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Acta Cryst. (2010). E66, m120    [ doi:10.1107/S1600536810000036 ]

Bis{2-ethoxy-6-[2-(methylammonio)ethyliminomethyl]phenolato}thiocyanatozinc(II) nitrate

C.-Y. Wang, Z.-P. Han, X. Wu, C.-J. Yuan and J.-B. Zhou

Abstract top

In the title compound, [Zn(NCS)(C12H18N2O2)2]NO3, the ZnII ion is chelated by the phenolate O and imine N atoms from two zwitterionic Schiff base ligands and is also coordinated by the N atom of a thiocyanate ligand, giving a distorted trigonal-bipyramidal geometry. Intramolecular N-H...O hydrogen bonds are observed in the complex cation. The nitrate anions are linked to the complex cations through N-H...O hydrogen bonds.

Comment top

As part of our investigations into novel urease inhibitors, we have synthesized the title compound, a new ZnII complex. The compound consists of a mononuclear zinc(II) complex cation and a nitrate anion. The Zn atom is chelated by the phenolate O and imine N atoms from two Schiff base ligands, and is coordinated by the N atom from a thiocyanate ligand, forming a trigonal-bipyramid geometry (Fig. 1). The coordinate bond lengths (Table 1) and angles are typical and are comparable with those observed in other similar zinc(II) complexes (Zhang & Wang, 2007; Adams et al., 2003). The amine N atoms of the Schiff base ligands are protonated and take no part in the coordination to the ZnII ion.

Related literature top

For related structures, see: Zhang & Wang (2007); Adams et al. (2003).

Experimental top

3-Ethoxysalicylaldehyde (0.2 mmol, 33.2 mg) and N-methylethane-1,2-diamine (0.2 mmol, 14.8 mg) were dissolved in MeOH (10 ml). The mixture was stirred at room temperature for 10 min to give a clear yellow solution. To this solution was added an aqueous solution (2 ml) of ammonium thiocyanate (0.2 mmol, 15.2 mg) and an aqueous solution (3 ml) of Zn(NO3)2.6H2O (0.1 mmol, 29.0 mg) with stirring. The resulting mixture was stirred for another 10 min at room temperature. After keeping the filtrate in air for a week, colourless block-shaped crystals were formed at the bottom of the vessel.

Refinement top

H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C–H distances in the range 0.93–0.97 Å, N–H distances of 0.90 Å, and with Uiso(H) set at 1.2Ueq(C,N) and 1.5Ueq(methyl C). During the refinement, the displacement parameters of atom O6 were restrained to an approximate isotropic behaviour. The unit cell contains four solvent accessible voids each with a volume of 53 Å3. But no significant electron density is found in these voids.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); 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 asymmetric unit of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.
Bis{2-ethoxy-6-[2-(methylammonio)ethyliminomethyl]phenolato}thiocyanatozinc(II) nitrate top
Crystal data top
[Zn(NCS)(C12H18N2O2)2]NO3F(000) = 1320
Mr = 630.03Dx = 1.329 Mg m−3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3892 reflections
a = 10.601 (2) Åθ = 2.3–25.5°
b = 23.335 (3) ŵ = 0.90 mm−1
c = 13.749 (2) ÅT = 298 K
β = 112.218 (3)°Block, colourless
V = 3148.6 (9) Å30.20 × 0.20 × 0.18 mm
Z = 4
Data collection top
Bruker SMART CCD area-detector
diffractometer		6818 independent reflections
Radiation source: fine-focus sealed tube3644 reflections with I > 2σ(I)
graphiteRint = 0.139
ω scanθmax = 27.0°, θmin = 1.8°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		h = −13→13
Tmin = 0.841, Tmax = 0.856k = −29→28
18443 measured reflectionsl = −17→15
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)] = 0.059Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.157H-atom parameters constrained
S = 0.91 w = 1/[σ2(Fo2) + (0.0647P)2]
where P = (Fo2 + 2Fc2)/3
6818 reflections(Δ/σ)max = 0.001
365 parametersΔρmax = 0.69 e Å−3
6 restraintsΔρmin = −0.63 e Å−3
Crystal data top
[Zn(NCS)(C12H18N2O2)2]NO3V = 3148.6 (9) Å3
Mr = 630.03Z = 4
Monoclinic, P21/cMo Kα radiation
a = 10.601 (2) ŵ = 0.90 mm−1
b = 23.335 (3) ÅT = 298 K
c = 13.749 (2) Å0.20 × 0.20 × 0.18 mm
β = 112.218 (3)°
Data collection top
Bruker SMART CCD area-detector
diffractometer		6818 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		3644 reflections with I > 2σ(I)
Tmin = 0.841, Tmax = 0.856Rint = 0.139
18443 measured reflectionsθmax = 27.0°
Refinement top
R[F2 > 2σ(F2)] = 0.059H-atom parameters constrained
wR(F2) = 0.157Δρmax = 0.69 e Å−3
S = 0.91Δρmin = −0.63 e Å−3
6818 reflectionsAbsolute structure: ?
365 parametersFlack parameter: ?
6 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
Zn10.89814 (4)0.910567 (18)0.15980 (3)0.04957 (18)
N10.9386 (4)0.99186 (14)0.1129 (3)0.0615 (9)
N20.7214 (3)1.05264 (13)0.1565 (2)0.0540 (8)
H2A0.76861.08550.16360.065*
H2B0.77051.02880.20850.065*
N30.8674 (3)0.82940 (12)0.2138 (3)0.0520 (8)
N41.1307 (3)0.78461 (14)0.2169 (3)0.0644 (9)
H4A1.13400.76100.26950.077*
H4B1.13520.82080.24040.077*
N50.1534 (6)0.6837 (2)0.3942 (4)0.1041 (16)
N60.7831 (4)0.88758 (17)0.0075 (3)0.0770 (11)
O11.0989 (3)0.89846 (11)0.2324 (2)0.0599 (7)
O21.3351 (3)0.86419 (17)0.3710 (3)0.0830 (10)
O30.8145 (3)0.94858 (10)0.24990 (18)0.0515 (6)
O40.8062 (3)1.02305 (12)0.3908 (2)0.0574 (7)
O50.1139 (4)0.73228 (16)0.4024 (3)0.1062 (12)
O60.2187 (7)0.6552 (2)0.4726 (4)0.175 (2)
O70.1510 (4)0.66460 (16)0.3124 (3)0.1077 (13)
S10.65759 (17)0.81681 (6)−0.16349 (11)0.1041 (5)
C11.1809 (5)0.9943 (2)0.2309 (4)0.0709 (13)
C21.1969 (4)0.9368 (2)0.2642 (3)0.0609 (11)
C31.3288 (5)0.9196 (3)0.3372 (4)0.0748 (14)
C41.4340 (6)0.9584 (3)0.3697 (5)0.106 (2)
H41.51960.94680.41600.128*
C51.4143 (8)1.0148 (4)0.3344 (5)0.124 (3)
H51.48681.04050.35760.149*
C61.2928 (7)1.0325 (3)0.2677 (4)0.0959 (19)
H61.28141.07040.24510.115*
C71.0547 (6)1.01704 (19)0.1556 (4)0.0741 (14)
H71.05791.05490.13530.089*
C80.8286 (5)1.0229 (2)0.0317 (4)0.0824 (15)
H8A0.80861.0040−0.03530.099*
H8B0.85931.06150.02610.099*
C90.7009 (5)1.02618 (19)0.0535 (3)0.0665 (12)
H9A0.63361.0483−0.00170.080*
H9B0.66480.98780.05160.080*
C100.5889 (4)1.0648 (2)0.1656 (4)0.0857 (15)
H10A0.53901.09220.11300.128*
H10B0.60471.08010.23410.128*
H10C0.53721.03000.15570.128*
C111.4620 (5)0.8444 (3)0.4510 (5)0.116 (2)
H11A1.48980.87050.51020.139*
H11B1.53290.84390.42250.139*
C121.4452 (7)0.7866 (3)0.4864 (6)0.146 (3)
H12A1.36610.78580.50450.219*
H12B1.52430.77670.54680.219*
H12C1.43400.75970.43100.219*
C130.8233 (3)0.86814 (17)0.3627 (3)0.0508 (9)
C140.8163 (3)0.92729 (16)0.3392 (3)0.0464 (9)
C150.8116 (3)0.96620 (18)0.4179 (3)0.0505 (10)
C160.8127 (4)0.9463 (2)0.5121 (3)0.0671 (12)
H160.81140.97210.56320.081*
C170.8156 (5)0.8877 (2)0.5319 (4)0.0801 (14)
H170.81500.87470.59570.096*
C180.8192 (4)0.8498 (2)0.4591 (4)0.0695 (12)
H180.81900.81080.47280.083*
C190.8394 (4)0.82363 (17)0.2956 (3)0.0559 (10)
H190.82810.78620.31430.067*
C200.8790 (4)0.77626 (17)0.1597 (4)0.0689 (12)
H20A0.79650.77120.09770.083*
H20B0.88660.74390.20590.083*
C210.9995 (4)0.77629 (18)0.1273 (3)0.0670 (12)
H21A1.00220.74020.09330.080*
H21B0.98810.80660.07640.080*
C221.2507 (5)0.7733 (2)0.1879 (4)0.0896 (15)
H22A1.24680.73460.16320.134*
H22B1.33310.77870.24840.134*
H22C1.24940.79930.13340.134*
C230.8179 (4)1.0643 (2)0.4712 (3)0.0668 (12)
H23A0.90291.05860.53060.080*
H23B0.74351.05940.49520.080*
C240.8139 (5)1.1231 (2)0.4286 (4)0.0909 (16)
H24A0.87931.12610.39600.136*
H24B0.83541.15040.48470.136*
H24C0.72441.13080.37750.136*
C250.7319 (5)0.85823 (19)−0.0634 (4)0.0663 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zn10.0578 (3)0.0483 (3)0.0503 (3)−0.0002 (2)0.0291 (2)−0.0045 (2)
N10.088 (3)0.054 (2)0.067 (2)0.003 (2)0.057 (2)0.0022 (18)
N20.061 (2)0.0538 (19)0.0544 (19)0.0034 (16)0.0300 (17)−0.0049 (16)
N30.0515 (19)0.0462 (18)0.060 (2)−0.0018 (15)0.0231 (17)−0.0066 (16)
N40.074 (2)0.057 (2)0.065 (2)0.0096 (18)0.029 (2)−0.0055 (18)
N50.161 (5)0.073 (3)0.075 (3)0.019 (3)0.040 (3)0.017 (3)
N60.094 (3)0.071 (2)0.058 (2)0.009 (2)0.020 (2)−0.007 (2)
O10.0493 (16)0.0565 (16)0.0770 (19)−0.0063 (12)0.0276 (15)−0.0131 (14)
O20.0466 (18)0.117 (3)0.082 (2)0.0016 (18)0.0202 (17)−0.016 (2)
O30.0676 (17)0.0498 (15)0.0483 (14)0.0008 (13)0.0346 (13)0.0014 (12)
O40.0657 (18)0.0639 (18)0.0540 (16)−0.0044 (14)0.0355 (14)−0.0120 (14)
O50.152 (3)0.074 (2)0.105 (3)0.027 (2)0.063 (3)0.007 (2)
O60.280 (5)0.103 (3)0.127 (3)0.022 (3)0.057 (3)0.006 (3)
O70.158 (4)0.098 (3)0.081 (2)0.029 (2)0.061 (3)0.000 (2)
S10.1313 (13)0.0791 (9)0.0851 (9)0.0145 (8)0.0218 (9)−0.0306 (8)
C10.093 (4)0.082 (3)0.064 (3)−0.037 (3)0.059 (3)−0.028 (3)
C20.064 (3)0.074 (3)0.063 (3)−0.021 (2)0.046 (2)−0.025 (2)
C30.057 (3)0.114 (4)0.068 (3)−0.027 (3)0.040 (3)−0.031 (3)
C40.076 (4)0.180 (7)0.077 (4)−0.052 (4)0.046 (3)−0.033 (4)
C50.124 (6)0.189 (8)0.086 (4)−0.103 (6)0.069 (4)−0.050 (5)
C60.131 (5)0.108 (4)0.081 (4)−0.071 (4)0.075 (4)−0.031 (3)
C70.123 (4)0.052 (3)0.086 (3)−0.013 (3)0.084 (4)−0.010 (3)
C80.125 (4)0.071 (3)0.077 (3)0.025 (3)0.067 (3)0.017 (3)
C90.084 (3)0.067 (3)0.052 (2)0.016 (2)0.030 (2)−0.007 (2)
C100.068 (3)0.116 (4)0.081 (3)0.021 (3)0.037 (3)−0.012 (3)
C110.057 (3)0.181 (7)0.100 (4)0.009 (4)0.018 (3)−0.027 (5)
C120.107 (5)0.160 (7)0.141 (6)0.053 (5)0.012 (5)0.010 (6)
C130.038 (2)0.064 (3)0.054 (2)0.0025 (18)0.0217 (18)0.010 (2)
C140.0313 (19)0.062 (2)0.050 (2)−0.0002 (17)0.0201 (17)−0.0017 (19)
C150.036 (2)0.073 (3)0.049 (2)0.0034 (18)0.0226 (18)−0.001 (2)
C160.059 (3)0.102 (4)0.046 (2)0.011 (2)0.026 (2)0.002 (2)
C170.078 (3)0.117 (4)0.057 (3)0.028 (3)0.038 (3)0.030 (3)
C180.064 (3)0.080 (3)0.072 (3)0.021 (2)0.034 (2)0.030 (3)
C190.046 (2)0.050 (2)0.069 (3)−0.0051 (18)0.020 (2)0.009 (2)
C200.076 (3)0.047 (2)0.084 (3)−0.008 (2)0.030 (3)−0.014 (2)
C210.079 (3)0.052 (2)0.072 (3)0.003 (2)0.031 (3)−0.020 (2)
C220.084 (3)0.098 (4)0.099 (4)0.014 (3)0.049 (3)−0.020 (3)
C230.053 (3)0.089 (3)0.060 (3)−0.002 (2)0.023 (2)−0.026 (3)
C240.104 (4)0.082 (4)0.105 (4)−0.024 (3)0.060 (3)−0.040 (3)
C250.078 (3)0.061 (3)0.059 (3)0.018 (2)0.024 (2)0.001 (2)
Geometric parameters (Å, °) top
Zn1—O31.985 (2)C8—C91.495 (6)
Zn1—O11.999 (3)C8—H8A0.97
Zn1—N62.056 (4)C8—H8B0.97
Zn1—N12.100 (3)C9—H9A0.97
Zn1—N32.104 (3)C9—H9B0.97
N1—C71.288 (6)C10—H10A0.96
N1—C81.465 (5)C10—H10B0.96
N2—C91.484 (5)C10—H10C0.96
N2—C101.485 (5)C11—C121.466 (8)
N2—H2A0.90C11—H11A0.97
N2—H2B0.90C11—H11B0.97
N3—C191.274 (5)C12—H12A0.96
N3—C201.475 (5)C12—H12B0.96
N4—C211.481 (5)C12—H12C0.96
N4—C221.494 (5)C13—C181.410 (6)
N4—H4A0.90C13—C141.413 (5)
N4—H4B0.90C13—C191.442 (5)
N5—O71.201 (5)C14—C151.428 (5)
N5—O51.229 (5)C15—C161.373 (5)
N5—O61.232 (6)C16—C171.392 (6)
N6—C251.147 (5)C16—H160.93
O1—C21.315 (4)C17—C181.347 (6)
O2—C31.368 (6)C17—H170.93
O2—C111.454 (6)C18—H180.93
O3—C141.318 (4)C19—H190.93
O4—C151.373 (5)C20—C211.504 (6)
O4—C231.435 (4)C20—H20A0.97
S1—C251.621 (5)C20—H20B0.97
C1—C21.407 (6)C21—H21A0.97
C1—C61.416 (6)C21—H21B0.97
C1—C71.448 (7)C22—H22A0.96
C2—C31.435 (6)C22—H22B0.96
C3—C41.373 (7)C22—H22C0.96
C4—C51.392 (9)C23—C241.486 (6)
C4—H40.93C23—H23A0.97
C5—C61.334 (9)C23—H23B0.97
C5—H50.93C24—H24A0.96
C6—H60.93C24—H24B0.96
C7—H70.93C24—H24C0.96
O3—Zn1—O1113.20 (11)N2—C10—H10B109.5
O3—Zn1—N6121.28 (14)H10A—C10—H10B109.5
O1—Zn1—N6125.52 (14)N2—C10—H10C109.5
O3—Zn1—N188.83 (11)H10A—C10—H10C109.5
O1—Zn1—N188.76 (13)H10B—C10—H10C109.5
N6—Zn1—N191.96 (15)O2—C11—C12110.4 (5)
O3—Zn1—N390.95 (11)O2—C11—H11A109.6
O1—Zn1—N388.52 (11)C12—C11—H11A109.6
N6—Zn1—N390.76 (14)O2—C11—H11B109.6
N1—Zn1—N3176.95 (14)C12—C11—H11B109.6
C7—N1—C8118.1 (4)H11A—C11—H11B108.1
C7—N1—Zn1122.9 (3)C11—C12—H12A109.5
C8—N1—Zn1119.0 (3)C11—C12—H12B109.5
C9—N2—C10111.0 (3)H12A—C12—H12B109.5
C9—N2—H2A109.4C11—C12—H12C109.5
C10—N2—H2A109.4H12A—C12—H12C109.5
C9—N2—H2B109.4H12B—C12—H12C109.5
C10—N2—H2B109.4C18—C13—C14119.6 (4)
H2A—N2—H2B108.0C18—C13—C19115.9 (4)
C19—N3—C20116.6 (3)C14—C13—C19124.5 (4)
C19—N3—Zn1121.7 (3)O3—C14—C13124.2 (3)
C20—N3—Zn1121.7 (3)O3—C14—C15118.3 (3)
C21—N4—C22112.4 (3)C13—C14—C15117.5 (4)
C21—N4—H4A109.1C16—C15—O4124.6 (4)
C22—N4—H4A109.1C16—C15—C14120.6 (4)
C21—N4—H4B109.1O4—C15—C14114.8 (3)
C22—N4—H4B109.1C15—C16—C17120.6 (4)
H4A—N4—H4B107.9C15—C16—H16119.7
O7—N5—O5122.7 (5)C17—C16—H16119.7
O7—N5—O6115.1 (5)C18—C17—C16120.3 (4)
O5—N5—O6121.1 (5)C18—C17—H17119.9
C25—N6—Zn1158.4 (4)C16—C17—H17119.9
C2—O1—Zn1128.9 (3)C17—C18—C13121.3 (4)
C3—O2—C11118.1 (4)C17—C18—H18119.4
C14—O3—Zn1124.1 (2)C13—C18—H18119.4
C15—O4—C23117.2 (3)N3—C19—C13127.7 (4)
C2—C1—C6120.2 (5)N3—C19—H19116.1
C2—C1—C7123.2 (4)C13—C19—H19116.1
C6—C1—C7116.6 (5)N3—C20—C21113.0 (3)
O1—C2—C1123.9 (4)N3—C20—H20A109.0
O1—C2—C3118.8 (4)C21—C20—H20A109.0
C1—C2—C3117.3 (4)N3—C20—H20B109.0
O2—C3—C4125.6 (6)C21—C20—H20B109.0
O2—C3—C2114.3 (4)H20A—C20—H20B107.8
C4—C3—C2120.1 (6)N4—C21—C20112.9 (4)
C3—C4—C5120.9 (6)N4—C21—H21A109.0
C3—C4—H4119.6C20—C21—H21A109.0
C5—C4—H4119.6N4—C21—H21B109.0
C6—C5—C4120.8 (6)C20—C21—H21B109.0
C6—C5—H5119.6H21A—C21—H21B107.8
C4—C5—H5119.6N4—C22—H22A109.5
C5—C6—C1120.8 (6)N4—C22—H22B109.5
C5—C6—H6119.6H22A—C22—H22B109.5
C1—C6—H6119.6N4—C22—H22C109.5
N1—C7—C1128.6 (4)H22A—C22—H22C109.5
N1—C7—H7115.7H22B—C22—H22C109.5
C1—C7—H7115.7O4—C23—C24109.5 (3)
N1—C8—C9113.2 (4)O4—C23—H23A109.8
N1—C8—H8A108.9C24—C23—H23A109.8
C9—C8—H8A108.9O4—C23—H23B109.8
N1—C8—H8B108.9C24—C23—H23B109.8
C9—C8—H8B108.9H23A—C23—H23B108.2
H8A—C8—H8B107.8C23—C24—H24A109.5
N2—C9—C8113.3 (4)C23—C24—H24B109.5
N2—C9—H9A108.9H24A—C24—H24B109.5
C8—C9—H9A108.9C23—C24—H24C109.5
N2—C9—H9B108.9H24A—C24—H24C109.5
C8—C9—H9B108.9H24B—C24—H24C109.5
H9A—C9—H9B107.7N6—C25—S1179.2 (5)
N2—C10—H10A109.5
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H2B···O30.901.962.750 (4)145
N2—H2B···O40.902.393.078 (4)133
N4—H4B···O10.901.852.697 (4)157
N4—H4B···O20.902.423.027 (5)125
N2—H2A···O7i0.902.012.898 (5)170
N2—H2A···O6i0.902.523.183 (6)131
N4—H4A···O5ii0.902.032.894 (5)160
N4—H4A···O7ii0.902.313.066 (5)141
Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x+1, y, z.
Table 1
Selected geometric parameters (Å) top
Zn1—O31.985 (2)Zn1—N12.100 (3)
Zn1—O11.999 (3)Zn1—N32.104 (3)
Zn1—N62.056 (4)
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N2—H2B···O30.901.962.750 (4)145
N2—H2B···O40.902.393.078 (4)133
N4—H4B···O10.901.852.697 (4)157
N4—H4B···O20.902.423.027 (5)125
N2—H2A···O7i0.902.012.898 (5)170
N2—H2A···O6i0.902.523.183 (6)131
N4—H4A···O5ii0.902.032.894 (5)160
N4—H4A···O7ii0.902.313.066 (5)141
Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x+1, y, z.
Acknowledgements top

This work was supported by the Natural Science Foundation of China (grant No. 30771696), the Natural Science Foundation of Zhejiang Province (grant No. Y407318) and the Science and Technology Plan of Huzhou (grant No. 2009 GG06).

references
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