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Communication

Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands

1
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
2
Chemical Engineering Department, Jiuquan Vocational Technical College, Jiuquan 735000, China
*
Author to whom correspondence should be addressed.
Crystals 2018, 8(11), 414; https://doi.org/10.3390/cryst8110414
Submission received: 11 October 2018 / Revised: 26 October 2018 / Accepted: 1 November 2018 / Published: 4 November 2018
(This article belongs to the Special Issue Crystal Structures of Boron Compounds)

Abstract

:
A hetero-hexanuclear Zn(II)-La(III) coordination compound, [{(ZnL)2La}2(bdc)2](NO3)2 (H2bdc = terephthalic acid) has been synthesized with a symmetric Salamo-like bisoxime, and characterized by elemental analyses, IR, UV-Vis, fluorescent spectroscopy, and single-crystal X-ray diffraction analysis. All of the Zn(II) ions are pentacoordinated by N2O2 donator atoms from the (L)2− unit and one oxygen atom from one terephthalate anion. The Zn(II) ions adopt trigonal bipyramidal geometries (τZn1 = 0.61, τZn2 = 0.56). The La(III) ions are decacoordinated in the Zn(II)-La(III) coordination compound and has a distorted bicapped square antiprism geometry. Meanwhile, the photophysical property of the Zn(II)-La(III) coordination compound was also measured and discussed.

Graphical Abstract

1. Introduction

Salen-like (N,N-bis(salicylidene)ethylenediamine) N2O2 compounds are a class of the most versatile multidentate chelating ligands and could form stable mono- or multi-nuclear metal coordination compounds with alkaline earth, rare earth, and d-block transition metal ions [1,2,3,4,5,6,7,8,9]. Salen-like ligands and their corresponding metal coordination compounds have been proverbially studied in recent decades [10,11,12,13,14,15,16], these metal coordination compounds are used as precursors to obtain a great deal of oligometallic coordination compounds own to the high coordination abilities [17,18,19,20,21]. In recent years, our research mostly concentrated on the syntheses, crystal structures and properties of Salamo-like (1,2-bis(salicylideneaminooxy)ethane) derivatives and their metal coordination compounds. Salamo-like derivatives are at least 104 times more stable than Salen-like ligands due to the unique structures of Salamo-like derivatives [22,23,24]. When 3-alkoxy groups are introduced of salicylidene moieties, the whole ligand molecule will have an O4 coordination site besides the N2O2 site. The O4 site of 3-alkoxy Salamo-like derivatives is suitable for alkali metals, alkaline earth metals and rare earth metal ions to obtain heteromulti-nuclear coordination compounds [25,26,27,28]. These hetero-metallic Salamo-like coordination compounds have been studied for their catalytic activities [29,30], biological activities [31], and fluorescence properties [32,33,34]. Meanwhile, supra-molecular chemistry has become increasingly prominent in the coordination chemistry, for Salamo-like derivatives, supra-molecular structures are formed mainly with the help of hydrogen bonding interactions [35,36,37,38]. In our previous studies, a number of Salamo-type derivatives and their hetero-nuclear coordination compounds have been synthesized [39,40,41,42]. However, 3d-4f hetero-nuclear Salamo-like coordination compounds containting auxiliary ligands have rarely been reported [43,44,45].
In order to explore the structures and optical properties of 3d-4f hetero-nuclear metal coordination compounds contained auxiliary ligands, herein the terephtalic acid was selected as a simple multidentate linker owing to its availability and application in the building of Salamo-like Zn(II)-Ln(III) coordination compound. we have successfully designed and synthesized a symmetric Salamo-like derivative H2L and its corresponding Zn(II)-La(III) coordination compound ([{(ZnL)2La}2(bdc)2](NO3)2). Furthermore, the supra-molecular features and photophysical properties of the Zn(II)-La(III) coordination compound are discussed in detail.

2. Experimental

2.1. Materials and Instrumentation

All chemical reagents were analytical pure reagents, which have not been purified before used. Carbon, nitrogen and hydrogen analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analyzer (Berlin, Germany). Elemental analyses for ZnII and LaIII were detected by an IRIS ER/S-WP-1 ICP atomic emission spectrometer (Berlin, Germany). Melting points were measured via a microscopic melting point apparatus (Beijing Taike Instrument Limited Company, Beijing, China). 1H and 13C NMR spectra were recorded in deuterated DMSO solution by German Bruker AVANCE DRX-400 spectroscopy (Bruker AVANCE, Billerica, MA, USA). Infrared spectra were measured with a VERTEX-70 FT-IR spectrophotometer (Bruker, Billerica, MA, USA), with samples prepared as KBr (400–4000 cm−1). UV-Vis absorption and fluorescence spectra were recorded on a Shimadzu UV-2550 (Shimadzu, Japan) and Hitachi F-7000 (Hitachi, Tokyo, Japan) spectrometers, respectively. Quantum yields in solid state were measured using an absolute method by integrating sphere on FLS920 of Edinburgh Instrument. X-ray single crystal structure determination was carried out on a Bruker Smart Apex CCD diffractometer (Bruker AVANCE, Billerica, MA, USA).

2.2. Preparation of Ligand H2L

Preparation of 1,2-bis(aminooxy)ethane was in accordance with the literature [46,47]. Yield: 71.5%. Anal. Calcd for C2H8N2O2 (%): C, 26.08; H, 8.76; N, 30.42. Found: C, 25.87; H, 8.68; N, 30.51. 1H NMR (400 MHz, CDCl3) δ 3.79 (s, 4H), 5.52 (s, 4H).
The ligand H2L was synthesized according to the procedure reported early [43]. Reaction of 1,2-bis(aminooxy)ethane with two equivalents of 3-methoxysalicylaldehyde in ethanol afforded the desired ligand H2L. The synthesis routes of the Salamo-like bisoxime derivative (H2L) and its Zn(II)-La(III) coordination compound are shown in Scheme 1. Yield: 81.6%. Mp: 132–134 °C. 1H NMR (400 MHz, CDCl3) δ 3.87 (s, 6H), 4.46 (s, 4H), 6.81 (dd, J = 7.9, 1.9 Hz, 2H), 6.86 (t, J = 7.9 Hz, 2H), 6.95 (dd, J = 7.9, 1.9 Hz, 2H), 8.23 (s, 2H), 9.70 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 57.4 (CH3), 72.8 (CH2), 115.3 (CH), 119.2 (C), 119.6 (CH), 124.1 (CH), 149.5 (C), 150.2 (C), 152.7 (CH=N). IR (KBr, cm−1): 3137 (m) [ν(O–H)], 1601 (m) [ν(C=N)], 1255 (m) [ν(Ar–O)]. Anal. Calcd for C18H20N2O6 (%): C, 59.99; H, 5.59; N, 7.77. Found: C, 60.07; H, 5.73; N, 7.61%.

2.3. Preparation of the Zn(II)-La(III) Coordination Compound

Synthesis route of the Zn(II)-La(III) coordination compound is shown in Scheme 1. To stirring colorless transparent solution of H2L (15.8 mg, 0.02 mmol) in CHCl3 (3 mL) was added Zn(OAc)2·2H2O (4.38 mg, 0.02 mmol) and La(NO3)3·6H2O (0.02 mmol) in CH3OH (2 mL). The color of the mixture immediately turns pale yellow and then allowed to mixing with terephthalic acid (0.01 mmol) in CH3OH (1 mL) and continues stirring for about 30 min at room temperature. After the mixed solution was filtered by absorbent cotton, leaves the filtrate at room temperature for about two weeks. Finally, light-yellow and block-shaped crystals were obtained with the volatilization of solvent. Yield: 60.5%. IR (KBr, cm−1): 1557 (m) [ν(C=N)], 1220 (m) [ν(Ar–O)], 449 (m) [ν(Zn–N)], 529 (m) [ν(Zn–O)]. Anal. Calcd for C88H80Zn4La2N10O38 (%): C, 43.59; H, 3.33; N, 5.78; Zn, 10.78; La, 11.46. Found: C, 43.71; H, 2.98; N, 5.46; Zn, 10.84; La, 11.39.

2.4. Structure Description of the Zn(II)-La(III) Coordination Compound

Crystal data of the Zn(II)-La(III) coordination compound were collected on a Bruker Smart Apex CCD diffractometer at 173(2) K (Mo-Kα radiation (λ = 0.71073 Å)). The LP factor and Semi-empirical absorption corrections were applied to the intensity data. The structure was solved by the direct methods and refined anisotropically using full-matrix least-squares methods on F2 with the SHELX-2018 program package. The hydrogen atoms were positioned geometrically and refined isotropically using the ‘riding’ model (SHELXL-2018). In addition, DELU and AFIX were applied in the structure refinement. The structure contained large in the void couldn’t be identified because it was highly disordered and had so small residual peak. Therefore, SQUEEZE in PLATON program was performed to remove the highly disordered solvent. (Solvent Accessible Volume = 914, Electrons Found in S.A.V. = 484). The nonhydrogen atoms were refined anisotropically. Crystal data and structure parameters for the Zn(II)-La(III) coordination compound are given in Table 1. Supplementary crystallographic data for this paper have been deposited at Cambridge Crystallographic Data Centre (1434632) and can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html.

3. Results and Discussion

3.1. Infrared Spectra

The infrared spectra of H2L and its Zn(II)-La(III) coordination compound exhibited various bands in the 400–4000 cm−1 range (Figure 1). The free ligand H2L exhibited an obvious characteristic band at 3137 cm−1 and can be attributed to the characteristic bands of the OH group. This band was dispeared in the infrared spectrum of the Zn(II)-La(III) coordination compound, indicating the interaction between the OH group and the Zn(II) ion leads to hydroxyl deprotonation [34]. In addition, the free ligand H2L showed an individual C=N stretching band at 1601 cm−1, while the C=N stretching band of the Zn(II)-La(III) coordination compound appeared at 1557 cm−1. For the ligand H2L, the Ar‒O stretching band appeared at 1255 cm−1, which was observed at 1220 cm−1 for the Zn(II)-La(III) coordination compound. The vibration of NO3 anion appeared at about 1459 cm−1 in the spectrum of the Zn(II)-La(III) coordination compound. The C=N and Ar–O stretching frequencies are shifted, indicating the formation of new chemical bonds (Zn–O and Zn–N) [25]. For the Zn(II)-La(III) coordination compound, the ν(Zn–O) and ν(Zn–N) frequencies were observed at 449 and 529 cm−1, respectively. Just as Percy and Thornton suggested [48], the M‒O and M‒N stretching frequency assignments are difficult sometimes.

3.2. UV-Vis Spectra

The UV-Vis spectra of H2L and its Zn(II)-La(III) coordination compound were measured in 1 × 10−5 mol·L−1 CH2Cl2 solution in freshly prepared solution are obtained in the range of 200–450 nm at room temperature, as shown in Figure 2. As can be seen from the diagram, the absorption peak of the Zn(II)-La(III) coordination compound is evidently different from the ligand before coordination. The absorption spectrum of H2L showed that two relatively strong absorption peaks appeared at ca. 266 nm (ε = 1.8 × 104 M−1·cm−1) and 322 nm (ε = 6.1 × 103 M−1·cm−1), which can be attributed to π-π* transitions of the benzene rings and the C=N bonds [17]. Compared with the free ligand H2L, the corresponding absorption peak of the Zn(II)-La(III) coordination compound appeared at ca. 278 nm (ε = 4.1 × 104 M−1·cm−1) was remarkably red shifted upon coordination to metal ions. The absorption peak at ca. 322 nm is absent in the Zn(II)-La(III) coordination compound. Meanwhile, a new absorption peak appeared at ca. 349 nm (ε = 1.2 × 104 M−1·cm−1) in the Zn(II)-La(III) coordination compound that might be owing to M→L (MLCT) charge-transfer transition, which is characteristic of the transition metal coordination compound with N2O2 coordination spheres [27].

3.3. Crystal Structure of Zn(II)-La(III) Coordination Compound

Crystal structure of the Zn(II)-La(III) coordination compound exhibited a symmetric hexanuclear structure, which is different from the common trinuclear bis(salamo)-type coordination compounds reported earlier [43,46]. The crystal structure of the Zn(II)-La(III) coordination compound and the coordination polyhedra of metal atoms are shown in Figure 3. Essential bond lengths and angles are listed in Table 2.
The Zn(II)-La(III) coordination compound crystallizes in the triclinic crystal system, space group P − 1 and the unit cell contains four Zn(II) ions, four (L)2− units, two (bdc)2− ions, two La(III) ions, and two free NO3 ions. The Zn(II)-La(III) coordination compound was assembled by two trinuclear units [(ZnL)2La] and two terephthalic acid, similar to the Zn(II)-Ln(III) coordination compounds reported [49].
In the crystal structure of the Zn(II)-La(III) coordination compound, each Zn(II) ion is located in the N2O2 coordination cavity, which have pentacoordinate environments, and the axial position is occupied by one oxygen atom of terephthalic acid. The four Zn(II) ions assumes a distorted trigonal bipyramidal geometries, which were inferred by calculating the value of τZn1 = 0.61, τZn2 = 0.56, respectively [50]. The La(III) ions have a decacoordinate environment, consisting of eight oxygen atoms (O1, O2, O5, O6, O7, O8, O11, and O12) come from two deprotonation (L)2− units, two oxygen atoms (O13 and O16) of two terephthalic acid. Thus, all of the La(III) ions adopt a distorted bicapped square antiprism geometry.
The hydrogen bonding interactions are listed in Table 3. In the crystal structure of the Zn(II)-La(III) coordination compound, the molecular structure is stabilized through intramolecular C‒H···O interactions (C9‒H9B···O14, C18‒H18B···O16, C27‒H27B···O15, and C36‒H36B···O13) (Figure 4). Intermolecular interactions, especially classical and non-classical hydrogen bonds, are playing a crucial role in the formation of crystalline solids and their physiochemical properties [51,52,53,54,55,56,57,58,59]. There are two inter-molecular C29‒H29···O10# and C31‒H31···O18 hydrogen bonding interactions, which can link each cell unit through inter-molecular hydrogen bondings (Figure 5). Additionally, the hydrogen bonding scheme of the Zn(II)-La(III) coordination compound is defective owing to suppression of the electron density originating from solvent molecules (used SQUEEZE) and subsequent exclusion of these solvent molecules from the refinement model.

3.4. Fluorescence Properties

The fluorescence properties of H2L and its Zn(II)-La(III) coordination compound were researched at room temperature (Figure 6).
With excitation at 360 nm, the free ligand H2L showed strong emission peak at about 419 nm, which can be attributed to the intra-ligand π-π* transition. Similarly, the Zn(II)-La(III) coordination compound also exhibited an intense luminescence with maximum emission at ca. 433 nm and the emission quantum yield Φ = 0.19% [49]. Compared with the ligand H2L, the fluorescence intensity of the Zn(II)-La(III) coordination compound showed a marked reduction, indicating that the addition of metal ions induced the change of fluorescence characteristics of the ligand; it is further explained that the (Zn/L)-center has absorbed and transferred energy to La(III) ion as a type of metal-organic antenna [43].

4. Conclusions

We have designed and synthesized a symmetric Salamo-like bioxime ligand H2L, and obtained a hetero-hexanuclear Zn(II)-La(III) coordination compound [{(ZnL)2La}2(bdc)2](NO3)2. The crystal structure of the Zn(II)-La(III) coordination compound showed that all of the Zn(II) ions have pentacoordinate environments and adopt distorted trigonal bipyramidal geometries. The La(III) ions adopt a distorted bicapped square antiprism geometry. The fluorescence behavior of H2L and its Zn(II)-La(III) coordination compounds was studied, compared with the ligand H2L, the fluorescence intensity of the Zn(II)-La(III) coordination compound showed a marked reduction, indicating that the addition of Zn(II)-La(III) ions induced the change of fluorescence characteristics.

Author Contributions

W.-K.D. conceived and designed the experiments; W.-T.G. and J.-C.M. performed the experiments; F.W. and Y.Z. analyzed the data; L.-Z.L. and M.Y. wrote the paper. W.-K.D. contributed reagents/materials/analysis tools.

Funding

This research were funded by the National Natural Science Foundation of China (21761018) and the Program for Excellent Team of Scientific Research in Lanzhou Jiaotong University (201706).

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21761018) and the Program for Excellent Team of Scientific Research in Lanzhou Jiaotong University (201706), which is gratefully acknowledged.

Conflicts of Interest

The authors declare no competing financial interests.

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Scheme 1. Synthesis routes of the Salamo-like derivative H2L and its Zn(II)-La(III) coordination compound.
Scheme 1. Synthesis routes of the Salamo-like derivative H2L and its Zn(II)-La(III) coordination compound.
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Figure 1. The infrared spectra of the ligand H2L and its Zn(II)-La(III) coordination compound.
Figure 1. The infrared spectra of the ligand H2L and its Zn(II)-La(III) coordination compound.
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Figure 2. UV-Vis spectra of H2L and its Zn(II)-La(III) coordination compound.
Figure 2. UV-Vis spectra of H2L and its Zn(II)-La(III) coordination compound.
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Figure 3. (a) Crystal structure of the Zn(II)-La(III) coordination compound (hydrogen atoms are omitted in structure). (b) Coordination polyhedra for metal atoms of the Zn(II)-La(III) coordination compound.
Figure 3. (a) Crystal structure of the Zn(II)-La(III) coordination compound (hydrogen atoms are omitted in structure). (b) Coordination polyhedra for metal atoms of the Zn(II)-La(III) coordination compound.
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Figure 4. Intramolecular hydrogen bonding interactions of the Zn(II)-La(III) coordination compound (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).
Figure 4. Intramolecular hydrogen bonding interactions of the Zn(II)-La(III) coordination compound (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).
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Figure 5. The one-dimensional structure of the Zn(II)-La(III) coordination compound with intermolecular hydrogen bondings (hydrogen atoms have been omitted except those formation of hydrogen bonds).
Figure 5. The one-dimensional structure of the Zn(II)-La(III) coordination compound with intermolecular hydrogen bondings (hydrogen atoms have been omitted except those formation of hydrogen bonds).
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Figure 6. Emission spectra of H2L (c = 1 × 10−5 M, λex = 360 nm) and its Zn(II)-La(III) coordination compound.
Figure 6. Emission spectra of H2L (c = 1 × 10−5 M, λex = 360 nm) and its Zn(II)-La(III) coordination compound.
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Table 1. Crystal data and structure parameters for the Zn(II)-La(III) coordination compound.
Table 1. Crystal data and structure parameters for the Zn(II)-La(III) coordination compound.
Coordination CompoundZn(II)-La(III)
Empirical formulaC88H80Zn4La2N10O38
Molecular weight, g·mol−12424.92
ColorYellow
Crystal size, mm30.15 × 0.12 × 0.06
HabitBlock-shaped
Crystal systemTriclinic
Space groupP − 1
Unit cell dimension
a (Å)12.5918(11)
b (Å)15.9312(15)
c (Å)16.1881(17)
α (°)68.980(12)
β (°)84.083(8)
γ (°)86.619(9)
V3)3014.3(6)
Z1
Z’0.5
Dc (g·cm−3)1.336
μ (mm−1)1.550
F(000)1216
θ Range (°)1.353–26.022
Index ranges−15 ≤ h ≤ 15, −18 ≤ k ≤ 19, 0 ≤ l ≤ 19
Reflections collected11813
Completeness (%)99.4
Data/restraints/parameters11812/11/644
Final R1/wR2 [I > 2σ(I)]R1 = 0.0397, wR2 = 0.1053
Final R1/wR2 (all data)R1 = 0.0521, wR2 = 0.1092
ρmax/min (e·Å−3)0.715 and −0.626
Table 2. Essential bond lengths (Å) and angles (°) for the Zn(II)-La(III) coordination compound.
Table 2. Essential bond lengths (Å) and angles (°) for the Zn(II)-La(III) coordination compound.
Bond Bond Bond
La1–O13 2.459(3)La1–O1 2.720(3)O14–Zn1 1.998(3)
La1–O16 #1 2.497(3)La1–O12 2.781(3)O5–Zn1 2.055(3)
La1–O82.506(2)La1–O6 2.813(3)N4–Zn2 1.992(4)
La1–O5 2.519(3)La1–Zn13.5369(7)N3–Zn2 2.122(3)
La1–O112.523(3)La1–Zn2 3.5491(7)O8–Zn2 1.976(3)
La1–O2 2.536(3)N1–Zn12.132(3)O11–Zn2 2.065(3)
La1–O7 2.690(3)N2–Zn12.034(4)O15–Zn2 #1 1.984(3)
Angles Angles Angles
O13–La1–O16 #175.54(9)O5–La1–O262.63(9)O12–La1–O6161.99(9)
O13–La1–O8152.43(9)O11–La1–O2118.54(9)O2–Zn1–O14113.20(13)
O16 #1–La1–O876.91(9)O13–La1–O7139.64(9)O2–Zn1–N2126.73(13)
O13–La1–O570.42(9)O16 #1–La1–O7123.92(9)O14–Zn1–N2119.87(14)
O16 #1–La1–O5107.80(9)O8–La1–O759.53(9)O2–Zn1–O581.13(11)
O8–La1–O5118.12(9)O5–La1–O769.87(9)O14–Zn1–O599.14(11)
O13–La1–O11108.48(9)O11–La1–O7111.38(9)N2–Zn1–O586.31(13)
O16 #1–La1–O1170.54(9)O2–La1–O781.02(8)O2–Zn1–N186.92(13)
O8–La1–O1162.21(9)O13–La1–O1122.61(9)O14–Zn1–N196.36(12)
O5–La1–O11178.28(9)O16 #1–La1–O1142.29(9)N2–Zn1–N191.52(14)
O13–La1–O274.77(9)O8–La1–O180.96(8)O5–Zn1–N1163.23(12)
O16 #1–La1–O2150.28(9)O5–La1–O1109.50(9)O8–Zn2–O15 #1112.61(12)
O8–La1–O2132.80(9)O11–La1–O172.20(9)O8–Zn2–N4130.16(15)
O7–La1–O166.05(9)O2–La1–O158.53(9)O15 #1–Zn2–N4116.62(15)
O11–La1–O1258.19(8)O13–La1–O1267.16(10)O8–Zn2–O1179.99(11)
O2–La1–O1269.32(9)O16 #1–La1–O1297.93(9)O15 #1–Zn2–O1197.48(11)
O7–La1–O12132.07(9)O8–La1–O12117.95(9)N4–Zn2–O1186.41(14)
O1–La1–O1266.44(9)O5–La1–O12121.99(8)O8–Zn2–N387.90(14)
O13–La1–O697.96(9)O7–La1–O665.84(8)O15 #1–Zn2–N397.41(12)
O16 #1–La1–O667.47(9)O1–La1–O6131.57(8)N4–Zn2–N393.10(15)
O8–La1–O670.46(9)O11–La1–O6121.87(8)O11–Zn2–N3163.57(13)
O5–La1–O657.34(8)O2–La1–O6118.01(9)
Symmetry transformations used to generate equivalent atoms: #1x + 2, −y + 1, −z.
Table 3. Putative hydrogen bonding interactions (Å, °) for the Zn(II)-La(III) coordination compound.
Table 3. Putative hydrogen bonding interactions (Å, °) for the Zn(II)-La(III) coordination compound.
D‒X···Ad(D‒X)d(X···A)d(D···A)∠DXASymmetry Code
C9‒H9B···O140.992.443.322(5)149
C18‒H18B···O160.982.483.098(5)121
C27‒H27B···O150.992.313.239(6)156
C29‒H29···O100.952.403.011(7)1221 − x, 2 − y, −z
C31‒H31···O180.951.812.748(8)169x, 1 + y, −1 + z
C36‒H36B···O130.982.493.122(6)122

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MDPI and ACS Style

Guo, W.-T.; Liu, L.-Z.; Yu, M.; Wang, F.; Ma, J.-C.; Dong, W.-K. Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands. Crystals 2018, 8, 414. https://doi.org/10.3390/cryst8110414

AMA Style

Guo W-T, Liu L-Z, Yu M, Wang F, Ma J-C, Dong W-K. Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands. Crystals. 2018; 8(11):414. https://doi.org/10.3390/cryst8110414

Chicago/Turabian Style

Guo, Wen-Ting, Ling-Zhi Liu, Meng Yu, Fei Wang, Jian-Chun Ma, and Wen-Kui Dong. 2018. "Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands" Crystals 8, no. 11: 414. https://doi.org/10.3390/cryst8110414

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