(E)-N′-(2,4,5-Trifluorobenzyl­idene)isonicotinohydrazide monohydrate

Naveenkumar, H.S.; Sadikun, A.; Ibrahim, P.; Yeap, C.S.; Fun, H.-K.

doi:10.1107/S1600536810004514

organic compounds

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ISSN: 2056-9890

Volume 66| Part 3| March 2010| Page o579

doi:10.1107/S1600536810004514

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(E)-N′-(2,4,5-Trifluorobenzylidene)isonicotinohydrazide monohydrate

H. S. Naveenkumar,^a Amirin Sadikun,^a ‡ Pazilah Ibrahim,^a Chin Sing Yeap ^b § and Hoong-Kun Fun ^b ^*¶

^aSchool of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, and ^bX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
^*Correspondence e-mail: hkfun@usm.my

(Received 2 February 2010; accepted 4 February 2010; online 10 February 2010)

In the Schiff base molecule of the title compound, C₁₃H₈F₃N₃O·H₂O, the benzene ring and the pyridine ring are nearly coplanar, making a dihedral angle of 6.64 (7)°. The molecule exists in an E configuration with respect to the C=N double bond. In the crystal structure, molecules are linked via the water molecules into two-dimensional planes parallel to the ab plane through intermolecular N—H⋯O, O—H⋯O O—H⋯N and C—H⋯O hydrogen bonds.

Related literature

For applications of isoniazid (isonicotinylhydrazine) derivatives, see: Janin (2007 ); Maccari et al. (2005 ); Slayden & Barry (2000 ); Kahwa et al. (1986 ). For the preparation of the title compound, see: Lourenco et al. (2008 ). For related structures, see: Naveenkumar et al. (2009 , 2010 ); Shi (2005 ).

Experimental

Crystal data

C₁₃H₈F₃N₃O·H₂O
M_r = 297.24
Triclinic, $[P \overline 1]$
a = 4.9241 (1) Å
b = 6.3915 (1) Å
c = 21.3387 (2) Å
α = 88.616 (1)°
β = 86.556 (1)°
γ = 76.056 (1)°
V = 650.58 (2) Å³
Z = 2
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 296 K
0.32 × 0.32 × 0.13 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.958, T_max = 0.984
14710 measured reflections
4024 independent reflections
2730 reflections with I > 2σ(I)
R_int = 0.022

Refinement

R[F² > 2σ(F²)] = 0.046
wR(F²) = 0.146
S = 1.05
4024 reflections
230 parameters
All H-atom parameters refined
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.22 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H1N2⋯O1W	0.883 (19)	1.921 (19)	2.7910 (13)	168.1 (16)
O1W—H1W1⋯O1ⁱ	0.79 (2)	2.03 (2)	2.8263 (17)	176.3 (18)
O1W—H2W1⋯O1ⁱⁱ	0.84 (2)	2.19 (2)	2.9670 (17)	155 (2)
O1W—H2W1⋯N1ⁱⁱ	0.84 (2)	2.47 (2)	3.1024 (14)	133.7 (19)
C7—H7A⋯O1W	0.967 (13)	2.492 (14)	3.2576 (16)	135.9 (12)
C13—H13A⋯O1W	0.963 (19)	2.427 (18)	3.3308 (19)	156.2 (14)
Symmetry codes: (i) x+1, y-1, z; (ii) x, y-1, z.

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/S1600536810004514/sj2725sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810004514/sj2725Isup2.hkl

checkCIF report

Comment top

In the search for new biologically active compounds, isoniazid (isonicotinylhydrazine) derivatives have been found to possess potential tuberculostatic activity (Janin, 2007; Maccari et al., 2005; Slayden & Barry, 2000). As part of our current work on the synthesis of (E)-N'-substituted isonicotinohydrazide derivatives, in this paper we present the crystal structure of the title compound, (I).

The asymmetric unit consists of one Schiff base molecule and one water molecule (Fig. 1). The geometric parameters are comparable to those related structures (Naveenkumar et al., 2009, 2010; Shi, 2005). The molecule is nearly coplanar with a dihedral angle between the benzene ring and the pyridine ring of 6.64 (7)°. The molecule exists in an E configuration with respect to the C7=N1 double bond. In the crystal structure, the water molecules link the molecules into two-dimensional planes parallel to the ab plane through intermolecular N–H···O, O–H···O O–H···N and C–H···O hydrogen bonds (Fig. 2, Table 1).

Related literature top

For applications of isoniazid (isonicotinylhydrazine) derivatives, see: Janin (2007); Maccari et al. (2005); Slayden & Barry (2000); Kahwa et al. (1986). For the preparation of the title compound, see: Lourenco et al. (2008). For related structures, see: Naveenkumar et al. (2009, 2010); Shi (2005).

Experimental top

The isoniazid derivative was prepared following a procedure reported by Lourenco et al., (2008). 2,4,5-triflurobenzaldehyde (1.0 eq) was added to isoniazid (1.0 eq) in ethanol/water. After stirring for 1-3 h at room temperature, the resulting mixture was concentrated under reduced pressure. The residue was purified by washing with cold ethanol and diethyl ether to give the pure derivative. Colourless single crystals suitable for X-ray analysis were obtained by re-crystallization from methanol.

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 (I) with atom labels and 50% probability ellipsoids for non-H atoms.
	Fig. 2. The crystal packing of (I), viewed down the a axis, showing the molecules are linked into 2-dimensional planes parallel to the ab plane. Intermolecular hydrogen bonds are shown as dashed lines.

(E)-N'-(2,4,5-Trifluorobenzylidene)isonicotinohydrazide monohydrate top

Crystal data top

C₁₃H₈F₃N₃O·H₂O	Z = 2
M_r = 297.24	F(000) = 304
Triclinic, P1	D_x = 1.517 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 4.9241 (1) Å	Cell parameters from 6031 reflections
b = 6.3915 (1) Å	θ = 2.9–30.8°
c = 21.3387 (2) Å	µ = 0.13 mm⁻¹
α = 88.616 (1)°	T = 296 K
β = 86.556 (1)°	Plate, colourless
γ = 76.056 (1)°	0.32 × 0.32 × 0.13 mm
V = 650.58 (2) Å³

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	4024 independent reflections
Radiation source: fine-focus sealed tube	2730 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.022
ϕ and ω scans	θ_max = 30.8°, θ_min = 2.9°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −6→7
T_min = 0.958, T_max = 0.984	k = −9→9
14710 measured reflections	l = −30→29

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.146	All H-atom parameters refined
S = 1.05	w = 1/[σ²(F_o²) + (0.0764P)² + 0.0515P] where P = (F_o² + 2F_c²)/3
4024 reflections	(Δ/σ)_max < 0.001
230 parameters	Δρ_max = 0.27 e Å⁻³
0 restraints	Δρ_min = −0.22 e Å⁻³

Crystal data top

C₁₃H₈F₃N₃O·H₂O	γ = 76.056 (1)°
M_r = 297.24	V = 650.58 (2) Å³
Triclinic, P1	Z = 2
a = 4.9241 (1) Å	Mo Kα radiation
b = 6.3915 (1) Å	µ = 0.13 mm⁻¹
c = 21.3387 (2) Å	T = 296 K
α = 88.616 (1)°	0.32 × 0.32 × 0.13 mm
β = 86.556 (1)°

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	4024 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	2730 reflections with I > 2σ(I)
T_min = 0.958, T_max = 0.984	R_int = 0.022
14710 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.046	0 restraints
wR(F²) = 0.146	All H-atom parameters refined
S = 1.05	Δρ_max = 0.27 e Å⁻³
4024 reflections	Δρ_min = −0.22 e Å⁻³
230 parameters

Special details top

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
F1	1.20930 (18)	0.63383 (14)	0.34682 (4)	0.0667 (3)
F2	1.2581 (2)	1.19398 (18)	0.48033 (4)	0.0824 (3)
F3	0.8111 (2)	1.44958 (15)	0.42966 (5)	0.0834 (3)
O1	0.1646 (2)	1.24750 (13)	0.19113 (5)	0.0552 (3)
N1	0.5532 (2)	1.00798 (15)	0.25981 (4)	0.0386 (2)
N2	0.4249 (2)	0.91747 (15)	0.21550 (4)	0.0377 (2)
N3	−0.1882 (3)	0.7926 (2)	0.04246 (6)	0.0592 (3)
C1	1.1071 (3)	0.8366 (2)	0.36730 (6)	0.0431 (3)
C2	1.2389 (3)	0.9080 (3)	0.41488 (6)	0.0532 (3)
C3	1.1375 (3)	1.1151 (3)	0.43436 (6)	0.0533 (3)
C4	0.9082 (3)	1.2479 (2)	0.40781 (6)	0.0520 (3)
C5	0.7792 (3)	1.1753 (2)	0.36057 (6)	0.0465 (3)
C6	0.8779 (2)	0.96531 (19)	0.33900 (5)	0.0381 (3)
C7	0.7429 (2)	0.87952 (19)	0.28944 (5)	0.0391 (3)
C8	0.2279 (2)	1.05161 (17)	0.18276 (5)	0.0381 (3)
C9	0.0888 (2)	0.95209 (18)	0.13457 (5)	0.0381 (3)
C10	−0.1271 (3)	1.0858 (2)	0.10359 (6)	0.0469 (3)
C11	−0.2587 (3)	0.9994 (3)	0.05883 (6)	0.0549 (3)
C12	0.0208 (4)	0.6670 (3)	0.07203 (7)	0.0645 (4)
C13	0.1642 (3)	0.7368 (2)	0.11825 (7)	0.0555 (4)
O1W	0.6042 (3)	0.46898 (15)	0.22162 (5)	0.0567 (3)
H2A	1.388 (4)	0.807 (3)	0.4315 (9)	0.079 (5)*
H5A	0.619 (4)	1.275 (3)	0.3436 (8)	0.069 (5)*
H7A	0.798 (3)	0.727 (2)	0.2805 (7)	0.054 (4)*
H10A	−0.178 (3)	1.237 (3)	0.1110 (7)	0.061 (4)*
H11A	−0.398 (4)	1.092 (3)	0.0388 (8)	0.069 (5)*
H12A	0.087 (4)	0.519 (3)	0.0585 (9)	0.084 (6)*
H13A	0.316 (4)	0.636 (3)	0.1371 (8)	0.073 (5)*
H1N2	0.479 (3)	0.776 (3)	0.2116 (8)	0.067 (5)*
H1W1	0.759 (4)	0.402 (3)	0.2127 (8)	0.071 (6)*
H2W1	0.499 (4)	0.384 (4)	0.2232 (10)	0.099 (7)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0610 (5)	0.0571 (5)	0.0724 (6)	0.0110 (4)	−0.0253 (4)	−0.0153 (4)
F2	0.0779 (6)	0.1120 (8)	0.0649 (6)	−0.0278 (6)	−0.0330 (5)	−0.0306 (5)
F3	0.0999 (8)	0.0612 (5)	0.0897 (7)	−0.0114 (5)	−0.0295 (6)	−0.0347 (5)
O1	0.0565 (6)	0.0337 (4)	0.0772 (6)	−0.0068 (4)	−0.0346 (5)	−0.0034 (4)
N1	0.0405 (5)	0.0378 (5)	0.0402 (5)	−0.0114 (4)	−0.0145 (4)	−0.0050 (4)
N2	0.0408 (5)	0.0331 (5)	0.0412 (5)	−0.0087 (4)	−0.0177 (4)	−0.0039 (4)
N3	0.0653 (8)	0.0712 (8)	0.0501 (6)	−0.0285 (6)	−0.0241 (5)	−0.0041 (6)
C1	0.0381 (6)	0.0491 (7)	0.0410 (6)	−0.0062 (5)	−0.0103 (5)	−0.0040 (5)
C2	0.0407 (7)	0.0730 (9)	0.0446 (7)	−0.0073 (6)	−0.0172 (5)	−0.0031 (6)
C3	0.0490 (7)	0.0758 (9)	0.0409 (6)	−0.0220 (7)	−0.0140 (5)	−0.0131 (6)
C4	0.0593 (8)	0.0503 (7)	0.0499 (7)	−0.0161 (6)	−0.0125 (6)	−0.0129 (5)
C5	0.0492 (7)	0.0431 (6)	0.0480 (7)	−0.0086 (5)	−0.0183 (5)	−0.0049 (5)
C6	0.0377 (6)	0.0422 (6)	0.0367 (5)	−0.0119 (4)	−0.0110 (4)	−0.0020 (4)
C7	0.0411 (6)	0.0361 (5)	0.0415 (6)	−0.0091 (4)	−0.0139 (5)	−0.0039 (4)
C8	0.0372 (6)	0.0355 (5)	0.0442 (6)	−0.0107 (4)	−0.0138 (5)	−0.0013 (4)
C9	0.0378 (6)	0.0433 (6)	0.0375 (6)	−0.0153 (5)	−0.0126 (4)	−0.0005 (4)
C10	0.0449 (7)	0.0509 (7)	0.0451 (7)	−0.0084 (5)	−0.0161 (5)	−0.0017 (5)
C11	0.0484 (7)	0.0724 (9)	0.0459 (7)	−0.0138 (7)	−0.0216 (6)	0.0011 (6)
C12	0.0858 (11)	0.0528 (8)	0.0630 (9)	−0.0250 (8)	−0.0335 (8)	−0.0060 (7)
C13	0.0671 (9)	0.0427 (7)	0.0603 (8)	−0.0132 (6)	−0.0322 (7)	−0.0036 (6)
O1W	0.0608 (7)	0.0322 (4)	0.0771 (7)	−0.0067 (4)	−0.0194 (5)	−0.0063 (4)

Geometric parameters (Å, º) top

F1—C1	1.3454 (15)	C5—C6	1.3922 (17)
F2—C3	1.3445 (13)	C5—H5A	0.969 (18)
F3—C4	1.3463 (16)	C6—C7	1.4660 (14)
O1—C8	1.2299 (13)	C7—H7A	0.965 (15)
N1—C7	1.2737 (15)	C8—C9	1.5025 (14)
N1—N2	1.3791 (11)	C9—C13	1.3835 (17)
N2—C8	1.3477 (14)	C9—C10	1.3843 (17)
N2—H1N2	0.881 (18)	C10—C11	1.3821 (17)
N3—C12	1.326 (2)	C10—H10A	0.953 (16)
N3—C11	1.3324 (19)	C11—H11A	0.911 (19)
C1—C2	1.3800 (17)	C12—C13	1.3882 (17)
C1—C6	1.3877 (16)	C12—H12A	0.966 (19)
C2—C3	1.363 (2)	C13—H13A	0.963 (18)
C2—H2A	0.93 (2)	O1W—H1W1	0.79 (2)
C3—C4	1.381 (2)	O1W—H2W1	0.83 (2)
C4—C5	1.3699 (16)

C7—N1—N2	116.55 (9)	N1—C7—C6	118.93 (10)
C8—N2—N1	117.36 (9)	N1—C7—H7A	121.8 (9)
C8—N2—H1N2	126.2 (11)	C6—C7—H7A	119.2 (9)
N1—N2—H1N2	116.5 (11)	O1—C8—N2	122.04 (9)
C12—N3—C11	116.24 (11)	O1—C8—C9	120.84 (10)
F1—C1—C2	118.25 (11)	N2—C8—C9	117.12 (9)
F1—C1—C6	118.70 (10)	C13—C9—C10	117.67 (10)
C2—C1—C6	123.04 (12)	C13—C9—C8	124.60 (10)
C3—C2—C1	117.80 (12)	C10—C9—C8	117.72 (10)
C3—C2—H2A	126.1 (11)	C11—C10—C9	119.15 (12)
C1—C2—H2A	116.1 (11)	C11—C10—H10A	119.8 (9)
F2—C3—C2	120.48 (12)	C9—C10—H10A	121.0 (9)
F2—C3—C4	118.53 (13)	N3—C11—C10	123.93 (13)
C2—C3—C4	120.99 (11)	N3—C11—H11A	119.1 (11)
F3—C4—C5	120.41 (12)	C10—C11—H11A	116.9 (11)
F3—C4—C3	118.89 (11)	N3—C12—C13	124.42 (14)
C5—C4—C3	120.70 (12)	N3—C12—H12A	117.9 (11)
C4—C5—C6	120.06 (12)	C13—C12—H12A	117.5 (11)
C4—C5—H5A	117.3 (10)	C9—C13—C12	118.58 (13)
C6—C5—H5A	122.7 (10)	C9—C13—H13A	121.8 (10)
C1—C6—C5	117.41 (10)	C12—C13—H13A	119.6 (10)
C1—C6—C7	120.67 (11)	H1W1—O1W—H2W1	108.0 (19)
C5—C6—C7	121.89 (10)

C7—N1—N2—C8	−178.64 (11)	N2—N1—C7—C6	−177.37 (10)
F1—C1—C2—C3	178.60 (12)	C1—C6—C7—N1	−172.44 (12)
C6—C1—C2—C3	−0.2 (2)	C5—C6—C7—N1	9.12 (19)
C1—C2—C3—F2	−179.70 (12)	N1—N2—C8—O1	0.66 (18)
C1—C2—C3—C4	0.8 (2)	N1—N2—C8—C9	−179.99 (9)
F2—C3—C4—F3	−1.2 (2)	O1—C8—C9—C13	174.03 (13)
C2—C3—C4—F3	178.33 (14)	N2—C8—C9—C13	−5.32 (19)
F2—C3—C4—C5	179.61 (13)	O1—C8—C9—C10	−4.90 (18)
C2—C3—C4—C5	−0.8 (2)	N2—C8—C9—C10	175.74 (11)
F3—C4—C5—C6	−178.86 (13)	C13—C9—C10—C11	0.8 (2)
C3—C4—C5—C6	0.3 (2)	C8—C9—C10—C11	179.78 (12)
F1—C1—C6—C5	−179.11 (12)	C12—N3—C11—C10	0.3 (2)
C2—C1—C6—C5	−0.3 (2)	C9—C10—C11—N3	−1.0 (2)
F1—C1—C6—C7	2.38 (18)	C11—N3—C12—C13	0.7 (3)
C2—C1—C6—C7	−178.84 (12)	C10—C9—C13—C12	0.1 (2)
C4—C5—C6—C1	0.3 (2)	C8—C9—C13—C12	−178.85 (13)
C4—C5—C6—C7	178.75 (12)	N3—C12—C13—C9	−0.9 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N2—H1N2···O1W	0.883 (19)	1.921 (19)	2.7910 (13)	168.1 (16)
O1W—H1W1···O1ⁱ	0.79 (2)	2.03 (2)	2.8263 (17)	176.3 (18)
O1W—H2W1···O1ⁱⁱ	0.84 (2)	2.19 (2)	2.9670 (17)	155 (2)
O1W—H2W1···N1ⁱⁱ	0.84 (2)	2.47 (2)	3.1024 (14)	133.7 (19)
C7—H7A···O1W	0.967 (13)	2.492 (14)	3.2576 (16)	135.9 (12)
C13—H13A···O1W	0.963 (19)	2.427 (18)	3.3308 (19)	156.2 (14)

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

Experimental details

Crystal data
Chemical formula	C₁₃H₈F₃N₃O·H₂O
M_r	297.24
Crystal system, space group	Triclinic, P1
Temperature (K)	296
a, b, c (Å)	4.9241 (1), 6.3915 (1), 21.3387 (2)
α, β, γ (°)	88.616 (1), 86.556 (1), 76.056 (1)
V (Å³)	650.58 (2)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.13
Crystal size (mm)	0.32 × 0.32 × 0.13

Data collection
Diffractometer	Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.958, 0.984
No. of measured, independent and observed [I > 2σ(I)] reflections	14710, 4024, 2730
R_int	0.022
(sin θ/λ)_max (Å⁻¹)	0.721

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.046, 0.146, 1.05
No. of reflections	4024
No. of parameters	230
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.22

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
N2—H1N2···O1W	0.883 (19)	1.921 (19)	2.7910 (13)	168.1 (16)
O1W—H1W1···O1ⁱ	0.79 (2)	2.03 (2)	2.8263 (17)	176.3 (18)
O1W—H2W1···O1ⁱⁱ	0.84 (2)	2.19 (2)	2.9670 (17)	155 (2)
O1W—H2W1···N1ⁱⁱ	0.84 (2)	2.47 (2)	3.1024 (14)	133.7 (19)
C7—H7A···O1W	0.967 (13)	2.492 (14)	3.2576 (16)	135.9 (12)
C13—H13A···O1W	0.963 (19)	2.427 (18)	3.3308 (19)	156.2 (14)

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

Footnotes

‡Additional Correspondence author: amirin@usm.my.

§Thomson Reuters ResearcherID: A-5523-2009.

¶Thomson Reuters ResearcherID: A-3561-2009.

Acknowledgements

This research was supported by Universiti Sains Malaysia (USM) under the University Research Grant (1001/PFARMASI/815005). HSNK and CSY each thank USM for the award of a USM Fellowship. HKF and CSY thank USM for the Research University Golden Goose Grant (1001/PFIZIK/811012).

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