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Acta Cryst. (2008). E64, m1392-m1393    [ doi:10.1107/S1600536808032017 ]

catena-Poly[[[aquatripyridinecobalt(II)]-[mu]-5-amino-2,4,6-triiodoisophthalato-[kappa]2O1:O3] pyridine solvate]

Y. Zhang, J. Zhao, G. Tang and Z. Jiang

Abstract top

The reaction of cobalt(II) nitrate with 5-amino-2,4,6-triiodoisophthalic acid (ATPA) in pyridine solution leads to the formation of the title compound, {[Co(C8H2I3NO4)(C5H5N)3(H2O)]·C5H5N}n. The Co2+ ion is six-coordinated by three N atoms, one water O atom and two O atoms from two ATPA ligands to form a distorted octahedral geometry. The two carboxylate groups of ATPA act as bridging ligands connecting the CoII metal centers to form one-dimensional zigzag chains along the c axis, with Co-O distances in the range 2.104 (4)-2.135 (4) Å. The average Co-N distance is 2.171 Å. A classical O-H...N hydrogen bond is formed by the coordinating water molecule and the pyridine solvent molecule. The structure was refined from a racemically twinned crystal with a twin ratio of approximately 8:1.

Comment top

The crystal structure of ATPA (Beck & Sheldrick, 2008) is the precursor of the synthesis of a wide range of contrast agents with different amide-bound aliphatic side chains, which modulate their physical and physiological properties (Ziegler et al. 1997). However, to the best of our knowledge, there is no information about the structural characterization of its transition metal complexes.

The molecular structure of the title complex comprises of polymeric chains which extend along the c-axis. In the chain, each Co atom shows a distorted octahedron environment with a [3N+3O] coordination: three nitrogen atoms originate from pyridines, one oxygen from a water molecule and two oxygen atoms from two ATPA ligands. The two CO2- groups of the ATPA ligand coordinate to Co2+, bridging the Co metal centers. The bond lengths of the distorted octahedron are presented in Table 1. The average Co—N bond distance of the three pyridine ligands is 2.171 Å. The Co—O bond lengths in the title complex are slightly longer than those in the reported coordination polymers of cobalt and 1,3,5-benzenetricarboxylate (2.055 (2) Å) (Livage et al., 2001). The bond angles shown in Table 1 demonstrate the distorted octahedron in the Co coordination center. Compared with the data of the free ligand ATPA (Beck & Sheldrick, 2008), the C—O bond lengths are lengthened, the C—I and C—N bond distances are almost unchanged and the O—C—O bond angles are slightly expanded when the carboxylate groups are coordinated to central cations. The Co—N(py) and Co—O(H2O) distances are in good agreement with those in diaqua-diformato-dipyridine-cobalt(II) (Zhu et al., 2004), where they are equal to 2.159 (4) Å and 2.143 (3) Å, respectively. A classic O—H···N hydrogen bond is formed by the coordinating water and the uncoordinated pyridine molecule (Table 2).

Related literature top

For the structure of a monohydrate of ATPA, see: Beck & Sheldrick (2008). For the Co coordination polymer of 1,3,5-benzenetricarboxylate, see: Livage et al. (2001). For the structure of diaquadiformatodipyridine CoII, see: Zhu et al. (2004). For a reduction of the organic iodine contrast agents in wastewater load, see: Ziegler et al. (1997).

Experimental top

0.29 g (1 mmol) Co(NO3)2.6H2O was dissolved in 10 ml ethanol, 0.54 g (1 mmol) 5-amino-2, 4, 6-triiodoisophthalic acid was dissolved in 10 ml pyridine. To mix two solutions gave a pale purple solution which was stirred at room temperature for 2 h, then filtered. After several days well formed light purple single crystals were obtained.

Refinement top

H atoms were positioned geometrically and refined using a riding model with C—H distances = 0.93 Å, N—H distances = 0.86 Å, and O—H distances = 0.85 Å with Uiso(H) = 1.2 times Ueq(C, N, O).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with atom labels and 30% probability displacement ellipsoids for non-H atoms. Atoms labelled with an A belong to the symmetry-related ligand ATPA with symmetry code [A = -x + 3/2, -y, z + 1/2)].
catena-Poly[[[aquatripyridinecobalt(II)]-µ-5-amino-2,4,6- triiodoisophthalato-κ2O1:O3] pyridine solvate] top
Crystal data top
[Co(C8H2I3NO4)(C5H5N)3(H2O)]·C5H5NF(000) = 1812
Mr = 950.15Dx = 1.974 Mg m−3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 7120 reflections
a = 9.7759 (2) Åθ = 4.7–43.0°
b = 16.9083 (4) ŵ = 3.48 mm−1
c = 19.3380 (4) ÅT = 296 K
V = 3196.45 (12) Å3Sheet, light purple
Z = 40.30 × 0.25 × 0.08 mm
Data collection top
Bruker APEXII CCD
diffractometer		6038 independent reflections
Radiation source: fine-focus sealed tube4577 reflections with I > 2σ(I)
graphiteRint = 0.027
φ and ω scansθmax = 26.0°, θmin = 1.6°
Absorption correction: multi-scan
(SADABS; Bruker, 2000)		h = −12→9
Tmin = 0.38, Tmax = 0.75k = −13→20
16692 measured reflectionsl = −15→23
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.041H-atom parameters constrained
wR(F2) = 0.065 w = 1/[σ2(Fo2) + (0.0243P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max = 0.001
6038 reflectionsΔρmax = 0.68 e Å−3
379 parametersΔρmin = −0.67 e Å−3
3 restraintsAbsolute structure: Flack (1983), with 2515 Friedel pairs
Primary atom site location: structure-invariant direct methodsFlack parameter: 0.13 (2)
Crystal data top
[Co(C8H2I3NO4)(C5H5N)3(H2O)]·C5H5NV = 3196.45 (12) Å3
Mr = 950.15Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 9.7759 (2) ŵ = 3.48 mm−1
b = 16.9083 (4) ÅT = 296 K
c = 19.3380 (4) Å0.30 × 0.25 × 0.08 mm
Data collection top
Bruker APEXII CCD
diffractometer		6038 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2000)		4577 reflections with I > 2σ(I)
Tmin = 0.38, Tmax = 0.75Rint = 0.027
16692 measured reflectionsθmax = 26.0°
Refinement top
R[F2 > 2σ(F2)] = 0.041H-atom parameters constrained
wR(F2) = 0.065Δρmax = 0.68 e Å−3
S = 1.04Δρmin = −0.67 e Å−3
6038 reflectionsAbsolute structure: Flack (1983), with 2515 Friedel pairs
379 parametersFlack parameter: 0.13 (2)
3 restraints
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
C10.8251 (6)0.2139 (3)0.8550 (3)0.0319 (15)
C20.8423 (6)0.2494 (3)0.7900 (3)0.0344 (16)
C30.7752 (6)0.2152 (3)0.7335 (3)0.0299 (15)
C40.6949 (6)0.1483 (3)0.7390 (3)0.0229 (14)
C50.6819 (6)0.1159 (3)0.8047 (3)0.0286 (15)
C60.7445 (6)0.1478 (3)0.8629 (3)0.0243 (14)
C70.6216 (7)0.1144 (3)0.6765 (3)0.0276 (15)
C80.7222 (7)0.1122 (3)0.9341 (3)0.0305 (15)
C90.9902 (7)0.0943 (4)1.1534 (4)0.052 (2)
H91.04680.05011.15400.063*
C101.0171 (8)0.1565 (5)1.1968 (4)0.067 (2)
H101.09090.15281.22700.080*
C110.9406 (10)0.2230 (5)1.1973 (4)0.078 (3)
H110.96070.26511.22660.093*
C120.8332 (9)0.2254 (5)1.1531 (4)0.078 (3)
H120.77680.26971.15200.093*
C130.8073 (7)0.1626 (4)1.1100 (4)0.060 (2)
H130.73420.16611.07930.072*
C141.1101 (6)−0.0851 (4)1.0269 (3)0.0397 (18)
H141.0619−0.12791.04470.048*
C151.2437 (7)−0.0963 (4)1.0090 (3)0.0488 (19)
H151.2859−0.14511.01510.059*
C161.3142 (7)−0.0329 (5)0.9817 (3)0.053 (2)
H161.4044−0.03910.96740.064*
C171.2528 (6)0.0377 (4)0.9759 (3)0.0471 (19)
H171.30000.08150.95920.057*
C181.1168 (7)0.0434 (4)0.9955 (3)0.0448 (18)
H181.07330.09210.99110.054*
C190.6591 (7)−0.1424 (4)0.9923 (4)0.0470 (19)
H190.6114−0.13051.03260.056*
C200.6061 (7)−0.1985 (4)0.9494 (4)0.057 (2)
H200.5249−0.22400.96080.068*
C210.6717 (9)−0.2166 (4)0.8905 (4)0.069 (2)
H210.6357−0.25360.85990.082*
C220.7916 (9)−0.1797 (4)0.8766 (4)0.063 (2)
H220.8416−0.19250.83720.076*
C230.8384 (7)−0.1222 (4)0.9223 (4)0.052 (2)
H230.9188−0.09560.91130.062*
C24−0.0436 (7)0.0013 (4)0.7430 (5)0.062 (2)
H24−0.1309−0.02020.74650.074*
C250.0132 (9)0.0325 (5)0.8004 (4)0.064 (2)
H25−0.03370.03210.84220.076*
C260.1384 (11)0.0640 (5)0.7959 (5)0.096 (3)
H260.18040.08550.83480.115*
C270.2020 (9)0.0641 (6)0.7351 (5)0.101 (3)
H270.28840.08670.73090.121*
C280.1404 (9)0.0313 (5)0.6790 (4)0.082 (3)
H280.18620.03110.63690.098*
Co10.83021 (7)−0.00406 (5)1.04654 (4)0.0312 (2)
I10.92570 (5)0.26385 (3)0.94026 (2)0.05269 (14)
I20.78262 (5)0.27575 (3)0.63848 (2)0.05874 (16)
I30.56454 (5)0.01146 (3)0.81795 (2)0.05039 (14)
N10.9245 (6)0.3143 (3)0.7821 (3)0.0630 (17)
H1A0.93570.33490.74180.076*
H1B0.96490.33450.81740.076*
N20.8833 (5)0.0964 (3)1.1102 (2)0.0393 (14)
N31.0452 (5)−0.0175 (3)1.0205 (2)0.0348 (13)
N40.7763 (6)−0.1033 (3)0.9799 (3)0.0379 (14)
N50.0172 (7)−0.0004 (4)0.6829 (3)0.0660 (19)
O10.6899 (4)0.0730 (2)0.6366 (2)0.0386 (11)
O20.5004 (5)0.1311 (3)0.6709 (2)0.0555 (14)
O30.8147 (4)0.0677 (2)0.95601 (19)0.0329 (10)
O40.6139 (4)0.1298 (2)0.9646 (2)0.0460 (12)
O50.6191 (3)0.0161 (2)1.05937 (18)0.0423 (11)
H5B0.59510.06031.04230.051*
H5A0.59630.01431.10180.051*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.041 (4)0.029 (4)0.026 (4)0.003 (3)−0.003 (3)−0.007 (3)
C20.043 (4)0.029 (4)0.032 (4)−0.014 (3)0.003 (3)−0.004 (3)
C30.038 (3)0.029 (4)0.023 (3)−0.005 (3)−0.004 (3)0.001 (3)
C40.026 (4)0.022 (3)0.020 (3)0.004 (3)−0.001 (3)−0.007 (3)
C50.032 (3)0.032 (4)0.022 (4)−0.002 (3)0.003 (3)−0.003 (3)
C60.033 (4)0.022 (3)0.017 (3)0.006 (3)−0.004 (3)−0.002 (3)
C70.041 (4)0.020 (4)0.021 (4)0.010 (3)0.005 (3)0.004 (3)
C80.045 (4)0.027 (4)0.019 (4)−0.006 (3)−0.005 (4)−0.007 (3)
C90.050 (4)0.053 (5)0.053 (5)−0.004 (4)−0.023 (4)0.006 (4)
C100.078 (6)0.071 (6)0.052 (5)−0.045 (5)−0.022 (5)−0.004 (5)
C110.122 (8)0.054 (6)0.058 (5)−0.033 (6)0.009 (6)−0.022 (5)
C120.103 (7)0.056 (6)0.075 (6)0.004 (5)−0.025 (5)−0.024 (5)
C130.067 (5)0.054 (5)0.059 (5)0.011 (5)−0.006 (5)−0.020 (4)
C140.042 (4)0.043 (4)0.035 (4)0.004 (4)0.001 (3)0.000 (4)
C150.046 (5)0.057 (5)0.043 (5)0.020 (4)0.002 (4)−0.008 (4)
C160.028 (4)0.088 (6)0.044 (5)0.013 (4)0.003 (3)−0.009 (4)
C170.032 (4)0.064 (6)0.045 (4)−0.008 (4)−0.001 (3)0.010 (4)
C180.046 (5)0.041 (4)0.048 (5)0.001 (4)0.003 (4)0.004 (4)
C190.048 (5)0.037 (4)0.056 (5)0.005 (4)0.003 (4)0.004 (4)
C200.047 (5)0.043 (5)0.080 (6)−0.017 (4)−0.010 (4)0.001 (5)
C210.088 (7)0.050 (5)0.068 (5)−0.009 (5)−0.026 (5)−0.008 (5)
C220.085 (6)0.060 (6)0.046 (5)0.000 (5)−0.004 (5)−0.028 (4)
C230.055 (5)0.051 (5)0.049 (5)−0.011 (4)0.006 (4)−0.005 (4)
C240.041 (5)0.061 (5)0.083 (6)0.005 (4)0.005 (5)−0.002 (6)
C250.078 (6)0.067 (6)0.046 (5)0.019 (5)0.010 (5)0.001 (5)
C260.115 (9)0.122 (8)0.050 (6)−0.044 (7)−0.034 (6)0.010 (6)
C270.059 (6)0.167 (10)0.078 (7)−0.047 (6)−0.011 (6)0.020 (8)
C280.063 (6)0.131 (9)0.051 (6)−0.003 (6)0.014 (5)0.023 (6)
Co10.0333 (4)0.0350 (5)0.0254 (5)−0.0001 (4)−0.0013 (4)0.0022 (5)
I10.0737 (3)0.0481 (3)0.0363 (3)−0.0171 (3)−0.0127 (3)−0.0058 (2)
I20.0883 (4)0.0569 (3)0.0311 (3)−0.0191 (3)0.0001 (3)0.0134 (3)
I30.0633 (3)0.0495 (3)0.0384 (3)−0.0231 (3)−0.0053 (2)0.0067 (2)
N10.092 (4)0.062 (4)0.035 (3)−0.045 (4)−0.014 (4)0.007 (3)
N20.048 (4)0.042 (4)0.027 (3)−0.004 (3)0.000 (3)−0.001 (3)
N30.031 (3)0.038 (3)0.035 (3)0.002 (3)0.003 (2)0.006 (3)
N40.043 (3)0.039 (4)0.031 (3)0.003 (3)0.002 (3)−0.002 (3)
N50.063 (4)0.089 (5)0.047 (4)0.014 (4)−0.012 (4)−0.011 (4)
O10.047 (3)0.041 (3)0.028 (2)−0.001 (2)0.002 (2)−0.013 (2)
O20.048 (3)0.075 (4)0.044 (3)0.015 (3)−0.012 (3)−0.020 (3)
O30.037 (3)0.036 (3)0.026 (2)0.001 (2)−0.005 (2)0.007 (2)
O40.049 (3)0.064 (3)0.025 (3)0.021 (2)0.010 (2)0.001 (2)
O50.045 (3)0.048 (3)0.034 (2)0.007 (2)0.006 (2)0.010 (2)
Geometric parameters (Å, °) top
C1—C61.376 (7)C18—N31.336 (7)
C1—C21.404 (7)C18—H180.9300
C1—I12.097 (6)C19—N41.344 (7)
C2—N11.368 (7)C19—C201.363 (9)
C2—C31.400 (7)C19—H190.9300
C3—C41.381 (7)C20—C211.342 (9)
C3—I22.105 (5)C20—H200.9300
C4—C51.389 (7)C21—C221.355 (9)
C4—C71.517 (8)C21—H210.9300
C5—C61.390 (7)C22—C231.391 (8)
C5—I32.122 (6)C22—H220.9300
C6—C81.519 (4)C23—N41.309 (7)
C7—O21.223 (6)C23—H230.9300
C7—O11.238 (6)C24—N51.306 (8)
C8—O41.248 (6)C24—C251.348 (9)
C8—O31.250 (6)C24—H240.9300
C9—N21.337 (7)C25—C261.338 (10)
C9—C101.372 (9)C25—H250.9300
C9—H90.9300C26—C271.331 (11)
C10—C111.350 (10)C26—H260.9300
C10—H100.9300C27—C281.359 (11)
C11—C121.355 (10)C27—H270.9300
C11—H110.9300C28—N51.321 (9)
C12—C131.373 (9)C28—H280.9300
C12—H120.9300Co1—O1i2.104 (4)
C13—N21.345 (7)Co1—O52.106 (3)
C13—H130.9300Co1—O32.135 (4)
C14—N31.312 (7)Co1—N22.161 (5)
C14—C151.365 (8)Co1—N32.173 (5)
C14—H140.9300Co1—N42.180 (5)
C15—C161.379 (9)N1—H1A0.8600
C15—H150.9300N1—H1B0.8600
C16—C171.342 (8)O1—Co1ii2.104 (4)
C16—H160.9300O5—H5B0.8500
C17—C181.386 (8)O5—H5A0.8499
C17—H170.9300
C6—C1—C2121.0 (5)C19—C20—H20120.2
C6—C1—I1120.6 (4)C20—C21—C22118.4 (8)
C2—C1—I1118.4 (4)C20—C21—H21120.8
N1—C2—C3121.3 (5)C22—C21—H21120.8
N1—C2—C1120.9 (5)C21—C22—C23118.7 (8)
C3—C2—C1117.8 (5)C21—C22—H22120.6
C4—C3—C2123.0 (5)C23—C22—H22120.6
C4—C3—I2119.1 (4)N4—C23—C22124.0 (7)
C2—C3—I2117.7 (4)N4—C23—H23118.0
C3—C4—C5116.5 (5)C22—C23—H23118.0
C3—C4—C7121.1 (5)N5—C24—C25123.6 (7)
C5—C4—C7122.5 (5)N5—C24—H24118.2
C4—C5—C6123.2 (5)C25—C24—H24118.2
C4—C5—I3119.2 (4)C26—C25—C24118.6 (8)
C6—C5—I3117.6 (4)C26—C25—H25120.7
C1—C6—C5118.5 (5)C24—C25—H25120.7
C1—C6—C8120.3 (5)C27—C26—C25119.0 (9)
C5—C6—C8121.1 (5)C27—C26—H26120.5
O2—C7—O1126.7 (7)C25—C26—H26120.5
O2—C7—C4116.2 (6)C26—C27—C28119.9 (8)
O1—C7—C4117.2 (5)C26—C27—H27120.1
O4—C8—O3126.7 (5)C28—C27—H27120.1
O4—C8—C6117.0 (6)N5—C28—C27121.6 (8)
O3—C8—C6116.2 (5)N5—C28—H28119.2
N2—C9—C10120.7 (7)C27—C28—H28119.2
N2—C9—H9119.6O1i—Co1—O584.29 (15)
C10—C9—H9119.6O1i—Co1—O3170.52 (16)
C11—C10—C9122.5 (8)O5—Co1—O386.29 (15)
C11—C10—H10118.7O1i—Co1—N289.21 (16)
C9—C10—H10118.7O5—Co1—N292.37 (17)
C10—C11—C12116.7 (8)O3—Co1—N292.18 (17)
C10—C11—H11121.7O1i—Co1—N3102.93 (17)
C12—C11—H11121.7O5—Co1—N3172.68 (17)
C11—C12—C13120.2 (8)O3—Co1—N386.47 (17)
C11—C12—H12119.9N2—Co1—N388.95 (19)
C13—C12—H12119.9O1i—Co1—N492.29 (17)
N2—C13—C12122.7 (7)O5—Co1—N487.53 (18)
N2—C13—H13118.7O3—Co1—N486.31 (16)
C12—C13—H13118.7N2—Co1—N4178.48 (19)
N3—C14—C15124.1 (6)N3—Co1—N491.0 (2)
N3—C14—H14118.0C2—N1—H1A120.0
C15—C14—H14118.0C2—N1—H1B120.0
C14—C15—C16117.8 (7)H1A—N1—H1B120.0
C14—C15—H15121.1C9—N2—C13117.2 (6)
C16—C15—H15121.1C9—N2—Co1121.5 (5)
C17—C16—C15120.0 (6)C13—N2—Co1121.3 (5)
C17—C16—H16120.0C14—N3—C18116.9 (5)
C15—C16—H16120.0C14—N3—Co1122.5 (4)
C16—C17—C18117.9 (7)C18—N3—Co1120.7 (4)
C16—C17—H17121.0C23—N4—C19115.3 (6)
C18—C17—H17121.0C23—N4—Co1125.4 (5)
N3—C18—C17123.2 (6)C19—N4—Co1118.7 (5)
N3—C18—H18118.4C24—N5—C28117.2 (7)
C17—C18—H18118.4C7—O1—Co1ii141.2 (4)
N4—C19—C20123.9 (7)C8—O3—Co1132.1 (4)
N4—C19—H19118.0Co1—O5—H5B111.5
C20—C19—H19118.0Co1—O5—H5A111.4
C21—C20—C19119.6 (7)H5B—O5—H5A109.4
C21—C20—H20120.2
Symmetry codes: (i) −x+3/2, −y, z+1/2; (ii) −x+3/2, −y, z−1/2.
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O5—H5A···N5iii0.851.942.748 (7)159
Symmetry codes: (iii) −x+1/2, −y, z+1/2.
Table 1
Selected geometric parameters (Å, °) top
Co1—O1i2.104 (4)Co1—N22.161 (5)
Co1—O52.106 (3)Co1—N32.173 (5)
Co1—O32.135 (4)Co1—N42.180 (5)
O1i—Co1—O3170.52 (16)O5—Co1—N3172.68 (17)
O1i—Co1—N3102.93 (17)N2—Co1—N4178.48 (19)
Symmetry codes: (i) −x+3/2, −y, z+1/2.
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O5—H5A···N5ii0.851.942.748 (7)159
Symmetry codes: (ii) −x+1/2, −y, z+1/2.
Acknowledgements top

This work was financially supported by the Natural Science Foundation of Jiangsu Province Education Office (grant No. 04KJB150015). We also thank Dr Zaichao Zhang for his support.

references
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