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The title compound, C21H14N4O2S, belongs to a family of mol­ecules possessing nonlinear optical properties in solution. Its structure has been solved from laboratory X-ray powder diffraction data using a new direct-space structure solution method, where the atomic coordinates are directly used as parameters and the mol­ecular geometry is described by restraints. The mol­ecular packing is controlled by two systems of π–π inter­actions and one weak edge-to-face inter­action.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270111039916/lg3066sup1.cif
Contains datablocks global, IB

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108270111039916/lg3066IBsup2.rtv
Contains datablock IB

cml

Chemical Markup Language (CML) file https://doi.org/10.1107/S0108270111039916/lg3066IBsup3.cml
Supplementary material

CCDC reference: 855957

Comment top

Organic materials exhibiting nonlinear optical (NLO) properties are generally constituted by conjugated organic compounds. Molinos-Gómez et al. (2005) described a new family of NLO push–pull DLA chromophores composed of a donor group (D) derived from 1,3-benzothiazol-2-amine, an acceptor group (A), viz. a nitro group, and a linker (L), viz. acridine, which also enhances the electrowithdrawing effect of the nitro group. To explain the unexpectedly high NLO response of these molecules, a tautomeric equilibrium between the amino and imino forms was proposed (see scheme). The two forms would possess different NLO properties, with the higher response being due to the imino form. In order to prove this hypothesis, the methyl-blocked compounds were synthesized, namely N-methyl-N-(2-nitroacridin-6-yl)-1,3-benzothiazol-2-amine [amino form, (IA)] and (Z)-3-methyl-N-(7-nitroacridin-3-yl)-2,3-dihydro-1,3-benzothiazol-2-imine [imino form, (IB)].

As predicted, (IB) exhibits the higher NLO response of this pair of chromophores in solution (Latorre et al., 2010). It also presents other interesting properties, such as fluorescence and thermal stability. For a better understanding of the properties of this molecule, crystals of (IB) were grown and their crystal structure was solved (Fig. 1). This previously unknown structure also served as a test case for a new structure solution method for molecular compounds from powder diffraction data (TALP program; Rius et al., 2011). The structure determination of (IB) was challenging due to the size of the unit cell, which caused severe peak overlaps in the powder pattern. TALP uses a global optimization technique based on the incremental least-squares refinement of randomly positioned fragments using a very fast Rietveld refinement program (Rius et al., 1990). Unlike most direct-space structure solution programs [for a review of direct-space methods, see Černý & Favre-Nicolin (2007)], it directly refines the atomic coordinates and not the torsion angles.

The starting molecular model was obtained by energy minimization using molecular mechanics with an MM2 force field (Allinger, 1977). The geometry of the complete molecule was described in terms of distance and plane restraints: distance restraints were obtained from the CCDC using Mogul (Bruno et al., 2004) and from International Tables for Crystallography (Vol. C; Allen et al., 2006); plane restraints were applied to the acridine (Acr) and benzothiazole (Bt) rings and to the nitro group. The EZ isomerism of the imine double bond was not fixed, starting randomly in each cycle and being able to evolve towards the E or the Z isomer during the iteration. The C11—N10 and C18—N26 bonds were also left completely free to rotate, so that no restriction was imposed on the planarity of the whole molecule. By using these conditions, 10 out of 50 TALP trials (40000 least-squares cycles per trial at ~25 min each) were correct solutions. A crystal structure proposal was given at the end of each TALP trial with an internal figure of merit (FoM), which essentially measures the discrepancy between the observed and calculated intensity profiles at the Bragg positions. The most probable solutions were identified by their low FoM values [in the case of (IB), the FoM values were ~1.3 times larger for wrong solutions than for correct ones]; the correctness of each solution was also checked by a visual inspection of observed and calculated powder patterns, and finally by checking the chemical sense of the proposed structure. Then, starting from any of the correct solutions, a final restrained Rietveld refinement could be performed with the program RIBOLS (Rius, 2009); the observed and calculated powder patterns are shown in Fig. 2.

In crystalline form, (IB) consists of two noncoplanar aromatic ring systems (Acr and Bt), with the respective mean planes forming a dihedral angle of 42.0 (2)°. The imine double bond has a slight planar distortion [torsion angle C11—N10—C2—S1 = -3.9 (17)°] and the nitro substituent is almost in the Acr plane, with a dihedral angle between their mean planes of 6.9 (5)°.

The molecular packing is controlled by ππ interactions (π stacking) between the aromatic systems in the molecule (Fig. 3). The π stacking of the Acr rings along c is characterized by: (i) a distance between central six-membered-ring centroids of 3.831 (4) Å; (ii) an angle of 23.3° between the centroid–centroid vector and the vector normal to the plane; and (iii) a dihedral angle of 1.5° (i.e. almost coplanar) between Acr mean planes. On the other hand, each Bt ring forms two types of arrangements with neighbouring Bt rings. The first allows π stacking between Bt rings, giving rise to molecular pairs which determine the unit-cell size in the a direction. This π stacking is characterized by: (i) a distance of 3.796 (6) Å between six-membered-ring centroids; (ii) an angle of 23.4° between the centroid–centroid vector and the vector normal to the plane; and (iii) a dihedral angle of 0° between the mean planes, imposed by the inversion centre. In the second arrangement, the Bt rings of adjacent molecules along the c axis form a dihedral angle of 73.0°, and the C8—H8 bond of one Bt ring points to the six-membered ring of the other at a distance of 2.80 Å (H8 to phenyl centroid) and an angle of 155° (C8—H8···centroid), allowing a weak intermolecular edge-to-face interaction (Jennings et al., 2001). The nitro O atoms interact weakly with neighbouring molecules; there is a weak C7—H7 hydrogen bond to atom O27 at (x + 1/2, y, -z + 1/2), and another from C23—H23 to atom O28 at (-x + 1/2, -y, -1/2 + z), although the π stackings are the most significant interactions in the crystal structure of (IB).

Related literature top

For related literature, see: Allen et al. (2006); Allinger (1977); Boultif & Louër (2004); Bruno et al. (2004); Jennings et al. (2001); Latorre et al. (2010); Molinos-Gómez, Vidal, Maymó, Velasco, Martorell & López-Calahorra (2005); Rius (2009, 2010); Rius et al. (1990, 2011); Rouse et al. (1970); Smith & Snyder (1979); Černý & Favre-Nicolin (2007); de Wolff (1968).

Experimental top

Compound (IB) was prepared following the procedure described in previous work (Latorre et al., 2010) and the orange powder obtained was loaded into a 0.3 mm Lindemann glass capillary.

Diffraction data were collected on a PANalytical X'Pert PRO MPD diffractometer (45 kV/40 mA) with Cu Kα1 radiation selected by a primary hybrid monochromator (X-ray mirror and channel-cut 220 Ge crystal) in transmission geometry, with the sample in a 0.3 mm glass capillary, using an X'Celerator multistrip detector with an active detection length of 2.122°. The measured 2θ interval was 3.5–56.0°, with a step size of 0.017° and an effective counting time (including the sweep of the strip detector) of 8955 s per step (72 h of total measuring time). In the refinement, data in the interval 4.41–55.97° were used. No absorption correction was applied, due to the low absorption coefficient and small capillary diameter. A cylindrical correction (Rouse et al., 1970) was tested and showed no improvement.

The powder pattern was indexed using DICVOL04 (Boultif & Louër, 2004) with figures of merit of M20 = 44.4 (de Wolff, 1968) and F20 = 96.7 (0.0029, 71) (Smith & Snyder, 1979). The large cell volume is consistent with Z = 8 and the systematic absences indicate the Pbca space group. Unit-cell parameter refinement and subsequent extraction of intensities (used for the structure solution with TALP; Rius et al., 2011) were performed with the whole-pattern matching program DAJUST2 (Rius, 2010).

Refinement top

The initial structure model supplied by TALP (Rius et al., 2011) was optimized by restrained Rietveld refinement (RIBOLS program; Rius, 2009). A total of 91 parameters were refined (atomic coordinates, scale factor, overall displacement parameter, profile coefficients, cell parameters and zero shift). 109 restraints were added, 32 for bond distances, 47 for bond angles, and 30 to define three planes, one for the acridine ring, one for the benzothiazole ring and the last for the nitro group. The same restraints were used for structure solution and for the final Rietveld refinement and these are detailed in the CIF. The planarity of the imine double bond was indirectly imposed by the addition of atom N10 to the definition of both the Acr and Bt planes.

H atoms were placed at calculated positions and constrained to the corresponding C atoms in the final refinement cycles. In the case of the methyl group, several orientations for the H atoms were tested and the one sterically more favourable was selected. For all atoms, an overall displacement parameter was used.

Computing details top

Data collection: X'pert Data Collector (PANalytical, 2003); cell refinement: DAJUST2 (Rius, 2010); data reduction: X'pert Highscore (PANalytical, 2003); program(s) used to solve structure: TALP (Rius et al., 2011); program(s) used to refine structure: RIBOLS (Rius, 2009); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of isomer (IB), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the ??% probability level. [Please complete]
[Figure 2] Fig. 2. The observed (points) and calculated (line) patterns, with the difference profile (bottom), obtained from Rietveld refinements of (IB).
[Figure 3] Fig. 3. A simplified scheme showing the ππ interactions (π stacking) between 2-nitroacridin-6-amine (Acr) groups and 1,3-benzothiazol-2-amine groups (Bt), and the edge-to-face interactions in the crystal structure of (IB).
(Z)-3-Methyl-N-(7-nitroacridin-3-yl)-2,3-dihydro- 1,3-benzothiazol-2-imine top
Crystal data top
C21H14N4O2SF(000) = 1600.0
Mr = 386.43Dx = 1.479 Mg m3
Orthorhombic, PbcaCu Kα1 radiation, λ = 1.54059 Å
a = 36.627 (4) ŵ = 1.88 mm1
b = 12.5071 (10) ÅT = 298 K
c = 7.5769 (4) Åorange
V = 3470.9 (4) Å3?, ? × ? × ? mm
Z = 8
Data collection top
PANalytical X'Pert PRO MPD
diffractometer
Data collection mode: transmission
Ge 220 monochromatorScan method: step
Specimen mounting: glass capillary2θmin = 4.41°, 2θmax = 55.97°, 2θstep = 0.017°
Refinement top
Least-squares matrix: fullProfile function: pseudo-Voigt
Rp = 0.03491 parameters
Rwp = 0.044109 restraints
Rexp = 0.026H-atom parameters constrained
RBragg = 0.075 1/Yobs
χ2 = 2.779(Δ/σ)max = 0.05
3034 data pointsBackground function: linear extrapolation of automatically determined points
Crystal data top
C21H14N4O2SV = 3470.9 (4) Å3
Mr = 386.43Z = 8
Orthorhombic, PbcaCu Kα1 radiation, λ = 1.54059 Å
a = 36.627 (4) ŵ = 1.88 mm1
b = 12.5071 (10) ÅT = 298 K
c = 7.5769 (4) Å?, ? × ? × ? mm
Data collection top
PANalytical X'Pert PRO MPD
diffractometer
Scan method: step
Specimen mounting: glass capillary2θmin = 4.41°, 2θmax = 55.97°, 2θstep = 0.017°
Data collection mode: transmission
Refinement top
Rp = 0.0343034 data points
Rwp = 0.04491 parameters
Rexp = 0.026109 restraints
RBragg = 0.075H-atom parameters constrained
χ2 = 2.779
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S10.4391 (3)0.2827 (5)0.0164 (7)0.068 (2)
C20.4170 (3)0.3826 (10)0.1376 (12)0.068 (2)
N30.4423 (4)0.4484 (9)0.2190 (11)0.068 (2)
C40.4793 (3)0.4199 (9)0.1871 (11)0.068 (2)
C50.5103 (4)0.4718 (8)0.2521 (10)0.068 (2)
C60.5439 (4)0.4302 (10)0.2032 (12)0.068 (2)
C70.5474 (4)0.3414 (11)0.0941 (12)0.068 (2)
C80.5165 (4)0.2917 (9)0.0325 (11)0.068 (2)
C90.4825 (4)0.3299 (9)0.0776 (11)0.068 (2)
N100.3841 (3)0.3981 (8)0.1516 (8)0.068 (2)
C110.3543 (3)0.3441 (7)0.0906 (7)0.068 (2)
C120.3236 (3)0.3909 (10)0.0326 (8)0.068 (2)
C130.2921 (3)0.3319 (9)0.0264 (9)0.068 (2)
N140.2619 (3)0.3836 (10)0.0846 (9)0.068 (2)
C150.2327 (3)0.3297 (9)0.1393 (9)0.068 (2)
C160.2002 (4)0.3837 (11)0.2021 (10)0.068 (2)
C170.1698 (3)0.3319 (10)0.2598 (10)0.068 (2)
C180.1699 (3)0.2159 (10)0.2565 (8)0.068 (2)
C190.1996 (3)0.1605 (10)0.1990 (9)0.068 (2)
C200.2320 (3)0.2140 (10)0.1382 (9)0.068 (2)
C210.2632 (3)0.1605 (10)0.0772 (9)0.068 (2)
C220.2941 (3)0.2161 (10)0.0198 (9)0.068 (2)
C230.3273 (3)0.1668 (10)0.0448 (9)0.068 (2)
C240.3558 (3)0.2273 (8)0.0979 (9)0.068 (2)
C250.4296 (5)0.5362 (9)0.3243 (11)0.068 (2)
N260.1382 (3)0.1575 (10)0.3245 (9)0.068 (2)
O270.1158 (4)0.2181 (12)0.3897 (9)0.068 (2)
O280.1369 (5)0.0611 (11)0.3127 (12)0.068 (2)
H50.50850.53150.32480.068 (2)
H60.56500.46290.24500.068 (2)
H70.57040.31580.063490.068 (2)
H80.51850.23180.03980.068 (2)
H120.32230.46510.02990.068 (2)
H160.20010.45800.20360.068 (2)
H170.14960.36950.30040.068 (2)
H190.19890.08620.19840.068 (2)
H210.26330.08610.07430.068 (2)
H230.32930.09270.05070.068 (2)
H240.37690.19480.140670.068 (2)
H25A0.40630.51810.37440.068 (2)
H25B0.44670.55050.41720.068 (2)
H25C0.42710.59850.25150.068 (2)
Geometric parameters (Å, º) top
S1—C21.749 (13)C15—C201.447 (17)
S1—C91.758 (17)C16—C171.360 (18)
O27—N261.221 (18)C17—C181.451 (18)
O28—N261.210 (19)C18—C191.361 (16)
N3—C21.384 (17)C19—C201.438 (16)
N3—C41.422 (18)C20—C211.403 (16)
N3—C251.435 (16)C21—C221.398 (16)
N10—C21.225 (16)C22—C231.449 (15)
N10—C111.364 (14)C23—C241.351 (15)
N14—C131.355 (15)C5—H50.9300
N14—C151.330 (15)C6—H60.9300
N26—C181.465 (15)C7—H70.9300
C4—C51.398 (17)C8—H80.9300
C4—C91.403 (15)C12—H120.9300
C5—C61.39 (2)C16—H160.9300
C6—C71.390 (17)C17—H170.9300
C7—C81.373 (19)C19—H190.9300
C8—C91.38 (2)C21—H210.9300
C11—C121.342 (15)C23—H230.9300
C11—C241.463 (13)C24—H240.9300
C12—C131.441 (15)C25—H25A0.9600
C13—C221.451 (17)C25—H25B0.9600
C15—C161.449 (17)C25—H25C0.9600
C2—S1—C992.3 (6)C15—C20—C19118.6 (10)
C2—N3—C4114.4 (10)C15—C20—C21117.7 (10)
C2—N3—C25119.1 (13)C19—C20—C21123.8 (11)
C4—N3—C25126.5 (12)C20—C21—C22121.7 (11)
C2—N10—C11132.8 (10)C13—C22—C21116.4 (10)
C13—N14—C15121.1 (11)C13—C22—C23118.6 (10)
O27—N26—O28128.5 (14)C21—C22—C23125.0 (11)
O27—N26—C18111.4 (12)C22—C23—C24120.7 (11)
O28—N26—C18120.1 (12)C11—C24—C23121.3 (10)
S1—C2—N3110.4 (9)C4—C5—H5122.00
S1—C2—N10127.9 (10)C6—C5—H5121.00
N3—C2—N10121.7 (11)C5—C6—H6119.00
N3—C4—C5126.7 (10)C7—C6—H6118.00
N3—C4—C9112.4 (10)C6—C7—H7120.00
C5—C4—C9120.9 (11)C8—C7—H7120.00
C4—C5—C6116.9 (9)C7—C8—H8120.00
C5—C6—C7122.7 (12)C9—C8—H8120.00
C6—C7—C8119.2 (13)C11—C12—H12119.00
C7—C8—C9120.3 (10)C13—C12—H12118.00
S1—C9—C4110.5 (10)C15—C16—H16118.00
S1—C9—C8129.5 (9)C17—C16—H16118.00
C4—C9—C8120.0 (12)C16—C17—H17121.00
N10—C11—C12124.4 (9)C18—C17—H17121.00
N10—C11—C24116.8 (9)C18—C19—H19119.00
C12—C11—C24118.7 (10)C20—C19—H19119.00
C11—C12—C13123.3 (11)C20—C21—H21119.00
N14—C13—C12120.7 (11)C22—C21—H21119.00
N14—C13—C22121.9 (10)C22—C23—H23120.00
C12—C13—C22117.4 (10)C24—C23—H23119.00
N14—C15—C16121.8 (11)C11—C24—H24119.00
N14—C15—C20121.3 (10)C23—C24—H24120.00
C16—C15—C20117.0 (10)N3—C25—H25A109.00
C15—C16—C17123.8 (12)N3—C25—H25B110.00
C16—C17—C18117.9 (11)N3—C25—H25C109.00
N26—C18—C17119.4 (10)H25A—C25—H25B110.00
N26—C18—C19119.5 (11)H25A—C25—H25C109.00
C17—C18—C19121.1 (10)H25B—C25—H25C109.00
C18—C19—C20121.7 (11)
C2—N10—C11—C2440.4 (13)C7—C8—C9—C40.1 (15)
C9—S1—C2—N30.4 (8)C7—C8—C9—S1179.5 (8)
C9—S1—C2—N10179.1 (10)C24—C11—C12—C131.2 (10)
C2—S1—C9—C40.2 (8)N10—C11—C24—C23178.3 (7)
C2—S1—C9—C8179.8 (10)N10—C11—C12—C13178.1 (7)
C4—N3—C2—S10.4 (11)C12—C11—C24—C231.2 (11)
C25—N3—C2—S1179.6 (8)C11—C12—C13—N14179.6 (7)
C4—N3—C2—N10179.2 (9)C11—C12—C13—C220.7 (11)
C25—N3—C2—N100.8 (15)N14—C13—C22—C23179.7 (7)
C25—N3—C4—C50.0 (16)C12—C13—C22—C21179.8 (7)
C2—N3—C4—C90.2 (12)N14—C13—C22—C210.2 (11)
C2—N3—C4—C5180.0 (9)C12—C13—C22—C230.1 (10)
C25—N3—C4—C9179.8 (9)N14—C15—C16—C17179.8 (8)
C11—N10—C2—S13.9 (17)C20—C15—C16—C170.4 (12)
C11—N10—C2—N3177.5 (9)N14—C15—C20—C19180.0 (7)
C2—N10—C11—C12142.6 (11)N14—C15—C20—C210.1 (11)
C13—N14—C15—C16179.9 (8)C16—C15—C20—C190.1 (11)
C15—N14—C13—C220.3 (12)C16—C15—C20—C21179.8 (7)
C13—N14—C15—C200.2 (12)C15—C16—C17—C180.6 (13)
C15—N14—C13—C12180.0 (7)C16—C17—C18—N26177.5 (7)
O27—N26—C18—C19171.9 (8)C16—C17—C18—C190.6 (11)
O28—N26—C18—C197.6 (13)N26—C18—C19—C20177.3 (7)
O28—N26—C18—C17175.4 (9)C17—C18—C19—C200.4 (11)
O27—N26—C18—C175.0 (11)C18—C19—C20—C150.2 (11)
N3—C4—C9—S10.1 (11)C18—C19—C20—C21179.8 (7)
C9—C4—C5—C60.0 (13)C15—C20—C21—C220.2 (11)
N3—C4—C5—C6179.7 (9)C19—C20—C21—C22179.8 (7)
C5—C4—C9—C80.1 (14)C20—C21—C22—C130.1 (11)
N3—C4—C9—C8179.7 (9)C20—C21—C22—C23180.0 (7)
C5—C4—C9—S1179.7 (7)C13—C22—C23—C240.1 (11)
C4—C5—C6—C70.3 (15)C21—C22—C23—C24179.9 (7)
C5—C6—C7—C80.5 (16)C22—C23—C24—C110.6 (11)
C6—C7—C8—C90.4 (15)

Experimental details

Crystal data
Chemical formulaC21H14N4O2S
Mr386.43
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)298
a, b, c (Å)36.627 (4), 12.5071 (10), 7.5769 (4)
V3)3470.9 (4)
Z8
Radiation typeCu Kα1, λ = 1.54059 Å
µ (mm1)1.88
Specimen shape, size (mm)?, ? × ? × ?
Data collection
DiffractometerPANalytical X'Pert PRO MPD
diffractometer
Specimen mountingGlass capillary
Data collection modeTransmission
Scan methodStep
2θ values (°)2θmin = 4.41 2θmax = 55.97 2θstep = 0.017
Refinement
R factors and goodness of fitRp = 0.034, Rwp = 0.044, Rexp = 0.026, RBragg = 0.075, χ2 = 2.779
No. of data points3034
No. of parameters91
No. of restraints109
H-atom treatmentH-atom parameters constrained

Computer programs: X'pert Data Collector (PANalytical, 2003), DAJUST2 (Rius, 2010), X'pert Highscore (PANalytical, 2003), TALP (Rius et al., 2011), RIBOLS (Rius, 2009), Mercury (Macrae et al., 2006), publCIF (Westrip, 2010) and PLATON (Spek, 2009).

 

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