Dichlorido(2-{[3-(morpholin-4-ium-4-yl)prop­yl]imino­meth­yl}phenolate)zinc

Ikmal Hisham, N.A.; Khaledi, H.; Mohd Ali, H.

doi:10.1107/S1600536811022021

metal-organic compounds

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ISSN: 2056-9890

Volume 67| Part 7| July 2011| Page m932

doi:10.1107/S1600536811022021

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Dichlorido(2-{[3-(morpholin-4-ium-4-yl)propyl]iminomethyl}phenolate)zinc

Nurul Azimah Ikmal Hisham,^a Hamid Khaledi ^a ^* and Hapipah Mohd Ali ^a

^aDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
^*Correspondence e-mail: khaledi@siswa.um.edu.my

(Received 12 April 2011; accepted 7 June 2011; online 18 June 2011)

In the zwitterionic zinc title complex, [ZnCl₂(C₁₄H₂₀N₂O₂)], the Zn^II ion is four-coordinated in a distorted tetrahedral geometry. The Schiff base ligand employs its phenolate O and imine N atoms to coordinate the metal atom in a bidentate mode. Two Cl atoms complete the tetrahedral coordination environment. In the crystal, a pair of N—H⋯O hydrogen bonds connect the molecules into a centrosymmetric dimer. C—H⋯O, C—H⋯Cl and C—H⋯π interactions are also observed.

Related literature

For related structures of similar zwitterionic ZnCl₂ complexes, see: Qiu (2006 ); Ye & You (2008 ); Zhu (2008 ).

Experimental

Crystal data

[ZnCl₂(C₁₄H₂₀N₂O₂)]
M_r = 384.59
Monoclinic, P 2₁ /c
a = 8.11276 (10) Å
b = 11.21021 (13) Å
c = 18.4097 (2) Å
β = 92.0168 (6)°
V = 1673.24 (4) Å³
Z = 4
Mo Kα radiation
μ = 1.79 mm⁻¹
T = 100 K
0.37 × 0.32 × 0.25 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.557, T_max = 0.663
14420 measured reflections
3824 independent reflections
3557 reflections with I > 2σ(I)
R_int = 0.017

Refinement

R[F² > 2σ(F²)] = 0.020
wR(F²) = 0.051
S = 1.07
3824 reflections
193 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.34 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2N⋯O1ⁱ	0.90 (1)	1.81 (1)	2.6954 (14)	170 (2)
C5—H5⋯O2ⁱⁱ	0.95	2.39	3.2161 (16)	146
C9—H9A⋯Cl1ⁱⁱⁱ	0.99	2.83	3.6732 (13)	144
C10—H10A⋯Cl1ⁱ	0.99	2.82	3.6905 (13)	147
C14—H14A⋯Cl2ⁱⁱⁱ	0.99	2.69	3.5486 (13)	146
C14—H14B⋯Cl2^iv	0.99	2.78	3.6890 (14)	153
C12—H12B⋯Cg1^v	0.99	2.57	3.4366 (2)	146
Symmetry codes: (i) -x, -y, -z+2; (ii) $[-x, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) -x+1, -y, -z+2; (iv) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (v) $[x, -y-{\script{1\over 2}}, z-{\script{3\over 2}}]$ .

Data collection: APEX2 (Bruker, 2007 ); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001 ); software used to prepare material for publication: SHELXL97 and publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811022021/is2701sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811022021/is2701Isup2.hkl

checkCIF report

Comment top

The title compound was obtained via the complexation of ZnCl₂ with the in situ prepared Schiff base. The Schiff base ligand coordinates the metal ion via its phenolate oxygen and imine nitrogen atoms. The morpholine ring N atom stays away from the coordination and is protonated, implying the zwitterionic nature of the molecule. The tetrahedral geometry around the zinc(II) ion is completed by two Cl atoms. The coordination bond lengths in the complex are comparable to the corresponding values in similar structures (Qiu, 2006; Ye & You, 2008; Zhu, 2008). In the crystal, N—H···O hydrogen bonding connects pairs of the molecules into centrosymmetric dimers. The dimers are linked through C—H···O, C—H···Cl and C—H···π interactions into a three-dimensional network.

Related literature top

For related structures of similar zwitterionic ZnCl₂ complexes, see: Qiu (2006); Ye & You (2008); Zhu (2008).

Experimental top

A mixture of salicylaldehyde (0.20 g, 1.64 mmol) and N-(3-aminopropyl)morpholine (0.24 g, 1.64 mmol) in ethanol (20 ml) was refluxed for 2 hr followed by addition of a solution of zinc(II) chloride (0.22 g, 1.64 mmol) in a minimum amount of water. The resulting solution was refluxed for 30 min, then the solvent was removed under reduced pressure. The impure product was recrystallized from methanol to give the yellow crystals of the title compound.

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2010).

Figures top

Fig. 1. Displacement ellipsoid plot of the title compound at the 50% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius.

Dichlorido(2-{[3-(morpholin-4-ium-4-yl)propyl]iminomethyl}phenolate)zinc top

Crystal data top

[ZnCl₂(C₁₄H₂₀N₂O₂)]	F(000) = 792
M_r = 384.59	D_x = 1.527 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9373 reflections
a = 8.11276 (10) Å	θ = 2.2–30.4°
b = 11.21021 (13) Å	µ = 1.79 mm⁻¹
c = 18.4097 (2) Å	T = 100 K
β = 92.0168 (6)°	Block, yellow
V = 1673.24 (4) Å³	0.37 × 0.32 × 0.25 mm
Z = 4

Data collection top

Bruker APEXII CCD diffractometer	3824 independent reflections
Radiation source: fine-focus sealed tube	3557 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.017
ϕ and ω scans	θ_max = 27.5°, θ_min = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −10→10
T_min = 0.557, T_max = 0.663	k = −14→14
14420 measured reflections	l = −23→23

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)] = 0.020	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.051	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	w = 1/[σ²(F_o²) + (0.0237P)² + 0.6991P] where P = (F_o² + 2F_c²)/3
3824 reflections	(Δ/σ)_max = 0.003
193 parameters	Δρ_max = 0.34 e Å⁻³
1 restraint	Δρ_min = −0.33 e Å⁻³

Crystal data top

[ZnCl₂(C₁₄H₂₀N₂O₂)]	V = 1673.24 (4) Å³
M_r = 384.59	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 8.11276 (10) Å	µ = 1.79 mm⁻¹
b = 11.21021 (13) Å	T = 100 K
c = 18.4097 (2) Å	0.37 × 0.32 × 0.25 mm
β = 92.0168 (6)°

Data collection top

Bruker APEXII CCD diffractometer	3824 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	3557 reflections with I > 2σ(I)
T_min = 0.557, T_max = 0.663	R_int = 0.017
14420 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.020	1 restraint
wR(F²) = 0.051	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	Δρ_max = 0.34 e Å⁻³
3824 reflections	Δρ_min = −0.33 e Å⁻³
193 parameters

Special details top

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
Zn1	0.187917 (17)	0.093296 (13)	1.107214 (8)	0.01475 (5)
Cl1	0.22466 (4)	−0.09919 (3)	1.084342 (19)	0.02075 (8)
Cl2	0.33968 (4)	0.15593 (3)	1.205005 (18)	0.01907 (7)
O1	−0.04186 (11)	0.13291 (8)	1.12739 (5)	0.01608 (18)
O2	0.13093 (14)	−0.02283 (10)	0.65039 (5)	0.0276 (2)
N1	0.20412 (13)	0.20247 (10)	1.02150 (6)	0.0159 (2)
N2	0.16476 (13)	0.05293 (10)	0.79901 (6)	0.0135 (2)
H2N	0.1344 (19)	−0.0140 (12)	0.8218 (8)	0.016*
C1	−0.12380 (15)	0.22475 (11)	1.09867 (7)	0.0137 (2)
C2	−0.28113 (16)	0.25169 (12)	1.12420 (7)	0.0163 (2)
H2	−0.3253	0.2032	1.1611	0.020*
C3	−0.37327 (16)	0.34666 (12)	1.09714 (7)	0.0186 (3)
H3	−0.4787	0.3627	1.1158	0.022*
C4	−0.31222 (17)	0.41883 (12)	1.04277 (8)	0.0196 (3)
H4	−0.3743	0.4849	1.0247	0.024*
C5	−0.16034 (17)	0.39287 (12)	1.01564 (7)	0.0173 (3)
H5	−0.1203	0.4405	0.9774	0.021*
C6	−0.06264 (15)	0.29814 (11)	1.04276 (7)	0.0142 (2)
C7	0.09231 (16)	0.28065 (11)	1.00702 (7)	0.0159 (2)
H7	0.1134	0.3336	0.9682	0.019*
C8	0.34713 (16)	0.19638 (13)	0.97446 (7)	0.0194 (3)
H8A	0.4473	0.1769	1.0044	0.023*
H8B	0.3641	0.2753	0.9518	0.023*
C9	0.32253 (16)	0.10212 (12)	0.91483 (7)	0.0170 (3)
H9A	0.4296	0.0847	0.8929	0.020*
H9B	0.2812	0.0274	0.9363	0.020*
C10	0.20034 (15)	0.14566 (11)	0.85628 (7)	0.0152 (2)
H10A	0.0960	0.1682	0.8790	0.018*
H10B	0.2452	0.2178	0.8331	0.018*
C11	0.02330 (16)	0.09176 (11)	0.74944 (7)	0.0171 (3)
H11A	0.0509	0.1679	0.7255	0.020*
H11B	−0.0763	0.1045	0.7780	0.020*
C12	−0.01012 (18)	−0.00338 (13)	0.69264 (7)	0.0224 (3)
H12A	−0.0405	−0.0787	0.7168	0.027*
H12B	−0.1042	0.0214	0.6604	0.027*
C13	0.26442 (19)	−0.06439 (14)	0.69587 (8)	0.0253 (3)
H13A	0.3610	−0.0801	0.6659	0.030*
H13B	0.2328	−0.1403	0.7190	0.030*
C14	0.31118 (16)	0.02596 (12)	0.75431 (7)	0.0180 (3)
H14A	0.4018	−0.0062	0.7860	0.022*
H14B	0.3505	0.1002	0.7315	0.022*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Zn1	0.01268 (8)	0.01573 (8)	0.01592 (9)	0.00041 (5)	0.00142 (6)	−0.00096 (5)
Cl1	0.01746 (15)	0.01744 (15)	0.02752 (17)	0.00001 (11)	0.00307 (13)	−0.00615 (12)
Cl2	0.01577 (14)	0.02111 (16)	0.02017 (16)	0.00145 (11)	−0.00147 (11)	−0.00506 (12)
O1	0.0137 (4)	0.0163 (4)	0.0184 (5)	0.0015 (3)	0.0024 (3)	0.0039 (4)
O2	0.0390 (6)	0.0322 (6)	0.0117 (5)	0.0108 (5)	0.0007 (4)	−0.0017 (4)
N1	0.0148 (5)	0.0191 (5)	0.0140 (5)	−0.0042 (4)	0.0023 (4)	−0.0036 (4)
N2	0.0153 (5)	0.0139 (5)	0.0114 (5)	0.0016 (4)	0.0022 (4)	0.0009 (4)
C1	0.0147 (6)	0.0137 (6)	0.0127 (6)	−0.0014 (4)	−0.0014 (4)	−0.0014 (4)
C2	0.0153 (6)	0.0170 (6)	0.0165 (6)	−0.0005 (5)	0.0010 (5)	0.0012 (5)
C3	0.0137 (6)	0.0202 (6)	0.0219 (7)	0.0011 (5)	−0.0010 (5)	−0.0014 (5)
C4	0.0192 (6)	0.0171 (6)	0.0220 (7)	0.0014 (5)	−0.0066 (5)	0.0019 (5)
C5	0.0219 (6)	0.0165 (6)	0.0134 (6)	−0.0039 (5)	−0.0035 (5)	0.0008 (5)
C6	0.0164 (6)	0.0139 (6)	0.0121 (6)	−0.0019 (4)	−0.0007 (5)	−0.0016 (4)
C7	0.0205 (6)	0.0157 (6)	0.0117 (6)	−0.0056 (5)	0.0011 (5)	−0.0013 (5)
C8	0.0141 (6)	0.0269 (7)	0.0173 (6)	−0.0057 (5)	0.0035 (5)	−0.0040 (5)
C9	0.0135 (6)	0.0222 (7)	0.0154 (6)	0.0004 (5)	0.0008 (5)	−0.0025 (5)
C10	0.0165 (6)	0.0150 (6)	0.0142 (6)	0.0001 (5)	0.0018 (5)	−0.0019 (5)
C11	0.0183 (6)	0.0189 (6)	0.0138 (6)	0.0042 (5)	−0.0017 (5)	0.0014 (5)
C12	0.0284 (7)	0.0240 (7)	0.0143 (6)	0.0020 (6)	−0.0042 (5)	0.0000 (5)
C13	0.0333 (8)	0.0257 (7)	0.0169 (7)	0.0105 (6)	0.0037 (6)	−0.0020 (5)
C14	0.0199 (6)	0.0194 (6)	0.0153 (6)	0.0055 (5)	0.0065 (5)	0.0020 (5)

Geometric parameters (Å, º) top

Zn1—O1	1.9644 (9)	C5—H5	0.9500
Zn1—N1	2.0049 (11)	C6—C7	1.4526 (18)
Zn1—Cl1	2.2206 (3)	C7—H7	0.9500
Zn1—Cl2	2.2570 (3)	C8—C9	1.5318 (18)
O1—C1	1.3254 (15)	C8—H8A	0.9900
O2—C12	1.4230 (17)	C8—H8B	0.9900
O2—C13	1.4238 (18)	C9—C10	1.5190 (18)
N1—C7	1.2825 (17)	C9—H9A	0.9900
N1—C8	1.4736 (16)	C9—H9B	0.9900
N2—C14	1.4995 (16)	C10—H10A	0.9900
N2—C10	1.5012 (16)	C10—H10B	0.9900
N2—C11	1.5052 (16)	C11—C12	1.5114 (18)
N2—H2N	0.898 (13)	C11—H11A	0.9900
C1—C2	1.4084 (17)	C11—H11B	0.9900
C1—C6	1.4206 (17)	C12—H12A	0.9900
C2—C3	1.3836 (18)	C12—H12B	0.9900
C2—H2	0.9500	C13—C14	1.516 (2)
C3—C4	1.392 (2)	C13—H13A	0.9900
C3—H3	0.9500	C13—H13B	0.9900
C4—C5	1.377 (2)	C14—H14A	0.9900
C4—H4	0.9500	C14—H14B	0.9900
C5—C6	1.4062 (18)

O1—Zn1—N1	95.72 (4)	C9—C8—H8A	109.3
O1—Zn1—Cl1	112.96 (3)	N1—C8—H8B	109.3
N1—Zn1—Cl1	115.53 (3)	C9—C8—H8B	109.3
O1—Zn1—Cl2	105.87 (3)	H8A—C8—H8B	108.0
N1—Zn1—Cl2	112.88 (3)	C10—C9—C8	110.63 (11)
Cl1—Zn1—Cl2	112.363 (13)	C10—C9—H9A	109.5
C1—O1—Zn1	124.48 (8)	C8—C9—H9A	109.5
C12—O2—C13	109.77 (10)	C10—C9—H9B	109.5
C7—N1—C8	118.38 (11)	C8—C9—H9B	109.5
C7—N1—Zn1	121.01 (9)	H9A—C9—H9B	108.1
C8—N1—Zn1	120.60 (9)	N2—C10—C9	112.36 (10)
C14—N2—C10	112.86 (10)	N2—C10—H10A	109.1
C14—N2—C11	109.11 (10)	C9—C10—H10A	109.1
C10—N2—C11	110.44 (10)	N2—C10—H10B	109.1
C14—N2—H2N	108.8 (10)	C9—C10—H10B	109.1
C10—N2—H2N	107.5 (10)	H10A—C10—H10B	107.9
C11—N2—H2N	108.0 (10)	N2—C11—C12	109.25 (10)
O1—C1—C2	118.76 (11)	N2—C11—H11A	109.8
O1—C1—C6	123.77 (11)	C12—C11—H11A	109.8
C2—C1—C6	117.47 (11)	N2—C11—H11B	109.8
C3—C2—C1	121.96 (12)	C12—C11—H11B	109.8
C3—C2—H2	119.0	H11A—C11—H11B	108.3
C1—C2—H2	119.0	O2—C12—C11	110.99 (12)
C2—C3—C4	120.32 (13)	O2—C12—H12A	109.4
C2—C3—H3	119.8	C11—C12—H12A	109.4
C4—C3—H3	119.8	O2—C12—H12B	109.4
C5—C4—C3	118.93 (12)	C11—C12—H12B	109.4
C5—C4—H4	120.5	H12A—C12—H12B	108.0
C3—C4—H4	120.5	O2—C13—C14	111.40 (11)
C4—C5—C6	122.09 (12)	O2—C13—H13A	109.3
C4—C5—H5	119.0	C14—C13—H13A	109.3
C6—C5—H5	119.0	O2—C13—H13B	109.3
C5—C6—C1	119.19 (12)	C14—C13—H13B	109.3
C5—C6—C7	115.28 (12)	H13A—C13—H13B	108.0
C1—C6—C7	125.44 (12)	N2—C14—C13	109.93 (11)
N1—C7—C6	127.96 (12)	N2—C14—H14A	109.7
N1—C7—H7	116.0	C13—C14—H14A	109.7
C6—C7—H7	116.0	N2—C14—H14B	109.7
N1—C8—C9	111.57 (10)	C13—C14—H14B	109.7
N1—C8—H8A	109.3	H14A—C14—H14B	108.2

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···O1ⁱ	0.90 (1)	1.81 (1)	2.6954 (14)	170 (2)
C5—H5···O2ⁱⁱ	0.95	2.39	3.2161 (16)	146
C9—H9A···Cl1ⁱⁱⁱ	0.99	2.83	3.6732 (13)	144
C10—H10A···Cl1ⁱ	0.99	2.82	3.6905 (13)	147
C14—H14A···Cl2ⁱⁱⁱ	0.99	2.69	3.5486 (13)	146
C14—H14B···Cl2^iv	0.99	2.78	3.6890 (14)	153
C12—H12B···Cg1^v	0.99	2.57	3.4366 (2)	146

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

Experimental details

Crystal data
Chemical formula	[ZnCl₂(C₁₄H₂₀N₂O₂)]
M_r	384.59
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	8.11276 (10), 11.21021 (13), 18.4097 (2)
β (°)	92.0168 (6)
V (Å³)	1673.24 (4)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	1.79
Crystal size (mm)	0.37 × 0.32 × 0.25

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.557, 0.663
No. of measured, independent and observed [I > 2σ(I)] reflections	14420, 3824, 3557
R_int	0.017
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.051, 1.07
No. of reflections	3824
No. of parameters	193
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.34, −0.33

Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), X-SEED (Barbour, 2001), SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···O1ⁱ	0.898 (13)	1.807 (13)	2.6954 (14)	169.6 (15)
C5—H5···O2ⁱⁱ	0.95	2.39	3.2161 (16)	146
C9—H9A···Cl1ⁱⁱⁱ	0.99	2.83	3.6732 (13)	144
C10—H10A···Cl1ⁱ	0.99	2.82	3.6905 (13)	147
C14—H14A···Cl2ⁱⁱⁱ	0.99	2.69	3.5486 (13)	146
C14—H14B···Cl2^iv	0.99	2.78	3.6890 (14)	153
C12—H12B···Cg1^v	0.99	2.57	3.43663 (15)	146

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

Acknowledgements

The authors thank the University of Malaya for funding this study (FRGS grant No. FP004/2010B).

References

Barbour, L. J. (2001). J. Supramol. Chem. 1, 189–191. CrossRef CAS Google Scholar
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Qiu, X.-Y. (2006). Acta Cryst. E62, m2173–m2174. Web of Science CSD CrossRef IUCr Journals Google Scholar
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Volume 67| Part 7| July 2011| Page m932

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