organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

4-[(Eth­oxy­imino)(phen­yl)meth­yl]-5-methyl-2-phenyl-1H-pyrazol-3(2H)-one

aSchool of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, People's Republic of China
*Correspondence e-mail: dongwk@mail.lzjtu.cn

(Received 12 August 2008; accepted 14 August 2008; online 20 August 2008)

In the mol­ecule of the title compound, C19H19N3O2, the central pyrazole ring makes dihedral angles of 9.89 (3) and 66.06 (5)° with the two phenyl rings, and the two phenyl rings form an angle of 74.05 (5)°. An intra­molecular C—H⋯O hydrogen bond forms a six-membered ring, producing an S(6) ring motif. In the crystal structure, inter­molecular N—H⋯O and C—H⋯O hydrogen bonds link each mol­ecule to two others, forming an infinite one-dimensional supra­molecular structure along the c axis.

Related literature

For related literature, see: Beeam et al. (1984[Beeam, C. F., Hall, H. L. & Huff, A. M. (1984). J. Heteroatom. Chem. 21, 1897-1902.]); Bonati (1980[Bonati, F. (1980). Chim. Ind. (Roma). 62, 323-328.]); Dong & Feng (2006[Dong, W.-K. & Feng, J.-H. (2006). Acta Cryst. E62, o3577-o3578.]); Dong et al. (2008a[Dong, W.-K., He, X.-N., Li, L., Lv, Z.-W. & Tong, J.-F. (2008a). Acta Cryst. E64, o1405.],b[Dong, W.-K., Zhao, C.-Y., Zhong, J.-K., Tang, X.-L. & Yu, T.-Z. (2008b). Acta Cryst. E64, o1323.]); Duan et al. (2007[Duan, J.-G., Dong, C.-M., Shi, J.-Y., Wu, L. & Dong, W.-K. (2007). Acta Cryst. E63, o2704-o2705.]).

[Scheme 1]

Experimental

Crystal data
  • C19H19N3O2

  • Mr = 321.37

  • Monoclinic, P 21 /c

  • a = 13.0046 (15) Å

  • b = 11.4657 (11) Å

  • c = 11.6874 (12) Å

  • β = 99.4530 (10)°

  • V = 1719.0 (3) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.08 mm−1

  • T = 298 (2) K

  • 0.50 × 0.18 × 0.16 mm

Data collection
  • Brucker SMART 1000 CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.960, Tmax = 0.987

  • 8480 measured reflections

  • 3028 independent reflections

  • 1756 reflections with I > 2σ(I)

  • Rint = 0.041

Refinement
  • R[F2 > 2σ(F2)] = 0.044

  • wR(F2) = 0.140

  • S = 1.02

  • 3028 reflections

  • 219 parameters

  • H-atom parameters constrained

  • Δρmax = 0.17 e Å−3

  • Δρmin = −0.23 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N3—H3⋯O2i 0.86 1.80 2.653 (2) 171
C15—H15⋯O2i 0.93 2.42 3.200 (3) 141
C19—H19⋯O2 0.93 2.32 2.900 (3) 120
Symmetry code: (i) [x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}].

Data collection: SMART (Siemens, 1996[Siemens (1996). SMART and SAINT. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Siemens, 1996[Siemens (1996). SMART and SAINT. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

The pyrazole ring is a prominent structural motif found in numerous pharmaceutically active compounds. Due to the easy preparation and rich biological activity, the pyrazole framework plays an essential role in biologically active compounds and therefore represents an interesting template for combinatorial as well as medicinal chemistry (Beeam et al., 1984; Bonati et al., 1980). As an extension of our work (Dong et al., 2006; Duan et al., 2007; Dong et al., 2008a; Dong et al., 2008b) on the structural characterization of oxime compounds, the title compound, (Fig. 1), is reported here.

The single-crystal structure of the title compound is built up by only the C19H19N3O2 molecules, in which all bond lengths are in normal ranges. In the title compound, the central pyrazole ring makes dihedral angles of 9.89 (3) and 66.06 (5)° with the two outer benzene rings, and the two outer benzene rings form an angle of 74.05 (5)°. An intramolecular C—H···O hydrogen bond forms a six-membered ring, producing an S(6) ring motif. In the crystal structure, intermolecular N—H···O and C—H···O hydrogen bonds link each molecule to two others, forming an infinite one-dimensional supramolecular structure along the c axis (Fig. 2).

Related literature top

For related literature, see: Beeam et al. (1984); Bonati (1980); Dong & Feng (2006); Dong et al. (2008a,b); Duan et al. (2007).

Experimental top

To a solution of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolon (5 mmol) in warm ethanol (5 ml) was added an ethanol (5 ml) solution of ethoxyamine (10 mmol). After stirring the reaction mixture at 338 K for 6 h, the solvent was removed under reduced pressure and the residue was recrystallized from ethanol to give the title compound. Yield, 68%. mp. 444–445 K. Anal. Calc. for C19H19N3O2: C, 71.01; H, 5.96; N, 13.08. Found: C, 71.32; H, 5.81; N, 13.15.

Colorless prismatic crystals suitable for single-crystal X-ray diffraction were obtained by recrystallization from ethanol at room temperature.

Refinement top

Non-H atoms were refined anisotropically. H atoms were treated as riding atoms with distances C—H = 0.96 (CH3), C—H = 0.97 (CH2), or 0.93 Å (CH), N—H = 0.86 Å, and Uiso(H) = 1.2 Ueq(C) and 1.5 Ueq(O).

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SMART (Siemens, 1996); data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. ORTEP representation of the title compound with atom numbering. Displacement ellipsoids for non-hydrogen atoms are drawn at the 30% probability level.
[Figure 2] Fig. 2. Part of the supramolecular structure of the title compound viewed along the b axis. Intra- and intermolecular hydrogen bonds are shown as dashed lines.
4-[(Ethoxyimino)(phenyl)methyl]-5-methyl-2-phenyl-1H-pyrazol-3(2H)-one top
Crystal data top
C19H19N3O2F(000) = 680
Mr = 321.37Dx = 1.242 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 1770 reflections
a = 13.0046 (15) Åθ = 2.4–22.5°
b = 11.4657 (11) ŵ = 0.08 mm1
c = 11.6874 (12) ÅT = 298 K
β = 99.453 (1)°Prismatic, colorless
V = 1719.0 (3) Å30.50 × 0.18 × 0.16 mm
Z = 4
Data collection top
Brucker SMART 1000 CCD area-detector
diffractometer
3028 independent reflections
Radiation source: fine-focus sealed tube1756 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.041
ϕ and ω scansθmax = 25.0°, θmin = 1.6°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 1515
Tmin = 0.960, Tmax = 0.987k = 139
8480 measured reflectionsl = 1313
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)] = 0.044Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.140H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0687P)2 + 0.0591P]
where P = (Fo2 + 2Fc2)/3
3028 reflections(Δ/σ)max < 0.001
219 parametersΔρmax = 0.17 e Å3
0 restraintsΔρmin = 0.24 e Å3
Crystal data top
C19H19N3O2V = 1719.0 (3) Å3
Mr = 321.37Z = 4
Monoclinic, P21/cMo Kα radiation
a = 13.0046 (15) ŵ = 0.08 mm1
b = 11.4657 (11) ÅT = 298 K
c = 11.6874 (12) Å0.50 × 0.18 × 0.16 mm
β = 99.453 (1)°
Data collection top
Brucker SMART 1000 CCD area-detector
diffractometer
3028 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
1756 reflections with I > 2σ(I)
Tmin = 0.960, Tmax = 0.987Rint = 0.041
8480 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0440 restraints
wR(F2) = 0.140H-atom parameters constrained
S = 1.02Δρmax = 0.17 e Å3
3028 reflectionsΔρmin = 0.24 e Å3
219 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
xyzUiso*/Ueq
N10.53222 (14)0.34824 (17)0.06367 (17)0.0486 (5)
N20.84502 (13)0.23475 (16)0.16076 (15)0.0369 (5)
N30.78882 (13)0.29323 (15)0.23325 (15)0.0386 (5)
H30.80640.29960.30720.046*
O10.49758 (11)0.28139 (15)0.02320 (14)0.0546 (5)
O20.82634 (12)0.20296 (15)0.03673 (13)0.0529 (5)
C10.38665 (18)0.2834 (2)0.0039 (3)0.0623 (8)
H1A0.35950.25050.07150.075*
H1B0.36170.36300.00610.075*
C20.3515 (2)0.2130 (3)0.0975 (3)0.0805 (10)
H2A0.37760.13490.09540.121*
H2B0.27670.21130.08590.121*
H2C0.37740.24740.17150.121*
C30.63196 (17)0.35862 (19)0.04638 (19)0.0395 (6)
C40.70377 (15)0.31546 (19)0.05486 (18)0.0363 (5)
C50.79385 (17)0.24753 (19)0.04860 (19)0.0371 (5)
C60.70309 (16)0.33834 (19)0.17079 (19)0.0360 (5)
C70.62708 (17)0.4013 (2)0.2301 (2)0.0496 (7)
H7A0.57350.34840.24460.074*
H7B0.59640.46400.18170.074*
H7C0.66220.43230.30230.074*
C80.67571 (18)0.4228 (2)0.1379 (2)0.0432 (6)
C90.6212 (2)0.4282 (2)0.2505 (2)0.0576 (7)
H90.55720.39080.26880.069*
C100.6611 (3)0.4881 (3)0.3347 (3)0.0755 (9)
H100.62380.49140.40970.091*
C110.7555 (3)0.5432 (3)0.3093 (3)0.0773 (9)
H110.78230.58320.36710.093*
C120.8107 (2)0.5397 (2)0.1988 (3)0.0664 (8)
H120.87430.57820.18110.080*
C130.77084 (19)0.4782 (2)0.1138 (2)0.0516 (7)
H130.80890.47430.03930.062*
C140.94564 (15)0.19033 (19)0.20265 (19)0.0358 (5)
C150.99788 (18)0.2239 (2)0.3093 (2)0.0517 (7)
H150.96780.27750.35350.062*
C161.09499 (19)0.1782 (3)0.3508 (2)0.0659 (8)
H161.12960.20050.42350.079*
C171.1406 (2)0.1007 (3)0.2862 (3)0.0667 (8)
H171.20630.07060.31430.080*
C181.0891 (2)0.0678 (2)0.1801 (3)0.0647 (8)
H181.12030.01530.13580.078*
C190.99121 (17)0.1113 (2)0.1374 (2)0.0520 (7)
H190.95640.08750.06520.062*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0485 (12)0.0550 (13)0.0405 (13)0.0035 (10)0.0019 (10)0.0055 (10)
N20.0349 (10)0.0546 (12)0.0209 (10)0.0067 (8)0.0036 (8)0.0001 (9)
N30.0394 (10)0.0560 (12)0.0200 (10)0.0020 (9)0.0038 (8)0.0052 (9)
O10.0391 (9)0.0719 (12)0.0507 (11)0.0002 (8)0.0010 (8)0.0123 (9)
O20.0585 (10)0.0778 (12)0.0223 (9)0.0200 (9)0.0069 (8)0.0005 (8)
C10.0402 (14)0.0705 (19)0.073 (2)0.0002 (13)0.0002 (14)0.0023 (16)
C20.0532 (17)0.109 (3)0.080 (2)0.0073 (16)0.0143 (16)0.007 (2)
C30.0398 (13)0.0446 (14)0.0328 (13)0.0031 (10)0.0020 (10)0.0023 (11)
C40.0359 (12)0.0465 (13)0.0258 (13)0.0004 (10)0.0034 (10)0.0039 (10)
C50.0396 (12)0.0490 (14)0.0225 (12)0.0010 (10)0.0039 (10)0.0016 (11)
C60.0354 (12)0.0423 (13)0.0297 (13)0.0027 (10)0.0036 (10)0.0004 (10)
C70.0479 (14)0.0618 (16)0.0400 (15)0.0050 (12)0.0098 (12)0.0069 (13)
C80.0518 (14)0.0436 (14)0.0332 (14)0.0124 (12)0.0038 (11)0.0021 (11)
C90.0661 (17)0.0619 (17)0.0428 (17)0.0110 (14)0.0026 (14)0.0081 (14)
C100.096 (2)0.084 (2)0.0456 (19)0.0188 (19)0.0093 (17)0.0216 (17)
C110.101 (3)0.076 (2)0.062 (2)0.0172 (19)0.034 (2)0.0259 (17)
C120.0723 (19)0.0598 (18)0.072 (2)0.0014 (15)0.0254 (17)0.0119 (16)
C130.0570 (16)0.0532 (16)0.0447 (16)0.0036 (13)0.0088 (13)0.0033 (13)
C140.0325 (12)0.0446 (13)0.0293 (13)0.0011 (10)0.0025 (10)0.0048 (11)
C150.0437 (14)0.0661 (17)0.0423 (16)0.0060 (12)0.0023 (12)0.0078 (13)
C160.0507 (16)0.086 (2)0.0528 (18)0.0087 (15)0.0162 (14)0.0103 (16)
C170.0473 (15)0.080 (2)0.066 (2)0.0174 (15)0.0093 (15)0.0000 (17)
C180.0568 (16)0.0708 (19)0.065 (2)0.0203 (14)0.0056 (15)0.0057 (16)
C190.0487 (14)0.0649 (17)0.0395 (15)0.0124 (13)0.0011 (12)0.0048 (13)
Geometric parameters (Å, º) top
N1—C31.285 (3)C8—C131.378 (3)
N1—O11.404 (2)C8—C91.389 (3)
N2—C51.377 (3)C9—C101.371 (4)
N2—N31.380 (2)C9—H90.9300
N2—C141.415 (3)C10—C111.369 (4)
N3—C61.333 (3)C10—H100.9300
N3—H30.8600C11—C121.371 (4)
O1—C11.423 (3)C11—H110.9300
O2—C51.254 (2)C12—C131.386 (3)
C1—C21.491 (4)C12—H120.9300
C1—H1A0.9700C13—H130.9300
C1—H1B0.9700C14—C151.373 (3)
C2—H2A0.9600C14—C191.379 (3)
C2—H2B0.9600C15—C161.380 (3)
C2—H2C0.9600C15—H150.9300
C3—C41.468 (3)C16—C171.363 (3)
C3—C81.487 (3)C16—H160.9300
C4—C61.382 (3)C17—C181.362 (4)
C4—C51.419 (3)C17—H170.9300
C6—C71.485 (3)C18—C191.383 (3)
C7—H7A0.9600C18—H180.9300
C7—H7B0.9600C19—H190.9300
C7—H7C0.9600
C3—N1—O1111.86 (18)H7B—C7—H7C109.5
C5—N2—N3108.11 (16)C13—C8—C9118.3 (2)
C5—N2—C14130.00 (18)C13—C8—C3121.2 (2)
N3—N2—C14121.03 (17)C9—C8—C3120.5 (2)
C6—N3—N2109.39 (17)C10—C9—C8120.5 (3)
C6—N3—H3125.3C10—C9—H9119.7
N2—N3—H3125.3C8—C9—H9119.7
N1—O1—C1108.28 (17)C11—C10—C9120.5 (3)
O1—C1—C2107.5 (2)C11—C10—H10119.7
O1—C1—H1A110.2C9—C10—H10119.7
C2—C1—H1A110.2C10—C11—C12120.2 (3)
O1—C1—H1B110.2C10—C11—H11119.9
C2—C1—H1B110.2C12—C11—H11119.9
H1A—C1—H1B108.5C11—C12—C13119.4 (3)
C1—C2—H2A109.5C11—C12—H12120.3
C1—C2—H2B109.5C13—C12—H12120.3
H2A—C2—H2B109.5C8—C13—C12121.1 (3)
C1—C2—H2C109.5C8—C13—H13119.5
H2A—C2—H2C109.5C12—C13—H13119.5
H2B—C2—H2C109.5C15—C14—C19119.5 (2)
N1—C3—C4126.0 (2)C15—C14—N2120.3 (2)
N1—C3—C8115.4 (2)C19—C14—N2120.1 (2)
C4—C3—C8118.62 (19)C14—C15—C16120.0 (2)
C6—C4—C5107.05 (19)C14—C15—H15120.0
C6—C4—C3128.4 (2)C16—C15—H15120.0
C5—C4—C3124.40 (19)C17—C16—C15120.6 (3)
O2—C5—N2122.71 (19)C17—C16—H16119.7
O2—C5—C4130.8 (2)C15—C16—H16119.7
N2—C5—C4106.46 (18)C18—C17—C16119.4 (2)
N3—C6—C4108.91 (19)C18—C17—H17120.3
N3—C6—C7119.62 (19)C16—C17—H17120.3
C4—C6—C7131.5 (2)C17—C18—C19121.0 (3)
C6—C7—H7A109.5C17—C18—H18119.5
C6—C7—H7B109.5C19—C18—H18119.5
H7A—C7—H7B109.5C14—C19—C18119.4 (2)
C6—C7—H7C109.5C14—C19—H19120.3
H7A—C7—H7C109.5C18—C19—H19120.3
C5—N2—N3—C62.1 (2)N1—C3—C8—C13155.2 (2)
C14—N2—N3—C6172.45 (18)C4—C3—C8—C1323.6 (3)
C3—N1—O1—C1174.5 (2)N1—C3—C8—C924.8 (3)
N1—O1—C1—C2179.5 (2)C4—C3—C8—C9156.4 (2)
O1—N1—C3—C44.5 (3)C13—C8—C9—C100.6 (4)
O1—N1—C3—C8176.79 (17)C3—C8—C9—C10179.4 (2)
N1—C3—C4—C655.2 (4)C8—C9—C10—C110.3 (4)
C8—C3—C4—C6123.5 (2)C9—C10—C11—C120.5 (4)
N1—C3—C4—C5130.1 (2)C10—C11—C12—C131.1 (4)
C8—C3—C4—C551.3 (3)C9—C8—C13—C121.1 (3)
N3—N2—C5—O2179.5 (2)C3—C8—C13—C12178.9 (2)
C14—N2—C5—O211.3 (4)C11—C12—C13—C81.4 (4)
N3—N2—C5—C40.3 (2)C5—N2—C14—C15155.0 (2)
C14—N2—C5—C4169.5 (2)N3—N2—C14—C1513.0 (3)
C6—C4—C5—O2177.7 (2)C5—N2—C14—C1926.1 (3)
C3—C4—C5—O26.7 (4)N3—N2—C14—C19165.9 (2)
C6—C4—C5—N21.4 (2)C19—C14—C15—C160.4 (4)
C3—C4—C5—N2174.25 (19)N2—C14—C15—C16178.5 (2)
N2—N3—C6—C43.0 (2)C14—C15—C16—C170.9 (4)
N2—N3—C6—C7177.33 (17)C15—C16—C17—C180.5 (4)
C5—C4—C6—N32.8 (2)C16—C17—C18—C190.3 (4)
C3—C4—C6—N3172.7 (2)C15—C14—C19—C180.4 (4)
C5—C4—C6—C7177.7 (2)N2—C14—C19—C18179.3 (2)
C3—C4—C6—C76.9 (4)C17—C18—C19—C140.8 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3···O2i0.861.802.653 (2)171
C15—H15···O2i0.932.423.200 (3)141
C19—H19···O20.932.322.900 (3)120
Symmetry code: (i) x, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC19H19N3O2
Mr321.37
Crystal system, space groupMonoclinic, P21/c
Temperature (K)298
a, b, c (Å)13.0046 (15), 11.4657 (11), 11.6874 (12)
β (°) 99.453 (1)
V3)1719.0 (3)
Z4
Radiation typeMo Kα
µ (mm1)0.08
Crystal size (mm)0.50 × 0.18 × 0.16
Data collection
DiffractometerBrucker SMART 1000 CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.960, 0.987
No. of measured, independent and
observed [I > 2σ(I)] reflections
8480, 3028, 1756
Rint0.041
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.044, 0.140, 1.02
No. of reflections3028
No. of parameters219
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.17, 0.24

Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3···O2i0.8601.8002.653 (2)170.88
C15—H15···O2i0.9302.4203.200 (3)141.00
C19—H19···O20.9302.3202.900 (3)120.00
Symmetry code: (i) x, y+1/2, z+1/2.
 

Acknowledgements

This work was supported by the Foundation of the Education Department of Gansu Province (No. 0604–01) and the `Qing Lan' Talent Engineering Funds of Lanzhou Jiaotong University (No. QL-03–01 A), which are gratefully acknowledged.

References

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