4-(4-Bromo­phenyl)-2-methyl-1,3-thia­zole

In the structure of the title compound, C₁₀H₈BrNS, the dihedral angles between the planes of the thia­zole and aryl rings, viz. 4.2 (6) and 7.5 (6)° for the two independent mol­ecules, are consistent with insignificant molecular perturbation by the weak intermolecular contacts. The mol­ecules are close to being related by a non-crystallographic inversion centre, with C—H...π and π–π intermolecular interactions observed.

S1. Comment

In earlier reports (Sánchez-Viesca & Gómez, 1998 and references cited therein; Sánchez-Viesca & Berros, 1999), we presented the synthesis of a large series of new polysubstituted 2,4-diarylthiazoles. An interesting structural feature of these compounds is the possibility of rotamery, as a result of free rotation around the σ bond joining the thiazole and aryl moieties due to the existence of weak hydrogen bonds. Clear evidence was found that preferred rotamers are present in solution, using ¹H NMR spectroscopy (Sánchez-Viesca & Berros, 2002), including experiments "at infinite dilution" and correlation techniques, such as NOESY (nuclear Overhauser effect spectroscopy) and HMBC (heteronuclear multiple-bond correlation). However, it remains difficult to predict which rotamer will be stabilized in the solid state. We suppose that potential intra- and intermolecular non-covalent interactions, mainly hydrogen bonds, are essential during the crystallization process of these compounds. In order to determine the parameters defining these interactions, the X-ray structure determination of 2,4-diarylthiazoles with a variety of substituents is a powerful tool.

In a previous work (Bernès et al., 2002), we concluded that, with the same substitutents on the aryl ring, the nature of the group at the 2-position of the thiazole moiety determines the rotamer stabilized in the solid state, viz. a flat rotamer for a poor donor group at the 2-position and a twisted rotamer for a group able to form intermolecular hydrogen bonds. In the title compound, (I), a methyl group is substituted on the thiazole ring, so a flat rotamer is expected in the solid state. The aryl moiety is a p-bromophenyl group, i.e. a fragment with local C_2v symmetry and ortho positions occupied by equivalent H atoms. Thus, there is only one possibility for the formation of an intramolecular hydrogen bond, considering the N-thiazole atom as a potential acceptor.

The asymmetric unit for (I) contains two independent molecules (Fig. 1) with very similar geometries (Table 1). Both residues are related by a non-crystallographic inversion center. An almost perfect fit is obtained between one molecule and the inverted second molecule, with a r.m.s. deviation of 0.037 Å. Both independent molecules are virtually planar; the r.m.s. deviation from the N1/C2/S1/C3–C10 least-squares plane is 0.034 (9) Å, while the corresponding deviation for the S2-containing molecule is 0.061 (10) Å. The dihedral angles between the mean planes formed by the thiazole ring and the aryl ring are 4.2 (6) and 7.5 (6)° for the S1- and S2-containing residues, respectively. The p-bromophenyl substituent at the 4-position exhibits no significant participation in the definition of the dihedral angle and does not participate in the intermolecular hydrogen-bonding scheme, as can be seen in related thiazole derivatives (Caldwell et al., 1987; Newton et al., 1967). Taking into consideration the partial π character of the C4—C5 and C14—C15 bonds (Table 1), (I) can be described as the aromatic rotamer of the thiazole under study. In other words, the aromatic planar nature of the molecules has not been disturbed by intermolecular interactions (see infra), at least in the solid state.

The flat conformation for (I) facilitates the interaction between the N-thiazole and H atom bonded to atom C6 (or C16). The observed N···H separations (Table 2) can be considered as actual contacts, the distance being 0.27 (S1-containing residue) and 0.29 Å (S2-containing residue) shorter than the van der Waals distance. However, D—H···A angles are characteristic of very low electrostatic interaction energies, i.e. with very weak intramolecular hydrogen bonds (Mascal, 1998).

The main intermolecular interaction is observed within the asymmetric unit; the non-crystallographic symmetry that relates independent residues allows π···π interactions between the five- and six-membered rings. The observed distances between the centroids of stacked rings are 3.751 (7) and 3.780 (7) Å. These pairs of molecules are stacked along the b axis, forming a crystal packing of segregated stacks (Fig. 2). However, these interactions are found to be significantly longer than those observed in similar crystal structures. For instance, in a thiabendazolium derivative (Prabakaran et al., 2000), the shortest π···π contacts involving the thiazole ring are 3.665 and 3.669 Å. In another report on the structure of 2,4,6-triphenoxy-1,3,5-triazine, very weak π···π contacts are reported, with a separation of 3.301 Å (Thalladi et al., 1998). The last kind of intermolecular interactions observed in (I) are C—H···π contacts between symmetry-related molecules (Malone et al., 1997), e.g. C20—H20A with a Br1-containing six-membered ring (symmetry code for the six-membered ring: 2 − x, −1/2 + y, 1/2 − z) with a C—H···π separation of 2.93 Å. The weakness of the π···π and C—H···π interactions observed in (I) could explain why finding a suitable single-crystal for the present study was difficult (see Experimental).

In conclusion, we established that, for the 2,4-substituted thiazole under consideration, a flat rotamer is stabilized in the solid state and remains unperturbed by weak intermolecular interactions. In line with our previous report (Bernès et al., 2002), the substituent on the aryl moiety has no significant participation in the definition of the stabilized rotamer.

S2. Experimental

The title compound was prepared according to the method described by Sánchez-Viesca & Berros (1999) and Katritzky & Rees (1984).

S3. Refinement

Compound (I) crystallizes as thin plates, with a tendency to systematically twin, making it difficult to select a suitable single-crystal and to obtain high-quality intensity data [<I/σ(I)> = 8.48 for 2θ_max = 50°]. Significant intensity decay was observed during data collection (ca 60 h). The completeness of the data was reduced to 95% because (i) 68 reflections were rejected when processing the raw data because they presented a large deviation from the expected Bragg maximum (default rejection criterion in XSCANS; Siemens,1996); (ii) in agreement with the habit of the crystal, an absorption correction was carried out using a thin-plate model, with a minimum glancing angle of 3°; (iii) reflection 011 was omitted as it was truncated by the beam stop. H-atoms were placed in idealized positions and refined as riding atoms, with fixed isotropic displacement parameters and constrained distances (C—H_aromatic = 0.93 Å and C—H_methyl = 0.96 Å).

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 1995); program(s) used to refine structure: SHELX97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus; software used to prepare material for publication: SHELX97 (Sheldrick, 1997).

Figures

	Fig. 1. A view of the asymmetric unit of (I), with displacement ellipsoids drawn at the 30% probability level.
	Fig. 2. The packing structure of (I). One complete cell (eight molecules) is displayed. For the asymmetric unit, π···π contacts between the rings are represented by dotted lines.

2-methyl-4(4-bromophenyl)-thiazole

Crystal data

C10H8BrNS	F(000) = 1008
Mr = 254.14	Dx = 1.693 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 58 reflections
a = 5.7339 (7) Å	θ = 4.8–11.6°
b = 14.8229 (15) Å	µ = 4.28 mm^−1
c = 23.469 (2) Å	T = 296 K
V = 1994.7 (4) Å^3	Plate, colourless
Z = 8	0.40 × 0.32 × 0.04 mm

Data collection

Siemens P4 diffractometer	1501 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.045
Graphite monochromator	θmax = 25.0°, θmin = 2.2°
ω scan	h = −6→4
Absorption correction: ψ scans XSCANS (Siemens, 1996)	k = −17→1
Tmin = 0.297, Tmax = 0.841	l = −27→1
3380 measured reflections	2 standard reflections every 48 reflections
2970 independent reflections	intensity decay: 8.9%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.065	H-atom parameters constrained
wR(F^2) = 0.166	w = 1/[σ^2(Fo^2) + (0.0629P)^2 + 8.6752P] where P = (Fo^2 + 2Fc^2)/3
S = 0.93	(Δ/σ)max < 0.001
2970 reflections	Δρmax = 0.35 e Å^−3
235 parameters	Δρmin = −0.48 e Å^−3
0 restraints	Absolute structure: Flack (1983); 1026 Friedel pairs measured
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.05 (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
Br1	0.5892 (3)	0.25452 (11)	0.94682 (6)	0.0763 (5)
S1	0.0034 (6)	0.2055 (3)	0.60919 (19)	0.0698 (12)
N1	0.3650 (18)	0.2679 (7)	0.6580 (4)	0.051 (3)
C1	0.381 (3)	0.2856 (10)	0.5528 (5)	0.083 (5)
H1B	0.5304	0.3125	0.5602	0.124*
H1C	0.2816	0.3290	0.5346	0.124*
H1D	0.4005	0.2342	0.5284	0.124*
C2	0.273 (2)	0.2563 (9)	0.6080 (6)	0.052 (3)
C3	0.020 (2)	0.1980 (8)	0.6809 (6)	0.056 (4)
H3A	−0.0954	0.1726	0.7038	0.067*
C4	0.223 (2)	0.2342 (8)	0.7013 (6)	0.042 (3)
C5	0.303 (2)	0.2394 (8)	0.7595 (5)	0.042 (3)
C6	0.514 (2)	0.2818 (8)	0.7722 (5)	0.049 (4)
H6A	0.6027	0.3061	0.7428	0.059*
C7	0.595 (3)	0.2883 (7)	0.8276 (5)	0.047 (3)
H7A	0.7342	0.3185	0.8349	0.056*
C8	0.472 (2)	0.2506 (8)	0.8720 (5)	0.050 (3)
C9	0.264 (3)	0.2076 (8)	0.8600 (6)	0.059 (4)
H9A	0.1781	0.1821	0.8895	0.071*
C10	0.183 (2)	0.2020 (8)	0.8054 (6)	0.054 (4)
H10A	0.0426	0.1723	0.7986	0.065*
Br2	−0.1102 (3)	0.47896 (12)	0.54082 (6)	0.0863 (6)
S2	0.4871 (6)	0.5208 (3)	0.87758 (17)	0.0659 (11)
N2	0.118 (2)	0.4618 (6)	0.8289 (4)	0.051 (3)
C11	0.106 (3)	0.4427 (9)	0.9337 (6)	0.074 (4)
H11A	−0.0439	0.4162	0.9265	0.111*
H11B	0.0875	0.4946	0.9577	0.111*
H11C	0.2045	0.3994	0.9523	0.111*
C12	0.214 (2)	0.4705 (8)	0.8786 (6)	0.054 (4)
C13	0.471 (2)	0.5269 (9)	0.8046 (6)	0.058 (4)
H13A	0.5854	0.5507	0.7810	0.069*
C14	0.268 (2)	0.4921 (8)	0.7867 (5)	0.040 (3)
C15	0.185 (2)	0.4868 (8)	0.7274 (5)	0.040 (3)
C16	−0.025 (2)	0.4443 (8)	0.7149 (6)	0.047 (3)
H16A	−0.1117	0.4191	0.7444	0.056*
C17	−0.111 (2)	0.4383 (8)	0.6593 (6)	0.055 (3)
H17A	−0.2464	0.4064	0.6514	0.066*
C18	0.010 (3)	0.4807 (9)	0.6169 (6)	0.059 (4)
C19	0.217 (3)	0.5232 (9)	0.6267 (7)	0.068 (4)
H19A	0.3004	0.5487	0.5968	0.082*
C20	0.301 (2)	0.5278 (8)	0.6826 (6)	0.058 (4)
H20A	0.4386	0.5592	0.6899	0.070*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0905 (12)	0.0872 (11)	0.0513 (8)	0.0002 (11)	−0.0003 (9)	0.0034 (9)
S1	0.054 (2)	0.075 (3)	0.080 (3)	−0.0107 (19)	−0.021 (2)	−0.001 (2)
N1	0.030 (6)	0.065 (7)	0.057 (7)	0.003 (6)	0.002 (6)	−0.012 (6)
C1	0.081 (11)	0.126 (13)	0.042 (8)	−0.001 (11)	−0.013 (10)	−0.007 (8)
C2	0.047 (9)	0.057 (8)	0.053 (8)	0.002 (7)	−0.012 (7)	−0.006 (9)
C3	0.044 (9)	0.049 (8)	0.075 (11)	0.006 (7)	−0.003 (8)	−0.003 (7)
C4	0.025 (7)	0.035 (8)	0.065 (9)	0.006 (6)	0.001 (8)	−0.010 (7)
C5	0.033 (8)	0.042 (8)	0.050 (8)	0.004 (6)	0.000 (7)	−0.007 (7)
C6	0.052 (9)	0.054 (9)	0.041 (8)	0.008 (7)	0.003 (7)	0.004 (6)
C7	0.041 (8)	0.056 (8)	0.042 (7)	−0.011 (7)	−0.005 (7)	0.002 (6)
C8	0.049 (9)	0.047 (8)	0.054 (8)	−0.004 (7)	0.011 (7)	−0.012 (7)
C9	0.066 (11)	0.060 (9)	0.052 (9)	0.007 (8)	0.023 (8)	0.004 (7)
C10	0.039 (9)	0.060 (9)	0.064 (10)	−0.006 (7)	0.014 (8)	−0.002 (8)
Br2	0.0897 (13)	0.1106 (13)	0.0587 (9)	−0.0073 (12)	−0.0037 (10)	0.0130 (9)
S2	0.052 (2)	0.071 (3)	0.075 (3)	−0.010 (2)	−0.010 (2)	−0.006 (2)
N2	0.044 (7)	0.052 (7)	0.056 (7)	0.003 (6)	−0.007 (7)	−0.005 (5)
C11	0.065 (10)	0.087 (10)	0.069 (10)	0.024 (9)	0.007 (10)	0.010 (8)
C12	0.049 (9)	0.055 (9)	0.059 (9)	0.005 (7)	0.000 (8)	0.010 (8)
C13	0.024 (8)	0.058 (9)	0.092 (11)	−0.010 (7)	0.000 (7)	0.002 (8)
C14	0.033 (7)	0.039 (7)	0.048 (8)	0.008 (6)	0.014 (7)	0.014 (6)
C15	0.033 (8)	0.031 (7)	0.056 (8)	0.005 (6)	0.011 (7)	−0.001 (6)
C16	0.037 (8)	0.049 (8)	0.054 (9)	0.003 (6)	0.011 (7)	0.004 (6)
C17	0.041 (8)	0.054 (8)	0.071 (10)	−0.004 (7)	0.007 (9)	0.012 (7)
C18	0.071 (11)	0.055 (9)	0.053 (9)	0.001 (8)	−0.004 (8)	0.012 (8)
C19	0.079 (12)	0.056 (10)	0.068 (11)	−0.008 (9)	0.017 (9)	0.008 (8)
C20	0.050 (9)	0.047 (9)	0.077 (11)	−0.011 (7)	0.012 (8)	0.010 (8)

Geometric parameters (Å, º)

Br1—C8	1.880 (12)	Br2—C18	1.914 (14)
S1—C3	1.690 (14)	S2—C13	1.718 (15)
S1—C2	1.719 (13)	S2—C12	1.733 (13)
N1—C2	1.298 (14)	N2—C12	1.295 (15)
N1—C4	1.395 (15)	N2—C14	1.384 (14)
C1—C2	1.501 (18)	C11—C12	1.493 (17)
C1—H1B	0.9600	C11—H11A	0.9600
C1—H1C	0.9600	C11—H11B	0.9600
C1—H1D	0.9600	C11—H11C	0.9600
C3—C4	1.370 (16)	C13—C14	1.341 (16)
C3—H3A	0.9300	C13—H13A	0.9300
C4—C5	1.443 (16)	C14—C15	1.471 (16)
C5—C10	1.393 (16)	C15—C20	1.384 (16)
C5—C6	1.397 (16)	C15—C16	1.395 (16)
C6—C7	1.384 (15)	C16—C17	1.395 (17)
C6—H6A	0.9300	C16—H16A	0.9300
C7—C8	1.378 (16)	C17—C18	1.364 (17)
C7—H7A	0.9300	C17—H17A	0.9300
C8—C9	1.382 (17)	C18—C19	1.363 (18)
C9—C10	1.367 (17)	C19—C20	1.401 (18)
C9—H9A	0.9300	C19—H19A	0.9300
C10—H10A	0.9300	C20—H20A	0.9300
C3—S1—C2	89.7 (7)	C13—S2—C12	89.2 (6)
C2—N1—C4	111.9 (10)	C12—N2—C14	110.4 (11)
C2—C1—H1B	109.5	C12—C11—H11A	109.5
C2—C1—H1C	109.5	C12—C11—H11B	109.5
H1B—C1—H1C	109.5	H11A—C11—H11B	109.5
C2—C1—H1D	109.5	C12—C11—H11C	109.5
H1B—C1—H1D	109.5	H11A—C11—H11C	109.5
H1C—C1—H1D	109.5	H11B—C11—H11C	109.5
N1—C2—C1	125.0 (12)	N2—C12—C11	125.1 (12)
N1—C2—S1	114.2 (10)	N2—C12—S2	114.5 (10)
C1—C2—S1	120.8 (10)	C11—C12—S2	120.4 (11)
C4—C3—S1	111.7 (11)	C14—C13—S2	109.8 (11)
C4—C3—H3A	124.2	C14—C13—H13A	125.1
S1—C3—H3A	124.2	S2—C13—H13A	125.1
C3—C4—N1	112.5 (11)	C13—C14—N2	116.0 (12)
C3—C4—C5	128.4 (12)	C13—C14—C15	126.5 (12)
N1—C4—C5	119.1 (11)	N2—C14—C15	117.5 (11)
C10—C5—C6	116.3 (12)	C20—C15—C16	117.0 (12)
C10—C5—C4	123.6 (12)	C20—C15—C14	122.8 (12)
C6—C5—C4	120.1 (12)	C16—C15—C14	120.1 (11)
C7—C6—C5	121.5 (12)	C15—C16—C17	122.0 (12)
C7—C6—H6A	119.2	C15—C16—H16A	119.0
C5—C6—H6A	119.2	C17—C16—H16A	119.0
C8—C7—C6	120.7 (13)	C18—C17—C16	118.4 (12)
C8—C7—H7A	119.6	C18—C17—H17A	120.8
C6—C7—H7A	119.6	C16—C17—H17A	120.8
C7—C8—C9	118.4 (12)	C19—C18—C17	122.0 (13)
C7—C8—Br1	120.7 (10)	C19—C18—Br2	118.5 (11)
C9—C8—Br1	120.9 (10)	C17—C18—Br2	119.5 (11)
C10—C9—C8	120.9 (13)	C18—C19—C20	118.8 (13)
C10—C9—H9A	119.6	C18—C19—H19A	120.6
C8—C9—H9A	119.6	C20—C19—H19A	120.6
C9—C10—C5	122.2 (13)	C15—C20—C19	121.6 (13)
C9—C10—H10A	118.9	C15—C20—H20A	119.2
C5—C10—H10A	118.9	C19—C20—H20A	119.2
C4—N1—C2—C1	179.5 (13)	C14—N2—C12—C11	−178.4 (12)
C4—N1—C2—S1	1.3 (14)	C14—N2—C12—S2	2.8 (14)
C3—S1—C2—N1	−1.1 (10)	C13—S2—C12—N2	−1.8 (11)
C3—S1—C2—C1	−179.4 (12)	C13—S2—C12—C11	179.4 (11)
C2—S1—C3—C4	0.5 (10)	C12—S2—C13—C14	0.2 (10)
S1—C3—C4—N1	0.0 (13)	S2—C13—C14—N2	1.4 (14)
S1—C3—C4—C5	−178.9 (10)	S2—C13—C14—C15	178.4 (10)
C2—N1—C4—C3	−0.8 (15)	C12—N2—C14—C13	−2.7 (16)
C2—N1—C4—C5	178.2 (11)	C12—N2—C14—C15	179.9 (11)
C3—C4—C5—C10	4 (2)	C13—C14—C15—C20	−7.7 (19)
N1—C4—C5—C10	−175.2 (11)	N2—C14—C15—C20	169.3 (11)
C3—C4—C5—C6	−178.0 (12)	C13—C14—C15—C16	176.6 (12)
N1—C4—C5—C6	3.1 (17)	N2—C14—C15—C16	−6.4 (16)
C10—C5—C6—C7	−1.9 (17)	C20—C15—C16—C17	3.6 (17)
C4—C5—C6—C7	179.7 (11)	C14—C15—C16—C17	179.6 (11)
C5—C6—C7—C8	2.0 (18)	C15—C16—C17—C18	−4.2 (18)
C6—C7—C8—C9	−1.1 (18)	C16—C17—C18—C19	4 (2)
C6—C7—C8—Br1	176.9 (9)	C16—C17—C18—Br2	−176.9 (9)
C7—C8—C9—C10	0.4 (18)	C17—C18—C19—C20	−4 (2)
Br1—C8—C9—C10	−177.7 (10)	Br2—C18—C19—C20	177.5 (10)
C8—C9—C10—C5	0 (2)	C16—C15—C20—C19	−3.0 (18)
C6—C5—C10—C9	1.1 (19)	C14—C15—C20—C19	−178.8 (12)
C4—C5—C10—C9	179.5 (12)	C18—C19—C20—C15	3 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C6—H6A···N1	0.93	2.48	2.822 (16)	102
C16—H16A···N2	0.93	2.46	2.813 (17)	102