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Acta Cryst. (2009). E65, o2379-o2380    [ doi:10.1107/S1600536809034990 ]

6-Hydroxysalvinolone

A. W. Salae, S. Chantrapromma, H.-K. Fun and C. Karalai

Abstract top

The title compound {systematic name: 5,6,10-trihydroxy-7-isopropyl-1,1,4a-trimethyl-2,3,4,4a-tetrahydrophenanthren-9(1H)-one}, C20H26O4, is a diterpenoid which was isolated from the roots of Premna obtusifolia. The molecule has three fused six-membered rings; the cyclohexane ring is in a twisted-boat conformation and the cyclohexene ring adopts a sofa form. Intramolecular O-H...O hydrogen bonds generate two S(5) ring motifs. In the crystal, molecules are linked into infinite one-dimensional chains along the [001] direction by O-H...O hydrogen bonds and weak C-H...O interactions.

Comment top

During the course of our studies on the chemical constituents and bioactive compounds from Thai medicinal plants, the title diterpenoid compound (I) known as 6-hydroxysalvinolone (Topcu & Ulubelen, 1996) or 14-deoxycoleon U (Fraga et al., 2005; Hueso-Rodríguez et al., 1983), was isolated from the roots of Premna obtusifolia. The previous report (Fraga et al., 2005) shows that this compound exhibits insecticidal activity. We report herein the crystal structure of (I).

The molecule of (I) has three fused six membered rings (Fig. 1). The cyclohexane ring is in a twisted boat conformation with the puckering parameters Q = 0.6874 (13) Å, θ = 96.44 (11)° and φ = 278.29 (11)° (Cremer & Pople, 1975) whereas the cyclohexene ring (C5–C10) adopts a sofa form with the slightly puckered C5 atom having the maximum deviation of -0.058 (1) Å. The C5···C14 ring system is nearly planar, rms deviation 0.0216 (13) Å and the O1, O3 and O4 hydroxyl O atoms lie close to this plane with deviations +0.0393 (13) for O1, -0.0316 (11) for O3 and +0.0305 (11) Å for O4. The bond angles around C6 are indicative of sp2 hybridization for this atom. The orientation of the propanyl group is described by the torsion angles C14–C13–C15–C16 = -25.4 (2) and C14–C13–C15–C17 = -80.49 (15) °. Intramolecular O1—H1O1···O2 and O4—H1O4···O3 hydrogen bonds (Table 1) generate two S(5) ring motifs (Fig. 1) (Bernstein et al., 1995). The bond distances and angles in (I) are within normal ranges (Allen et al., 1987). The absolute configuration of this structure were deduced from an earlier publication (Hueso-Rodríguez et al., 1983). The absolute configuration is R and not S at C10.

The crystal packing of (I) is stabilized by intermolecular O—H···O hydrogen bonds and weak C—H···O interactions (Fig. 2 and Table 1). The molecules are linked into infinite one dimensional chains along the [0 0 1] direction (Fig. 2).

Related literature top

For hydrogen bond motifs, see: Bernstein et al. (1995). For ring conformations, see: Cremer & Pople (1975). For bond-length data, see: Allen et al. (1987). For background to diterpenes and their activities, see: Fraga et al. (2005); Hueso-Rodríguez et al. (1983); Topcu et al. (1996). For the stability of the temperature controller used in the data collection, see Cosier & Glazer, (1986).

Experimental top

The air-dried roots of Premna obtusifolia (4.5 kg) were extracted with CH2Cl2 (2 x 20 L) at room temperature. The combined extracts were concentrated under reduced pressure to afford a dark yellow extract (40.5 g) which was subjected to quick column chromatography (QCC) over silica gel using solvents of increasing polarity from n-hexane to EtOAc to afford 12 fractions (F1—F12). Fraction F7 was further purified by QCC using hexane-EtOAc (9.5:0.5), yielding the title compound (212.0 mg). Colourless block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystallized from CH2Cl2/CH3OH (1:1, v/v) after several days.

Refinement top

Hydroxy H atoms attached to O1 and O4 were located from the difference map and isotropically refined. The remaining H atoms were placed in calculated positions with d(O—H) = 0.82 Å and d(C—H) = 0.93 Å for aromatic, 0.98 for CH, 0.97 for CH2 and 0.96 Å for CH3 atoms. The Uiso values were constrained to be 1.5Ueq of the carrier atom for hydroxy and methyl H atoms and 1.2Ueq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.67 Å from C12 and the deepest hole is located at 0.47 Å from H1O4. A total of 3037 Friedel pairs were merged before final refinement as there is no large anomalous dispersion for the determination of the absolute configuration.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); 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
[Figure 1] Fig. 1. The structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme. Intramolecular hydrogen bonds are shown as dashed lines.
[Figure 2] Fig. 2. The crystal packing of (I) viewed along the a axis, showing one dimensional chains along the [0 0 1] direction. Hydrogen bonds are shown as dashed lines.
5,6,10-trihydroxy-7-isopropyl-1,1,4a-trimethyl-2,3,4,4a- tetrahydrophenanthren-9(1H)-one top
Crystal data top
C20H26O4F(000) = 712
Mr = 330.41Dx = 1.271 Mg m−3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 3890 reflections
a = 9.4946 (1) Åθ = 2.1–34.0°
b = 13.1716 (1) ŵ = 0.09 mm−1
c = 13.8124 (1) ÅT = 100 K
V = 1727.37 (3) Å3Block, colourless
Z = 40.35 × 0.30 × 0.27 mm
Data collection top
Bruker APEXII CCD area-detector
diffractometer		3890 independent reflections
Radiation source: sealed tube3530 reflections with I > 2σ(I)
graphiteRint = 0.031
φ and ω scansθmax = 34.0°, θmin = 2.1°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		h = −14→14
Tmin = 0.970, Tmax = 0.977k = −20→19
36584 measured reflectionsl = −21→21
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.039Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.114H atoms treated by a mixture of independent and constrained refinement
S = 1.09 w = 1/[σ2(Fo2) + (0.065P)2 + 0.2832P]
where P = (Fo2 + 2Fc2)/3
3890 reflections(Δ/σ)max = 0.001
230 parametersΔρmax = 0.36 e Å−3
0 restraintsΔρmin = −0.41 e Å−3
Crystal data top
C20H26O4V = 1727.37 (3) Å3
Mr = 330.41Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 9.4946 (1) ŵ = 0.09 mm−1
b = 13.1716 (1) ÅT = 100 K
c = 13.8124 (1) Å0.35 × 0.30 × 0.27 mm
Data collection top
Bruker APEXII CCD area-detector
diffractometer		3890 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		3530 reflections with I > 2σ(I)
Tmin = 0.970, Tmax = 0.977Rint = 0.031
36584 measured reflectionsθmax = 34.0°
Refinement top
R[F2 > 2σ(F2)] = 0.039H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.114Δρmax = 0.36 e Å−3
S = 1.09Δρmin = −0.41 e Å−3
3890 reflectionsAbsolute structure: ?
230 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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
xyzUiso*/Ueq
O10.26452 (14)0.14460 (7)0.64485 (7)0.0216 (2)
H1O10.269 (3)0.2000 (18)0.6119 (16)0.041 (7)*
O20.25851 (15)0.33755 (7)0.66826 (6)0.0238 (2)
O30.24282 (12)0.46627 (7)1.11140 (6)0.01532 (17)
H1O30.24340.52851.11120.023*
O40.25735 (12)0.27209 (7)1.09834 (6)0.01710 (18)
H1O40.255 (3)0.3196 (17)1.1358 (17)0.036 (6)*
C10.14764 (15)0.10997 (9)0.98617 (9)0.0161 (2)
H1A0.18680.10471.05090.019*
H1B0.06730.15530.98950.019*
C20.09602 (14)0.00517 (10)0.95499 (9)0.0168 (2)
H2A0.0690−0.03331.01190.020*
H2B0.01320.01290.91450.020*
C30.20820 (14)−0.05358 (9)0.89937 (9)0.0152 (2)
H3A0.1749−0.12190.88680.018*
H3B0.2931−0.05830.93820.018*
C40.24219 (15)−0.00022 (9)0.80244 (8)0.01321 (19)
C50.24938 (13)0.11553 (8)0.81616 (8)0.01206 (19)
C60.25713 (15)0.17857 (9)0.73871 (8)0.0149 (2)
C70.25656 (15)0.28915 (9)0.74601 (8)0.0148 (2)
C80.25181 (14)0.33614 (8)0.84122 (7)0.01221 (19)
C90.25195 (13)0.27427 (8)0.92386 (7)0.01059 (18)
C100.26085 (13)0.15838 (8)0.91835 (8)0.01090 (18)
C110.25257 (14)0.32476 (8)1.01300 (8)0.01188 (19)
C120.24742 (13)0.43145 (8)1.01841 (7)0.01168 (19)
C130.24969 (14)0.49232 (9)0.93547 (8)0.01231 (19)
C140.25199 (14)0.44240 (9)0.84711 (8)0.0138 (2)
H14A0.25370.48030.79030.017*
C150.24938 (15)0.60771 (8)0.94329 (8)0.0140 (2)
H15A0.30630.62600.99990.017*
C160.3149 (2)0.65916 (11)0.85549 (11)0.0284 (3)
H16A0.40400.62810.84130.043*
H16B0.32870.73000.86900.043*
H16C0.25330.65190.80080.043*
C170.09920 (15)0.64681 (10)0.96124 (11)0.0208 (3)
H17A0.10120.71920.96920.031*
H17B0.06200.61591.01880.031*
H17C0.04060.62970.90700.031*
C180.12286 (15)−0.02886 (11)0.73086 (10)0.0202 (3)
H18A0.14130.00140.66890.030*
H18B0.0345−0.00440.75530.030*
H18C0.1189−0.10130.72410.030*
C190.38326 (14)−0.04045 (10)0.76210 (10)0.0184 (2)
H19A0.4574−0.02580.80720.028*
H19B0.4032−0.00800.70140.028*
H19C0.3768−0.11250.75260.028*
C200.41271 (13)0.13255 (10)0.95434 (9)0.0154 (2)
H20A0.48050.16080.91040.023*
H20B0.42420.06020.95700.023*
H20C0.42670.16081.01770.023*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0436 (6)0.0122 (4)0.0090 (3)0.0012 (5)0.0006 (4)−0.0013 (3)
O20.0489 (6)0.0129 (4)0.0097 (3)0.0008 (5)0.0007 (4)0.0023 (3)
O30.0266 (4)0.0104 (4)0.0090 (3)−0.0009 (4)0.0012 (3)−0.0018 (3)
O40.0305 (5)0.0127 (4)0.0081 (3)0.0004 (4)−0.0006 (4)0.0015 (3)
C10.0209 (5)0.0107 (5)0.0166 (5)−0.0020 (4)0.0060 (4)0.0002 (4)
C20.0184 (5)0.0138 (5)0.0183 (5)−0.0026 (4)0.0044 (4)−0.0001 (4)
C30.0205 (5)0.0093 (5)0.0160 (5)−0.0002 (4)0.0013 (4)0.0009 (4)
C40.0177 (5)0.0087 (4)0.0132 (4)0.0010 (4)−0.0008 (4)−0.0007 (3)
C50.0156 (5)0.0094 (4)0.0112 (4)0.0009 (5)−0.0005 (4)−0.0001 (3)
C60.0245 (5)0.0103 (5)0.0100 (4)0.0006 (5)−0.0002 (4)−0.0013 (3)
C70.0248 (6)0.0100 (4)0.0096 (4)0.0009 (5)−0.0003 (4)0.0003 (3)
C80.0179 (5)0.0098 (4)0.0089 (4)0.0006 (5)−0.0001 (4)0.0001 (3)
C90.0141 (4)0.0084 (4)0.0093 (4)0.0002 (4)0.0002 (4)0.0002 (3)
C100.0140 (4)0.0088 (4)0.0100 (4)0.0003 (4)−0.0003 (4)0.0007 (3)
C110.0160 (5)0.0105 (4)0.0091 (4)0.0000 (5)0.0000 (4)0.0006 (3)
C120.0152 (5)0.0104 (4)0.0095 (4)0.0006 (5)0.0001 (4)−0.0011 (3)
C130.0167 (4)0.0097 (4)0.0106 (4)0.0003 (4)0.0001 (4)0.0003 (3)
C140.0217 (5)0.0095 (4)0.0100 (4)−0.0001 (5)0.0002 (4)0.0001 (3)
C150.0223 (5)0.0077 (4)0.0121 (4)0.0001 (5)0.0018 (4)0.0000 (3)
C160.0519 (10)0.0117 (5)0.0215 (6)0.0005 (6)0.0146 (6)0.0016 (5)
C170.0232 (6)0.0134 (5)0.0259 (6)0.0024 (5)−0.0017 (5)−0.0024 (5)
C180.0257 (6)0.0155 (6)0.0194 (5)−0.0024 (5)−0.0048 (5)−0.0027 (5)
C190.0232 (6)0.0130 (5)0.0189 (5)0.0031 (5)0.0045 (5)−0.0007 (4)
C200.0164 (5)0.0130 (5)0.0168 (5)0.0017 (4)−0.0034 (4)−0.0003 (4)
Geometric parameters (Å, °) top
O1—C61.3733 (14)C9—C111.3993 (15)
O1—H1O10.86 (2)C9—C101.5307 (16)
O2—C71.2490 (14)C10—C201.5626 (17)
O3—C121.3645 (13)C11—C121.4081 (15)
O3—H1O30.8200C12—C131.3984 (15)
O4—C111.3685 (13)C13—C141.3864 (15)
O4—H1O40.81 (2)C13—C151.5237 (16)
C1—C21.5268 (18)C14—H14A0.9300
C1—C101.5619 (17)C15—C161.5222 (18)
C1—H1A0.9700C15—C171.5362 (19)
C1—H1B0.9700C15—H15A0.9800
C2—C31.5242 (18)C16—H16A0.9600
C2—H2A0.9700C16—H16B0.9600
C2—H2B0.9700C16—H16C0.9600
C3—C41.5462 (17)C17—H17A0.9600
C3—H3A0.9700C17—H17B0.9600
C3—H3B0.9700C17—H17C0.9600
C4—C51.5378 (16)C18—H18A0.9600
C4—C191.5444 (19)C18—H18B0.9600
C4—C181.5504 (18)C18—H18C0.9600
C5—C61.3562 (16)C19—H19A0.9600
C5—C101.5240 (15)C19—H19B0.9600
C6—C71.4600 (16)C19—H19C0.9600
C7—C81.4542 (15)C20—H20A0.9600
C8—C141.4020 (15)C20—H20B0.9600
C8—C91.4025 (14)C20—H20C0.9600
C6—O1—H1O1103.0 (15)O4—C11—C9121.14 (10)
C12—O3—H1O3109.5O4—C11—C12117.47 (9)
C11—O4—H1O499.1 (16)C9—C11—C12121.39 (10)
C2—C1—C10114.88 (10)O3—C12—C13125.37 (10)
C2—C1—H1A108.5O3—C12—C11112.74 (9)
C10—C1—H1A108.5C13—C12—C11121.88 (10)
C2—C1—H1B108.5C14—C13—C12116.71 (10)
C10—C1—H1B108.5C14—C13—C15122.37 (10)
H1A—C1—H1B107.5C12—C13—C15120.91 (10)
C3—C2—C1112.14 (11)C13—C14—C8121.63 (10)
C3—C2—H2A109.2C13—C14—H14A119.2
C1—C2—H2A109.2C8—C14—H14A119.2
C3—C2—H2B109.2C16—C15—C13112.76 (10)
C1—C2—H2B109.2C16—C15—C17111.02 (12)
H2A—C2—H2B107.9C13—C15—C17110.34 (11)
C2—C3—C4110.58 (10)C16—C15—H15A107.5
C2—C3—H3A109.5C13—C15—H15A107.5
C4—C3—H3A109.5C17—C15—H15A107.5
C2—C3—H3B109.5C15—C16—H16A109.5
C4—C3—H3B109.5C15—C16—H16B109.5
H3A—C3—H3B108.1H16A—C16—H16B109.5
C5—C4—C19110.25 (11)C15—C16—H16C109.5
C5—C4—C3110.69 (9)H16A—C16—H16C109.5
C19—C4—C3109.72 (10)H16B—C16—H16C109.5
C5—C4—C18110.63 (10)C15—C17—H17A109.5
C19—C4—C18108.68 (10)C15—C17—H17B109.5
C3—C4—C18106.80 (10)H17A—C17—H17B109.5
C6—C5—C10119.99 (10)C15—C17—H17C109.5
C6—C5—C4120.81 (10)H17A—C17—H17C109.5
C10—C5—C4118.97 (9)H17B—C17—H17C109.5
C5—C6—O1123.23 (11)C4—C18—H18A109.5
C5—C6—C7123.79 (10)C4—C18—H18B109.5
O1—C6—C7112.98 (10)H18A—C18—H18B109.5
O2—C7—C8124.11 (10)C4—C18—H18C109.5
O2—C7—C6116.73 (10)H18A—C18—H18C109.5
C8—C7—C6119.15 (10)H18B—C18—H18C109.5
C14—C8—C9122.20 (10)C4—C19—H19A109.5
C14—C8—C7118.51 (10)C4—C19—H19B109.5
C9—C8—C7119.25 (10)H19A—C19—H19B109.5
C11—C9—C8116.10 (10)C4—C19—H19C109.5
C11—C9—C10121.16 (9)H19A—C19—H19C109.5
C8—C9—C10122.62 (9)H19B—C19—H19C109.5
C5—C10—C9114.30 (9)C10—C20—H20A109.5
C5—C10—C1110.80 (10)C10—C20—H20B109.5
C9—C10—C1109.83 (9)H20A—C20—H20B109.5
C5—C10—C20106.26 (10)C10—C20—H20C109.5
C9—C10—C20104.61 (10)H20A—C20—H20C109.5
C1—C10—C20110.81 (9)H20B—C20—H20C109.5
C10—C1—C2—C329.06 (15)C6—C5—C10—C20−103.51 (13)
C1—C2—C3—C4−65.02 (14)C4—C5—C10—C2071.15 (14)
C2—C3—C4—C541.24 (14)C11—C9—C10—C5176.26 (11)
C2—C3—C4—C19163.14 (10)C8—C9—C10—C5−7.91 (17)
C2—C3—C4—C18−79.24 (12)C11—C9—C10—C151.02 (15)
C19—C4—C5—C668.23 (16)C8—C9—C10—C1−133.15 (12)
C3—C4—C5—C6−170.18 (12)C11—C9—C10—C20−67.95 (14)
C18—C4—C5—C6−52.01 (17)C8—C9—C10—C20107.89 (13)
C19—C4—C5—C10−106.38 (12)C2—C1—C10—C525.02 (15)
C3—C4—C5—C1015.20 (16)C2—C1—C10—C9152.24 (11)
C18—C4—C5—C10133.38 (11)C2—C1—C10—C20−92.68 (13)
C10—C5—C6—O1171.98 (12)C8—C9—C11—O4−177.87 (12)
C4—C5—C6—O1−2.6 (2)C10—C9—C11—O4−1.77 (19)
C10—C5—C6—C7−8.9 (2)C8—C9—C11—C122.54 (19)
C4—C5—C6—C7176.56 (13)C10—C9—C11—C12178.63 (11)
C5—C6—C7—O2−177.17 (14)O4—C11—C12—O3−2.26 (19)
O1—C6—C7—O22.0 (2)C9—C11—C12—O3177.35 (11)
C5—C6—C7—C82.0 (2)O4—C11—C12—C13176.62 (11)
O1—C6—C7—C8−178.82 (12)C9—C11—C12—C13−3.8 (2)
O2—C7—C8—C14−1.2 (2)O3—C12—C13—C14−178.94 (13)
C6—C7—C8—C14179.71 (13)C11—C12—C13—C142.33 (19)
O2—C7—C8—C9−179.12 (14)O3—C12—C13—C151.0 (2)
C6—C7—C8—C91.8 (2)C11—C12—C13—C15−177.76 (12)
C14—C8—C9—C11−0.13 (19)C12—C13—C14—C80.1 (2)
C7—C8—C9—C11177.69 (12)C15—C13—C14—C8−179.81 (13)
C14—C8—C9—C10−176.16 (12)C9—C8—C14—C13−1.2 (2)
C7—C8—C9—C101.66 (19)C7—C8—C14—C13−179.04 (12)
C6—C5—C10—C911.32 (18)C14—C13—C15—C16−25.4 (2)
C4—C5—C10—C9−174.02 (10)C12—C13—C15—C16154.74 (13)
C6—C5—C10—C1136.05 (13)C14—C13—C15—C1799.41 (15)
C4—C5—C10—C1−49.30 (15)C12—C13—C15—C17−80.49 (15)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1O1···O20.86 (2)1.97 (2)2.5626 (13)124.5 (19)
O3—H1O3···O2i0.821.932.7008 (13)156
O4—H1O4···O30.81 (2)1.96 (2)2.5677 (13)131 (2)
C14—H14A···O3ii0.932.573.4712 (14)163
C15—H15A···O2i0.982.453.1908 (14)132
C18—H18A···O10.962.242.9053 (18)125
C19—H19B···O10.962.533.1360 (17)121
C20—H20C···O40.962.443.0838 (16)124
Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) −x+1/2, −y+1, z−1/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1O1···O20.86 (2)1.97 (2)2.5626 (13)124.5 (19)
O3—H1O3···O2i0.821.932.7008 (13)156
O4—H1O4···O30.81 (2)1.96 (2)2.5677 (13)131 (2)
C14—H14A···O3ii0.932.573.4712 (14)163
C15—H15A···O2i0.982.453.1908 (14)132
C18—H18A···O10.962.242.9053 (18)125
C19—H19B···O10.962.533.1360 (17)121
C20—H20C···O40.962.443.0838 (16)124
Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) −x+1/2, −y+1, z−1/2.
Acknowledgements top

AWS thanks the Graduate School, Prince of Songkla University, for partial financial support. The authors thank the Prince of Songkla University for financial support through the Crystal Materials Research Unit. The authors also thank Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012.

references
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