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Acta Cryst. (2009). E65, o1513-o1514    [ doi:10.1107/S1600536809021084 ]

4,4'-Dianilino-3,3'-(4-chlorobenzylidene)bis[furan-2(5H)-one]

F. Shi, D.-X. Zhou and S.-J. Tu

Abstract top

In the molecule of the title compound, C27H21ClN2O4, the dihedral angle between the furan rings is 67.00 (3)°. The chlorophenyl ring is oriented at dihedral angles of 76.61 (3) and 69.36 (3)° with respect to the furan rings. An intramolecular N-H...O interaction results in the formation of an eight-membered ring with a twisted conformation. In the crystal structure, intermolecular N-H...O and C-H...O interactions link the molecules into a three-dimensional network, forming R22(16) ring motifs. Three weak C-H...[pi] interactions are also found.

Comment top

Tetronic acid derivatives and their metabolites have gained much attention from synthetic and medicinal chemists because of their prominent antibiotic (Ley et al., 1991), antico-agulant (Witiak et al., 1982), anti-inflammatory (Foden et al., 1975) and anti-HIV (Roggo et al., 1994) activities. Among them, open-chain derivatives of bistetronic acid, which contain two tetronic acid skeletons in one molecule, may display important pharmacological activities (Altenbach et al., 2006). We report herein the crystal structure of the title compound.

In the molecule of the title compound (Fig 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges. Rings A (O1/C1-C4), B (O3/C5-C8), C (C10-C15), D (C16-C21) and E (C22-C27) are, of course, planar. The dihedral angles between them are A/B = 67.00 (3), A/C = 76.61 (3), B/C = 69.36 (3), A/D = 14.64 (3) and B/E = 32.61 (3) °. Intramolecular N-H···O interaction (Table 1) results in the formation of an eight-membered ring F (O4/N1/C2/C3/C5/C6/C9/H1), having twisted conformation.

In the crystal structure, intermolecular N-H···O and C-H···O interactions (Table 1) link the molecules into a three-dimensional network forming R22(16) ring motifs (Bernstein et al., 1995), in which they may be effective in the stabilization of the structure. There also exist three weak C—H···π interactions (Table 1).

Related literature top

For the biologicalbiological activity of tetronic acid derivatives and their metabolites, see: Altenbach et al. (2006); Foden et al. (1975); Ley et al. (1991); Roggo et al. (1994); Witiak et al. (1982). For bond-length data, see: Allen et al. (1987). For hydrogen-bond ring motifs, see: Bernstein et al. (1995). Cg3, Cg4 and Cg5 are the centroids of the C10–C15, C16–C21 and C22–C27 rings, respectively.

Experimental top

The title compound was prepared by the reaction of 4-chlorobenzaldehyde (0.5 mmol) with 4-phenylamino-2,5-dihydrofuran-2-one (1 mmol) in glycol at 373 K under microwave irradiation (maximum power 200 W, initial power 100 W) for 10 min (yield; 92%, m.p. 508–509 K). Crystals suitable for X-ray analysis were obtained from an ethanol solution by slow evaporation.

Refinement top

H atoms were positioned geometrically, with N-H = 0.86 Å (for NH) and C-H = 0.93, 0.98 and 0.97 Å for aromatic, methine and methylene H, respectively, and constrained to ride on their parent atoms, with Uiso(H) = 1.2Ueq(C,N).

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); 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. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
4,4'-Dianilino-3,3'-(4-chlorobenzylidene)bis[furan-2(5H)-one] top
Crystal data top
C27H21ClN2O4F(000) = 984
Mr = 472.91Dx = 1.413 Mg m−3
Monoclinic, P21/nMelting point = 508–509 K
Hall symbol: -P 2ynMo Kα radiation, λ = 0.71073 Å
a = 10.973 (5) ÅCell parameters from 1079 reflections
b = 11.566 (5) Åθ = 2.4–19.9°
c = 17.795 (8) ŵ = 0.21 mm−1
β = 100.232 (7)°T = 298 K
V = 2222.6 (17) Å3Block, yellow
Z = 40.28 × 0.15 × 0.12 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer		3913 independent reflections
Radiation source: fine-focus sealed tube1802 reflections with I > 2σ(I)
graphiteRint = 0.087
φ and ω scansθmax = 25.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		h = −13→12
Tmin = 0.943, Tmax = 0.975k = −13→13
11368 measured reflectionsl = −11→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)] = 0.067Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.251H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2)]
3913 reflections(Δ/σ)max < 0.001
307 parametersΔρmax = 0.25 e Å−3
0 restraintsΔρmin = −0.28 e Å−3
Crystal data top
C27H21ClN2O4V = 2222.6 (17) Å3
Mr = 472.91Z = 4
Monoclinic, P21/nMo Kα radiation
a = 10.973 (5) ŵ = 0.21 mm−1
b = 11.566 (5) ÅT = 298 K
c = 17.795 (8) Å0.28 × 0.15 × 0.12 mm
β = 100.232 (7)°
Data collection top
Bruker SMART CCD area-detector
diffractometer		3913 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		1802 reflections with I > 2σ(I)
Tmin = 0.943, Tmax = 0.975Rint = 0.087
11368 measured reflectionsθmax = 25.0°
Refinement top
R[F2 > 2σ(F2)] = 0.067H-atom parameters constrained
wR(F2) = 0.251Δρmax = 0.25 e Å−3
S = 1.03Δρmin = −0.28 e Å−3
3913 reflectionsAbsolute structure: ?
307 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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
Cl10.72987 (15)0.38409 (13)0.15930 (11)0.0740 (6)
O10.5201 (3)1.0941 (3)0.2030 (2)0.0537 (10)
O20.5296 (3)1.0511 (3)0.0810 (2)0.0620 (11)
O30.0934 (3)0.7208 (3)0.0853 (2)0.0498 (10)
O40.2460 (3)0.6755 (3)0.1814 (2)0.0502 (10)
N10.3811 (4)0.8428 (4)0.2747 (3)0.0503 (12)
H10.36910.77670.25250.060*
N20.2308 (4)0.9098 (4)−0.0373 (3)0.0517 (12)
H20.30810.9226−0.03670.062*
C10.5027 (5)1.0208 (4)0.1418 (4)0.0487 (14)
C20.4502 (4)0.9143 (4)0.1609 (3)0.0385 (12)
C30.4320 (4)0.9225 (4)0.2347 (3)0.0388 (12)
C40.4770 (5)1.0372 (4)0.2651 (3)0.0458 (13)
H4A0.41051.08090.28100.055*
H4B0.54381.02870.30850.055*
C50.2134 (4)0.7262 (4)0.1207 (3)0.0407 (13)
C60.2842 (4)0.7961 (4)0.0774 (3)0.0384 (12)
C70.2060 (4)0.8381 (4)0.0164 (3)0.0414 (13)
C80.0777 (4)0.7922 (5)0.0181 (3)0.0482 (14)
H8A0.02030.85480.02170.058*
H8B0.04730.7471−0.02730.058*
C90.4220 (4)0.8188 (4)0.1024 (3)0.0403 (13)
H90.45040.84810.05670.048*
C100.4950 (4)0.7072 (4)0.1233 (3)0.0379 (12)
C110.4592 (5)0.6052 (4)0.0851 (3)0.0508 (15)
H110.38580.60390.04970.061*
C120.5286 (5)0.5052 (5)0.0977 (3)0.0560 (15)
H120.50150.43710.07230.067*
C130.6382 (5)0.5084 (4)0.1484 (3)0.0474 (14)
C140.6747 (5)0.6063 (5)0.1892 (3)0.0526 (15)
H140.74670.60660.22580.063*
C150.6030 (4)0.7050 (5)0.1754 (3)0.0469 (14)
H150.62900.77200.20240.056*
C160.3439 (5)0.8482 (4)0.3466 (3)0.0442 (13)
C170.2643 (5)0.7626 (5)0.3627 (3)0.0541 (15)
H170.23860.70490.32700.065*
C180.2233 (6)0.7624 (5)0.4310 (4)0.0669 (18)
H180.16890.70490.44080.080*
C190.2606 (5)0.8448 (5)0.4849 (4)0.0625 (17)
H190.23320.84300.53150.075*
C200.3380 (5)0.9292 (5)0.4697 (3)0.0584 (16)
H200.36250.98620.50600.070*
C210.3816 (5)0.9328 (5)0.4016 (3)0.0526 (15)
H210.43560.99110.39250.063*
C220.1487 (5)0.9681 (5)−0.0949 (3)0.0485 (14)
C230.0411 (6)0.9218 (5)−0.1334 (4)0.0694 (19)
H230.01890.8469−0.12240.083*
C24−0.0353 (6)0.9854 (6)−0.1886 (4)0.0719 (19)
H24−0.10870.9525−0.21370.086*
C25−0.0056 (6)1.0951 (5)−0.2070 (4)0.0646 (17)
H25−0.05761.1376−0.24390.078*
C260.1045 (6)1.1405 (5)−0.1688 (4)0.0619 (17)
H260.12761.2147−0.18060.074*
C270.1799 (5)1.0788 (5)−0.1142 (3)0.0543 (15)
H270.25361.1116−0.08950.065*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.0781 (11)0.0616 (10)0.0802 (14)0.0182 (8)0.0080 (10)0.0048 (9)
O10.063 (2)0.047 (2)0.054 (3)−0.0074 (18)0.020 (2)−0.006 (2)
O20.068 (3)0.067 (3)0.057 (3)−0.015 (2)0.027 (2)0.007 (2)
O30.039 (2)0.059 (2)0.049 (2)−0.0080 (16)0.0042 (19)0.011 (2)
O40.055 (2)0.059 (2)0.037 (2)−0.0088 (17)0.0071 (19)0.0074 (19)
N10.067 (3)0.047 (3)0.041 (3)−0.008 (2)0.020 (3)−0.007 (2)
N20.039 (2)0.063 (3)0.051 (3)−0.001 (2)0.002 (2)0.018 (3)
C10.043 (3)0.047 (3)0.059 (4)−0.001 (2)0.016 (3)0.001 (3)
C20.026 (2)0.056 (3)0.033 (3)−0.002 (2)0.003 (2)−0.003 (3)
C30.035 (3)0.041 (3)0.041 (3)−0.001 (2)0.007 (3)0.001 (3)
C40.050 (3)0.052 (3)0.037 (3)0.000 (3)0.013 (3)−0.002 (3)
C50.034 (3)0.048 (3)0.040 (3)−0.004 (2)0.005 (3)−0.004 (3)
C60.033 (2)0.046 (3)0.036 (3)−0.003 (2)0.005 (2)−0.003 (3)
C70.042 (3)0.045 (3)0.038 (3)−0.004 (2)0.008 (3)−0.002 (3)
C80.040 (3)0.058 (3)0.045 (4)−0.006 (2)0.003 (3)0.007 (3)
C90.033 (3)0.051 (3)0.037 (3)−0.007 (2)0.006 (2)−0.001 (3)
C100.039 (3)0.045 (3)0.029 (3)−0.002 (2)0.005 (2)−0.007 (3)
C110.041 (3)0.065 (4)0.041 (4)−0.004 (3)−0.009 (3)−0.010 (3)
C120.054 (3)0.058 (4)0.054 (4)0.001 (3)0.003 (3)−0.011 (3)
C130.048 (3)0.045 (3)0.049 (4)0.002 (2)0.008 (3)0.000 (3)
C140.041 (3)0.069 (4)0.044 (4)−0.002 (3)−0.005 (3)−0.001 (3)
C150.042 (3)0.051 (3)0.047 (4)−0.004 (3)0.004 (3)−0.009 (3)
C160.051 (3)0.050 (3)0.032 (3)0.005 (3)0.009 (3)0.003 (3)
C170.058 (3)0.064 (4)0.041 (4)−0.015 (3)0.011 (3)−0.004 (3)
C180.070 (4)0.077 (4)0.058 (5)−0.013 (3)0.023 (4)−0.002 (4)
C190.064 (4)0.083 (4)0.041 (4)0.005 (3)0.010 (3)0.008 (4)
C200.071 (4)0.064 (4)0.039 (4)0.007 (3)0.005 (3)−0.004 (3)
C210.061 (4)0.056 (3)0.040 (4)−0.009 (3)0.007 (3)−0.005 (3)
C220.051 (3)0.054 (3)0.039 (3)0.001 (3)0.004 (3)0.005 (3)
C230.065 (4)0.063 (4)0.068 (5)−0.020 (3)−0.020 (4)0.014 (4)
C240.060 (4)0.087 (5)0.061 (5)−0.016 (3)−0.013 (4)0.009 (4)
C250.060 (4)0.072 (4)0.058 (4)0.014 (3)0.002 (3)0.010 (4)
C260.070 (4)0.055 (4)0.061 (4)0.002 (3)0.012 (4)0.007 (3)
C270.051 (3)0.060 (4)0.051 (4)0.000 (3)0.004 (3)−0.001 (3)
Geometric parameters (Å, °) top
Cl1—C131.745 (5)C11—H110.9300
O1—C11.366 (6)C12—C131.369 (7)
O1—C41.436 (6)C12—H120.9300
O2—C11.223 (6)C13—C141.367 (7)
O3—C51.357 (6)C14—C151.383 (7)
O3—C81.439 (6)C14—H140.9300
O4—C51.224 (6)C15—H150.9300
N1—C31.345 (6)C16—C171.384 (7)
N1—C161.412 (6)C16—C211.394 (7)
N1—H10.8600C17—C181.369 (8)
N2—C71.329 (6)C17—H170.9300
N2—C221.410 (6)C18—C191.362 (8)
N2—H20.8600C18—H180.9300
C1—C21.427 (7)C19—C201.353 (8)
C2—C31.366 (7)C19—H190.9300
C2—C91.512 (7)C20—C211.381 (8)
C3—C41.484 (7)C20—H200.9300
C4—H4A0.9700C21—H210.9300
C4—H4B0.9700C22—C231.365 (7)
C5—C61.436 (7)C22—C271.385 (7)
C6—C71.349 (7)C23—C241.384 (8)
C6—C91.522 (6)C23—H230.9300
C7—C81.509 (6)C24—C251.364 (8)
C8—H8A0.9700C24—H240.9300
C8—H8B0.9700C25—C261.381 (8)
C9—C101.530 (6)C25—H250.9300
C9—H90.9800C26—C271.360 (8)
C10—C151.369 (7)C26—H260.9300
C10—C111.383 (6)C27—H270.9300
C11—C121.381 (7)
C1—O1—C4108.2 (4)C10—C11—H11118.8
C5—O3—C8108.8 (4)C13—C12—C11118.6 (5)
C3—N1—C16131.5 (5)C13—C12—H12120.7
C3—N1—H1114.2C11—C12—H12120.7
C16—N1—H1114.2C14—C13—C12120.9 (5)
C7—N2—C22129.4 (4)C14—C13—Cl1121.0 (5)
C7—N2—H2115.3C12—C13—Cl1118.2 (4)
C22—N2—H2115.3C13—C14—C15119.0 (5)
O2—C1—O1120.4 (5)C13—C14—H14120.5
O2—C1—C2129.0 (5)C15—C14—H14120.5
O1—C1—C2110.5 (5)C10—C15—C14122.2 (5)
C3—C2—C1107.7 (5)C10—C15—H15118.9
C3—C2—C9131.7 (5)C14—C15—H15118.9
C1—C2—C9120.6 (5)C17—C16—C21118.5 (5)
N1—C3—C2127.3 (5)C17—C16—N1116.8 (5)
N1—C3—C4124.2 (5)C21—C16—N1124.7 (5)
C2—C3—C4108.4 (4)C18—C17—C16120.3 (6)
O1—C4—C3105.2 (4)C18—C17—H17119.8
O1—C4—H4A110.7C16—C17—H17119.8
C3—C4—H4A110.7C19—C18—C17121.3 (6)
O1—C4—H4B110.7C19—C18—H18119.4
C3—C4—H4B110.7C17—C18—H18119.4
H4A—C4—H4B108.8C20—C19—C18118.9 (6)
O4—C5—O3119.6 (4)C20—C19—H19120.5
O4—C5—C6129.9 (5)C18—C19—H19120.5
O3—C5—C6110.4 (5)C19—C20—C21121.8 (6)
C7—C6—C5107.9 (4)C19—C20—H20119.1
C7—C6—C9129.1 (5)C21—C20—H20119.1
C5—C6—C9123.0 (5)C20—C21—C16119.2 (5)
N2—C7—C6128.4 (5)C20—C21—H21120.4
N2—C7—C8123.0 (5)C16—C21—H21120.4
C6—C7—C8108.6 (5)C23—C22—C27117.9 (5)
O3—C8—C7104.2 (4)C23—C22—N2124.2 (5)
O3—C8—H8A110.9C27—C22—N2118.0 (5)
C7—C8—H8A110.9C22—C23—C24120.6 (6)
O3—C8—H8B110.9C22—C23—H23119.7
C7—C8—H8B110.9C24—C23—H23119.7
H8A—C8—H8B108.9C25—C24—C23121.6 (6)
C2—C9—C6113.4 (4)C25—C24—H24119.2
C2—C9—C10114.5 (4)C23—C24—H24119.2
C6—C9—C10112.1 (4)C24—C25—C26117.4 (6)
C2—C9—H9105.2C24—C25—H25121.3
C6—C9—H9105.2C26—C25—H25121.3
C10—C9—H9105.2C27—C26—C25121.3 (6)
C15—C10—C11116.9 (5)C27—C26—H26119.3
C15—C10—C9122.2 (4)C25—C26—H26119.3
C11—C10—C9120.7 (4)C26—C27—C22121.1 (6)
C12—C11—C10122.3 (5)C26—C27—H27119.4
C12—C11—H11118.8C22—C27—H27119.4
C4—O1—C1—O2178.2 (5)C7—C6—C9—C10−133.2 (5)
C4—O1—C1—C2−0.8 (5)C5—C6—C9—C1049.9 (6)
O2—C1—C2—C3−177.5 (5)C2—C9—C10—C15−20.6 (7)
O1—C1—C2—C31.3 (6)C6—C9—C10—C15−151.7 (5)
O2—C1—C2—C91.1 (8)C2—C9—C10—C11164.8 (4)
O1—C1—C2—C9180.0 (4)C6—C9—C10—C1133.7 (7)
C16—N1—C3—C2−170.5 (5)C15—C10—C11—C12−0.6 (8)
C16—N1—C3—C48.6 (8)C9—C10—C11—C12174.3 (5)
C1—C2—C3—N1177.9 (5)C10—C11—C12—C13−1.7 (8)
C9—C2—C3—N1−0.5 (9)C11—C12—C13—C144.0 (8)
C1—C2—C3—C4−1.3 (5)C11—C12—C13—Cl1−176.0 (4)
C9—C2—C3—C4−179.7 (5)C12—C13—C14—C15−3.9 (8)
C1—O1—C4—C30.0 (5)Cl1—C13—C14—C15176.1 (4)
N1—C3—C4—O1−178.4 (4)C11—C10—C15—C140.8 (8)
C2—C3—C4—O10.9 (5)C9—C10—C15—C14−174.1 (5)
C8—O3—C5—O4176.8 (5)C13—C14—C15—C101.5 (8)
C8—O3—C5—C6−2.7 (5)C3—N1—C16—C17162.7 (5)
O4—C5—C6—C7−176.9 (5)C3—N1—C16—C21−17.4 (9)
O3—C5—C6—C72.5 (6)C21—C16—C17—C180.6 (8)
O4—C5—C6—C90.5 (8)N1—C16—C17—C18−179.5 (5)
O3—C5—C6—C9179.9 (4)C16—C17—C18—C19−0.9 (9)
C22—N2—C7—C6−169.7 (5)C17—C18—C19—C201.1 (9)
C22—N2—C7—C88.8 (9)C18—C19—C20—C21−1.1 (9)
C5—C6—C7—N2177.4 (5)C19—C20—C21—C160.8 (9)
C9—C6—C7—N20.2 (9)C17—C16—C21—C20−0.6 (8)
C5—C6—C7—C8−1.2 (6)N1—C16—C21—C20179.6 (5)
C9—C6—C7—C8−178.4 (5)C7—N2—C22—C23−37.0 (9)
C5—O3—C8—C71.9 (5)C7—N2—C22—C27143.6 (6)
N2—C7—C8—O3−179.0 (5)C27—C22—C23—C24−1.5 (9)
C6—C7—C8—O3−0.3 (6)N2—C22—C23—C24179.1 (6)
C3—C2—C9—C665.9 (7)C22—C23—C24—C250.7 (10)
C1—C2—C9—C6−112.3 (5)C23—C24—C25—C260.5 (10)
C3—C2—C9—C10−64.5 (7)C24—C25—C26—C27−0.8 (9)
C1—C2—C9—C10117.3 (5)C25—C26—C27—C22−0.1 (9)
C7—C6—C9—C295.1 (7)C23—C22—C27—C261.2 (9)
C5—C6—C9—C2−81.7 (6)N2—C22—C27—C26−179.4 (5)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O40.862.052.797 (3)145
N2—H2···O2i0.862.092.907 (3)158
C4—H4A···O4ii0.972.243.206 (3)178
C8—H8A···Cg5iii0.972.983.721 (3)134
C8—H8B···Cg4iv0.972.913.617 (3)131
C19—H19···Cg3v0.932.903.766 (3)156
Symmetry codes: (i) −x+1, −y+2, −z; (ii) −x+1/2, y+1/2, −z+1/2; (iii) −x+1, −y+1, −z+1; (iv) x−1/2, −y−1/2, z−1/2; (v) x−1/2, −y−1/2, z−3/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O40.862.052.797 (3)145
N2—H2···O2i0.862.092.907 (3)158
C4—H4A···O4ii0.972.243.206 (3)178
C8—H8A···Cg5iii0.972.983.721 (3)134
C8—H8B···Cg4iv0.972.913.617 (3)131
C19—H19···Cg3v0.932.903.766 (3)156
Symmetry codes: (i) −x+1, −y+2, −z; (ii) −x+1/2, y+1/2, −z+1/2; (iii) −x+1, −y+1, −z+1; (iv) x−1/2, −y−1/2, z−1/2; (v) x−1/2, −y−1/2, z−3/2.
Acknowledgements top

We thank the Natural Science Foundation of China (grant No. 20672090), the Preliminary Item of Xuzhou Normal University on National Natural Science Foundation of China (grant No. 08XLY04) and the Science & Technology Foundation of Xuzhou City (grant No. XM08C027) for support.

references
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