2-(4-Chloro­phen­yl)-2-oxoethyl 3-(trifluoro­meth­yl)benzoate

Fun, H.-K.; Loh, W.-S.; Garudachari, B.; Isloor, A.M.; Satyanarayan, M.N.

doi:10.1107/S1600536811020629

organic compounds

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ISSN: 2056-9890

Volume 67| Part 7| July 2011| Page o1597

doi:10.1107/S1600536811020629

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2-(4-Chlorophenyl)-2-oxoethyl 3-(trifluoromethyl)benzoate

Hoong-Kun Fun,^a ^*‡ Wan-Sin Loh,^a § B. Garudachari,^b Arun M. Isloor ^b and M. N. Satyanarayan ^c

^aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, ^bOrganic Chemistry Division, Department of Chemistry, National Institute of Technology – Karnataka, Surathkal, Mangalore 575 025, India, and ^cDepartment of Physics, National Institute of Technology – Karnataka, Surathkal, Mangalore 575 025, India
^*Correspondence e-mail: hkfun@usm.my

(Received 24 May 2011; accepted 30 May 2011; online 11 June 2011)

In the title compound, C₁₆H₁₀ClF₃O₃, the two benzene rings are slightly twisted from each other, with a dihedral angle of 15.50 (8)° between the planes. In the crystal, intermolecular C—H⋯O hydrogen bonds link the molecules into a layer parallel to the bc plane.

Related literature

For the background and applications of phenacyl benzoates, see: Sheehan & Umezaw (1973 ); Ruzicka et al. (2002 ); Litera et al. (2006 ); Rather & Reid (1919 ); Huang et al. (1996 ); Gandhi et al. (1995 ). For bond-length data, see: Allen et al. (1987 ). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 ).

Experimental

Crystal data

C₁₆H₁₀ClF₃O₃
M_r = 342.69
Monoclinic, P 2₁ /c
a = 14.3036 (7) Å
b = 12.1335 (6) Å
c = 8.5464 (4) Å
β = 101.444 (1)°
V = 1453.76 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.31 mm⁻¹
T = 100 K
0.28 × 0.16 × 0.11 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.919, T_max = 0.966
15629 measured reflections
3822 independent reflections
2963 reflections with I > 2σ(I)
R_int = 0.046

Refinement

R[F² > 2σ(F²)] = 0.048
wR(F²) = 0.121
S = 1.04
3822 reflections
208 parameters
H-atom parameters constrained
Δρ_max = 0.52 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1A⋯O1ⁱ	0.95	2.53	3.205 (2)	128
C4—H4A⋯O3ⁱⁱ	0.95	2.53	3.289 (2)	137
C8—H8A⋯O3ⁱⁱⁱ	0.99	2.48	3.474 (2)	177
Symmetry codes: (i) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (ii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) $[x, -y+{\script{3\over 2}}, z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; 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/S1600536811020629/is2720sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811020629/is2720Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811020629/is2720Isup3.cml

checkCIF report

Comment top

Phenacyl benzoates derivatives are very important in identification of organic acids (Rather & Reid, 1919), they undergo photolysis in neutral and mild conditions (Sheehan & Umezaw, 1973; Ruzicka et al., 2002; Litera et al., 2006). They find applications in the field of synthetic chemistry for the synthesis of oxazoles, imidazoles (Huang et al., 1996), benzoxazepine (Gandhi et al., 1995). We hereby report the crystal structure of 2-(4-chlorophenyl)-2-oxoethyl 3-(trifluoromethyl) benzoate of potential commercial importance.

In the title compound (Fig. 1), the chlorophenyl (C1–C6/CL1) group is slightly twisted away from the benzene ring (C10–C15) with a dihedral angle of 15.50 (8)°. Bond lengths (Allen et al., 1987) and angles are within the normal ranges.

In the crystal packing (Fig. 2), intermolecular C1—H1A···O1ⁱ, C4—H4A···O3ⁱⁱ and C8—H8A···O3ⁱⁱⁱ hydrogen bonds (Table 1) link the molecules into a layer parallel to the bc plane.

Related literature top

For the background and applications of phenacyl benzoates, see: Sheehan & Umezaw (1973); Ruzicka et al. (2002); Litera et al. (2006); Rather & Reid (1919); Huang et al. (1996); Gandhi et al. (1995). For bond-length data, see: Allen et al. (1987). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986).

Experimental top

A mixture of 3-(trifluoromethyl)benzoic acid (1.0 g, 0.0052 mol), potassium carbonate (0.80 g, 0.0057 mol) and 2-bromo-1-(4-chlorophenyl)ethanone (1.21 g, 0.0052 mol) in dimethylformamide (10 ml) was stirred at room temperature for 2 h. On cooling, colourless needle-shaped crystals, 2-(4-chlorophenyl)-2-oxoethyl 3-(trifluoromethyl)benzoate begin to separate. It was collected by filtration and recrystallized from ethanol. Yield: 1.60 g, 88.88%, m.p.: 387–388 K.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); 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 50% probability displacement ellipsoids and the atom-numbering scheme.
	Fig. 2. The crystal packing of the title compound, viewed along the b axis. H atoms not involved in the intermolecular interactions (dashed lines) have been omitted for clarity.

2-(4-Chlorophenyl)-2-oxoethyl 3-(trifluoromethyl)benzoate top

Crystal data top

C₁₆H₁₀ClF₃O₃	F(000) = 696
M_r = 342.69	D_x = 1.566 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3750 reflections
a = 14.3036 (7) Å	θ = 2.9–29.9°
b = 12.1335 (6) Å	µ = 0.31 mm⁻¹
c = 8.5464 (4) Å	T = 100 K
β = 101.444 (1)°	Block, colourless
V = 1453.76 (12) Å³	0.28 × 0.16 × 0.11 mm
Z = 4

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3822 independent reflections
Radiation source: fine-focus sealed tube	2963 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.046
ϕ and ω scans	θ_max = 29.0°, θ_min = 1.5°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −19→19
T_min = 0.919, T_max = 0.966	k = −10→16
15629 measured reflections	l = −11→11

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.048	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.121	H-atom parameters constrained
S = 1.04	w = 1/[σ²(F_o²) + (0.0486P)² + 1.0347P] where P = (F_o² + 2F_c²)/3
3822 reflections	(Δ/σ)_max = 0.001
208 parameters	Δρ_max = 0.52 e Å⁻³
0 restraints	Δρ_min = −0.33 e Å⁻³

Crystal data top

C₁₆H₁₀ClF₃O₃	V = 1453.76 (12) Å³
M_r = 342.69	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 14.3036 (7) Å	µ = 0.31 mm⁻¹
b = 12.1335 (6) Å	T = 100 K
c = 8.5464 (4) Å	0.28 × 0.16 × 0.11 mm
β = 101.444 (1)°

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3822 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	2963 reflections with I > 2σ(I)
T_min = 0.919, T_max = 0.966	R_int = 0.046
15629 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.048	0 restraints
wR(F²) = 0.121	H-atom parameters constrained
S = 1.04	Δρ_max = 0.52 e Å⁻³
3822 reflections	Δρ_min = −0.33 e Å⁻³
208 parameters

Special details top

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

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 (Å²) top

	x	y	z	U_iso*/U_eq
Cl1	0.22643 (4)	0.86068 (4)	1.07291 (6)	0.02896 (14)
F1	0.92991 (14)	0.87892 (13)	0.01853 (17)	0.0580 (5)
F2	1.04777 (11)	0.85923 (17)	0.2147 (2)	0.0727 (6)
F3	0.93614 (10)	0.73951 (11)	0.17107 (16)	0.0371 (3)
O1	0.53911 (10)	1.07226 (11)	0.66621 (15)	0.0222 (3)
O2	0.66428 (9)	0.93394 (11)	0.59360 (15)	0.0214 (3)
O3	0.69311 (10)	0.76708 (11)	0.49795 (17)	0.0260 (3)
C1	0.43295 (14)	0.83441 (15)	0.8232 (2)	0.0202 (4)
H1A	0.4678	0.7774	0.7845	0.024*
C2	0.36390 (14)	0.80774 (16)	0.9092 (2)	0.0225 (4)
H2A	0.3509	0.7329	0.9297	0.027*
C3	0.31378 (14)	0.89225 (16)	0.9650 (2)	0.0207 (4)
C4	0.33093 (13)	1.00257 (16)	0.9356 (2)	0.0202 (4)
H4A	0.2957	1.0593	0.9742	0.024*
C5	0.39992 (13)	1.02787 (15)	0.8495 (2)	0.0191 (4)
H5A	0.4122	1.1028	0.8285	0.023*
C6	0.45214 (13)	0.94487 (15)	0.7924 (2)	0.0171 (4)
C7	0.52797 (13)	0.97681 (15)	0.7041 (2)	0.0182 (4)
C8	0.59082 (14)	0.88503 (15)	0.6632 (2)	0.0199 (4)
H8A	0.6195	0.8437	0.7609	0.024*
H8B	0.5526	0.8332	0.5868	0.024*
C9	0.71079 (13)	0.86489 (15)	0.5125 (2)	0.0190 (4)
C10	0.78492 (13)	0.92229 (15)	0.4433 (2)	0.0185 (4)
C11	0.80562 (14)	1.03401 (16)	0.4691 (2)	0.0219 (4)
H11A	0.7732	1.0758	0.5358	0.026*
C12	0.87340 (15)	1.08395 (17)	0.3975 (3)	0.0276 (4)
H12A	0.8872	1.1601	0.4149	0.033*
C13	0.92112 (15)	1.02351 (17)	0.3007 (2)	0.0264 (4)
H13A	0.9673	1.0580	0.2511	0.032*
C14	0.90109 (14)	0.91177 (17)	0.2764 (2)	0.0228 (4)
C15	0.83340 (13)	0.86101 (16)	0.3467 (2)	0.0198 (4)
H15A	0.8200	0.7848	0.3292	0.024*
C16	0.95338 (16)	0.84786 (19)	0.1713 (3)	0.0314 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl1	0.0281 (3)	0.0281 (3)	0.0351 (3)	−0.0017 (2)	0.0170 (2)	0.0031 (2)
F1	0.1082 (15)	0.0398 (9)	0.0358 (8)	0.0034 (9)	0.0380 (9)	−0.0024 (6)
F2	0.0272 (8)	0.0992 (15)	0.0989 (14)	−0.0158 (8)	0.0301 (8)	−0.0676 (12)
F3	0.0439 (8)	0.0256 (7)	0.0466 (8)	0.0074 (6)	0.0204 (6)	−0.0064 (6)
O1	0.0289 (7)	0.0134 (6)	0.0255 (6)	−0.0011 (5)	0.0082 (6)	0.0029 (5)
O2	0.0242 (7)	0.0165 (6)	0.0263 (6)	−0.0022 (5)	0.0121 (5)	−0.0020 (5)
O3	0.0311 (8)	0.0137 (6)	0.0362 (8)	−0.0031 (6)	0.0140 (6)	−0.0030 (6)
C1	0.0241 (9)	0.0131 (9)	0.0243 (9)	0.0023 (7)	0.0070 (7)	0.0001 (7)
C2	0.0257 (10)	0.0162 (9)	0.0272 (9)	0.0001 (7)	0.0088 (8)	0.0023 (7)
C3	0.0212 (9)	0.0214 (9)	0.0210 (8)	−0.0017 (7)	0.0078 (7)	0.0011 (7)
C4	0.0214 (9)	0.0167 (9)	0.0219 (8)	0.0035 (7)	0.0030 (7)	−0.0010 (7)
C5	0.0224 (9)	0.0140 (8)	0.0199 (8)	0.0012 (7)	0.0020 (7)	0.0013 (7)
C6	0.0200 (9)	0.0140 (8)	0.0175 (7)	−0.0005 (7)	0.0039 (6)	0.0007 (7)
C7	0.0212 (9)	0.0153 (8)	0.0173 (8)	−0.0007 (7)	0.0021 (7)	0.0010 (7)
C8	0.0232 (9)	0.0152 (9)	0.0225 (8)	−0.0007 (7)	0.0074 (7)	0.0011 (7)
C9	0.0203 (9)	0.0170 (9)	0.0200 (8)	0.0011 (7)	0.0046 (7)	−0.0008 (7)
C10	0.0186 (9)	0.0156 (9)	0.0214 (8)	0.0003 (7)	0.0038 (7)	0.0018 (7)
C11	0.0227 (9)	0.0175 (9)	0.0268 (9)	0.0015 (7)	0.0078 (7)	−0.0019 (7)
C12	0.0265 (10)	0.0168 (10)	0.0413 (11)	−0.0027 (8)	0.0112 (9)	−0.0028 (8)
C13	0.0249 (10)	0.0237 (10)	0.0323 (10)	−0.0034 (8)	0.0100 (8)	0.0020 (8)
C14	0.0210 (9)	0.0238 (10)	0.0246 (9)	0.0010 (8)	0.0068 (7)	−0.0039 (8)
C15	0.0216 (9)	0.0161 (9)	0.0219 (8)	0.0000 (7)	0.0043 (7)	−0.0014 (7)
C16	0.0298 (11)	0.0325 (12)	0.0356 (11)	−0.0061 (9)	0.0155 (9)	−0.0119 (9)

Geometric parameters (Å, º) top

Cl1—C3	1.7364 (19)	C5—H5A	0.9500
F1—C16	1.336 (3)	C6—C7	1.490 (3)
F2—C16	1.335 (3)	C7—C8	1.515 (3)
F3—C16	1.338 (3)	C8—H8A	0.9900
O1—C7	1.222 (2)	C8—H8B	0.9900
O2—C9	1.344 (2)	C9—C10	1.486 (3)
O2—C8	1.435 (2)	C10—C15	1.394 (3)
O3—C9	1.215 (2)	C10—C11	1.396 (3)
C1—C2	1.381 (3)	C11—C12	1.385 (3)
C1—C6	1.403 (3)	C11—H11A	0.9500
C1—H1A	0.9500	C12—C13	1.383 (3)
C2—C3	1.389 (3)	C12—H12A	0.9500
C2—H2A	0.9500	C13—C14	1.393 (3)
C3—C4	1.393 (3)	C13—H13A	0.9500
C4—C5	1.378 (3)	C14—C15	1.381 (3)
C4—H4A	0.9500	C14—C16	1.495 (3)
C5—C6	1.398 (3)	C15—H15A	0.9500

C9—O2—C8	115.72 (14)	O3—C9—O2	123.20 (17)
C2—C1—C6	120.70 (17)	O3—C9—C10	124.57 (17)
C2—C1—H1A	119.6	O2—C9—C10	112.22 (16)
C6—C1—H1A	119.6	C15—C10—C11	119.79 (17)
C1—C2—C3	118.83 (18)	C15—C10—C9	117.65 (17)
C1—C2—H2A	120.6	C11—C10—C9	122.55 (17)
C3—C2—H2A	120.6	C12—C11—C10	120.03 (18)
C2—C3—C4	121.75 (18)	C12—C11—H11A	120.0
C2—C3—Cl1	119.64 (15)	C10—C11—H11A	120.0
C4—C3—Cl1	118.61 (15)	C13—C12—C11	120.28 (19)
C5—C4—C3	118.75 (17)	C13—C12—H12A	119.9
C5—C4—H4A	120.6	C11—C12—H12A	119.9
C3—C4—H4A	120.6	C12—C13—C14	119.61 (19)
C4—C5—C6	120.98 (17)	C12—C13—H13A	120.2
C4—C5—H5A	119.5	C14—C13—H13A	120.2
C6—C5—H5A	119.5	C15—C14—C13	120.71 (18)
C5—C6—C1	118.99 (17)	C15—C14—C16	120.48 (19)
C5—C6—C7	118.83 (16)	C13—C14—C16	118.80 (18)
C1—C6—C7	122.16 (16)	C14—C15—C10	119.58 (18)
O1—C7—C6	121.81 (17)	C14—C15—H15A	120.2
O1—C7—C8	121.41 (17)	C10—C15—H15A	120.2
C6—C7—C8	116.78 (15)	F2—C16—F1	106.7 (2)
O2—C8—C7	107.97 (14)	F2—C16—F3	106.1 (2)
O2—C8—H8A	110.1	F1—C16—F3	105.40 (17)
C7—C8—H8A	110.1	F2—C16—C14	112.24 (17)
O2—C8—H8B	110.1	F1—C16—C14	112.5 (2)
C7—C8—H8B	110.1	F3—C16—C14	113.35 (18)
H8A—C8—H8B	108.4

C6—C1—C2—C3	−0.1 (3)	O2—C9—C10—C15	−175.47 (15)
C1—C2—C3—C4	0.5 (3)	O3—C9—C10—C11	−177.10 (18)
C1—C2—C3—Cl1	179.84 (15)	O2—C9—C10—C11	3.2 (2)
C2—C3—C4—C5	−0.4 (3)	C15—C10—C11—C12	0.7 (3)
Cl1—C3—C4—C5	−179.73 (14)	C9—C10—C11—C12	−178.00 (18)
C3—C4—C5—C6	−0.1 (3)	C10—C11—C12—C13	−0.2 (3)
C4—C5—C6—C1	0.4 (3)	C11—C12—C13—C14	−0.4 (3)
C4—C5—C6—C7	−178.17 (16)	C12—C13—C14—C15	0.7 (3)
C2—C1—C6—C5	−0.3 (3)	C12—C13—C14—C16	179.9 (2)
C2—C1—C6—C7	178.24 (17)	C13—C14—C15—C10	−0.2 (3)
C5—C6—C7—O1	−7.6 (2)	C16—C14—C15—C10	−179.49 (17)
C1—C6—C7—O1	173.85 (17)	C11—C10—C15—C14	−0.4 (3)
C5—C6—C7—C8	172.43 (16)	C9—C10—C15—C14	178.31 (16)
C1—C6—C7—C8	−6.1 (2)	C15—C14—C16—F2	−128.0 (2)
C9—O2—C8—C7	−163.11 (14)	C13—C14—C16—F2	52.7 (3)
O1—C7—C8—O2	5.7 (2)	C15—C14—C16—F1	111.7 (2)
C6—C7—C8—O2	−174.34 (14)	C13—C14—C16—F1	−67.6 (2)
C8—O2—C9—O3	−0.2 (3)	C15—C14—C16—F3	−7.8 (3)
C8—O2—C9—C10	179.50 (14)	C13—C14—C16—F3	172.98 (18)
O3—C9—C10—C15	4.2 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1A···O1ⁱ	0.95	2.53	3.205 (2)	128
C4—H4A···O3ⁱⁱ	0.95	2.53	3.289 (2)	137
C8—H8A···O3ⁱⁱⁱ	0.99	2.48	3.474 (2)	177

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

Experimental details

Crystal data
Chemical formula	C₁₆H₁₀ClF₃O₃
M_r	342.69
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	14.3036 (7), 12.1335 (6), 8.5464 (4)
β (°)	101.444 (1)
V (Å³)	1453.76 (12)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.31
Crystal size (mm)	0.28 × 0.16 × 0.11

Data collection
Diffractometer	Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.919, 0.966
No. of measured, independent and observed [I > 2σ(I)] reflections	15629, 3822, 2963
R_int	0.046
(sin θ/λ)_max (Å⁻¹)	0.682

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.048, 0.121, 1.04
No. of reflections	3822
No. of parameters	208
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.52, −0.33

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), 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
C1—H1A···O1ⁱ	0.9500	2.5300	3.205 (2)	128.00
C4—H4A···O3ⁱⁱ	0.9500	2.5300	3.289 (2)	137.00
C8—H8A···O3ⁱⁱⁱ	0.99	2.48	3.474 (2)	177.4

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

Footnotes

‡Thomson Reuters ResearcherID: A-3561-2009.

§Thomson Reuters ResearcherID: C-7581-2009.

Acknowledgements

H-KF and W-SL thank Universiti Sains Malaysia (USM) for a Research University Grant (No. 1001/PFIZIK/811160). W-SL also thanks the Malaysian government and USM for the award of a Research Fellowship. AMI is thankful to the Department of Atomic Energy, Board for Research in Nuclear Sciences, Government of India, for a `Young Scientist' award. BG thanks the Department of Information Technology, New Delhi, India, for the financial support.

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