Crystal structures of 5-amino-N-phenyl-3H-1,2,4-dithiazol-3-iminium chloride and 5-amino-N-(4-chlorophenyl)-3H-1,2,4-dithiazol-3-iminium chloride monohydrate

The five-membered 1,2,4-dithiazole rings in the cations of (I) and (II) are almost planar, but in each case the overall cation is twisted with dihedral angles between the planes of the heterocycle and the pendant aryl ring of 9.05 (12) and 15.60 (12)° in (I) and (II), respectively. In both compounds, the bond lengths in the H2N—C—N—C—N backbones imply considerable delocalization of π-electron density.

The crystal and molecular structures of the title salt, C 8 H 8 N 3 S 2 + ÁCl À , (I), and salt hydrate, C 8 H 7 ClN 3 S 2 + ÁCl À ÁH 2 O, (II), are described. The heterocyclic ring in (I) is statistically planar and forms a dihedral angle of 9.05 (12) with the pendant phenyl ring. The comparable angle in (II) is 15.60 (12) , indicating a greater twist in this cation. An evaluation of the bond lengths in the H 2 N-C-N-C-N sequence of each cation indicates significant delocalization of -electron density over these atoms. The common feature of the crystal packing in (I) and (II) is the formation of charge-assisted amino-N-HÁ Á ÁCl À hydrogen bonds, leading to helical chains in (I) and zigzag chains in (II). In (I), these are linked by chains mediated by charge-assisted iminium-N + -HÁ Á ÁCl À hydrogen bonds into a three-dimensional architecture. In (II), the chains are linked into a layer by charge-assisted water-O-HÁ Á ÁCl À and water-O-HÁ Á ÁO(water) hydrogen bonds with charge-assisted iminium-N + -HÁ Á ÁO(water) hydrogen bonds providing the connections between the layers to generate the three-dimensional packing. In (II), the chloride anion and water molecules are resolved into two proximate sites with the major component being present with a site occupancy factor of 0.9327 (18).

Chemical context
The title salts were isolated as a part of a research programme into the crystal engineering aspects and biological potential of phosphanegold(I) carbonimidothioates, i.e. molecules of the general formula R 3 PAu[SC(OR 0 ) NR 00 ]; R, R 0 , R 00 = aryl and/ or alkyl. While earlier work focussed on supramolecular aggregation patterns (Kuan et al., 2008) and solid-state luminescence (Ho et al., 2006), more recent endeavours have focussed upon biological studies. For example, the Ph 3 PAu[SC(O-alkyl) N(p-tolyl)] compounds prove to be very potent against Gram-positive bacteria (Yeo, Sim et al., 2013). In addition, Ph 3 PAu[SC(O-alkyl) N(aryl)] compounds exhibit significant cytotoxicity and kill cancer cells by initiating a variety of apoptotic pathways (Yeo, Ooi et al., 2013;Ooi, Yeo et al., 2015). A focus of recent synthetic efforts has been to increase the functionality of the thiocarbamide molecules in order to produce gold complexes of higher nuclearity. During this work bipodal {1,4-[MeOC( S)N(H)] 2 C 6 H 4 } was synthesized along with its binuclear phosphanegold(I) complexes . As an expansion of these studies, the 1:2 reactions of thiourea with arylisothiocyanates were undertaken which, rather than yielding bipodal molecules, gave the 1:1 cyclization products, isolated as salts. These and related compounds have been described in the patent litera- ISSN 2056-9890 ture as having a range of biological properties, e.g. as bactericides, fungicides and plant-growth inhibitors (Rö thling et al., 1989). Herein, the crystal and molecular structures of two examples of these products, i.e. the salt, [C 8 H 8

Structural commentary
The asymmetric unit of (I), comprising a cation and chloride anion, is shown in Fig. 1. The five-membered 1,2,4-dithiazole ring of the cation in (I) is strictly planar with the maximum deviation being less than AE0.003 (2) Å . However, the entire cation is not planar with the dihedral angle between the rings being 9.05 (12) . Selected geometric parameters are collected in Table 1. While the S-S and S-C bond lengths correspond to single bonds, an evaluation of the C-N bonds, internal and external to the ring, suggest a high level of delocalization of -electron density across these atoms. The angles subtended at the S atoms are nearly right-angles. The trigonal angles around the C1 atom are all approximately 120 but there is a range of 10 for the angles about the C2 atom, with the widest angle being N2-C2-N3, consistent with double-bond character in the C-N bonds. The widest angle in the molecule is that subtended at the N3 atom, an observation that correlates with the C2 N3 double bond and the presence of the small H atom on the N3 atom.
The asymmetric unit of (II), comprising a cation, a chloride anion and a water molecule of crystallization, is illustrated in Fig. 2. As for (I), the cation is almost planar with the maximum deviation being 0.010 (2) Å for the N2 atom; the r.m.s. deviation for the fitted atoms is 0.010 Å . A greater overall twist in the molecule is evident, as seen in the dihedral angle of 15.60 (12) formed between the rings. In terms of bond lengths, Table 1, the discussion above for (I), holds true for (II). Similarly, for the bond angles except that the range of angles about the C2 atom is narrower at 6 .  The asymmetric unit for (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. The dashed lines indicate hydrogen bonds. Table 1 Geometric data (Å , ) for (I) and (II).

Figure 2
The asymmetric unit for (II), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. The dashed lines indicate hydrogen bonds.

Supramolecular features
Geometric parameters characterizing the intermolecular interactions operating in the crystal structures of (I) and (II) are collected in Tables 2 and 3, respectively. The presence of charge-assisted N-HÁ Á ÁCl À and N + -HÁ Á ÁCl À hydrogen bonds are crucial in establishing the threedimensional architecture in the crystal structure of (I). The structure is conveniently described as comprising columns of cations aligned along the a axis connected through hydrogen bonds to rows of chloride ions, also aligned along the a axis. As illustrated in Fig. 4, charge-assisted amino-N-HÁ Á ÁCl À hydrogen bonds lead to helical chains along [100], being generated by 2 1 screw symmetry. The chains are linked to neighbouring chains by charge-assisted iminium-N + -HÁ Á ÁCl À hydrogen bonds, that in themselves lead to chains aligned along [011]. In this way, a three-dimensional architecture is constructed as shown in projection in Fig. 5.
A more complicated pattern of hydrogen bonding occurs in the crystal structure of (II). The amino-H atoms form chargeassisted N-HÁ Á ÁCl À hydrogen bonds while the iminium-H atom forms a charge-assisted N + -HÁ Á ÁO hydrogen bond to the water molecule of crystallization. The water molecule also forms two donor interactions, one to another water molecule and the second, charge-assisted, to the chloride anion. Hence, all donor atoms participate in the hydrogen-bonding scheme and each of the chloride and water species forms three hydrogen bonds. A diagram showing the detail of the hydrogen bonding is shown in Fig. 6. The amino-N-HÁ Á ÁCl À bridges clearly persist, as for (I), but lead to zigzag chains (glide symmetry) along the c axis. As pairs of water molecules are linked via water-O-HÁ Á ÁO(water) hydrogen bonds across a centre of inversion and each forms a charge-assisted water-  Table 2 Hydrogen-bond geometry (Å , ) for (I). (2) 3.084 (2) 169 (2) Symmetry codes: (i) Àx þ 3 2 ; Ày þ 1; z þ 1 2 ; (ii) Àx þ 2; y À 1 2 ; Àz þ 1 2 . Table 3 Hydrogen-bond geometry (Å , ) for (II).

Figure 3
Overlay diagram of the cations in (I), red image, and (II), blue image. The cations have been overlapped so that the five-membered rings are coincident.

Figure 4
Detail of the hydrogen bonding operating in the crystal structure of (I).
The charge-assisted amino-N-HÁ Á ÁCl À hydrogen bonds are shown as orange dashed lines and lead to helical chains along [100]. The chargeassisted imino-N + -HÁ Á ÁCl À hydrogen bonds are shown as blue dashed lines and lead to chains along [011]. For reasons of clarity, H atoms not involved in hydrogen bonding have been omitted and only one of the chains along [011] is shown.

Figure 5
Unit-cell contents for (I) shown in projection down the a axis. The chargeassisted amino-N-HÁ Á ÁCl À and imino-N + -HÁ Á ÁCl À hydrogen bonds are shown as orange and blue dashed lines, respectively.
O-HÁ Á ÁCl À hydrogen bond, the water molecules form links between the zigzag chains resulting in supramolecular layers. Finally, the water molecules accept charge-assisted imino-N + -HÁ Á ÁO(water) hydrogen bonds, providing links between the layers so that a three-dimensional architecture ensues. As seen from Fig. 7, globally, the structure may be described as comprising layers of cations parallel to [001] that define rectangular channels parallel to [001] incorporating the anions and internalized water molecules. Not shown in Fig. 5, are indications of close Cl1Á Á ÁCl1 i contacts of 3.3510 (10) Å which occur within layers rather than between layers; symmetry operation (ii): 1 À x, y, À 1 2 À z.

Database survey
A search of the Cambridge Structural Database (Groom & Allen, 2014), revealed there are no direct analogues of (I) and (II) in the crystallographic literature. The structure of a closely related neutral species, i.e. 5-(dimethylamino)-3-(phenylimino)-1,2,4-dithiazole, characterized in its 1:1 co-crystal with 2-(dimethylcarboxamido-imino)benzothiazole, (III) in the scheme below, has been reported (Flippen, 1977), along with several benzoyl derivatives, as exemplified by 3-(4-methylbenzoylimino)-5-phenylamino-3H-1,2,4-dithiazole (IV) (Kleist et al., 1994). An evaluation of the bond lengths in the N-C-N-C-N sequences in these molecules suggests a greater contribution of the canonical structure with formal C N bonds, i.e. N-C N-C N. This difference is traced to the influence of the formal charge on the iminium-N atom.

Synthesis and crystallization
Synthesis of (I Detail of the hydrogen bonding operating in the crystal structure of (II).   Synthesis of (II). The p-chloro derivative (II) was prepared as described above but using 4-chlorophenyl isothiocyanate (Sigma-Aldrich) as the unique reagent. Yellow prismatic crystals were isolated after 4 weeks. Yield: 0.581 g (39%). M.p.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. For (I) and (II), carbon-bound H atoms were placed in calculated positions (C-H = 0.95 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) set to 1.2U eq (C). The N-bound Hatoms were located in a difference Fourier map but were refined with a distance restraint of N-H = 0.88AE0.01 Å , and with U iso (H) set to 1.2U eq (N). For (I), owing to poor agreement, one reflection, i.e. (020), was omitted from the final cycles of refinement. For (II), disorder was noted in the structure, involving the Cl2 anion and water molecule of crystallization so that two proximate positions were resolved for the heteroatoms. The major component refined to a site occupancy factor of 0.9327 (18   program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), QMol (Gans & Shalloway, 2001) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

(I) 5-Amino-N-phenyl-3H-1,2,4-dithiazol-3-iminium chloride
Crystal data  (Parsons et al., 2013). Absolute structure parameter: 0.08 (5) 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.