2-(1,3-Benzoxazol-2-ylsulfan­yl)-1-phenyl­ethanone

Loghmani-Khouzani, H.; Hajiheidari, D.; Robinson, W.T.; Abdul Rahman, N.; Kia, R.

doi:10.1107/S1600536809033960

organic compounds

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ISSN: 2056-9890

Volume 65| Part 9| September 2009| Page o2287

doi:10.1107/S1600536809033960

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2-(1,3-Benzoxazol-2-ylsulfanyl)-1-phenylethanone

Hossein Loghmani-Khouzani,^a Dariush Hajiheidari,^a Ward T. Robinson,^b Noorsaadah Abdul Rahman ^b and Reza Kia ^c ^*‡

^aChemistry Department, University of Isfahan, Isfahan 81746-73441, Iran, ^bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia, and ^cDepartment of Chemistry, Science and Research Campus, Islamic Azad University, Poonak, Tehran, Iran
^*Correspondence e-mail: loghmani_h@yahoo.com

(Received 10 August 2009; accepted 25 August 2009; online 29 August 2009)

In the title compound, C₁₅H₁₁NO₂S, a new thio-benzoxazole derivative, the dihedral angle between the benzoxazole ring and the phenyl ring is 9.91 (9)°. An interesting feature of the crystal structure is the short C⋯S [3.4858 (17) Å] contact, which is shorter than the sum of the van der Waals radii of these atoms. In the crystal structure, molecules are linked together by zigzag intermolecular C—H⋯N interactions into a column along the a axis. The crystal structure is further stabilized by intermolecular π–π interactions [centroid–centroid = 3.8048 (10) Å].

Related literature

For applications of 2-(benzo[d]oxazol-2-ylthio)-1-phenylethanone and β-keto-sulfones in organic synthesis, see: Marco et al. (1995 ); Fuju et al. (1988 ); Ni et al. (2006 ). For uses of haloalkyl sulfones, see: Grossert et al. (1984 ); Oishi et al. (1988 ); Antane et al. (2004 ). For their biological activity, see: Padmavathi et al. (2008 ). For bond-length data, see: Allen et al. (1987 ). For hydrogen-bond motifs, see: Bernstein et al. (1995 ).

Experimental

Crystal data

C₁₅H₁₁NO₂S
M_r = 269.31
Orthorhombic, P 2₁ 2₁ 2₁
a = 4.8580 (2) Å
b = 14.0780 (5) Å
c = 18.6840 (7) Å
V = 1277.82 (8) Å³
Z = 4
Mo Kα radiation
μ = 0.25 mm⁻¹
T = 296 K
0.50 × 0.10 × 0.10 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ) T_min = 0.886, T_max = 0.976
13902 measured reflections
3659 independent reflections
3175 reflections with I > 2σ(I)
R_int = 0.037

Refinement

R[F² > 2σ(F²)] = 0.040
wR(F²) = 0.093
S = 1.04
3659 reflections
172 parameters
H-atom parameters constrained
Δρ_max = 0.35 e Å⁻³
Δρ_min = −0.19 e Å⁻³
Absolute structure: Flack (1983 ), 1514 Friedel pairs
Flack parameter: 0.07 (7)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5A⋯N1ⁱ	0.93	2.56	3.395 (2)	149
Symmetry code: (i) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ .

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SIR2004 (Burla et al., 2004 ); program(s) used to refine structure: SHELXTL (Sheldrick, 2008 ); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809033960/at2859sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809033960/at2859Isup2.hkl

checkCIF report

Comment top

2-(Benzo[d]oxazol-2-ylthio)-1-phenylethanone is of great importance in organic synthesis and β-Keto-sulfones are a very important group of intermediates as they are precursors for Michael and Knoevenagel reactions and are used in the preparation of acetylenes, allenes, chalcones, vinyl sulfones, polyfunctionalized 4H-pyrans and ketones (Marco et al., 1995; Fuju et al., 1988; Ni et al., 2006). In addition, β-keto-sulfones can be converted into optically active β-hydroxy-sulfones, halomethyl sulfones and dihalomethyl sulfones. Halomethyl sulfones and dihalomethyl sulfones are very good α-carbanion stabilizing substituents and precursors for the preparation of alkenes, aziridines, epoxides, and β-hydroxy-sulfones. Haloalkyl sulfones are useful in preventing aquatic organisms from attaching to fishing nets and ship hulls (Grossert et al., 1984; Oishi et al., 1988; Antane et al., 2004). They also possess other biological properties such as herbicidal, bactericidal antifungal and insecticidal. Recently sulfone-linked heterocycles were prepared and have been showed antimicrobial activity (Padmavathi et al., 2008). We prepared this compound as a precursor for synthesis of gem-difluoromethylene- containing heterocycle.

In the molecule of the title compound, (Fig. 1), a new thio-benzoxazole derivative, the dihedral angle between the benzoxazole ring and the phenyl ring is 9.91 (9)°. The interesting feature of the crystal structure is the short C6···S1ⁱ [3.4858 (17) Å; (i) -1 + x, y, z] contact which is shorter than the sum of the van der Waals radii of these atoms. In the crystal structure, the molecules are linked together by a zig-zag intermolecular C—H···N interactions (Table 1) which packed into a column along the a axis (Fig. 2). The crystal structure is further stabilized by the intramolecular π–π interactions [Cg1···Cg2ⁱ = 3.8048 (10) Å].

Related literature top

For applications of 2-(benzo[d]oxazol-2-ylthio)-1-phenylethanone and β-keto-sulfones in organic synthesis, see: Marco et al. (1995); Fuju et al. (1988); Ni et al. (2006). For uses of haloalkyl sulfones, see: Grossert et al. (1984); Oishi et al. (1988); Antane et al. (2004). For their biological activity, see: Padmavathi et al. (2008). For bond-length data, see: Allen et al. (1987). For hydrogen-bond motifs, see: Bernstein et al. (1995).

Experimental top

Sodium carbonate (4.5 mmol) was added to a stirred solution of 2-mercaptobenzoxazole (3 mmol) in ethanol (15 mL) and water (15 mL) and stirred in room temperature for 30 min. α-Bromoacetophenone (3 mmol) was added to the reaction mixture and stirring was continued for 1h. The reaction was monitored by TLC and after 60 min. showed the complete disappearance of starting material. The reaction mixture was poured into 100 mL of 1M HCl containing 50 g of crushed ice. The product was filtered under vacuum and filtrate washed with 10 mL ice-cold ethanol and 10 mL water. Recrystalization from petrol ether and filtration gave the title compound. m.p.: 397-398 K; ¹H NMR (400 MHz; CDCl₃): δ 7.86-7.21 (m, 9H), 4.58 (s, 2H). ¹³C NMR (126 MHz; CDCl₃): δ 194.1 (C═O), 164.3, 148.9, 140.8, 136.1, 132.6, 128.0, 127.8, 124.1, 122.9, 118.3, 109.6, 37.3. IR (KBr, cm^-1 ): 3027, 2581, 1671 (C═O), 1593, 1492, 1447, 1382, 1326, 1291, 1230, 1182, 1025, 993, 738. Analysis calculated for C₁₅H₁₁NO₂S: C 66.89, H 4.12, N 5.20%. Found: C 66.96, H 4.06, N 5.17%.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SIR2004 (Burla et al., 2004); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top

	Fig. 1. The molecular structure of the title compound, showing 40% probability displacement ellipsoids and the atomic numbering.
	Fig. 2. The crystal packing of the title compound, viewed down the c-axis, showing linking of the molecules along the a-axis through intermolecular C—H···N interactions. Intermolecular interactions are drawn as dashed lines.

2-(1,3-Benzoxazol-2-ylsulfanyl)-1-phenylethanone top

Crystal data top

C₁₅H₁₁NO₂S	D_x = 1.400 Mg m⁻³
M_r = 269.31	Melting point: 398 K
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 4173 reflections
a = 4.8580 (2) Å	θ = 2.6–28.2°
b = 14.0780 (5) Å	µ = 0.25 mm⁻¹
c = 18.6840 (7) Å	T = 296 K
V = 1277.82 (8) Å³	Needle, colourless
Z = 4	0.50 × 0.10 × 0.10 mm
F(000) = 560

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3659 independent reflections
Radiation source: fine-focus sealed tube	3175 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.037
ϕ and ω scans	θ_max = 30.0°, θ_min = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −6→6
T_min = 0.886, T_max = 0.976	k = −19→19
13902 measured reflections	l = −26→26

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.040	H-atom parameters constrained
wR(F²) = 0.093	w = 1/[σ²(F_o²) + (0.0487P)² + 0.1389P] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max = 0.001
3659 reflections	Δρ_max = 0.35 e Å⁻³
172 parameters	Δρ_min = −0.19 e Å⁻³
0 restraints	Absolute structure: Flack (1983), 1514 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.07 (7)

Crystal data top

C₁₅H₁₁NO₂S	V = 1277.82 (8) Å³
M_r = 269.31	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 4.8580 (2) Å	µ = 0.25 mm⁻¹
b = 14.0780 (5) Å	T = 296 K
c = 18.6840 (7) Å	0.50 × 0.10 × 0.10 mm

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3659 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2005)	3175 reflections with I > 2σ(I)
T_min = 0.886, T_max = 0.976	R_int = 0.037
13902 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.040	H-atom parameters constrained
wR(F²) = 0.093	Δρ_max = 0.35 e Å⁻³
S = 1.04	Δρ_min = −0.19 e Å⁻³
3659 reflections	Absolute structure: Flack (1983), 1514 Friedel pairs
172 parameters	Absolute structure parameter: 0.07 (7)
0 restraints

Special details top

Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.

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.

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 > 2sigma(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 (Å²) top

	x	y	z	U_iso*/U_eq
S1	0.01065 (10)	0.44145 (3)	0.66514 (2)	0.02920 (11)
O1	0.3102 (3)	0.29909 (9)	0.71157 (6)	0.0295 (3)
N1	0.4022 (3)	0.33643 (10)	0.59627 (7)	0.0250 (3)
C1	0.5079 (4)	0.23556 (11)	0.68726 (8)	0.0262 (3)
C2	0.6325 (4)	0.16254 (14)	0.72375 (10)	0.0346 (4)
H2A	0.5895	0.1480	0.7710	0.042*
C3	0.8271 (4)	0.11206 (14)	0.68500 (10)	0.0366 (4)
H3A	0.9193	0.0621	0.7071	0.044*
C4	0.8889 (4)	0.13370 (13)	0.61400 (10)	0.0341 (4)
H4A	1.0209	0.0980	0.5900	0.041*
C5	0.7576 (4)	0.20749 (13)	0.57839 (9)	0.0292 (4)
H5A	0.7982	0.2218	0.5310	0.035*
C6	0.5639 (3)	0.25876 (12)	0.61651 (8)	0.0244 (3)
C7	0.2612 (3)	0.35517 (12)	0.65300 (8)	0.0251 (3)
C8	−0.0098 (4)	0.47588 (12)	0.57236 (8)	0.0289 (3)
H8A	0.1664	0.5008	0.5567	0.035*
H8B	−0.0536	0.4209	0.5432	0.035*
C9	−0.2291 (3)	0.55059 (12)	0.56314 (9)	0.0266 (3)
C10	−0.2762 (4)	0.58747 (12)	0.48943 (9)	0.0264 (3)
C11	−0.4792 (4)	0.65637 (12)	0.47888 (10)	0.0337 (4)
H11A	−0.5823	0.6780	0.5175	0.040*
C12	−0.5275 (5)	0.69250 (13)	0.41129 (11)	0.0396 (5)
H12A	−0.6630	0.7383	0.4045	0.048*
C13	−0.3744 (4)	0.66049 (14)	0.35363 (11)	0.0397 (5)
H13A	−0.4070	0.6850	0.3082	0.048*
C14	−0.1733 (4)	0.59220 (15)	0.36330 (10)	0.0375 (4)
H14A	−0.0713	0.5707	0.3244	0.045*
C15	−0.1237 (4)	0.55572 (14)	0.43100 (10)	0.0312 (4)
H15A	0.0120	0.5099	0.4374	0.037*
O2	−0.3588 (3)	0.57915 (10)	0.61422 (7)	0.0390 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0334 (2)	0.0325 (2)	0.02181 (18)	0.0053 (2)	0.00128 (18)	−0.00418 (15)
O1	0.0362 (7)	0.0345 (6)	0.0179 (5)	0.0024 (5)	0.0020 (5)	0.0012 (5)
N1	0.0279 (7)	0.0290 (7)	0.0180 (6)	0.0018 (6)	−0.0013 (5)	−0.0011 (5)
C1	0.0289 (8)	0.0297 (7)	0.0200 (6)	−0.0035 (8)	0.0007 (7)	0.0003 (5)
C2	0.0439 (11)	0.0348 (9)	0.0253 (8)	−0.0017 (8)	−0.0021 (8)	0.0072 (7)
C3	0.0413 (11)	0.0305 (9)	0.0381 (10)	0.0046 (8)	−0.0074 (8)	0.0052 (8)
C4	0.0343 (9)	0.0313 (9)	0.0367 (10)	0.0049 (8)	0.0024 (8)	−0.0049 (8)
C5	0.0322 (9)	0.0335 (9)	0.0219 (8)	−0.0007 (8)	0.0020 (7)	−0.0034 (7)
C6	0.0283 (9)	0.0263 (8)	0.0185 (7)	−0.0028 (6)	−0.0038 (6)	−0.0009 (6)
C7	0.0276 (8)	0.0279 (8)	0.0198 (7)	−0.0024 (7)	−0.0030 (6)	−0.0012 (6)
C8	0.0290 (8)	0.0332 (8)	0.0243 (7)	0.0037 (8)	0.0008 (8)	0.0017 (6)
C9	0.0253 (8)	0.0227 (7)	0.0316 (8)	−0.0029 (7)	0.0008 (6)	−0.0021 (7)
C10	0.0251 (8)	0.0221 (8)	0.0322 (9)	−0.0040 (6)	−0.0028 (7)	0.0011 (6)
C11	0.0319 (9)	0.0282 (8)	0.0409 (9)	0.0010 (8)	−0.0054 (8)	−0.0018 (7)
C12	0.0377 (11)	0.0300 (9)	0.0512 (11)	0.0011 (9)	−0.0159 (10)	0.0046 (8)
C13	0.0438 (11)	0.0370 (10)	0.0383 (10)	−0.0096 (9)	−0.0134 (8)	0.0083 (8)
C14	0.0359 (10)	0.0449 (11)	0.0317 (9)	−0.0048 (9)	−0.0024 (8)	0.0045 (8)
C15	0.0287 (8)	0.0335 (9)	0.0313 (8)	0.0005 (8)	−0.0023 (7)	0.0035 (8)
O2	0.0440 (8)	0.0376 (7)	0.0355 (7)	0.0095 (6)	0.0076 (6)	−0.0020 (6)

Geometric parameters (Å, º) top

S1—C7	1.7343 (17)	C8—C9	1.507 (2)
S1—C8	1.8028 (16)	C8—H8A	0.9700
O1—C7	1.3704 (19)	C8—H8B	0.9700
O1—C1	1.389 (2)	C9—O2	1.212 (2)
N1—C7	1.290 (2)	C9—C10	1.489 (2)
N1—C6	1.398 (2)	C10—C15	1.393 (3)
C1—C2	1.374 (2)	C10—C11	1.397 (3)
C1—C6	1.389 (2)	C11—C12	1.381 (2)
C2—C3	1.387 (3)	C11—H11A	0.9300
C2—H2A	0.9300	C12—C13	1.385 (3)
C3—C4	1.394 (3)	C12—H12A	0.9300
C3—H3A	0.9300	C13—C14	1.383 (3)
C4—C5	1.389 (3)	C13—H13A	0.9300
C4—H4A	0.9300	C14—C15	1.386 (3)
C5—C6	1.383 (2)	C14—H14A	0.9300
C5—H5A	0.9300	C15—H15A	0.9300

C7—S1—C8	95.81 (8)	S1—C8—H8A	109.7
C7—O1—C1	103.29 (12)	C9—C8—H8B	109.7
C7—N1—C6	103.67 (14)	S1—C8—H8B	109.7
C2—C1—O1	128.62 (15)	H8A—C8—H8B	108.2
C2—C1—C6	124.18 (18)	O2—C9—C10	122.17 (16)
O1—C1—C6	107.20 (14)	O2—C9—C8	120.60 (16)
C1—C2—C3	115.13 (17)	C10—C9—C8	117.23 (14)
C1—C2—H2A	122.4	C15—C10—C11	119.18 (16)
C3—C2—H2A	122.4	C15—C10—C9	122.08 (16)
C2—C3—C4	122.13 (18)	C11—C10—C9	118.74 (16)
C2—C3—H3A	118.9	C12—C11—C10	120.30 (18)
C4—C3—H3A	118.9	C12—C11—H11A	119.8
C5—C4—C3	121.36 (18)	C10—C11—H11A	119.9
C5—C4—H4A	119.3	C11—C12—C13	120.01 (18)
C3—C4—H4A	119.3	C11—C12—H12A	120.0
C6—C5—C4	117.13 (16)	C13—C12—H12A	120.0
C6—C5—H5A	121.4	C14—C13—C12	120.29 (18)
C4—C5—H5A	121.4	C14—C13—H13A	119.9
C5—C6—C1	120.06 (16)	C12—C13—H13A	119.9
C5—C6—N1	130.61 (15)	C13—C14—C15	119.98 (19)
C1—C6—N1	109.33 (15)	C13—C14—H14A	120.0
N1—C7—O1	116.50 (15)	C15—C14—H14A	120.0
N1—C7—S1	128.59 (13)	C14—C15—C10	120.25 (17)
O1—C7—S1	114.90 (11)	C14—C15—H15A	119.9
C9—C8—S1	109.67 (12)	C10—C15—H15A	119.9
C9—C8—H8A	109.7

C7—O1—C1—C2	−179.71 (19)	C1—O1—C7—S1	178.11 (12)
C7—O1—C1—C6	0.52 (17)	C8—S1—C7—N1	8.41 (18)
O1—C1—C2—C3	−178.94 (17)	C8—S1—C7—O1	−170.44 (13)
C6—C1—C2—C3	0.8 (3)	C7—S1—C8—C9	177.42 (12)
C1—C2—C3—C4	−0.5 (3)	S1—C8—C9—O2	0.7 (2)
C2—C3—C4—C5	0.0 (3)	S1—C8—C9—C10	−179.75 (13)
C3—C4—C5—C6	0.3 (3)	O2—C9—C10—C15	178.88 (17)
C4—C5—C6—C1	0.0 (2)	C8—C9—C10—C15	−0.7 (2)
C4—C5—C6—N1	179.14 (16)	O2—C9—C10—C11	−0.8 (3)
C2—C1—C6—C5	−0.5 (3)	C8—C9—C10—C11	179.60 (16)
O1—C1—C6—C5	179.26 (15)	C15—C10—C11—C12	0.0 (3)
C2—C1—C6—N1	−179.86 (17)	C9—C10—C11—C12	179.69 (17)
O1—C1—C6—N1	−0.08 (18)	C10—C11—C12—C13	0.0 (3)
C7—N1—C6—C5	−179.68 (17)	C11—C12—C13—C14	0.2 (3)
C7—N1—C6—C1	−0.43 (18)	C12—C13—C14—C15	−0.2 (3)
C6—N1—C7—O1	0.83 (19)	C13—C14—C15—C10	0.1 (3)
C6—N1—C7—S1	−178.00 (13)	C11—C10—C15—C14	0.0 (3)
C1—O1—C7—N1	−0.89 (19)	C9—C10—C15—C14	−179.73 (17)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5A···N1ⁱ	0.93	2.56	3.395 (2)	149

Symmetry code: (i) x+1/2, −y+1/2, −z+1.

Experimental details

Crystal data
Chemical formula	C₁₅H₁₁NO₂S
M_r	269.31
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	296
a, b, c (Å)	4.8580 (2), 14.0780 (5), 18.6840 (7)
V (Å³)	1277.82 (8)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.25
Crystal size (mm)	0.50 × 0.10 × 0.10

Data collection
Diffractometer	Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2005)
T_min, T_max	0.886, 0.976
No. of measured, independent and observed [I > 2σ(I)] reflections	13902, 3659, 3175
R_int	0.037
(sin θ/λ)_max (Å⁻¹)	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.040, 0.093, 1.04
No. of reflections	3659
No. of parameters	172
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.35, −0.19
Absolute structure	Flack (1983), 1514 Friedel pairs
Absolute structure parameter	0.07 (7)

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SIR2004 (Burla et al., 2004), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5A···N1ⁱ	0.93	2.56	3.395 (2)	148.8

Symmetry code: (i) x+1/2, −y+1/2, −z+1.

Footnotes

‡Additional corresponding author, e-mail: zsrkk@yahoo.com. Thomson Reuters ResearcherID: A-5471-2009.

Acknowledgements

We thank the University of Isfahan and the University of Malaya for supporting this work.

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