å in (II), indicative of significant delocalization of the positive charge into the amino group with significant contributions to the electronic structure from the forms (A) and (B), comparable to an amidinium cation (see Scheme). This explains not only why the site of protonation is exclusively at the ring N atom, since protonation of the amino group would not permit any charge delocalization, but also the observation that the amino N atom does not act as a hydrogen-bond acceptor.
In the picrate anion of (II), two of the three independent nitro groups adopt two different orientations and the occupancies for the two orientations bonded to atoms C32 and C36 are 0.769 (7) and 0.231 (7), and 0.789 (6) and 0.211 (6) respectively (Fig. 4). The major and minor conformations at C32 make dihedral angles of 17.9 (3) and 27.2 (7) with the ring, with an angle of 44.9 (7) between the two orientations, and the corresponding values for the nitro group at C36 are 12.0 (2), 39.0 (8) and 50.4 (8) . By contrast, the fully ordered nitro group at C34 makes a dihedral angle of only 4.5 (2) with the ring. The C-O distance, 1.241 (3), is short for its type [mean value (Allen et al., 1987) 1.362 Å , lower quartile value 1.353 Å ], and the C-N distances, range 1.442 (3)-1.458 (3) Å , are all somewhat short for their type (mean value 1.468 Å , lower quartile value 1.460 Å ): in addition, the bonds C31-C32 and C31-C36 are significantly longer than the other C-C distances in this ring. These observation, taken together, indicate that the quinonoid form (D), and its o-quinonoid isomers, and the ketonic form (E) are significant contributors to the overall electronic structure of the anion in addition to the classically delocalized form (C) (see Scheme).

Supramolecular interactions
The major and minor conformers of the cation in (I) and those of both ions in (II) are involved in very similar patterns of hydrogen bonding (Tables 1 and 2), so that it is necessary to discuss only those formed by the major conformers. Because of the charge delocalization in both ions in each of (I) and (II), as noted above, all of the N-HÁ Á ÁO interactions in both compounds can be regarded as charge-assisted hydrogen bonds (Gilli et al., 1994). In addition to the two N-HÁ Á ÁO hydrogen bonds within the selected asymmetric unit of 1322  The independent ionic components of compound (II), showing the atomlabelling scheme. For the sake of clarity, only the major disorder components are shown. Displacement ellipsoids are drawn at the 30% probability level, and the N-HÁ Á ÁO hydrogen bonds within the selected asymmetric unit are shown as dashed lines.

Figure 4
The disordered anion in compound (II), showing the two orientations of two of the nitro groups: for the sake of clarity the H atoms have been omitted, compound (I) (Fig. 1), the structure contains a third such interaction which links the cation-anion pairs which are related by the c-glide plane at y = 0.5 into a C 1 2 (4) C 1 2 (8)[R 2 2 (8)] chain of rings running parallel to the [001] direction (Fig. 5).
In addition, the N-HÁ Á ÁO hydrogen bonds within the selected asymmetric unit of (II) (Fig. 3), the structure contains one further three-centre N-HÁ Á Á(O) 2 hydrogen bond, and the hydrogen bonds together generate a four-ion aggregate in which a centrosymmetric R 2 2 4(8) ring is surrounded by three inversion-related pairs of rings, one each of R 2 1 (4), R 2 1 (6) and R 1 2 (6) types, so that, in total, there are seven hydrogen-bonded rings of four different types in the aggregate (Fig. 6). It is notable that only one of the nitro groups in (II) participates in the hydrogen bonding, and that both C-HÁ Á Á(arene) and aromaticstacking interactions are absent from both structures.

Database survey
It is of interest briefly to survey the structures of some related amino-substituted benzo-1,3-thiazoles. In the structure of 2-amino-6-nitrobenzo-1,3-thiazole (Glidewell et al., 2001), a combination of N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds generates a three-dimensional framework structure, while the monohydrate of the same benzothiazole, also forms a threedimensional framework structure, but now built from a Part of the crystal structure of compound (I) showing the formation of a chain of rings running parallel to [001]. Hydrogen bonds are shown as dashed lines and for the sake of clarity the H atoms bonded to C atoms have been omitted.

Figure 6
Part of the crystal structure of compound (II) showing the formation of a centrosymmetric four-ion aggregate. For the sake of clarity, only the major disorder components are shown, and the H atoms bonded to C atoms and the unit cell outline have been omitted. The atoms marked with an asterisk (*) are at the symmetry position (1 À x, Ày, 1 À z). Table 1 Hydrogen-bond geometry (Å , ) for (I).   (Lynch, 2002): in neither of these structures does the amino N atom act as a hydrogen-bond acceptor, just as found here in the structures of (I) and (II). We note also that in trans-bis(2-amino-6-nitrobenzo-1,3-thiazole)dichloroplatinum(II), which crystallizes as a tetrakis(dimethylformamide) solvate (Lynch & Duckhouse, 2001), the benzothiazole ligand coordinates to the metal centre via the ring N atom, rather than via the amino N atom. Finally in 2-amino-6-nitrobenzo-1.3-thiazol-3-ium hydrogen sulfate (Qian & Huang, 2011), the protonation of the benzothiazole component occurs exclusively at the ring N atoms and the ions are linked by a combination of N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds to form a sheet structure, again with the amino group acting as a double donor of hydrogen bonds, but not as an acceptor.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. It was apparent from an early stage in the refinements that in both (I) and (II) the cation was disordered over two sets of atomic sights corresponding to two different conformations of the six-membered ring, and that two of the nitro groups in the anion of (II) were disordered, again over two sets of atomic sites corresponding to different orientations relative to the aryl ring. For the minor conformers of the cations, the bonded distances and the one-angle nonbonded distances were restrained to be the same as the corresponding distances in the major conformer, subject to s.u.s of 0.005 and 0.01 Å , respectively; similar restraints were applied to the minor conformations of the disordered nitro groups in the anion of (II). In addition, the anisotropic displacement parameters for pairs of atoms occupying essentially the same physical space were constrained to be identical. Subject to these conditions, the occupancies of the two cation conformations in (I) refined to 0.721 (5)   -Absolute structure parameter 0.061 (7) -those in (II) refined to 0.575 (4) and 0.425 (4), while those of the nitro groups in (II) bonded to C32 and C36 refined to 0.769 (7) and 0.231 (7), and 0.789 (6) and 0.211 (6) respectively. All H were treated as riding atoms in geometrically idealized positions with distances C-H = 0.93 Å (aromatic), 0.96 Å (CH 3 ) or 0.97 Å (CH 2 ) and N-H = 0.86 Å , and with U iso (H) = kU eq (C), where k = 1.5 for the methyl groups which were permitted to rotate but not to tilt and 1.2 for all other H atoms. One bad outlier reflection (391) was omitted from the final refinement of (I).

Computing details
For both structures, data collection: APEX2 (Bruker, 2012); cell refinement: APEX2 (Bruker, 2012); data reduction: SAINT-Plus (Bruker, 2012); program(s) used to solve structure: SHELXS86 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2014 and PLATON.   (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.

2-Amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium 2,4,6-trinitrophenolate (II)
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.