supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportsimilar papers Open access

Acta Cryst. (2008). E64, o2313-o2314    [ doi:10.1107/S1600536808036350 ]

3-[1-(4-Isobutylphenyl)ethyl]-4-[(E)-4-methylbenzylideneamino]-1H-1,2,4-triazole-5(4H)-thione

H.-K. Fun, S. R. Jebas, K. V. Sujith and B. Kalluraya

Abstract top

In the title compound, C22H26N4S, the dihedral angles formed by the triazole ring with the two benzene rings are 87.51 (3) and 20.98 (3)°. The benzene rings are inclined at 71.88 (2)°. An intramolecular C-H...S hydrogen bond generates an S(6) ring motif. The crystal packing is strengthened by intermolecular N-H...S hydrogen bonding and [pi]-[pi] stacking interactions between the triazole and benzene rings, with a centroid-centroid distance of 3.6618 (5) Å, together with N...N [2.1299 (9)-2.2121 (9) Å] short contacts and C-H...[pi] interactions. In the crystal packing, molecules are stacked along the a axis.

Comment top

Several compounds containing 1,2,4-triazole rings are well known as drugs. For example, Fluconazole is used as an antimicrobial drug (Shujuan et al., 2004), while Vorozole, Letrozole and Anastrozole are non-steroidal drugs used for the treatment of cancer (Clemons et al., 2004) and Loreclezole is used as an anticonvulsant (Johnston et al., 2002). Some Schiff base derivatives of acetic acid hydrazides containing 1,2,4-triazole-5-one ring have displayed anti-tumor activity against breast cancer, while 2-phenyl ethylideneamino and 2-phenyl ethylamino derivatives of 4-amino-1,2,4-triazol-5-ones have been found to be effective towards lung cell cancer and breast cancer (Demirbas et al., 2004, 2002). Due to the progress that occurs in dealing with the chemistry of substituted 4-amino-1,2,4-triazole-3-thiones and their derivatives as well as their biological activity, we synthesized and here report the crystal structure of 1,2,4-triazole Schiff base.

Bond lengths and angles in (I) (Fig. 1) are found to have normal values (Allen et al., 1987). The two benzene rings are essentially planar with the maximum deviation from planarity being 0.017 (1)Å for atom C6 and 0.013 (1)Å for atom C14 respectively. The dihedral angle formed by the triazole (N1/N2/C9/N3/C8) ring with the two benzene rings (C1—C6; C11—C16) are 87.51 (3)° and 20.98 (3)° respectively. The benzene rings (C1—C6; C11—C16) form dihedral angle of 71.88 (2)°, indicating that they are inclined to each other. An intramolecular C—H···S hydrogen bond generates an S(6) ring motif (Bernstein et al., 1995).

The crystal packing is consolidated by intermolecular N—H···S hydrogen bonding (Table.1). Furthermore the packing is strengthened by π—π stacking interactions involving the triazole (N1/N2/C9/N3/C8) (Cg1) ring and the symmetry related (C11—C16) ring (Cg3) [Cg1···Cg3i = 3.6618 (5) Å; symmetry code: (i) 2-X,-Y,2-Z] together with N···N = 2.1299 (9)–2.2121 (9)Å short contacts and C—H···π interactions. In the crystal packing, the molecules are stacked along the a axis (Fig. 2).

Related literature top

For related literature on componds containing a triazole ring, see: Clemons et al. (2004); Demirbas & Ugurluoglu (2004); Demirbas et al. (2002); Johnston et al. (2002); Shujuan et al. (2004); For bond-length data, see: Allen et al. (1987). For graph-set analysis of hydrogen bonding, see: Bernstein et al. (1995). Cg2 is the centroid of the C1–C6 ring.

Experimental top

The title Schiff-base compound was obtained by refluxing 4-amino-5-[1-(4-isobutylphenyl)ethyl]- 4H-1,2,4-triazole-3-thiol (0.01 mol) and 4-methylbenzaldehyde (0.01 mol) in ethanol (50 ml) by adding 3 drops of concentrated Sulfuric acid for 3 h. The solid product obtained was collected by filtration, washed with ethanol and dried. The product obtained was then recrystallized using ethanol. Crystals suitable for X-ray analysis were obtained from acetone–N,N-dimethylformamide (DMF) (1:3) solution by slow evaporation. (Yield 63%; m.p. 415 K, M.F C22H26N4S)

Refinement top

The amino and methylene H atoms were located in a difference map and refined with restraints of N—H=0.85 (1)Å and C—H=0.96 (1) Å. The remaining H atoms were positioned geometrically [C—H=0.93–0.98Å (aromatic) or 0.96Å (methyl)] and refined using a riding model, with Uiso(H)=1.2Uequ(aromatic C) and 1.5Uequ (methyl C). A rotating group model was used for the methyl group.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (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, 2003).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom numbering scheme.
[Figure 2] Fig. 2. The crystal packing of the title compound,viewed down the a axis.
3-[1-(4-Isobutylphenyl)ethyl]-4-[(E)-4-methylbenzylideneamino]- 1H-1,2,4-triazole-5(4H)-thione top
Crystal data top
C22H26N4SZ = 2
Mr = 378.53F(000) = 404
Triclinic, P1Dx = 1.242 Mg m−3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.7614 (2) ÅCell parameters from 9961 reflections
b = 10.7649 (2) Åθ = 2.6–26.3°
c = 12.9552 (2) ŵ = 0.17 mm−1
α = 85.900 (1)°T = 100 K
β = 78.575 (1)°Block, colourless
γ = 72.542 (1)°0.61 × 0.40 × 0.17 mm
V = 1012.01 (4) Å3
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer		8863 independent reflections
Radiation source: fine-focus sealed tube7661 reflections with I > 2σ(I)
graphiteRint = 0.021
φ and ω scansθmax = 35.0°, θmin = 1.6°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		h = −12→12
Tmin = 0.902, Tmax = 0.971k = −17→16
27492 measured reflectionsl = −20→20
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)] = 0.038Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.110H atoms treated by a mixture of independent and constrained refinement
S = 1.05 w = 1/[σ2(Fo2) + (0.059P)2 + 0.2347P]
where P = (Fo2 + 2Fc2)/3
8863 reflections(Δ/σ)max < 0.001
260 parametersΔρmax = 0.62 e Å−3
3 restraintsΔρmin = −0.33 e Å−3
Crystal data top
C22H26N4Sγ = 72.542 (1)°
Mr = 378.53V = 1012.01 (4) Å3
Triclinic, P1Z = 2
a = 7.7614 (2) ÅMo Kα radiation
b = 10.7649 (2) ŵ = 0.17 mm−1
c = 12.9552 (2) ÅT = 100 K
α = 85.900 (1)°0.61 × 0.40 × 0.17 mm
β = 78.575 (1)°
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer		8863 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		7661 reflections with I > 2σ(I)
Tmin = 0.902, Tmax = 0.971Rint = 0.021
27492 measured reflectionsθmax = 35.0°
Refinement top
R[F2 > 2σ(F2)] = 0.038H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.110Δρmax = 0.62 e Å−3
S = 1.05Δρmin = −0.33 e Å−3
8863 reflectionsAbsolute structure: ?
260 parametersFlack parameter: ?
3 restraintsRogers parameter: ?
Special details top

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

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
S10.83244 (3)−0.312534 (18)1.075041 (15)0.01912 (5)
N11.05221 (9)−0.33177 (6)0.77577 (5)0.01633 (12)
N20.98892 (9)−0.37998 (6)0.87246 (5)0.01608 (11)
N30.91368 (8)−0.17456 (6)0.89131 (5)0.01308 (10)
N40.86457 (9)−0.04642 (6)0.92483 (5)0.01403 (11)
C10.77565 (11)0.10391 (8)0.71426 (6)0.01826 (13)
H1A0.84350.14360.74530.022*
C20.59831 (11)0.17417 (8)0.70084 (7)0.01935 (14)
H2A0.54990.26000.72310.023*
C30.49225 (10)0.11785 (7)0.65462 (6)0.01578 (12)
C40.57282 (11)−0.00989 (8)0.61889 (6)0.01597 (12)
H4A0.5068−0.04880.58570.019*
C50.75003 (10)−0.07996 (7)0.63202 (6)0.01550 (12)
H5A0.8006−0.16460.60720.019*
C60.85251 (10)−0.02490 (7)0.68188 (5)0.01447 (12)
C71.03785 (10)−0.10614 (7)0.70691 (6)0.01530 (12)
H7A1.0913−0.04830.73670.018*
C81.00579 (10)−0.20638 (7)0.78940 (5)0.01400 (12)
C90.90821 (10)−0.28846 (7)0.94628 (6)0.01424 (12)
C100.72862 (10)−0.01464 (7)1.00254 (6)0.01398 (12)
H10A0.6706−0.07631.03220.017*
C110.66417 (9)0.11699 (7)1.04473 (5)0.01333 (11)
C120.52948 (11)0.14034 (7)1.13612 (6)0.01629 (13)
H12A0.48190.07381.16640.020*
C130.46617 (11)0.26249 (8)1.18207 (6)0.01813 (13)
H13A0.37730.27661.24320.022*
C140.53423 (10)0.36416 (7)1.13763 (6)0.01632 (13)
C150.66461 (11)0.34123 (7)1.04410 (6)0.01662 (13)
H15A0.70780.40901.01200.020*
C160.73062 (10)0.21915 (7)0.99839 (6)0.01555 (12)
H16A0.81900.20520.93700.019*
C170.29282 (11)0.18675 (8)0.64939 (6)0.01881 (14)
C180.23940 (11)0.33496 (8)0.63355 (7)0.02000 (14)
H18A0.27040.37260.69160.024*
C190.34375 (14)0.37502 (10)0.53048 (8)0.02956 (19)
H19A0.30820.46830.52420.044*
H19B0.31530.33910.47240.044*
H19C0.47350.34290.52990.044*
C200.03200 (13)0.38811 (10)0.63867 (9)0.0304 (2)
H20A−0.00200.48130.63200.046*
H20B−0.03080.36380.70490.046*
H20C−0.00150.35260.58230.046*
C220.47296 (13)0.49376 (9)1.19093 (8)0.02463 (17)
H22A0.34110.52361.20700.037*
H22B0.51800.55571.14490.037*
H22C0.52060.48481.25490.037*
C211.17512 (11)−0.17176 (9)0.61034 (6)0.02119 (15)
H21A1.2908−0.21670.63040.032*
H21B1.1919−0.10690.55770.032*
H21C1.1287−0.23290.58240.032*
H17A0.2165 (17)0.1675 (13)0.7137 (8)0.027 (3)*
H17B0.2573 (18)0.1510 (13)0.5935 (9)0.027 (3)*
H1N21.0236 (18)−0.4620 (8)0.8863 (11)0.026 (3)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.02447 (10)0.01202 (8)0.01508 (8)−0.00159 (7)0.00310 (6)0.00220 (6)
N10.0200 (3)0.0127 (3)0.0138 (2)−0.0021 (2)−0.0016 (2)0.0001 (2)
N20.0210 (3)0.0098 (2)0.0149 (2)−0.0019 (2)−0.0014 (2)−0.00002 (19)
N30.0153 (2)0.0094 (2)0.0127 (2)−0.00191 (19)−0.00099 (18)0.00014 (18)
N40.0164 (2)0.0096 (2)0.0144 (2)−0.0017 (2)−0.00228 (19)−0.00062 (19)
C10.0216 (3)0.0136 (3)0.0202 (3)−0.0035 (3)−0.0077 (3)−0.0007 (2)
C20.0223 (3)0.0130 (3)0.0222 (3)−0.0010 (3)−0.0081 (3)−0.0031 (3)
C30.0184 (3)0.0140 (3)0.0139 (3)−0.0027 (2)−0.0038 (2)−0.0002 (2)
C40.0193 (3)0.0145 (3)0.0142 (3)−0.0047 (2)−0.0037 (2)−0.0001 (2)
C50.0195 (3)0.0121 (3)0.0136 (3)−0.0033 (2)−0.0022 (2)−0.0002 (2)
C60.0172 (3)0.0123 (3)0.0124 (3)−0.0030 (2)−0.0022 (2)0.0017 (2)
C70.0158 (3)0.0144 (3)0.0141 (3)−0.0033 (2)−0.0014 (2)0.0019 (2)
C80.0149 (3)0.0126 (3)0.0125 (3)−0.0016 (2)−0.0017 (2)0.0001 (2)
C90.0160 (3)0.0103 (3)0.0145 (3)−0.0022 (2)−0.0013 (2)0.0009 (2)
C100.0149 (3)0.0109 (3)0.0152 (3)−0.0027 (2)−0.0025 (2)0.0000 (2)
C110.0138 (3)0.0112 (3)0.0139 (3)−0.0021 (2)−0.0025 (2)−0.0004 (2)
C120.0187 (3)0.0133 (3)0.0156 (3)−0.0047 (2)0.0001 (2)−0.0011 (2)
C130.0195 (3)0.0156 (3)0.0172 (3)−0.0042 (3)0.0011 (2)−0.0034 (2)
C140.0168 (3)0.0122 (3)0.0189 (3)−0.0023 (2)−0.0031 (2)−0.0027 (2)
C150.0179 (3)0.0122 (3)0.0191 (3)−0.0043 (2)−0.0019 (2)−0.0007 (2)
C160.0161 (3)0.0128 (3)0.0165 (3)−0.0038 (2)−0.0008 (2)−0.0007 (2)
C170.0179 (3)0.0180 (3)0.0196 (3)−0.0027 (3)−0.0049 (2)−0.0013 (3)
C180.0183 (3)0.0173 (3)0.0218 (3)−0.0004 (3)−0.0048 (3)−0.0015 (3)
C190.0284 (4)0.0265 (4)0.0291 (4)−0.0038 (3)−0.0043 (3)0.0082 (3)
C200.0196 (4)0.0248 (4)0.0423 (5)0.0017 (3)−0.0076 (3)−0.0024 (4)
C220.0285 (4)0.0154 (3)0.0273 (4)−0.0048 (3)0.0010 (3)−0.0070 (3)
C210.0191 (3)0.0231 (4)0.0175 (3)−0.0038 (3)0.0017 (2)0.0005 (3)
Geometric parameters (Å, °) top
S1—C91.6843 (7)C12—C131.3904 (11)
N1—C81.3039 (10)C12—H12A0.9300
N1—N21.3769 (9)C13—C141.3945 (11)
N2—C91.3434 (9)C13—H13A0.9300
N2—H1N20.859 (8)C14—C151.4001 (11)
N3—C91.3809 (9)C14—C221.5030 (11)
N3—C81.3839 (9)C15—C161.3883 (10)
N3—N41.3932 (9)C15—H15A0.9300
N4—C101.2868 (9)C16—H16A0.9300
C1—C61.3937 (11)C17—C181.5328 (12)
C1—C21.3957 (11)C17—H17A0.970 (8)
C1—H1A0.9300C17—H17B0.965 (8)
C2—C31.3966 (11)C18—C191.5243 (13)
C2—H2A0.9300C18—C201.5276 (12)
C3—C41.3988 (11)C18—H18A0.9800
C3—C171.5153 (11)C19—H19A0.9600
C4—C51.3933 (11)C19—H19B0.9600
C4—H4A0.9300C19—H19C0.9600
C5—C61.3937 (11)C20—H20A0.9600
C5—H5A0.9300C20—H20B0.9600
C6—C71.5260 (10)C20—H20C0.9600
C7—C81.5031 (10)C22—H22A0.9600
C7—C211.5317 (11)C22—H22B0.9600
C7—H7A0.9800C22—H22C0.9600
C10—C111.4607 (10)C21—H21A0.9600
C10—H10A0.9300C21—H21B0.9600
C11—C121.3973 (10)C21—H21C0.9600
C11—C161.3997 (11)
C8—N1—N2104.10 (6)C12—C13—H13A119.6
C9—N2—N1113.95 (6)C14—C13—H13A119.6
C9—N2—H1N2123.7 (9)C13—C14—C15118.39 (7)
N1—N2—H1N2120.6 (9)C13—C14—C22120.58 (7)
C9—N3—C8108.26 (6)C15—C14—C22121.01 (7)
C9—N3—N4131.25 (6)C16—C15—C14121.17 (7)
C8—N3—N4119.96 (6)C16—C15—H15A119.4
C10—N4—N3115.74 (6)C14—C15—H15A119.4
C6—C1—C2120.96 (7)C15—C16—C11119.99 (7)
C6—C1—H1A119.5C15—C16—H16A120.0
C2—C1—H1A119.5C11—C16—H16A120.0
C1—C2—C3121.17 (7)C3—C17—C18117.04 (7)
C1—C2—H2A119.4C3—C17—H17A108.6 (8)
C3—C2—H2A119.4C18—C17—H17A108.0 (8)
C2—C3—C4117.51 (7)C3—C17—H17B109.9 (8)
C2—C3—C17122.25 (7)C18—C17—H17B107.4 (8)
C4—C3—C17120.10 (7)H17A—C17—H17B105.3 (11)
C5—C4—C3121.31 (7)C19—C18—C20110.91 (8)
C5—C4—H4A119.3C19—C18—C17112.08 (7)
C3—C4—H4A119.3C20—C18—C17109.57 (8)
C4—C5—C6120.88 (7)C19—C18—H18A108.0
C4—C5—H5A119.6C20—C18—H18A108.0
C6—C5—H5A119.6C17—C18—H18A108.0
C1—C6—C5118.09 (7)C18—C19—H19A109.5
C1—C6—C7120.91 (7)C18—C19—H19B109.5
C5—C6—C7120.86 (7)H19A—C19—H19B109.5
C8—C7—C6108.52 (6)C18—C19—H19C109.5
C8—C7—C21110.40 (6)H19A—C19—H19C109.5
C6—C7—C21113.55 (6)H19B—C19—H19C109.5
C8—C7—H7A108.1C18—C20—H20A109.5
C6—C7—H7A108.1C18—C20—H20B109.5
C21—C7—H7A108.1H20A—C20—H20B109.5
N1—C8—N3110.74 (6)C18—C20—H20C109.5
N1—C8—C7126.21 (7)H20A—C20—H20C109.5
N3—C8—C7123.00 (6)H20B—C20—H20C109.5
N2—C9—N3102.85 (6)C14—C22—H22A109.5
N2—C9—S1127.09 (6)C14—C22—H22B109.5
N3—C9—S1129.97 (6)H22A—C22—H22B109.5
N4—C10—C11120.87 (7)C14—C22—H22C109.5
N4—C10—H10A119.6H22A—C22—H22C109.5
C11—C10—H10A119.6H22B—C22—H22C109.5
C12—C11—C16119.12 (7)C7—C21—H21A109.5
C12—C11—C10117.53 (7)C7—C21—H21B109.5
C16—C11—C10123.35 (6)H21A—C21—H21B109.5
C13—C12—C11120.40 (7)C7—C21—H21C109.5
C13—C12—H12A119.8H21A—C21—H21C109.5
C11—C12—H12A119.8H21B—C21—H21C109.5
C12—C13—C14120.87 (7)
C8—N1—N2—C9−1.39 (9)C6—C7—C8—N3−66.34 (9)
C9—N3—N4—C10−33.22 (11)C21—C7—C8—N3168.62 (7)
C8—N3—N4—C10156.15 (7)N1—N2—C9—N32.75 (9)
C6—C1—C2—C30.00 (13)N1—N2—C9—S1−174.08 (6)
C1—C2—C3—C4−2.26 (12)C8—N3—C9—N2−2.97 (8)
C1—C2—C3—C17173.47 (8)N4—N3—C9—N2−174.43 (7)
C2—C3—C4—C52.09 (11)C8—N3—C9—S1173.73 (6)
C17—C3—C4—C5−173.73 (7)N4—N3—C9—S12.27 (12)
C3—C4—C5—C60.34 (11)N3—N4—C10—C11−179.96 (6)
C2—C1—C6—C52.44 (12)N4—C10—C11—C12−173.19 (7)
C2—C1—C6—C7−173.48 (7)N4—C10—C11—C166.71 (11)
C4—C5—C6—C1−2.61 (11)C16—C11—C12—C13−1.82 (11)
C4—C5—C6—C7173.32 (7)C10—C11—C12—C13178.09 (7)
C1—C6—C7—C8108.52 (8)C11—C12—C13—C140.56 (12)
C5—C6—C7—C8−67.29 (9)C12—C13—C14—C151.58 (12)
C1—C6—C7—C21−128.32 (8)C12—C13—C14—C22−176.58 (8)
C5—C6—C7—C2155.87 (9)C13—C14—C15—C16−2.50 (12)
N2—N1—C8—N3−0.65 (8)C22—C14—C15—C16175.66 (8)
N2—N1—C8—C7−178.19 (7)C14—C15—C16—C111.26 (12)
C9—N3—C8—N12.37 (9)C12—C11—C16—C150.92 (11)
N4—N3—C8—N1174.96 (6)C10—C11—C16—C15−178.99 (7)
C9—N3—C8—C7180.00 (7)C2—C3—C17—C1835.20 (11)
N4—N3—C8—C7−7.40 (10)C4—C3—C17—C18−149.19 (7)
C6—C7—C8—N1110.92 (8)C3—C17—C18—C1960.72 (10)
C21—C7—C8—N1−14.12 (11)C3—C17—C18—C20−175.71 (7)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H1N2···S1i0.86 (1)2.41 (1)3.2619 (7)171 (1)
C10—H10A···S10.932.553.1834 (8)126
C12—H12A···Cg2ii0.932.703.5531 (9)152
C21—H21B···Cg2iii0.962.993.8326 (9)148
Symmetry codes: (i) −x+2, −y−1, −z+2; (ii) −x+1, −y, −z+2; (iii) −x+2, −y, −z+1.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H1N2···S1i0.86 (1)2.41 (1)3.2619 (7)171 (1)
C10—H10A···S10.932.553.1834 (8)126
C12—H12A···Cg2ii0.932.703.5531 (9)152
C21—H21B···Cg2iii0.962.993.8326 (9)148
Symmetry codes: (i) −x+2, −y−1, −z+2; (ii) −x+1, −y, −z+2; (iii) −x+2, −y, −z+1.
Acknowledgements top

FHK and SRJ thank the Malaysian Government and Universiti Sains Malaysia for the Science Fund grant No. 305/PFIZIK/613312. SRJ thanks Universiti Sains Malaysia for a post–doctoral research fellowship.

references
References top

Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–19.

Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.

Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.

Clemons, M., Coleman, R. E. & Verma, S. (2004). Cancer Treat. Rev. 30, 325–332.

Demirbas, N. & Ugurluoglu, R. (2004). Turk. J. Chem. 28, 679–690.

Demirbas, N., Ugurluoglu, R. & Demirbasx, A. (2002). Bioorg. Med. Chem. 10, 3717–3723.

Johnston, G. A. R. (2002). Curr. Top. Med. Chem. 2, 903–913.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Shujuan, S., Hongxiang, L., Gao, Y., Fan, P., Ma, B., Ge, W. & Wang, X. (2004). J. Pharm. Biomed. Anal. 34, 1117–1124.

Spek, A. L. (2003). J. Appl. Cryst., 36, 7–13.