4,4′-[(1E,1′E)-(2-Chloro­pyrimidine-4,6-di­yl)bis(ethene-2,1-di­yl)]bis­(N,N-di­ethyl­aniline)

Hu, L.; Wang, H.; Zhang, Q.

doi:10.1107/S241431461601590X

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 1| Part 10| October 2016| x161590

https://doi.org/10.1107/S241431461601590X

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4,4′-[(1E,1′E)-(2-Chloropyrimidine-4,6-diyl)bis(ethene-2,1-diyl)]bis(N,N-diethylaniline)

Lei Hu,^a,^b Hui Wang ^a,^b and Qiong Zhang ^a,^b ^*

^aDepartment of Chemistry, Anhui University, Hefei 230039, People's Republic of China, and ^bKey Laboratory of Functional Inorganic Materials Chemistry, Hefei 230039, People's Republic of China
^*Correspondence e-mail: zhangqiong.314@163.com

Edited by D.-J. Xu, Zhejiang University (Yuquan Campus), China (Received 2 September 2016; accepted 8 October 2016; online 18 October 2016)

In the title molecule, C₂₈H₃₃ClN₄, the central pyrimidine ring is twisted with respect to the two benzene rings, making dihedral angles of 13.56 (19) and 23.1 (2)°. In the crystal, weak C—H⋯π interactions link the molecules into supramolecular chains propagating along the c-axis direction.

Keywords: crystal structure; pyrimidine ring; C—H⋯π interaction.

CCDC reference: 1502094

Structure description

Pyrimidine derivatives are considered important compounds because of their wide range of biological activities, and also because of their high electron affinity and good planarity, making them suitable building blocks for the construction of chromophores for non-linear optical materials (Wang et al., 2014 ). The pyrimidine ring also has well known reactivity with an aromatic aldehyde under solvent-free conditions (Li et al., 2009 ). Moreover, pyrimidine derivatives are excellent candidates for sensor materials with two-photon properties as they involve two N atoms in positions 2 and 4, forming an effective coordinating dentate for metal cations that can be applied to generate various useful materials (Zhang et al., 2016 ).

In the title compound (Fig. 1), the pyrimidine ring is nearly planar [maximum deviation of 0.008 (4) Å for atom C14) and is twisted with respect to the C5–C10 and C18–C23 benzene rings, making dihedral angles of 13.56 (19) and 23.1 (2)°, respectively.

Figure 1
The molecular structure with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

In the crystal, weak C—H⋯π interactions (Table 1) link the molecules into supramolecular chains propagating along the c-axis direction.

Table 1
Hydrogen-bond geometry (Å, °)

Cg3 is the centroid of the C18–C23 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3A⋯Cg3ⁱ	0.97	2.73	3.606 (8)	151
Symmetry code: (i) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Synthesis and crystallization

A mixture of 4-(diethylamino)benzaldehyde (0.39 g, 2.20 mmol), 2-chloro-4,6-dimethyl pyrimidine (0.14 g, 1 mmol) and ^tBuOK (0.56 g, 5 mmol) was milled vigorously for about 10 min. The reaction was monitored by TLC. After the reaction was completed, the mixture was dispersed in water. The solution was extracted with CH₂Cl₂ several times. The organic layer was washed with water, saturated brine and dried over anhydrous MgSO₄. After removing solvent under reduced pressure, the crude product was obtained and purified by flash column chromatography (silica, 8:1 petroleum ether:ethyl acetate) to obtain red crystals. Yield: 60%. ¹H NMR (400 MHz, CDCl₃-d₆)1.42 (t, 12H), 3.41 (q, 8H), 6.66 (d, 4H), 7.47 (d, 4H),6.68 (d, 2H), 7.81 (d, 2H), 6.59 (s, 1H).

Refinement

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

Table 2
Experimental details

Crystal data
Chemical formula	C₂₈H₃₃ClN₄
M_r	461.03
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	11.791 (5), 15.005 (5), 14.711 (5)
β (°)	92.716 (5)
V (Å³)	2599.8 (17)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.17
Crystal size (mm)	0.10 × 0.10 × 0.10

Data collection
Diffractometer	Bruker SMART 1000 CCD area-detector
No. of measured, independent and observed [I > 2σ(I)] reflections	14693, 4334, 1777
R_int	0.087
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.057, 0.203, 0.91
No. of reflections	4334
No. of parameters	302
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.14, −0.18
Computer programs: SMART and SAINT (Bruker, 2002 ), SHELXS97, SHELXL97 and SHELXTL (Sheldrick, 2008 ).

Structural data

CCDC reference: 1502094

Crystal structure: contains datablocks I, Global. DOI: https://doi.org/10.1107/S241431461601590X/xu4013sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S241431461601590X/xu4013Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S241431461601590X/xu4013Isup3.cml

checkCIF report

Computing details top

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); 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).

4,4'-[(1E,1'E)-(2-Chloropyrimidine-4,6-diyl)bis(ethene-2,1-diyl)]bis(N,N-diethylaniline) top

Crystal data top

C₂₈H₃₃ClN₄	F(000) = 984
M_r = 461.03	D_x = 1.178 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1048 reflections
a = 11.791 (5) Å	θ = 2.2–17.4°
b = 15.005 (5) Å	µ = 0.17 mm⁻¹
c = 14.711 (5) Å	T = 296 K
β = 92.716 (5)°	Prism, red
V = 2599.8 (17) Å³	0.1 × 0.1 × 0.1 mm
Z = 4

Data collection top

Bruker SMART 1000 CCD area-detector diffractometer	1777 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.087
Graphite monochromator	θ_max = 25.0°, θ_min = 1.9°
phi and ω scans	h = −14→14
14693 measured reflections	k = −17→17
4334 independent reflections	l = −16→15

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.057	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.203	H-atom parameters constrained
S = 0.91	w = 1/[σ²(F_o²) + (0.1P)²] where P = (F_o² + 2F_c²)/3
4334 reflections	(Δ/σ)_max < 0.001
302 parameters	Δρ_max = 0.14 e Å⁻³
0 restraints	Δρ_min = −0.18 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. 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 > 2sigma(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

	x	y	z	U_iso*/U_eq
Cl1	0.23269 (13)	0.36886 (9)	1.30455 (8)	0.0911 (5)
C8	0.1371 (3)	0.5278 (3)	0.8928 (3)	0.0512 (11)
N2	0.2846 (3)	0.2363 (2)	1.2017 (2)	0.0622 (10)
N4	0.4462 (3)	−0.3125 (2)	1.0323 (3)	0.0667 (10)
C17	0.3370 (3)	0.0536 (3)	1.0462 (3)	0.0589 (12)
H17	0.3143	0.0797	0.9910	0.071*
C15	0.2972 (3)	0.1987 (3)	1.1188 (3)	0.0544 (11)
C14	0.2743 (3)	0.2474 (3)	1.0400 (3)	0.0545 (11)
H14	0.2845	0.2221	0.9832	0.065*
C22	0.4249 (4)	−0.2226 (3)	1.0348 (3)	0.0586 (12)
C16	0.3342 (4)	0.1056 (3)	1.1189 (3)	0.0592 (12)
H16	0.3576	0.0809	1.1746	0.071*
C18	0.3711 (4)	−0.0388 (3)	1.0425 (3)	0.0577 (12)
C13	0.2362 (3)	0.3337 (3)	1.0470 (3)	0.0524 (11)
C28	0.2489 (3)	0.3195 (3)	1.1987 (3)	0.0568 (11)
C11	0.1623 (3)	0.4685 (3)	0.9688 (3)	0.0538 (11)
H11	0.1431	0.4892	1.0256	0.065*
N1	0.2235 (3)	0.3717 (2)	1.1294 (3)	0.0576 (9)
C9	0.0828 (3)	0.6091 (3)	0.9065 (3)	0.0609 (12)
H9	0.0591	0.6225	0.9644	0.073*
C23	0.4283 (4)	−0.0820 (3)	1.1142 (3)	0.0632 (12)
H23	0.4492	−0.0496	1.1662	0.076*
N3	0.0790 (4)	0.7150 (3)	0.6822 (3)	0.0945 (14)
C7	0.1674 (4)	0.5118 (3)	0.8045 (3)	0.0622 (12)
H7	0.2020	0.4578	0.7917	0.075*
C20	0.3713 (4)	−0.1784 (3)	0.9612 (3)	0.0661 (13)
H20	0.3519	−0.2100	0.9084	0.079*
C5	0.0961 (4)	0.6541 (3)	0.7508 (3)	0.0686 (13)
C10	0.0631 (4)	0.6696 (3)	0.8384 (3)	0.0679 (13)
H10	0.0265	0.7227	0.8512	0.081*
C12	0.2097 (3)	0.3877 (3)	0.9671 (3)	0.0546 (11)
H12	0.2269	0.3645	0.9108	0.066*
C6	0.1489 (4)	0.5712 (3)	0.7351 (3)	0.0712 (14)
H6	0.1713	0.5572	0.6771	0.085*
C26	0.3941 (4)	−0.3692 (3)	0.9608 (3)	0.0737 (14)
H26A	0.3211	−0.3441	0.9413	0.088*
H26B	0.3806	−0.4278	0.9858	0.088*
C21	0.4554 (4)	−0.1709 (3)	1.1112 (3)	0.0630 (12)
H21	0.4946	−0.1971	1.1607	0.076*
C19	0.3467 (4)	−0.0892 (3)	0.9652 (3)	0.0664 (13)
H19	0.3124	−0.0617	0.9143	0.080*
C24	0.4983 (4)	−0.3591 (3)	1.1105 (3)	0.0738 (14)
H24A	0.5564	−0.3213	1.1391	0.089*
H24B	0.5350	−0.4126	1.0896	0.089*
C27	0.4660 (5)	−0.3787 (3)	0.8790 (3)	0.0968 (17)
H27A	0.4810	−0.3209	0.8545	0.145*
H27B	0.4262	−0.4142	0.8335	0.145*
H27C	0.5364	−0.4072	0.8970	0.145*
C2	0.0210 (5)	0.8003 (4)	0.6974 (4)	0.107 (2)
H2A	−0.0384	0.7908	0.7398	0.128*
H2B	−0.0149	0.8202	0.6402	0.128*
C25	0.4139 (5)	−0.3846 (3)	1.1809 (4)	0.1001 (18)
H25A	0.3784	−0.3319	1.2031	0.150*
H25B	0.4529	−0.4150	1.2306	0.150*
H25C	0.3570	−0.4233	1.1536	0.150*
C3	0.1174 (6)	0.6985 (5)	0.5922 (5)	0.124 (3)
H3A	0.1883	0.6657	0.5970	0.149*
H3B	0.1321	0.7551	0.5631	0.149*
C4	0.0333 (7)	0.6472 (6)	0.5340 (5)	0.165 (3)
H4A	0.0148	0.5928	0.5642	0.248*
H4B	0.0654	0.6337	0.4768	0.248*
H4C	−0.0342	0.6822	0.5236	0.248*
C1	0.0994 (6)	0.8730 (4)	0.7342 (6)	0.157 (3)
H1A	0.1369	0.8534	0.7900	0.235*
H1B	0.0560	0.9257	0.7454	0.235*
H1C	0.1550	0.8861	0.6905	0.235*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl1	0.1296 (12)	0.0957 (10)	0.0472 (8)	0.0198 (8)	−0.0046 (7)	−0.0099 (7)
C8	0.051 (3)	0.055 (3)	0.047 (3)	−0.006 (2)	0.001 (2)	0.002 (2)
N2	0.075 (3)	0.061 (2)	0.051 (3)	0.0008 (19)	0.000 (2)	0.003 (2)
N4	0.077 (3)	0.059 (2)	0.064 (3)	0.000 (2)	−0.001 (2)	−0.006 (2)
C17	0.069 (3)	0.061 (3)	0.046 (3)	−0.010 (2)	−0.002 (2)	0.004 (2)
C15	0.059 (3)	0.056 (3)	0.048 (3)	−0.009 (2)	0.003 (2)	0.000 (2)
C14	0.068 (3)	0.051 (3)	0.044 (3)	−0.004 (2)	0.003 (2)	−0.002 (2)
C22	0.057 (3)	0.058 (3)	0.062 (3)	−0.004 (2)	0.011 (2)	0.000 (3)
C16	0.073 (3)	0.057 (3)	0.047 (3)	−0.008 (2)	0.000 (2)	0.009 (2)
C18	0.072 (3)	0.050 (3)	0.051 (3)	−0.003 (2)	0.004 (2)	0.004 (2)
C13	0.054 (3)	0.063 (3)	0.040 (3)	−0.008 (2)	−0.001 (2)	0.003 (2)
C28	0.063 (3)	0.071 (3)	0.036 (3)	−0.005 (2)	−0.002 (2)	−0.005 (2)
C11	0.055 (3)	0.056 (3)	0.050 (3)	−0.007 (2)	0.001 (2)	−0.002 (2)
N1	0.061 (2)	0.066 (2)	0.046 (3)	−0.0033 (18)	−0.0008 (19)	0.002 (2)
C9	0.060 (3)	0.063 (3)	0.060 (3)	−0.001 (2)	0.008 (2)	−0.002 (2)
C23	0.077 (3)	0.057 (3)	0.055 (3)	0.002 (2)	−0.003 (2)	−0.002 (2)
N3	0.092 (3)	0.105 (3)	0.089 (4)	0.037 (3)	0.027 (3)	0.051 (3)
C7	0.066 (3)	0.071 (3)	0.050 (3)	0.009 (2)	0.008 (2)	0.011 (2)
C20	0.081 (3)	0.066 (3)	0.051 (3)	−0.006 (3)	0.000 (3)	−0.009 (3)
C5	0.056 (3)	0.080 (3)	0.070 (4)	0.013 (2)	0.013 (3)	0.020 (3)
C10	0.067 (3)	0.057 (3)	0.080 (4)	0.011 (2)	0.008 (3)	0.008 (3)
C12	0.057 (3)	0.062 (3)	0.045 (3)	−0.007 (2)	0.002 (2)	−0.003 (2)
C6	0.074 (3)	0.091 (3)	0.050 (3)	0.016 (3)	0.015 (3)	0.018 (3)
C26	0.069 (3)	0.068 (3)	0.084 (4)	−0.009 (2)	0.003 (3)	−0.007 (3)
C21	0.072 (3)	0.059 (3)	0.057 (3)	0.002 (2)	−0.008 (2)	−0.001 (2)
C19	0.080 (3)	0.068 (3)	0.051 (3)	−0.002 (3)	0.004 (3)	0.001 (3)
C24	0.070 (3)	0.061 (3)	0.090 (4)	0.009 (2)	0.003 (3)	−0.008 (3)
C27	0.099 (4)	0.104 (4)	0.087 (4)	−0.009 (3)	0.003 (3)	−0.034 (3)
C2	0.074 (4)	0.106 (4)	0.141 (5)	0.034 (4)	0.015 (4)	0.058 (4)
C25	0.098 (4)	0.108 (4)	0.095 (4)	0.013 (3)	0.011 (3)	0.026 (3)
C3	0.106 (5)	0.168 (6)	0.100 (6)	0.054 (5)	0.034 (4)	0.078 (5)
C4	0.151 (7)	0.262 (10)	0.084 (6)	0.068 (7)	0.010 (5)	0.029 (6)
C1	0.100 (5)	0.113 (5)	0.257 (10)	0.000 (4)	0.014 (6)	0.061 (6)

Geometric parameters (Å, º) top

Cl1—C28	1.743 (4)	C7—H7	0.9300
C8—C7	1.385 (5)	C20—C19	1.371 (5)
C8—C9	1.397 (5)	C20—H20	0.9300
C8—C11	1.448 (5)	C5—C10	1.384 (6)
N2—C28	1.317 (5)	C5—C6	1.414 (6)
N2—C15	1.358 (5)	C10—H10	0.9300
N4—C22	1.373 (5)	C12—H12	0.9300
N4—C24	1.457 (5)	C6—H6	0.9300
N4—C26	1.464 (5)	C26—C27	1.512 (6)
C17—C16	1.325 (5)	C26—H26A	0.9700
C17—C18	1.446 (5)	C26—H26B	0.9700
C17—H17	0.9300	C21—H21	0.9300
C15—C14	1.386 (5)	C19—H19	0.9300
C15—C16	1.463 (5)	C24—C25	1.519 (6)
C14—C13	1.376 (5)	C24—H24A	0.9700
C14—H14	0.9300	C24—H24B	0.9700
C22—C20	1.395 (6)	C27—H27A	0.9600
C22—C21	1.399 (5)	C27—H27B	0.9600
C16—H16	0.9300	C27—H27C	0.9600
C18—C19	1.384 (5)	C2—C1	1.514 (8)
C18—C23	1.387 (5)	C2—H2A	0.9700
C13—N1	1.355 (5)	C2—H2B	0.9700
C13—C12	1.449 (5)	C25—H25A	0.9600
C28—N1	1.309 (5)	C25—H25B	0.9600
C11—C12	1.336 (5)	C25—H25C	0.9600
C11—H11	0.9300	C3—C4	1.492 (9)
C9—C10	1.363 (5)	C3—H3A	0.9700
C9—H9	0.9300	C3—H3B	0.9700
C23—C21	1.373 (5)	C4—H4A	0.9600
C23—H23	0.9300	C4—H4B	0.9600
N3—C5	1.369 (5)	C4—H4C	0.9600
N3—C3	1.442 (7)	C1—H1A	0.9600
N3—C2	1.473 (6)	C1—H1B	0.9600
C7—C6	1.365 (5)	C1—H1C	0.9600

C7—C8—C9	115.3 (4)	C13—C12—H12	117.7
C7—C8—C11	124.4 (4)	C7—C6—C5	120.6 (4)
C9—C8—C11	120.3 (4)	C7—C6—H6	119.7
C28—N2—C15	114.4 (4)	C5—C6—H6	119.7
C22—N4—C24	121.4 (4)	N4—C26—C27	113.3 (4)
C22—N4—C26	121.2 (4)	N4—C26—H26A	108.9
C24—N4—C26	115.9 (4)	C27—C26—H26A	108.9
C16—C17—C18	127.8 (4)	N4—C26—H26B	108.9
C16—C17—H17	116.1	C27—C26—H26B	108.9
C18—C17—H17	116.1	H26A—C26—H26B	107.7
N2—C15—C14	120.4 (4)	C23—C21—C22	120.9 (4)
N2—C15—C16	116.2 (4)	C23—C21—H21	119.6
C14—C15—C16	123.4 (4)	C22—C21—H21	119.6
C13—C14—C15	119.0 (4)	C20—C19—C18	122.1 (4)
C13—C14—H14	120.5	C20—C19—H19	119.0
C15—C14—H14	120.5	C18—C19—H19	119.0
N4—C22—C20	121.6 (4)	N4—C24—C25	113.2 (4)
N4—C22—C21	121.7 (4)	N4—C24—H24A	108.9
C20—C22—C21	116.7 (4)	C25—C24—H24A	108.9
C17—C16—C15	125.5 (4)	N4—C24—H24B	108.9
C17—C16—H16	117.3	C25—C24—H24B	108.9
C15—C16—H16	117.3	H24A—C24—H24B	107.7
C19—C18—C23	116.4 (4)	C26—C27—H27A	109.5
C19—C18—C17	120.5 (4)	C26—C27—H27B	109.5
C23—C18—C17	123.0 (4)	H27A—C27—H27B	109.5
N1—C13—C14	120.9 (4)	C26—C27—H27C	109.5
N1—C13—C12	117.5 (4)	H27A—C27—H27C	109.5
C14—C13—C12	121.6 (4)	H27B—C27—H27C	109.5
N1—C28—N2	130.8 (4)	N3—C2—C1	113.6 (5)
N1—C28—Cl1	114.2 (3)	N3—C2—H2A	108.8
N2—C28—Cl1	114.9 (4)	C1—C2—H2A	108.8
C12—C11—C8	127.9 (4)	N3—C2—H2B	108.8
C12—C11—H11	116.1	C1—C2—H2B	108.8
C8—C11—H11	116.1	H2A—C2—H2B	107.7
C28—N1—C13	114.5 (4)	C24—C25—H25A	109.5
C10—C9—C8	122.5 (4)	C24—C25—H25B	109.5
C10—C9—H9	118.7	H25A—C25—H25B	109.5
C8—C9—H9	118.7	C24—C25—H25C	109.5
C21—C23—C18	122.4 (4)	H25A—C25—H25C	109.5
C21—C23—H23	118.8	H25B—C25—H25C	109.5
C18—C23—H23	118.8	N3—C3—C4	112.7 (6)
C5—N3—C3	121.4 (4)	N3—C3—H3A	109.0
C5—N3—C2	121.5 (5)	C4—C3—H3A	109.0
C3—N3—C2	117.1 (4)	N3—C3—H3B	109.0
C6—C7—C8	123.3 (4)	C4—C3—H3B	109.0
C6—C7—H7	118.4	H3A—C3—H3B	107.8
C8—C7—H7	118.4	C3—C4—H4A	109.5
C19—C20—C22	121.4 (4)	C3—C4—H4B	109.5
C19—C20—H20	119.3	H4A—C4—H4B	109.5
C22—C20—H20	119.3	C3—C4—H4C	109.5
N3—C5—C10	122.4 (4)	H4A—C4—H4C	109.5
N3—C5—C6	121.2 (4)	H4B—C4—H4C	109.5
C10—C5—C6	116.4 (4)	C2—C1—H1A	109.5
C9—C10—C5	121.9 (4)	C2—C1—H1B	109.5
C9—C10—H10	119.1	H1A—C1—H1B	109.5
C5—C10—H10	119.1	C2—C1—H1C	109.5
C11—C12—C13	124.5 (4)	H1A—C1—H1C	109.5
C11—C12—H12	117.7	H1B—C1—H1C	109.5

Hydrogen-bond geometry (Å, º) top

Cg3 is the centroid of the C18–C23 ring.

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3A···Cg3ⁱ	0.97	2.73	3.606 (8)	151

Symmetry code: (i) x, −y+1/2, z−1/2.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21501001).

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