Dimethyl (7-hy­droxy-4-methyl-2-oxo-2H-chromen-3-yl)phospho­nate

Li, Y.; Xiao, Y.; Zhang, X.; Yang, L.; Yuan, J.; Mao, P.

doi:10.1107/S2414314617011191

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 2| Part 8| August 2017| x171119

https://doi.org/10.1107/S2414314617011191

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Dimethyl (7-hydroxy-4-methyl-2-oxo-2H-chromen-3-yl)phosphonate

Yunfei Li,^a Yongmei Xiao,^a Xinchi Zhang,^a Liangru Yang,^a ^* Jinwei Yuan ^a and Pu Mao ^a

^aCollege of Chemistry and Chemical engineering, Henan University of Technology, Zhengzhou 450001, People's Republic of China
^*Correspondence e-mail: lryang@haut.edu.cn

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 26 July 2017; accepted 30 July 2017; online 4 August 2017)

In the title compound, C₁₂H₁₃O₆P, the coumarin ring system is essentially planar [dihedral angle between the rings = 1.32 (16)°] and the methoxy groups and double-bonded O atom of the phosphonate group are disordered over two sets of sites [occupancy ratio 0.537 (2):0.463 (2)]. In the crystal, C—H⋯O hydrogen bonds involving the disordered phosphonate O atom as acceptor occur, which generate [100] chains. Weak C—H⋯O and aromatic π–π stacking interactions [minimum centroid–centroid separation = 3.713 (2) Å] are also observed.

Keywords: crystal structure; 3-phosphorated coumarin; hydrogen bonding.

CCDC reference: 1565652

Structure description

Several 3-phosphorated coumarins have been proved to exhibit cytotoxicity on some human leukemia cell lines as well as having high alkylating activity (Budzisz et al., 2003 ) and the selective synthesis of phosphorated coumarins has been a quite active topic (Yuan et al., 2015 ; Mi et al., 2013 ). Our group has investigated the phosphorylation of coumarins catalysed by chelating N-heterocyclic palladium complexes and obtained 3-phosphorated coumarins selectively (Yang et al., 2016 ). The structure of one of these products, viz.: the title compound, was characterized unambiguously by single-crystal X-ray diffraction studies.

As shown in Fig. 1, the coumarin ring system is essentially planar [dihedral angle between the rings = 1.32 (16)°]. The methoxyl groups and the double-bonded oxygen atom of the phosphonate group show disorder, with the major and minor components of the disorder having an occupancy factor of 0.537 (2) and 0.463 (2), respectively. In the crystal, O—H⋯O hydrogen bonds (Table 1) involving the disordered phosphonate group are observed, which generate [100] chains. Weak C—H⋯O and aromatic π-π stacking interactions [minimum centroid–centroid separation = 3.713 (2) Å] are also observed.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O4ⁱ	0.82	1.78	2.562 (6)	159
O3—H3⋯O4Aⁱ	0.82	2.01	2.812 (7)	168
C8—H8⋯O1ⁱⁱ	0.93	2.44	3.220 (4)	142
C10—H10B⋯O4	0.96	2.22	2.831 (6)	121
C12—H12A⋯O1	0.96	2.20	2.96 (5)	135
Symmetry codes: (i) x+1, y, z; (ii) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Figure 1
The molecular structure of the title compound, showing 50% probability displacement ellipsoids. Only the major disorder component is shown.

Synthesis and crystallization

The synthesis of the title compound is based on our reported literature procedure (Yang et al., 2016). A Schlenk tube charged with 7-hydroxy-4-methyl coumarin (0.5 mmol, 88 mg), dimethyl phosphite (1.0 mmol, 110 mg), NHC palladium complex (0.05 mmol), AgNO₃ (1.0 mmol, 170 mg) and CH₃CN (2 ml) was heated at 80°C for 10 h. The mixture was then cooled, filtered and the filtrate was evaporated. Purification of the residue by column chromatography (silica, petroleum ether/ethyl acetate = 2/11/4, v/v) produced the pure products. Recrystallization of the product from CH₂Cl₂/diethyl ether (1/1, v/v) solution afforded the title compound as colourless prisms.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₂H₁₃O₆P
M_r	284.19
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	293
a, b, c (Å)	9.9684 (7), 7.8695 (6), 16.6927 (10)
β (°)	106.097 (7)
V (Å³)	1258.13 (16)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.24
Crystal size (mm)	0.25 × 0.12 × 0.1

Data collection
Diffractometer	Agilent Xcalibur Eos
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku Oxford Diffraction, 2015 $[Rigaku OD (2011). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ )
T_min, T_max	0.007, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	5507, 2572, 1364
R_int	0.043
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.058, 0.173, 1.01
No. of reflections	2572
No. of parameters	194
No. of restraints	26
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.30, −0.28
Computer programs: CrysAlis PRO (Rigaku OD, 2015 $[Rigaku OD (2011). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ) and OLEX2 (Dolomanov et al., 2009 ).

Structural data

CCDC reference: 1565652

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2414314617011191/hb4160sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314617011191/hb4160Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314617011191/hb4160Isup3.cdx

Supporting information file. DOI: https://doi.org/10.1107/S2414314617011191/hb4160Isup4.cml

checkCIF report

Computing details top

Data collection: CrysAlis PRO (Rigaku OD, 2015); cell refinement: CrysAlis PRO (Rigaku OD, 2015); data reduction: CrysAlis PRO (Rigaku OD, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Dimethyl (7-hydroxy-4-methyl-2-oxo-2H-chromen-3-yl)phosphonate top

Crystal data top

C₁₂H₁₃O₆P	F(000) = 592
M_r = 284.19	D_x = 1.500 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.9684 (7) Å	Cell parameters from 1046 reflections
b = 7.8695 (6) Å	θ = 3.8–25.4°
c = 16.6927 (10) Å	µ = 0.24 mm⁻¹
β = 106.097 (7)°	T = 293 K
V = 1258.13 (16) Å³	Prism, colourless
Z = 4	0.25 × 0.12 × 0.1 mm

Data collection top

Agilent Xcalibur Eos diffractometer	2572 independent reflections
Radiation source: fine-focus sealed X-ray tube, Enhance (Mo) X-ray Source	1364 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.043
Detector resolution: 16.2312 pixels mm^-1	θ_max = 26.4°, θ_min = 2.1°
ω scans	h = −12→11
Absorption correction: multi-scan (CrysAlis PRO; Rigaku Oxford Diffraction, 2015)	k = −6→9
T_min = 0.007, T_max = 1.000	l = −20→20
5507 measured reflections

Refinement top

Refinement on F²	26 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.058	H-atom parameters constrained
wR(F²) = 0.173	w = 1/[σ²(F_o²) + (0.0763P)²] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
2572 reflections	Δρ_max = 0.30 e Å⁻³
194 parameters	Δρ_min = −0.28 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Aromatic H atoms were placed geometrically and refined as riding, with C—H = 0.93–0.97 Å, and with U_iso(H) = 1.2 U_eq(C). The H atoms associated to hydroxyl and methyl groups were refined as rotating groups, with U_iso(H) = 1.5 U_eq(C). The O5A—C11A and O6A—C12A bonds were refined with restrained distances of 1.55 (2) Å.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
C1	0.4062 (3)	0.3873 (5)	0.6581 (2)	0.0552 (10)
C2	0.2791 (3)	0.3234 (4)	0.6012 (2)	0.0468 (8)
C3	0.2797 (3)	0.2579 (5)	0.5251 (2)	0.0486 (9)
C4	0.4104 (3)	0.2502 (4)	0.5029 (2)	0.0451 (8)
C5	0.5316 (3)	0.3061 (4)	0.56004 (19)	0.0450 (8)
C6	0.6615 (3)	0.3005 (5)	0.5456 (2)	0.0547 (10)
H6	0.7404	0.3383	0.5858	0.066*
C7	0.6715 (4)	0.2381 (5)	0.4706 (2)	0.0552 (10)
C8	0.5532 (4)	0.1831 (5)	0.4109 (2)	0.0617 (10)
H8	0.5604	0.1421	0.3600	0.074*
C9	0.4261 (4)	0.1891 (5)	0.4269 (2)	0.0562 (10)
H9	0.3476	0.1516	0.3862	0.067*
C10	0.1510 (3)	0.1924 (6)	0.4629 (2)	0.0725 (12)
H10A	0.0967	0.2863	0.4345	0.109*
H10B	0.0965	0.1275	0.4912	0.109*
H10C	0.1774	0.1213	0.4230	0.109*
C11	0.209 (3)	0.077 (3)	0.733 (2)	0.086 (5)	0.537 (2)
H11A	0.1408	0.0093	0.6941	0.129*	0.537 (2)
H11B	0.2170	0.0382	0.7888	0.129*	0.537 (2)
H11C	0.2979	0.0652	0.7215	0.129*	0.537 (2)
C11A	0.209 (4)	0.036 (4)	0.723 (2)	0.086 (5)	0.463 (2)
H11D	0.2358	−0.0589	0.6947	0.129*	0.463 (2)
H11E	0.1707	−0.0036	0.7660	0.129*	0.463 (2)
H11F	0.2893	0.1057	0.7466	0.129*	0.463 (2)
C12	0.151 (5)	0.598 (2)	0.738 (2)	0.085 (3)	0.537 (2)
H12A	0.2501	0.6123	0.7468	0.127*	0.537 (2)
H12B	0.1341	0.5309	0.7816	0.127*	0.537 (2)
H12C	0.1082	0.7076	0.7366	0.127*	0.537 (2)
C12A	0.153 (6)	0.609 (3)	0.727 (3)	0.085 (3)	0.463 (2)
H12D	0.1767	0.6525	0.6793	0.127*	0.463 (2)
H12E	0.2202	0.6479	0.7770	0.127*	0.463 (2)
H12F	0.0618	0.6493	0.7272	0.127*	0.463 (2)
O1	0.4182 (3)	0.4547 (4)	0.72427 (15)	0.0756 (9)
O2	0.5290 (2)	0.3705 (3)	0.63588 (13)	0.0581 (7)
O3	0.7946 (3)	0.2292 (4)	0.45079 (16)	0.0806 (9)
H3	0.8580	0.2619	0.4905	0.121*
O4	0.0015 (5)	0.2510 (8)	0.5818 (3)	0.0693 (13)	0.537 (2)
O4A	0.0032 (6)	0.3910 (9)	0.5761 (4)	0.0693 (13)	0.463 (2)
O5	0.1688 (5)	0.2446 (7)	0.7256 (3)	0.0615 (10)	0.537 (2)
O5A	0.1013 (5)	0.1394 (7)	0.6613 (3)	0.0615 (10)	0.463 (2)
O6	0.0938 (5)	0.5143 (6)	0.6592 (3)	0.0679 (11)	0.537 (2)
O6A	0.1527 (6)	0.4150 (8)	0.7252 (3)	0.0679 (11)	0.463 (2)
P1	0.12560 (9)	0.32787 (13)	0.63845 (6)	0.0535 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0398 (19)	0.077 (3)	0.052 (2)	0.0053 (19)	0.0172 (17)	0.003 (2)
C2	0.0335 (16)	0.054 (2)	0.0544 (19)	0.0022 (16)	0.0142 (15)	0.0028 (18)
C3	0.0357 (18)	0.050 (2)	0.059 (2)	0.0072 (16)	0.0105 (16)	0.0102 (18)
C4	0.0351 (17)	0.051 (2)	0.0491 (19)	0.0040 (16)	0.0114 (15)	0.0039 (16)
C5	0.0386 (18)	0.052 (2)	0.0452 (18)	0.0016 (16)	0.0134 (15)	0.0002 (16)
C6	0.0325 (17)	0.076 (3)	0.055 (2)	−0.0001 (17)	0.0104 (16)	0.0016 (19)
C7	0.0388 (19)	0.076 (3)	0.054 (2)	0.0070 (19)	0.0188 (17)	0.0088 (19)
C8	0.052 (2)	0.081 (3)	0.055 (2)	0.009 (2)	0.0203 (19)	−0.002 (2)
C9	0.0441 (19)	0.074 (3)	0.0492 (19)	0.0051 (19)	0.0100 (16)	−0.0008 (18)
C10	0.038 (2)	0.106 (4)	0.070 (2)	−0.003 (2)	0.0088 (18)	−0.015 (2)
C11	0.106 (4)	0.060 (11)	0.104 (5)	0.016 (7)	0.048 (5)	0.017 (7)
C11A	0.106 (4)	0.060 (11)	0.104 (5)	0.016 (7)	0.048 (5)	0.017 (7)
C12	0.081 (4)	0.076 (4)	0.102 (8)	0.012 (3)	0.035 (5)	−0.012 (3)
C12A	0.081 (4)	0.076 (4)	0.102 (8)	0.012 (3)	0.035 (5)	−0.012 (3)
O1	0.0553 (15)	0.117 (3)	0.0575 (15)	−0.0005 (16)	0.0202 (13)	−0.0220 (16)
O2	0.0334 (12)	0.088 (2)	0.0542 (14)	−0.0038 (12)	0.0136 (11)	−0.0117 (13)
O3	0.0454 (15)	0.130 (3)	0.0747 (17)	0.0084 (18)	0.0302 (14)	0.0004 (18)
O4	0.0325 (15)	0.106 (4)	0.069 (2)	−0.003 (3)	0.0146 (15)	−0.004 (3)
O4A	0.0325 (15)	0.106 (4)	0.069 (2)	−0.003 (3)	0.0146 (15)	−0.004 (3)
O5	0.059 (2)	0.064 (3)	0.069 (2)	0.0066 (19)	0.030 (2)	0.0139 (18)
O5A	0.059 (2)	0.064 (3)	0.069 (2)	0.0066 (19)	0.030 (2)	0.0139 (18)
O6	0.069 (3)	0.067 (3)	0.076 (3)	0.018 (2)	0.033 (2)	0.008 (2)
O6A	0.069 (3)	0.067 (3)	0.076 (3)	0.018 (2)	0.033 (2)	0.008 (2)
P1	0.0368 (5)	0.0680 (7)	0.0595 (6)	0.0055 (5)	0.0196 (4)	0.0059 (5)

Geometric parameters (Å, º) top

C1—C2	1.446 (5)	C11—H11B	0.9600
C1—O1	1.200 (4)	C11—H11C	0.9600
C1—O2	1.381 (4)	C11—O5	1.38 (2)
C2—C3	1.373 (4)	C11A—H11D	0.9600
C2—P1	1.805 (3)	C11A—H11E	0.9600
C3—C4	1.451 (4)	C11A—H11F	0.9600
C3—C10	1.501 (5)	C11A—O5A	1.499 (19)
C4—C5	1.387 (4)	C12—H12A	0.9600
C4—C9	1.405 (4)	C12—H12B	0.9600
C5—C6	1.382 (4)	C12—H12C	0.9600
C5—O2	1.370 (4)	C12—O6	1.43 (4)
C6—H6	0.9300	C12A—H12D	0.9600
C6—C7	1.374 (5)	C12A—H12E	0.9600
C7—C8	1.385 (5)	C12A—H12F	0.9600
C7—O3	1.358 (4)	C12A—O6A	1.529 (19)
C8—H8	0.9300	O3—H3	0.8200
C8—C9	1.366 (4)	O4—P1	1.464 (5)
C9—H9	0.9300	O4A—P1	1.454 (6)
C10—H10A	0.9600	O5—P1	1.543 (4)
C10—H10B	0.9600	O5A—P1	1.567 (5)
C10—H10C	0.9600	O6—P1	1.561 (5)
C11—H11A	0.9600	O6A—P1	1.556 (6)

O1—C1—C2	127.1 (3)	O5—C11—H11C	109.5
O1—C1—O2	114.8 (3)	H11D—C11A—H11E	109.5
O2—C1—C2	118.0 (3)	H11D—C11A—H11F	109.5
C1—C2—P1	116.0 (2)	H11E—C11A—H11F	109.5
C3—C2—C1	120.7 (3)	O5A—C11A—H11D	109.5
C3—C2—P1	123.2 (3)	O5A—C11A—H11E	109.5
C2—C3—C4	119.1 (3)	O5A—C11A—H11F	109.5
C2—C3—C10	123.2 (3)	H12A—C12—H12B	109.5
C4—C3—C10	117.7 (3)	H12A—C12—H12C	109.5
C5—C4—C3	118.9 (3)	H12B—C12—H12C	109.5
C5—C4—C9	115.9 (3)	O6—C12—H12A	109.5
C9—C4—C3	125.2 (3)	O6—C12—H12B	109.5
C6—C5—C4	123.3 (3)	O6—C12—H12C	109.5
O2—C5—C4	121.1 (3)	H12D—C12A—H12E	109.5
O2—C5—C6	115.5 (3)	H12D—C12A—H12F	109.5
C5—C6—H6	120.7	H12E—C12A—H12F	109.5
C7—C6—C5	118.6 (3)	O6A—C12A—H12D	109.5
C7—C6—H6	120.7	O6A—C12A—H12E	109.5
C6—C7—C8	120.3 (3)	O6A—C12A—H12F	109.5
O3—C7—C6	122.6 (3)	C5—O2—C1	121.9 (3)
O3—C7—C8	117.1 (3)	C7—O3—H3	109.5
C7—C8—H8	120.0	C11—O5—P1	119.4 (15)
C9—C8—C7	120.0 (3)	C11A—O5A—P1	123.3 (17)
C9—C8—H8	120.0	C12—O6—P1	125.5 (12)
C4—C9—H9	119.0	C12A—O6A—P1	117.5 (19)
C8—C9—C4	121.9 (3)	O4—P1—C2	114.5 (2)
C8—C9—H9	119.0	O4—P1—O5	113.5 (3)
C3—C10—H10A	109.5	O4—P1—O6	110.2 (3)
C3—C10—H10B	109.5	O4A—P1—C2	112.6 (2)
C3—C10—H10C	109.5	O4A—P1—O5A	110.0 (3)
H10A—C10—H10B	109.5	O4A—P1—O6A	114.2 (3)
H10A—C10—H10C	109.5	O5—P1—C2	105.91 (19)
H10B—C10—H10C	109.5	O5—P1—O6	102.1 (3)
H11A—C11—H11B	109.5	O5A—P1—C2	105.6 (2)
H11A—C11—H11C	109.5	O6—P1—C2	109.8 (2)
H11B—C11—H11C	109.5	O6A—P1—C2	112.6 (2)
O5—C11—H11A	109.5	O6A—P1—O5A	100.9 (3)
O5—C11—H11B	109.5

C1—C2—C3—C4	1.3 (5)	C7—C8—C9—C4	0.0 (6)
C1—C2—C3—C10	−179.0 (3)	C9—C4—C5—C6	−1.2 (5)
C1—C2—P1—O4	−175.7 (4)	C9—C4—C5—O2	179.1 (3)
C1—C2—P1—O4A	135.4 (4)	C10—C3—C4—C5	−178.5 (3)
C1—C2—P1—O5	−49.9 (4)	C10—C3—C4—C9	1.3 (5)
C1—C2—P1—O5A	−104.6 (3)	C11—O5—P1—C2	−63.3 (18)
C1—C2—P1—O6	59.7 (3)	C11—O5—P1—O4	63.1 (18)
C1—C2—P1—O6A	4.6 (4)	C11—O5—P1—O6	−178.3 (18)
C2—C1—O2—C5	4.3 (5)	C11A—O5A—P1—C2	57 (2)
C2—C3—C4—C5	1.3 (5)	C11A—O5A—P1—O4A	179 (2)
C2—C3—C4—C9	−178.9 (3)	C11A—O5A—P1—O6A	−60 (2)
C3—C2—P1—O4	1.8 (4)	C12—O6—P1—C2	−87 (2)
C3—C2—P1—O4A	−47.0 (4)	C12—O6—P1—O4	146 (2)
C3—C2—P1—O5	127.6 (3)	C12—O6—P1—O5	25 (2)
C3—C2—P1—O5A	73.0 (4)	C12A—O6A—P1—C2	80 (2)
C3—C2—P1—O6	−122.8 (3)	C12A—O6A—P1—O4A	−50 (2)
C3—C2—P1—O6A	−177.9 (3)	C12A—O6A—P1—O5A	−168 (2)
C3—C4—C5—C6	178.6 (3)	O1—C1—C2—C3	176.1 (4)
C3—C4—C5—O2	−1.1 (5)	O1—C1—C2—P1	−6.3 (5)
C3—C4—C9—C8	−178.9 (4)	O1—C1—O2—C5	−175.8 (3)
C4—C5—C6—C7	0.6 (6)	O2—C1—C2—C3	−4.1 (5)
C4—C5—O2—C1	−1.8 (5)	O2—C1—C2—P1	173.5 (2)
C5—C4—C9—C8	0.9 (5)	O2—C5—C6—C7	−179.7 (3)
C5—C6—C7—C8	0.4 (6)	O3—C7—C8—C9	−179.9 (4)
C5—C6—C7—O3	179.5 (3)	P1—C2—C3—C4	−176.1 (2)
C6—C5—O2—C1	178.5 (3)	P1—C2—C3—C10	3.6 (5)
C6—C7—C8—C9	−0.7 (6)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O4ⁱ	0.82	1.78	2.562 (6)	159
O3—H3···O4Aⁱ	0.82	2.01	2.812 (7)	168
C8—H8···O1ⁱⁱ	0.93	2.44	3.220 (4)	142
C10—H10B···O4	0.96	2.22	2.831 (6)	121
C12—H12A···O1	0.96	2.20	2.96 (5)	135

Symmetry codes: (i) x+1, y, z; (ii) x, −y+1/2, z−1/2.

Acknowledgements

The authors thank Ms Y. Zhu for technical assistance.

Funding information

Funding for this research was provided by: National Natural Science Foundation of China (grant No. 21172055); Foundation of Henan Education Committee (grant No. 18A150004); the Program for Innovative Research Team from Zhengzhou (grant No. 131PCXTD605); Natural Science Foundation of Henan University of Technology (grant No. 2017RCJH08).

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