2,3-Dihydro-1,3-benzothia­zol-2-iminium monohydrogen sulfate and 2-iminio-2,3-dihydro-1,3-benzothia­zole-6-sulfonate: a combined structural and theoretical study

The 2-amino­benzothia­zole sulfonation inter­mediate 2,3-di­hy­dro-1,3-benzothia­zol-2-iminium monohydrogen sulfate, C₇H₇N₂S⁺·HSO₄^-, (I), and the final product 2-iminio-2,3-dihydro-1,3-benzothia­zole-6-sulfonate, C₇H₆N₂O₃S₂, (II), both have the endocyclic N atom protonated; compound (I) exists as an ion pair and (II) forms a zwitterion. Inter­molecular N-H...O and O-H...O hydrogen bonds are seen in both structures, with bonding energy (calculated on the basis of density functional theory) ranging from 1.06 to 14.15 kcal mol^-1. Hydrogen bonding in (I) and (II) creates DDDD and C(8)C(9)C(9) first-level graph sets, respectively. Face-to-face stacking inter­actions are observed in both (I) and (II), but they are extremely weak.

S1. Comment

Benzothiazoles comprise a class of compounds that exhibit complex biological properties. Substituted benzothiazoles serve as selective antitumor agents (Akhtar et al., 2008; Bradshaw et al., 2002; Mortimer et al., 2006), neurotransmission blockers (Jimonet et al., 1999), and anti-infective and antifungal agents (Mortimer et al., 2006). In recent years, benzothiazoles have gained attention as part of the structure of the radical cation derived from 2,2'-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid, which is used for evaluation of antioxidant efficiency (Osman et al., 2006; Pellegrini et al., 2003; Walker & Everette, 2009). They have been recognized as therapeutic active skeletons that are useful for making fatty acid amide hydrolase inhibitors (Wang et al., 2009). Sulfonated benzothiazoles represent a novel class of potent and selective antitrypanosomal agents (Tellez-Valencia et al., 2002; Espinoza-Fonseca & Trujillo-Ferrara, 2005). Molecular docking simulations revealed that they form more energetically stable complexes with trypanosomal triosephosphate isomerase (TIM) than with human TIM, which is a crucial aspect for the design of new anti-parasitic drugs, including those acrtive against Trypanosoma cruzi, which causes Chagas disease. The origin of the selectivity of these compounds has not yet been identified. It was postulated that bonding of the different drugs to the macromolecular species via noncovalent interactions has crucial importance (Szatyłowicz, 2008). In this context, the synthesis, structure and intermolecular interactions of new sulfonated 2-aminobenzothiazole derivatives are of interest. Hence, the solid-state characterization of the 2-aminobenzothiazole sulfonation intermediate and the final products, namely 2,3-dihydro-1,3-benzothiazol-2-iminium monohydrogen sulfate, (I), and 2-iminio-2,3-dihydro-1,3-benzothiazol-6-sulfonate, (II), as well as the results of quantum mechanical calculations, are reported here.

In both compounds, one of the acid group H atoms is transferred to the N atom of the 2-aminobenzothiazole molecule, so that the asymmetric unit of (I) consists of a 2,3-dihydro-1,3-benzothiazol-2-iminium ion and sulfuric acid in the monoionized state, i.e. monohydrogen sulfate (Fig. 1), and compound (II) exists in the form of a zwitterion (Fig. 2). The 2,3-dihydro-1,3-benzothiazol-2-iminium moiety is slightly distorted from planarity, the largest deviation from the weighted least-squares plane calculated through all non-H atoms of this moiety being for atom N2 [0.0218 (13) Å in (I) and 0.0980 (13) Å in (II)]. The slightly larger deviation of atom N2 in (II) probably originates from an out-of-plane N2—H2B···O1^vi hydrogen bond [symmetry code: (vi) -x, y - 1, -z + 1/2], which may influence the position of N2 atom [in (I), the N2—H···O bonds are almost in the plane of the cation]. In (II), atom S2 lies 0.3235 (17) Å from above-mentioned plane. Each of the five- and six-membered rings of the cation of (I) can be considered planar, and they are inclined at 0.26 (10)° to each other. The five- and six-membered rings of the molecule of (II) show some deviation from planarity [the most highly deviating atoms C1 and C2 lie 0.0184 (10) and 0.0195 (12) Å from the ring weighted least-squares planes, respectively, as above], and they are inclined at 4.43 (6)° to each other.

The bond distances and angles within the anion show no unusual values (Table 1). The bond lengths and angles of the 2,3-dihydro-1,3-benzothiazol-2-iminium moiety (in both title compounds) are within the ranges reported for its adducts with organic anions (Lynch et al., 1998, 1999; Smith et al., 1999; Trzesowska-Kruszynska & Kruszynski, 2009), and are close to those of pure 2-aminobenzothiazole (ABT; Goubitz et al., 2001). In comparison with ABT, the C2—N1, S1—C3 and C1—N2 bonds of (I) and (II) are shortened by an insignificant amount [by 0.017 (11), 0.024 (9) and 0.019 (12) Å, respectively, for (I), and by 0.009 (11), 0.011 (9) and 0.022 (12) Å, respectively, for (II)], while the C1—N1 bond is elongated by 0.052 (8) and 0.059 (8) Å, respectively, for (I) and (II). For similar 2-amino heterocyclic compounds, shortening of the C—NH₂ bond has been explained by the attraction of a more electron-accepting heterocyclic ring (Lynch & Jones, 2004). In both title compounds, the C1—N2 distance (Tables 1 and 2) is close to that of the exocyclic C═N double bonds found in iminobenzothiazole derivatives, i.e. to 1.312 (4) Å in [(1,3-benzothiazol-2(3H)-ylidene)amido]-O,O'-diethylphosphate sulfide (Garcia-Hernandez et al., 2006), to 1.300 (3) Å in diethyl [(6-chloro-2,3-dihydrobenzothiazol-2-ylidene)amido]thiophosphate (Shi et al., 2003) and to 1.302 (4) Å in 1-(benzothiazol-2-ylidene)-3,3-dimethylthiourea (Tellez et al., 2004). These observations point to a significant contribution of the exocyclic iminium resonance form, i.e. the 2,3-dihydro-1,3-benzothiazol-2-iminium ion and 2-iminio-2,3-dihydro-1,3-benzothiazol-6-suphonate, to the overall molecular electronic structures, with a lesser contribution from the 2-aminobenzothiazolium and 2-aminobenzothiazolium-6-sulfonate forms, respectively, for (I) and (II). Exocyclic imines or iminium ions in equilibrium with endocyclic imines have previously been found and discussed for other compounds containing the N_exoCN_endo group (Lynch & Jones, 2004; Lynch et al., 2000; Low et al., 2003; Donga et al., 2002). The anion of (I) shows S—O distances typical for the HSO₄^- moiety with three almost equal shorter bonds lengths (Table 1) close to the mean value of 1.446 (2) Å obtained for 147 HSO₄^- ions existing in 115 structures and a longer S—OH bond almost equal to the mean value of 1.559 (1) Å obtained for 93 HSO₄^- ions existing in 74 structures (Allen, 2002) (the Kolmogorov–Smirnov test shows deviations from normal distribution and the skewness was 1.996, thus statistically asymmetric data of 41 structures were excluded from the calculation). The S—O distances in the sulphonate group of (II) (Table 2) are also typical for ionized sulphonic acids.

The cations and anions of (I) are linked by N—H···O hydrogen bonds (Table 3) to form a hydrogen-bonded ribbon extending along the [010] axis (Fig. 3) and comprising N₁DDDD and N₂C₂¹(4)C₂²(6)C₂²(8)C₂²(8)[R₁²(4)R₂²(8)] basic graph sets (Bernstein et al., 1995). The anions of (I) are connected via O—H···O hydrogen bonds (Table 3) to form a hydrogen-bonded chain progressing along the [001] axis and comprising N₁C(4) motifs. These two types of interactions join ions of (I) to form a two-dimensional net parallel to the (100) plane. The zwitterions of (II) are connected by N—H···O hydrogen bonds (Fig. 4) to form a layer extending along the (101) plane and comprising patterns described by an N₁C(8)C(9)C(9) basic graph set. An interesting feature of the structures of (I) and (II) is the presence of stacking interactions (along the [001] axis) between the almost parallel (Table 4) five-membered heterocyclic and benzene rings of adjacent amines. These stacking interactions provide some linkage within the hydrogen-bonded two-dimensional net of (I) and between the hydrogen-bonded sheets of (II). Moreover, there is a short intramolecular C—H···O contact in the structure of (II) which, according to Desiraju & Steiner (1999), can be classified as a weak hydrogen bond (Table 3).

The molecular electronic properties of (I) and (II) have been calculated at a single point for both diffraction-derived coordinates and the optimized structures. The structural parameters were used as the starting model in each calculation. Sets containing from one to five cation–anion pairs were used for the calculations for (I). The cation and anion of each pair were arranged in hydrogen-bonded sheets (three pairs) and in stacking interactions (next two pairs). The electrostatic interaction energies between anions and cations were estimated using the counterpoise method (Boys & Bernardi, 1970); for this purpose, additional computations were made in which the counterpoise method subsets contained odd numbers of cations and anions. For (II), the sets contained from two to seven zwitterions, and molecules were added one by one to the hydrogen-bond donors and acceptors of the starting molecule. The atomic and molecular properties were calculated at 298.15 K. The optimized geometrical parameters were in good agreement with those found from X-ray measurements, although geometrically optimized molecules show a typical elongation of the C—H, N—H and O—H bonds (from 0.03 to 0.19 Å). This effect leads to a slight narrowing of the D—H···A angles, but the D···A distances remain unchanged. The B3LYP functional (Becke, 1993; Lee et al., 1988) in the triple-ζ 6–31++G(3df,2p) basis set was used, as implemented in GAUSSIAN03 (Frisch et al., 2004). The differences in electronic properties and energies originating from the different numbers of molecules used in the calculations are given in parentheses in Table 3, as standard deviations of the arithmetic mean values. Where no deviation is given, the values were the same within the range of reported precision. The atomic charges were calculated according to the natural population analysis (NPA; Foster & Weinhold, 1980; Reed & Weinhold, 1985; Reed et al., 1988), Merz–Kollman–Singh (MKS; Singh & Kollman,1984; Besler et al., 1990) and Breneman (Breneman & Wiberg, 1990) schemes. Although the calculation of effective atomic charges plays an important role in the application of quantum mechanical calculations to molecular systems, the unambiguous division of the overall molecular charge density into atomic contributions is still an unresolved problem, and none of the known procedures give completely reliable values of atomic charges. Thus, a discussion of atomic charges should cover more than one algorithm used for charge density division. Generally, it can be stated that less reliable values are given by the Mulliken population analysis and more reliable results are provided by the Breneman method [for a detailed discussion of the methodology and reliability of the methods used, see Martin & Zipse (2005), and references therein].

In general all N—H···O and O—H···O hydrogen bonds in (I) and (II) can be considered as medium strength or weak intermolecular bonding interactions.

The second-order perturbation theory analysis of the Fock matrix in the natural bond orbital (NBO) basis leads to the conclusion that N—H···O interactions are formed mostly by hydrogen-bond-acceptor lone pairs donating electron density to the antibonding orbitals of D—H bonds, and these 'delocalization' energies [E_del(1)] are collected in Table 3. The second most energetic interactions [E_del(2)] have the same contributions of atomic orbitals; however, the other lone pairs of the O atoms are used. The E_del(2) values are distinctly lower than E_del(1) in all cases [for example, for N1—H1···O1ⁱ, E_del(2) = 3.28 kcal mol^-1; symmetry code: (i) -x + 1, -y + 1, -z + 2]. These weaker interactions are multiple interactions between acceptor lone pairs and one-center Rydberg antibonding orbitals of H atoms. These results are in opposition to previous findings for ether and nitric group O atoms acting as a donors of hydrogen bonds (Kruszynski, 2008, 2009), where E_del(2) interactions were related to one-center Rydberg antibonding orbitals of hydrogen-bond donors. This can be explained by the different character of O atoms in monoionized sulfate or sulphonate compared with that in uncharged groups that form part of organic molecules. The localization of negative charge on the O atoms in (I) and (II) leads to the formation of an additional electron lone pair, which is able to donate its internal electron density to other species. On the basis of the geometrical parameters, the intramolecular C4—H4···O2 interaction can be regarded as a weak hydrogen bond; however, the very low energy of this interaction (Table 3) suggests that it originates from an accidental molecular arrangement (enforced by other geometric and energetic factors). The stacking interactions are formed by bonding π orbitals of one ring donating electron density to the antibonding π orbitals of the second ring and to one-center Rydberg antibonding orbitals of π-bonded atoms of the rings. These interactions are extremely weak (Table 4) but they are still bonding in character. The energies of intermolecular interactions, calculated on the basis of total self-consistent field energy [E_SCF, corrected for basis-set superposition error estimated by use of the counterpoise method (Boys & Bernardi, 1970)], are very close to the respective NBO total energies (E, Tables 3 and 4) or their sums [N1—H1···O1ⁱ + N2—H2A···O3ⁱ and N2—H2B···O3ⁱⁱ + N2—H2B···O4ⁱⁱ; symmetry code: (ii) x + 1, -y + 1/2, z + 1/2]. The differences are not larger than 0.48 kcal mol^-1 for N—H···O and O—H···O hydrogen bonds, and than 0.02 kcal mol^-1 for C—H···O and each π–π interaction. In all cases, the E_SCF values are slightly larger than those obtained on the NBO basis. For N—H···O and O—H···O hydrogen bonds it is caused by bonding σ orbitals of the acceptor donating electron density to the one-center Rydberg antibonding orbitals of the donor H atoms, and for other interactions the above-mentioned enlargement originates from contributions of acceptor occupied orbitals other than those of the lone pairs (e.g. one-center Rydberg antibonding orbitals). In general, the strength of the N—H···O and O—H···O interactions does not correlate directly with the enlargement of the D···A distance or D—H···A angle, but a general relationship of increasing hydrogen-bond energy with both decreasing D···A distance and increasing D—H···A angle is observed (Fig. 5). As expected, in (I), there is a large electrostatic attractive interaction between ions of the opposite charge; this is equal to about 62.9 and 70.6 kcal mol^-1, respectively, for cations and anions connected by N1—H1···O1ⁱ and N2—H2B···O3ⁱⁱ intermolecular interactions. The repulsive force between neighbouring anions is about 31.17 kcal mol^-1 and that between neighbouring cations is about 55.4 kcal mol^-1. Quantum-mechanical study of the electronic structure of the C—N bonds shows the same behaviours as previously described for 2,3-dihydro-1,3-benzothiazol-2-iminium hydrogen oxydiacetate (Trzesowska-Kruszynska & Kruszynski, 2009), which confirms that electron density is localized in the exocyclic rather than heterocyclic C—N bond, and, in consequence, that the exocyclic iminium resonance form is predominant.

Analysis of the NPA and MKS charges and those derived from electrostatic properties using the Breneman radii shows that, in general, the atomic charges do not depend on the method used for calculation. In both compounds, all N atoms are negatively charged [the N1 atoms slightly less than the N2 atoms; charges are, respectively, -0.46 (3) and -0.69 (7) a.u. for (I), and -0.50 (6) and -0.68 (6) a.u. for (II), where a.u. denotes the atomic unit, equal to the charge of one electron], but the NH group of the thiazole ring has a negative group charge [-0.19 (2) and -0.20 (1) a.u., respectively, for (I) and (II)], whereas the NH₂ group has a positive group charge [0.21 (2) and 0.18 (1) a.u., respectively, for (I) and (II)]. Such a distribution of charges is observed only in the 2,3-dihydro-1,3-benzothiazol-2-iminium ion, so these calculated values confirm again the postulated dominance of the exocyclic iminium resonance form. The O atoms of the monohydrogen sulfate and sulfonate group are negatively charged but a difference of about 0.1 a.u. is observed between the O atom of the hydroxy group [possessing a -0.90 (3) a.u. charge] and the other O atoms of (I) and (II) [having charges from -1.00 (4) to -1.06 (3) a.u]. It is noteworthy that in the case of calculations performed for separated (non-interacting) ions or molecules the positive charges on H atoms [0.18 (3)–0.43 (1) a.u.] involved in hydrogen bonds are about 0.03 a.u. larger, and negative charges on hydrogen-bonds-acceptor O atoms are about 0.02 a.u. smaller than those in interacting molecules. This confirms that during the formation of an intermolecular interaction a transfer of electron density occurs.

Related literature

For related literature, see: Akhtar et al. (2008); Allen (2002); Becke (1993); Bernstein et al. (1995); Besler et al. (1990); Bradshaw et al. (2002); Breneman & Wiberg (1990); Desiraju & Steiner (1999); Donga et al. (2002); Espinoza-Fonseca & Trujillo-Ferrara (2005); Foster & Weinhold (1980); Frisch et al. (2004); Garcia-Hernandez, Flores-Parra, Grevy, Ramos-Organillo & Contreras (2006); Goubitz et al. (2001); Jimonet et al. (1999); Kruszynski (2008, 2009); Lee et al. (1988); Low et al. (2003); Lynch & Jones (2004); Lynch et al. (1998, 1999, 2000); Martin & Zipse (2005); Mortimer et al. (2006); Osman et al. (2006); Pellegrini et al. (2003); Reed & Weinhold (1985); Reed et al. (1988); Sheldrick (2008); Shi et al. (2003); Singh & Kollman (1984); Smith et al. (1999); Szatyłowicz (2008); Tellez et al. (2004); Tellez-Valencia, Avila-Rios, Perez-Montfort, Rodriguez-Romero, de Gomez-Puyou, Lopez-Calahorra & Gomez-Puyou (2002); Trzesowska-Kruszynska & Kruszynski (2009); Walker & Everette (2009); Wang et al. (2009).

S2. Experimental

Commercially available 2-aminobenzothiazole (0.05 mol, 7.5099 g) was dissolved in 96% sulfuric acid (2.8 ml, 0.05 mol), and water (2.0 ml) was added dropwise over a period of 10 min to avoid overheating. The solution was stored at 283.2 (3) K for 14 h. during which time a crystalline product was formed. The crystals of (I) were filtered off using a Buchner filter funnel with integral sintered glass disc (G3 type) placed in an ice cooling jacket. The product was dried in a vacuum desiccator (at a pressure of 200 Pa) for 6 h (yield 83%). The crystal for measurement was selected directly from the dry sample.

Commercially available 2-aminobenzothiazole (0.02 mol, 3.0040 g) was dissolved in 96% sulfuric acid (10.0 ml, 0.18 mol). The mixture was heated [at 433 (1) K] under reflux for 35 min, cooled to room temperature and poured into cold water. Compound (II), which is insoluble in water, precipitated at the bottom of the beaker, was washed with water (7 ml) three times by decantation and was transferred quantitatively to a Buchner filter funnel with integral sintered glass disc (G5 type). The product was washed with water (5 × 10 ml) and dried in a vacuum desiccator (at a pressure of 200 Pa) for 9 h; yield 98.7%). Crystals suitable for measurement were obtained by dissolving (II) (2.3026 g) in 96% sulfuric acid (4 ml) and adding small portions of water (0.02 ml) every 10 min for 8 d. The obtained crystals were filtered off using a Buchner filter funnel with integral sintered glass disc (G5 type), washed with water (5 × 5 ml) and dried in a vacuum desiccator (at a pressure of 200 Pa) for 14 h. Compound (II) can be also obtained by moisture [treatment?] of pulverized (I) (2.4827 g, 0.01 mol) with 96% sulfuric acid (0.3 ml) and heating of the sample at 403 K for 1 h [compound (I) is converted to (II) in stochiometric quantity].

Vibrational analysis was carried out for both compounds. The IR spectra (400–4000 cm^-1) were taken in KBr discs in a Bruker spectrophotometer. The IR spectra of (I) and (II) contain characteristic bands of stretching vibrations of the NH₂, NH and CH groups in the region of 3600–3000 cm^-1. The single band at 1645 cm^-1 is attributed to the CN stretching vibrations and NH bending vibrations. The bands around 1600, 1580 and 1470 cm^-1 confirm the presence of aromatic C—C bonds. The medium intensity bands at 750 cm^-1 in (I) and 840 cm^-1 in (II) correspond to vibrations of aryl CH bonds. An important spectral feature that can be used to distinguish the hydrogen sulfate and sulfonate ions is the CS stretching vibration, which typically occurs at 1140 and 735 cm^-1. The bands corresponding to this vibration appear at 1143 and 731 cm^-1 only in the IR spectrum of compound (II). The broad split absorption bands in the frequency range 1170–1210 cm^-1 are attributed to the asymmetric S═O vibrations of the sulfate [in (I)] and sulfonate [in (II)] groups. The broadening is caused by the presence of noncovalent interactions in the solid state. The symmetric S═O vibrations appear as a strong bands at 1005 cm^-1 for (I) and 1028 cm^-1 for (II). Additionally, the IR spectrum of (I) showed a medium intensity band at 1067 cm^-1 originating from stretching vibrations of OH bonds from the HSO₄^- anion, whereas the broad band in the frequency range 850–883 cm^-1 can be attributed to vibrations of S—OH groups. Could this paragraph be condensed into the standard shorthand format?

S3. Refinement

C-bonded H atoms were placed in calculated positions (C—H = 0.93Å), while other H atoms were found from difference Fourier syntheses after eight cycles of anisotropic refinement and their fractional coordinates were used directly in a riding model with fixed U values [U_iso(H) = 1.2U_eq(C,N) and 1.5U_eq(O)]. Further details of the refinements are available in the archived CIF file

Computing details

For both compounds, data collection: CrysAlis CCD (UNIL IC & Kuma, 2000); cell refinement: CrysAlis RED (UNIL IC & Kuma, 2000); data reduction: CrysAlis RED (UNIL IC & Kuma, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL/PC (Sheldrick, 2008) and ORTEP-3 (Version 1.062; Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radii.
	Fig. 2. The molecular structure of (II). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radii.
	Fig. 3. Part of the packing of molecules in (I), showing the hydrogen-bonded ribbon extending along the [010] axis. Dashed lines indicate N—H···O hydrogen bonds. [Symmetry codes: (i) -x + 1, -y + 1, -z + 2; (ii) x + 1, -y + 1/2, z + 1/2.]
	Fig. 4. Part of the packing of molecules in (II), showing N—H···O hydrogen bonds (as dashed lines). [Symmetry codes: (iv) x, y - 1, z; (v) x + 1/2, -y + 3/2, z + 1/2; (vi) -x, y - 1, -z + 1/2.]
	Fig. 5. A surface plot showing the relationship between hydrogen-bond energy (E, Table 3) and D···A distances/D—H···A angles. The values of E for (I) and (II) are indicated by dots.

(I) 2,3-dihydro-1,3-benzothiazol-2-iminium monohydrogen sulfate

Crystal data

C7H7N2S^+·HSO4^−	F(000) = 512
Mr = 248.27	Dx = 1.635 Mg m^−3 Dm = 1.63 Mg m^−3 Dm measured by Berman density torsion balance
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 7115 reflections
a = 11.1693 (4) Å	θ = 2–25°
b = 10.2261 (3) Å	µ = 0.52 mm^−1
c = 9.0551 (3) Å	T = 291 K
β = 102.799 (3)°	Prism, light grey
V = 1008.56 (6) Å^3	0.31 × 0.15 × 0.12 mm
Z = 4

Data collection

Kuma KM-4 CCD diffractometer	1797 independent reflections
Radiation source: fine-focus sealed tube	1603 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
Detector resolution: 1048576 pixels mm^-1	θmax = 25.1°, θmin = 2.7°
ω scans	h = −13→12
Absorption correction: numerical (X-RED; Stoe & Cie, 1999)	k = −12→12
Tmin = 0.908, Tmax = 0.941	l = −10→10
9680 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.031	Hydrogen site location: mixed
wR(F^2) = 0.090	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0503P)^2 + 0.4404P] where P = (Fo^2 + 2Fc^2)/3
1797 reflections	(Δ/σ)max < 0.001
136 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.44 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

C-bonded H atoms were placed in calculated positions (C—H = 0.93 Å), while other H atoms were found from difference Fourier syntheses after eight cycles of anisotropic refinement and their fractional coordinates were used directly in a riding model. The isotropic displacement parameters of these latter H atoms were then refined to check the correctness of their positions. After eight cycles, the refinement reached stable convergence with isotropic displacement parameters of 0.045, 0.064, 0.063, 0.076, 0.047, 0.043 and 0.053, respectively, for atoms H1, H2A, H2B and H2C of (I) and atoms H1, H2A and H2B of (II). The fact that the values of the isotropic displacement parameters of the N and O-bonded H atoms have reasonable values proves the correctness of these H-atom positions. All H atoms were subsequently refined as riding on the parent atom with fixed U values [U_iso(H) = 1.2U_eq(C,N) and U_iso(H) = 1.5U_eq(O)]. The 100 reflection, affected by the beam stop (F_o² = 57.23, F_c² = 3851.90, diffraction angle τ = 1.87°), was excluded from the refinement of (I). During the final cycle of refinement of (I) the SHELXL97 software (Sheldrick, 2008) suggested the possibility of extinction correction requirement, but closer inspection of measured data shows that some very strong reflections are weakened, whereas some are strengthened, and there is no systematic dependence between increasing and decreasing of observed intensities, even at similar diffraction geometry. Additionally, the refinement with introduced extinction correction leads to small extinction coefficient of 0.0055 (10) close to the range of experimental error. Thus, it was assumed that there is no real extinction effect in the measured crystal and the small improvement of some structural parameters during refinement with the use of an extinction correction is caused by the intensity adjustment performed by the SHELXL97 EXTI command.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.79808 (13)	0.41532 (15)	0.94524 (17)	0.0402 (4)
H1	0.7922	0.4993	0.9434	0.048*
C1	0.88099 (16)	0.35471 (19)	1.0512 (2)	0.0380 (4)
S1	0.87240 (5)	0.18694 (5)	1.03628 (6)	0.04806 (18)
N2	0.96031 (14)	0.41741 (17)	1.15642 (18)	0.0483 (4)
H2A	0.9539	0.4982	1.1687	0.058*
H2B	1.0096	0.3739	1.2248	0.058*
C2	0.72012 (17)	0.33215 (19)	0.8471 (2)	0.0410 (4)
C3	0.74847 (18)	0.2013 (2)	0.8810 (2)	0.0456 (5)
C4	0.6814 (2)	0.1030 (2)	0.7959 (3)	0.0635 (6)
H4	0.6989	0.0153	0.8179	0.076*
C5	0.5875 (3)	0.1398 (3)	0.6772 (3)	0.0747 (8)
H5	0.5410	0.0754	0.6184	0.090*
C6	0.5603 (2)	0.2695 (3)	0.6431 (3)	0.0701 (7)
H6	0.4967	0.2904	0.5614	0.084*
C7	0.62588 (18)	0.3691 (3)	0.7279 (2)	0.0541 (5)
H7	0.6075	0.4566	0.7058	0.065*
S2	0.20448 (4)	0.25030 (4)	0.91593 (5)	0.03675 (17)
O1	0.24567 (14)	0.31567 (13)	1.06190 (14)	0.0469 (4)
O2	0.31006 (13)	0.28407 (16)	0.83571 (15)	0.0527 (4)
H2C	0.2908	0.2578	0.7446	0.079*
O3	0.09389 (13)	0.30901 (14)	0.82772 (17)	0.0543 (4)
O4	0.19623 (16)	0.11193 (15)	0.92507 (18)	0.0646 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0407 (8)	0.0359 (8)	0.0428 (9)	−0.0006 (6)	0.0068 (7)	−0.0001 (7)
C1	0.0354 (9)	0.0403 (10)	0.0401 (10)	0.0006 (7)	0.0119 (8)	0.0037 (8)
S1	0.0553 (3)	0.0360 (3)	0.0542 (3)	0.0014 (2)	0.0151 (2)	0.0034 (2)
N2	0.0447 (9)	0.0449 (9)	0.0489 (9)	0.0013 (7)	−0.0032 (7)	0.0039 (7)
C2	0.0375 (9)	0.0486 (11)	0.0394 (10)	−0.0059 (8)	0.0135 (8)	−0.0048 (8)
C3	0.0495 (11)	0.0486 (11)	0.0431 (11)	−0.0078 (9)	0.0193 (9)	−0.0053 (8)
C4	0.0788 (16)	0.0572 (14)	0.0597 (14)	−0.0252 (12)	0.0268 (12)	−0.0165 (11)
C5	0.0798 (18)	0.090 (2)	0.0585 (15)	−0.0442 (16)	0.0251 (13)	−0.0275 (14)
C6	0.0475 (13)	0.114 (2)	0.0465 (13)	−0.0225 (14)	0.0062 (10)	−0.0081 (14)
C7	0.0435 (11)	0.0723 (15)	0.0458 (11)	−0.0018 (10)	0.0087 (9)	0.0009 (11)
S2	0.0450 (3)	0.0343 (3)	0.0293 (3)	−0.00024 (18)	0.00491 (19)	−0.00076 (16)
O1	0.0672 (9)	0.0454 (8)	0.0258 (6)	0.0063 (6)	0.0051 (6)	−0.0006 (5)
O2	0.0513 (8)	0.0743 (10)	0.0318 (7)	−0.0134 (7)	0.0078 (6)	−0.0087 (6)
O3	0.0499 (8)	0.0572 (9)	0.0488 (8)	0.0081 (7)	−0.0043 (6)	−0.0073 (7)
O4	0.0910 (12)	0.0358 (8)	0.0649 (10)	−0.0047 (7)	0.0125 (9)	0.0008 (7)

Geometric parameters (Å, º)

N1—C1	1.330 (2)	C4—H4	0.9300
N1—C2	1.388 (2)	C5—C6	1.380 (4)
N1—H1	0.8615	C5—H5	0.9300
C1—N2	1.315 (2)	C6—C7	1.383 (4)
C1—S1	1.722 (2)	C6—H6	0.9300
S1—C3	1.747 (2)	C7—H7	0.9300
N2—H2A	0.8384	S2—O4	1.4216 (16)
N2—H2B	0.8566	S2—O3	1.4447 (14)
C2—C7	1.383 (3)	S2—O1	1.4616 (13)
C2—C3	1.393 (3)	S2—O2	1.5546 (15)
C3—C4	1.382 (3)	O2—H2C	0.8487
C4—C5	1.377 (4)
C1—N1—C2	114.44 (16)	C3—C4—H4	121.3
C1—N1—H1	121.1	C4—C5—C6	121.9 (2)
C2—N1—H1	124.4	C4—C5—H5	119.0
N2—C1—N1	123.03 (18)	C6—C5—H5	119.0
N2—C1—S1	124.01 (14)	C5—C6—C7	121.3 (2)
N1—C1—S1	112.96 (14)	C5—C6—H6	119.3
C1—S1—C3	89.99 (9)	C7—C6—H6	119.3
C1—N2—H2A	120.8	C6—C7—C2	116.7 (2)
C1—N2—H2B	119.5	C6—C7—H7	121.6
H2A—N2—H2B	118.4	C2—C7—H7	121.6
C7—C2—N1	126.37 (19)	O4—S2—O3	112.79 (10)
C7—C2—C3	122.04 (19)	O4—S2—O1	114.46 (9)
N1—C2—C3	111.59 (17)	O3—S2—O1	111.66 (8)
C4—C3—C2	120.5 (2)	O4—S2—O2	108.30 (10)
C4—C3—S1	128.52 (19)	O3—S2—O2	107.07 (9)
C2—C3—S1	111.00 (15)	O1—S2—O2	101.63 (8)
C5—C4—C3	117.5 (2)	S2—O2—H2C	109.2
C5—C4—H4	121.3

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^i	0.86	1.94	2.792 (2)	172
N2—H2A···O3^i	0.84	2.05	2.873 (2)	169
N2—H2B···O3^ii	0.86	2.21	2.995 (2)	153
N2—H2B···O4^ii	0.86	2.45	3.180 (2)	144
O2—H2C···O1^iii	0.85	1.79	2.6296 (18)	173

Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) x+1, −y+1/2, z+1/2; (iii) x, −y+1/2, z−1/2.

(II) 2-iminio-2,3-dihydro-1,3-benzothiazole-6-sulfonate

Crystal data

C7H6N2O3S2	F(000) = 944
Mr = 230.26	Dx = 1.778 Mg m^−3 Dm = 1.78 Mg m^−3 Dm measured by Berman density torsion balance
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 6409 reflections
a = 18.9085 (11) Å	θ = 2–25°
b = 8.2360 (6) Å	µ = 0.60 mm^−1
c = 12.9684 (10) Å	T = 291 K
β = 121.605 (9)°	Prism, light brown
V = 1720.0 (2) Å^3	0.28 × 0.28 × 0.26 mm
Z = 8

Data collection

Kuma KM-4 CCD diffractometer	1531 independent reflections
Radiation source: fine-focus sealed tube	1497 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.050
Detector resolution: 1048576 pixels mm^-1	θmax = 25.1°, θmin = 3.7°
ω scans	h = −22→22
Absorption correction: numerical (X-RED; Stoe & Cie, 1999)	k = −9→9
Tmin = 0.847, Tmax = 0.860	l = −15→14
8399 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.034	Hydrogen site location: mixed
wR(F^2) = 0.089	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0464P)^2 + 2.7921P] where P = (Fo^2 + 2Fc^2)/3
1531 reflections	(Δ/σ)max < 0.001
127 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.53 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.04499 (10)	0.3832 (2)	0.16742 (14)	0.0242 (4)
H1	0.0224	0.2851	0.1643	0.029*
C1	0.12703 (12)	0.4084 (2)	0.23036 (17)	0.0239 (4)
S1	0.15208 (3)	0.61324 (6)	0.23350 (4)	0.02512 (18)
N2	0.18321 (11)	0.2945 (2)	0.28470 (16)	0.0338 (4)
H2A	0.2365	0.3268	0.3294	0.041*
H2B	0.1697	0.1887	0.2985	0.041*
C2	−0.00297 (12)	0.5237 (2)	0.12224 (16)	0.0214 (4)
C3	0.04578 (11)	0.6631 (2)	0.15213 (16)	0.0226 (4)
C4	0.01027 (12)	0.8167 (2)	0.12427 (16)	0.0237 (4)
H4	0.0427	0.9099	0.1453	0.028*
C5	−0.07616 (12)	0.8254 (2)	0.06345 (16)	0.0229 (4)
C6	−0.12549 (11)	0.6857 (3)	0.02871 (16)	0.0239 (4)
H6	−0.1830	0.6955	−0.0142	0.029*
C7	−0.08952 (12)	0.5328 (2)	0.05762 (16)	0.0232 (4)
H7	−0.1220	0.4394	0.0347	0.028*
S2	−0.12587 (3)	1.01716 (6)	0.03579 (5)	0.02906 (18)
O1	−0.18586 (12)	1.0030 (2)	0.07288 (19)	0.0499 (5)
O2	−0.06123 (11)	1.1334 (2)	0.1081 (2)	0.0621 (6)
O3	−0.16516 (11)	1.0460 (2)	−0.09426 (16)	0.0514 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0252 (8)	0.0173 (8)	0.0293 (8)	−0.0031 (6)	0.0137 (7)	−0.0021 (6)
C1	0.0264 (10)	0.0221 (10)	0.0242 (9)	−0.0018 (8)	0.0140 (8)	−0.0019 (7)
S1	0.0212 (3)	0.0218 (3)	0.0305 (3)	−0.00376 (18)	0.0122 (2)	−0.00193 (18)
N2	0.0267 (9)	0.0246 (10)	0.0428 (10)	−0.0003 (7)	0.0133 (8)	0.0013 (8)
C2	0.0256 (9)	0.0190 (10)	0.0206 (9)	−0.0029 (7)	0.0128 (8)	−0.0023 (7)
C3	0.0207 (9)	0.0243 (10)	0.0223 (9)	−0.0038 (8)	0.0110 (7)	−0.0023 (7)
C4	0.0251 (10)	0.0189 (10)	0.0272 (9)	−0.0053 (8)	0.0137 (8)	−0.0008 (8)
C5	0.0248 (9)	0.0198 (10)	0.0218 (9)	−0.0004 (8)	0.0107 (8)	0.0012 (7)
C6	0.0210 (9)	0.0270 (11)	0.0214 (9)	−0.0033 (8)	0.0095 (7)	−0.0008 (7)
C7	0.0249 (10)	0.0207 (10)	0.0231 (9)	−0.0069 (8)	0.0120 (8)	−0.0039 (7)
S2	0.0237 (3)	0.0178 (3)	0.0400 (3)	−0.00199 (18)	0.0127 (2)	0.00068 (19)
O1	0.0573 (11)	0.0330 (9)	0.0814 (13)	0.0017 (8)	0.0514 (11)	−0.0049 (8)
O2	0.0341 (9)	0.0207 (9)	0.0960 (16)	−0.0081 (7)	0.0095 (10)	−0.0086 (9)
O3	0.0431 (10)	0.0558 (12)	0.0464 (10)	0.0202 (9)	0.0174 (8)	0.0216 (9)

Geometric parameters (Å, º)

N1—C1	1.337 (3)	C4—C5	1.395 (3)
N1—C2	1.396 (2)	C4—H4	0.9300
N1—H1	0.9052	C5—C6	1.399 (3)
C1—N2	1.312 (3)	C5—S2	1.776 (2)
C1—S1	1.747 (2)	C6—C7	1.387 (3)
S1—C3	1.7604 (19)	C6—H6	0.9300
N2—H2A	0.9001	C7—H7	0.9300
N2—H2B	0.9510	S2—O2	1.4454 (18)
C2—C3	1.394 (3)	S2—O1	1.4503 (18)
C2—C7	1.396 (3)	S2—O3	1.4628 (18)
C3—C4	1.388 (3)
C1—N1—C2	114.70 (16)	C3—C4—H4	121.4
C1—N1—H1	122.4	C5—C4—H4	121.4
C2—N1—H1	122.3	C4—C5—C6	121.69 (18)
N2—C1—N1	124.77 (18)	C4—C5—S2	119.95 (15)
N2—C1—S1	123.02 (15)	C6—C5—S2	118.26 (15)
N1—C1—S1	112.21 (14)	C7—C6—C5	120.69 (17)
C1—S1—C3	90.05 (9)	C7—C6—H6	119.7
C1—N2—H2A	116.9	C5—C6—H6	119.7
C1—N2—H2B	122.3	C6—C7—C2	117.74 (17)
H2A—N2—H2B	118.0	C6—C7—H7	121.1
C3—C2—N1	112.13 (17)	C2—C7—H7	121.1
C3—C2—C7	121.28 (18)	O2—S2—O1	112.37 (13)
N1—C2—C7	126.56 (17)	O2—S2—O3	112.73 (13)
C4—C3—C2	121.25 (17)	O1—S2—O3	112.49 (12)
C4—C3—S1	127.83 (15)	O2—S2—C5	106.27 (10)
C2—C3—S1	110.81 (15)	O1—S2—C5	106.54 (10)
C3—C4—C5	117.24 (17)	O3—S2—C5	105.81 (10)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2^i	0.91	1.84	2.690 (2)	156
N2—H2A···O3^ii	0.90	1.90	2.774 (2)	164
N2—H2B···O1^iii	0.95	2.16	3.013 (3)	148
C4—H4···O2	0.93	2.55	2.895 (3)	102

Symmetry codes: (i) x, y−1, z; (ii) x+1/2, −y+3/2, z+1/2; (iii) −x, y−1, −z+1/2.