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Journal logoCRYSTALLOGRAPHIC
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ISSN: 2056-9890
Volume 65| Part 8| August 2009| Pages o1854-o1855

Bis(2,3-di­amino­pyridinium) succinate trihydrate

aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: hkfun@usm.my

(Received 24 June 2009; accepted 7 July 2009; online 15 July 2009)

In the title salt, 2C5H8N3+·C4H4O42−·3H2O, the asymmetric unit contains a protonated 2,3-diamino­pyridinium cation, half of a succinate dianion (disposed about a centre of inversion), and one and a half water mol­ecules. One of the water mol­ecules is disordered over two sites with occupancies of 0.670 (17) and 0.330 (17). The other water mol­ecule has an occupancy of 0.5 (from refinement). The pyridine N atom of the 2,3-diamino­pyridine mol­ecule is protonated. The protonated N atom and one of the 2-amino H atoms are hydrogen bonded to the succinate anion through a pair of N—H⋯O hydrogen bonds, forming an R22(8) ring motif. In the crystal, mol­ecules are consolidated into a three-dimensional network by N—H⋯O and O—H⋯O inter­actions.

Related literature

For substituted pyridines, see: Pozharski et al. (1997[Pozharski, A. F., Soldatenkov, A. T. & Katritzky, A. R. (1997). Heterocycles in Life and Society. New York: Wiley.]); Katritzky et al. (1996[Katritzky, A. R., Rees, C. W. & Scriven, E. F. V. (1996). Comprehensive Heterocyclic Chemistry II. Oxford: Pergamon Press.]); Jeffrey & Saenger (1991[Jeffrey, G. A. & Saenger, W. (1991). Hydrogen Bonding in Biological Structures. Berlin: Springer.]); Jeffrey (1997[Jeffrey, G. A. (1997). An Introduction to Hydrogen Bonding. Oxford University Press.]); Scheiner (1997[Scheiner, S. (1997). Hydrogen Bonding, A Theoretical Perspective. Oxford University Press.]). For related structures, see: De Cires-Mejias et al. (2004[De Cires-Mejias, C., Tanase, S., Reedijk, J., Gonzalez-Vilchez, F., Vilaplana, R., Mills, A. M., Kooijman, H. & Spek, A. L. (2004). Inorg. Chim. Acta, 357, 1494-1498.]); Fun & Balasubramani (2009[Fun, H.-K. & Balasubramani, K. (2009). Acta Cryst. E65, o1496-o1497.]); Balasubramani & Fun (2009a[Balasubramani, K. & Fun, H.-K. (2009a). Acta Cryst. E65, o1511-o1512.],b[Balasubramani, K. & Fun, H.-K. (2009b). Acta Cryst. E65, o1519.]). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986[Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst. 19, 105-107.]). For hydrogen-bond motifs, see: Bernstein et al. (1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]).

[Scheme 1]

Experimental

Crystal data
  • 2C5H8N3+·C4H4O42−·3H2O

  • Mr = 195.20

  • Monoclinic, P 21 /c

  • a = 12.7159 (4) Å

  • b = 3.9024 (1) Å

  • c = 18.7734 (6) Å

  • β = 94.933 (2)°

  • V = 928.13 (5) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.11 mm−1

  • T = 100 K

  • 0.17 × 0.13 × 0.06 mm

Data collection
  • Bruker SMART APEXII CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2005[Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.981, Tmax = 0.993

  • 10934 measured reflections

  • 2121 independent reflections

  • 1364 reflections with I > 2σ(I)

  • Rint = 0.056

Refinement
  • R[F2 > 2σ(F2)] = 0.062

  • wR(F2) = 0.129

  • S = 1.06

  • 2121 reflections

  • 178 parameters

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.26 e Å−3

  • Δρmin = −0.24 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N2—H2N2⋯O1i 0.90 (3) 2.14 (3) 2.978 (3) 155 (3)
N3—H1N3⋯O1i 0.85 (3) 2.14 (3) 2.993 (3) 176 (3)
N3—H2N3⋯O1WAii 0.91 (3) 2.34 (3) 3.243 (6) 172 (2)
O1WA—H2WA⋯O2 0.85 1.93 2.764 (5) 165
N2—H1N2⋯O1 0.89 (3) 2.04 (3) 2.929 (3) 175 (2)
N1—H1N1⋯O2 0.96 (3) 1.69 (3) 2.643 (3) 171 (2)
Symmetry codes: (i) [-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]; (ii) [x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}].

Data collection: APEX2 (Bruker, 2005[Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2005[Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


Comment top

Pyridine and its derivatives play an important role in heterocyclic chemistry (Pozharski et al., 1997; Katritzky et al., 1996). Further, pyridine and its substituted derivatives are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991; Jeffrey, 1997;Scheiner, 1997). The crystal structures of 2,3-diaminopyridinium 4-hydroxybenzoate (Fun & Balasubramani, 2009), 2,3-diaminopyridinium 4-nitrobenzoate (Balasubramani & Fun, 2009a) and 2,3-diaminopyridinium benzoate (Balasubramani & Fun, 2009b) have been reported by us recently. In the hope to study some interesting hydrogen-bonding interactions, the title compound (I) was synthesized. Its molecular and crystal structure is presented here.

The asymmetric unit of (I) (Fig. 1), contains a protonated 2,3-diaminopyridinium cation, a half molecule of succinate anion (disposed about a centre of inversion), and one and half water molecules. In the 2,3-diaminopyridinium cation, protonatation N1 atom has lead to a slight increase (ca. 4 °) in the C1—N1—C5 angle to 123.6 (2)° compared with the unprotonated structure (De Cires-Mejias et al., 2004). The 2,3-diaminopyridinium cation is planar, with a maximum deviation of 0.004 (2) Å for atom C2.

In the crystal packing (Fig. 2), the protonated N1 atom and a nitrogen atom of the 2-amino group (N2) are hydrogen-bonded to the succinate oxygen atoms (O2 and O1) via a pair of N—H···O hydrogen bonds forming a ring motif R22(8) (Bernstein et al., 1995). The 2-amino groups (N2 and N3) are involved in N—H···O hydrogen-bonding interactions to form a R21(7) ring motif. The crystal structure is further stabilized by water molecules via O(water)—H···O and N—H···O(water) hydrogen bonding (Table 1 and Fig. 2).

Related literature top

For substituted pyridines, see: Pozharski et al. (1997); Katritzky et al. (1996); Jeffrey & Saenger (1991); Jeffrey (1997); Scheiner (1997). For related structures, see: De Cires-Mejias et al. (2004); Fun & Balasubramani (2009); Balasubramani & Fun (2009a,b). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986). For hydrogen-bond motifs, see: Bernstein et al. (1995).

Experimental top

An aqueous solution of hot methanol (10 ml/ 10 ml) of 2,3-diaminopyridine (27 mg, Aldrich) and succinic acid (29 mg, Merck) were mixed and warmed over a heating magnetic stirrer for 5 minutes. The resulting solution was allowed to cool slowly at room temperature. Crystals of (I) appeared from the mother liquor after a few days.

Refinement top

All the H atoms (other than the water H-atoms) were located from the difference Fourier map and allowed to refine freely [N–H = 0.85 (3)–0.96 (3) Å & C–H = 0.93 (2)–0.98 (2) Å]. The water H-atoms were located from the difference Fourier map but constrained to 0.85 Å from the parent atom with Uiso(H) = 1.5Ueq(O).

One water molecule has a refined occupancy of 0.495 (7) which was then fixed as 0.5 in the final refinement. The other water molecule is disordered (O1WA & O1WB) over two sites with occupancies of 0.670 (17) and 0.330 (17).

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 molecular structure of (I), showing 50% probability displacement ellipsoids and the atom numbering scheme. Dashed lines indicate the hydrogen bonding. The O1 water molecule is disordered over two positions. Symmetry operation A:-x, 2-y, 1-z.
[Figure 2] Fig. 2. Part of the crystal packing showing the overall 3-D hydrogen-bonding network in (I). Dashed lines indicate the hydrogen bonding.
Bis(2,3-diaminopyridinium) succinate trihydrate top
Crystal data top
2C5H8N3+·C4H4O42·3H2OF(000) = 416
Mr = 195.20Dx = 1.397 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2108 reflections
a = 12.7159 (4) Åθ = 2.2–30.0°
b = 3.9024 (1) ŵ = 0.11 mm1
c = 18.7734 (6) ÅT = 100 K
β = 94.933 (2)°Block, brown
V = 928.13 (5) Å30.17 × 0.13 × 0.06 mm
Z = 4
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer
2121 independent reflections
Radiation source: fine-focus sealed tube1364 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.056
ϕ and ω scansθmax = 27.5°, θmin = 2.6°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)
h = 1616
Tmin = 0.981, Tmax = 0.993k = 45
10934 measured reflectionsl = 2421
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)] = 0.062Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.129H atoms treated by a mixture of independent and constrained refinement
S = 1.06 w = 1/[σ2(Fo2) + (0.041P)2 + 0.7373P]
where P = (Fo2 + 2Fc2)/3
2121 reflections(Δ/σ)max < 0.001
178 parametersΔρmax = 0.26 e Å3
0 restraintsΔρmin = 0.24 e Å3
Crystal data top
2C5H8N3+·C4H4O42·3H2OV = 928.13 (5) Å3
Mr = 195.20Z = 4
Monoclinic, P21/cMo Kα radiation
a = 12.7159 (4) ŵ = 0.11 mm1
b = 3.9024 (1) ÅT = 100 K
c = 18.7734 (6) Å0.17 × 0.13 × 0.06 mm
β = 94.933 (2)°
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer
2121 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)
1364 reflections with I > 2σ(I)
Tmin = 0.981, Tmax = 0.993Rint = 0.056
10934 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0620 restraints
wR(F2) = 0.129H atoms treated by a mixture of independent and constrained refinement
S = 1.06Δρmax = 0.26 e Å3
2121 reflectionsΔρmin = 0.24 e Å3
178 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 s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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*/UeqOcc. (<1)
O10.02464 (12)0.7567 (4)0.37851 (8)0.0251 (4)
O20.18198 (12)0.6548 (5)0.43615 (8)0.0264 (4)
N10.25383 (14)0.2963 (5)0.33114 (10)0.0204 (5)
N20.10876 (15)0.4334 (6)0.25459 (12)0.0243 (5)
N30.20743 (19)0.1167 (7)0.14153 (12)0.0328 (6)
C10.20422 (17)0.2863 (6)0.26523 (12)0.0201 (5)
C20.25526 (17)0.1188 (6)0.20981 (12)0.0221 (6)
C30.35320 (18)0.0256 (7)0.22796 (13)0.0243 (6)
C40.40151 (18)0.0059 (7)0.29740 (13)0.0248 (6)
C50.35068 (18)0.1562 (7)0.34840 (13)0.0241 (6)
C60.08824 (17)0.7727 (6)0.43321 (12)0.0207 (5)
C70.05630 (18)0.9358 (7)0.50147 (12)0.0207 (5)
O1WA0.3424 (4)0.840 (3)0.5375 (3)0.082 (3)0.670 (17)
H1WA0.38030.66250.53410.123*0.670 (17)
H2WA0.28980.82220.50660.123*0.670 (17)
O1WB0.3443 (6)0.583 (4)0.5327 (3)0.039 (4)0.330 (17)
H1WB0.33120.79540.53650.058*0.330 (17)
H2WB0.31730.51820.49190.058*0.330 (17)
O2W0.4593 (3)0.248 (2)0.5467 (3)0.110 (3)0.50
H1W20.51190.35430.53220.165*0.50
H2W20.44620.07940.51870.165*0.50
H4A0.4676 (19)0.100 (7)0.3090 (12)0.027 (7)*
H5A0.3781 (17)0.185 (6)0.3960 (13)0.022 (6)*
H3A0.3854 (18)0.140 (7)0.1902 (13)0.030 (7)*
H7B0.0722 (17)0.759 (6)0.5381 (12)0.020 (6)*
H7A0.1062 (18)1.118 (7)0.5145 (12)0.026 (7)*
H2N20.076 (2)0.445 (8)0.2102 (16)0.047 (9)*
H1N30.142 (2)0.154 (7)0.1337 (14)0.037 (8)*
H1N20.0799 (19)0.537 (7)0.2905 (14)0.028 (7)*
H2N30.239 (2)0.022 (8)0.1105 (15)0.045 (9)*
H1N10.2213 (19)0.418 (7)0.3676 (13)0.030 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0211 (8)0.0345 (11)0.0203 (8)0.0028 (8)0.0054 (7)0.0005 (7)
O20.0188 (8)0.0361 (11)0.0253 (9)0.0030 (8)0.0074 (7)0.0010 (8)
N10.0177 (10)0.0213 (12)0.0235 (10)0.0029 (9)0.0084 (8)0.0007 (9)
N20.0203 (11)0.0296 (13)0.0239 (11)0.0020 (10)0.0066 (9)0.0041 (10)
N30.0263 (13)0.0450 (16)0.0277 (12)0.0052 (12)0.0056 (10)0.0071 (11)
C10.0172 (11)0.0179 (13)0.0259 (12)0.0052 (10)0.0067 (9)0.0016 (10)
C20.0219 (12)0.0213 (14)0.0242 (12)0.0050 (11)0.0074 (10)0.0006 (10)
C30.0229 (12)0.0215 (15)0.0304 (13)0.0033 (11)0.0134 (10)0.0025 (11)
C40.0153 (12)0.0234 (14)0.0366 (14)0.0026 (11)0.0067 (10)0.0008 (12)
C50.0204 (12)0.0251 (15)0.0269 (13)0.0031 (11)0.0028 (10)0.0024 (11)
C60.0219 (12)0.0185 (14)0.0229 (12)0.0022 (11)0.0082 (10)0.0049 (10)
C70.0207 (12)0.0212 (14)0.0204 (12)0.0003 (11)0.0035 (10)0.0027 (11)
O1WA0.068 (3)0.111 (8)0.061 (3)0.030 (3)0.026 (2)0.022 (3)
O1WB0.031 (4)0.064 (9)0.020 (3)0.009 (4)0.002 (2)0.009 (3)
O2W0.039 (3)0.210 (8)0.078 (4)0.015 (4)0.016 (3)0.006 (4)
Geometric parameters (Å, º) top
O1—C61.253 (3)C4—H4A0.93 (2)
O2—C61.274 (3)C5—H5A0.94 (2)
N1—C11.340 (3)C6—C71.517 (3)
N1—C51.361 (3)C7—C7i1.513 (4)
N1—H1N10.96 (3)C7—H7B0.98 (2)
N2—C11.342 (3)C7—H7A0.97 (3)
N2—H2N20.90 (3)O1WA—H1WA0.8500
N2—H1N20.89 (3)O1WA—H2WA0.8501
N3—C21.371 (3)O1WA—H1WB0.2257
N3—H1N30.85 (3)O1WB—H1WA0.5518
N3—H2N30.91 (3)O1WB—H2WA1.2381
C1—C21.431 (3)O1WB—H1WB0.8500
C2—C31.383 (3)O1WB—H2WB0.8502
C3—C41.395 (3)O2W—H1W20.8500
C3—H3A0.96 (3)O2W—H2W20.8501
C4—C51.357 (3)
C1—N1—C5123.6 (2)C4—C5—H5A124.5 (14)
C1—N1—H1N1118.5 (14)N1—C5—H5A115.7 (14)
C5—N1—H1N1117.9 (14)O1—C6—O2123.6 (2)
C1—N2—H2N2120.3 (18)O1—C6—C7120.8 (2)
C1—N2—H1N2120.5 (15)O2—C6—C7115.61 (19)
H2N2—N2—H1N2119 (2)C7i—C7—C6115.4 (2)
C2—N3—H1N3120.8 (18)C7i—C7—H7B113.3 (13)
C2—N3—H2N3114.7 (17)C6—C7—H7B104.0 (13)
H1N3—N3—H2N3118 (3)C7i—C7—H7A111.3 (14)
N1—C1—N2118.2 (2)C6—C7—H7A107.7 (14)
N1—C1—C2118.5 (2)H7B—C7—H7A104.4 (18)
N2—C1—C2123.2 (2)H1WA—O1WA—H2WA107.4
N3—C2—C3123.1 (2)H1WA—O1WA—H1WB73.7
N3—C2—C1119.4 (2)H2WA—O1WA—H1WB54.6
C3—C2—C1117.5 (2)H1WA—O1WB—H2WA91.7
C2—C3—C4121.5 (2)H1WA—O1WB—H1WB67.4
C2—C3—H3A116.1 (14)H2WA—O1WB—H1WB35.9
C4—C3—H3A122.3 (14)H1WA—O1WB—H2WB118.6
C5—C4—C3119.1 (2)H2WA—O1WB—H2WB72.5
C5—C4—H4A119.8 (15)H1WB—O1WB—H2WB107.4
C3—C4—H4A121.1 (15)H1W2—O2W—H2W2107.4
C4—C5—N1119.7 (2)
C5—N1—C1—N2180.0 (2)C1—C2—C3—C40.8 (4)
C5—N1—C1—C20.2 (3)C2—C3—C4—C50.6 (4)
N1—C1—C2—N3177.7 (2)C3—C4—C5—N10.0 (4)
N2—C1—C2—N32.6 (4)C1—N1—C5—C40.4 (4)
N1—C1—C2—C30.4 (3)O1—C6—C7—C7i1.6 (4)
N2—C1—C2—C3179.4 (2)O2—C6—C7—C7i177.9 (3)
N3—C2—C3—C4177.2 (2)
Symmetry code: (i) x, y+2, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2N2···O1ii0.90 (3)2.14 (3)2.978 (3)155 (3)
N3—H1N3···O1ii0.85 (3)2.14 (3)2.993 (3)176 (3)
N3—H2N3···O1WAiii0.91 (3)2.34 (3)3.243 (6)172 (2)
O1WA—H2WA···O20.851.932.764 (5)165
N2—H1N2···O10.89 (3)2.04 (3)2.929 (3)175 (2)
N1—H1N1···O20.96 (3)1.69 (3)2.643 (3)171 (2)
Symmetry codes: (ii) x, y1/2, z+1/2; (iii) x, y+1/2, z1/2.

Experimental details

Crystal data
Chemical formula2C5H8N3+·C4H4O42·3H2O
Mr195.20
Crystal system, space groupMonoclinic, P21/c
Temperature (K)100
a, b, c (Å)12.7159 (4), 3.9024 (1), 18.7734 (6)
β (°) 94.933 (2)
V3)928.13 (5)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.17 × 0.13 × 0.06
Data collection
DiffractometerBruker SMART APEXII CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2005)
Tmin, Tmax0.981, 0.993
No. of measured, independent and
observed [I > 2σ(I)] reflections
10934, 2121, 1364
Rint0.056
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.062, 0.129, 1.06
No. of reflections2121
No. of parameters178
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.26, 0.24

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2N2···O1i0.90 (3)2.14 (3)2.978 (3)155 (3)
N3—H1N3···O1i0.85 (3)2.14 (3)2.993 (3)176 (3)
N3—H2N3···O1WAii0.91 (3)2.34 (3)3.243 (6)172 (2)
O1WA—H2WA···O20.851.932.764 (5)165
N2—H1N2···O10.89 (3)2.04 (3)2.929 (3)175 (2)
N1—H1N1···O20.96 (3)1.69 (3)2.643 (3)171 (2)
Symmetry codes: (i) x, y1/2, z+1/2; (ii) x, y+1/2, z1/2.
 

Footnotes

Thomson Reuters ResearcherID: A-3561-2009.

§Thomson Reuters ResearcherID: A-5523-2009.

Acknowledgements

HKF and KBS thank the Malaysian Government and Universiti Sains Malaysia for Science Fund grant No. 305/PFIZIK/613312. KBS thanks Universiti Sains Malaysia for a post–doctoral research fellowship. HKF also thanks Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012.

References

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Volume 65| Part 8| August 2009| Pages o1854-o1855
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