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• Lanthanide elements not only have a unique 4f electronic layer structure and attractive structure but also have potential applications in magnetism, catalysis^[1-3], sensing materials^[4-6], and luminescent materials^[7-9]. Currently, lanthanide complexes of various structural motifs of 1D, 2D, and 3D have been synthesized. Unfortunately, due to the spin-blocking transitions of the f-f transition, the excitation efficiency of lanthanide ion (Ln³⁺) is reduced^[10]. Moreover, the most common coordination numbers of lanthanide complexes are eight and nine, and the geometric coordination configurations are diverse. Therefore, the factors required to control the synthesis of structurally desirable lanthanide complexes remain a great challenge^[11-12]. Fortunately, the common way to avoid the above defects is to select organic ligands with strong absorption ability, and then the absorbed energy is transferred from the ligand to lanthanide ions through a non-radiative process^[13-15]. In addition, it is commonly admitted that lanthanides have a strong affinity for oxygen atoms. Therefore, oxygen-containing organic ligands can be used for the synthesis of lanthanide complexes^[16-17]. Carboxylic acid ligands are the most widely used ligands, acting as "antennas"^[18] and having flexible coordination modes and strong coordination ability. The lanthanide complexes constructed by them have become the focus of current coordination chemistry research.

  In this work, two new lanthanide complexes [Pr(2-Cl-4-FBA)₃(5, 5′-DM-2, 2′-bipy)]₂ (1) and [Dy(2-Cl-4-FBA)₃(5, 5′-DM-2, 2′-bipy)]₂·2(2-Cl-4-FHBA) (2), where 2-Cl-4-FHBA=2-chloro-4-fluorobenzoic acid and 5, 5′-DM-2, 2′-bipy=5, 5′-dimethyl-2, 2′-bipyridine, have been prepared. The two complexes were fully characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectra, Raman spectra, and elemental analysis. Moreover, thermogravimetry-differential scanning calorimetry (TG-DSC)/FTIR technology was employed to study the thermal behavior of the obtained complexes. In addition, the fluorescence property of complex 2 has been studied.

  1.   Experimental

  1.1   Materials and general methods

  The contents of carbon, hydrogen, and nitrogen were acquired on a Vario-EL Ⅲ element analyzer, while the metal content was assayed using the EDTA titration method. Raman spectra were recorded by scanning 64 times with the BRUKER VERTEX-70 FTIR-RAMAN Ⅱ instrument under an excitation power of 300 mW and liquid nitrogen cooling. The PXRD data were obtained from a Bruker D8 Advance X-ray diffraction at a working voltage of 40 kV and a working current of 40 mA in a 2θ range of 5°-45° with Cu Kα radiation (λ=0.154 18 nm) at 298 K.

  TG-DTG (derivative thermogravimetry)/DSC and evolved gas analysis of the obtained lanthanide complexes were carried out using a NETASCH STA 449 F3 instrument with a Bruker TENSOR 27 Fourier transform infrared spectrometer. Also, the luminescence spectra were measured on FS5 spectrometer.

  1.2   Synthesis

  0.06 mmol 2-Cl-4-FHBA and 0.20 mmol 5, 5′-DM-2, 2′-bipy were dissolved in 95% ethanol. Then a NaOH solution (1 mol·L^-1) was used to adjust the pH of the reaction solution to 5-6. The mixture was stirred into a solution of lanthanum (Pr/Dy) nitrate dissolved in 3.5 mL water. The solution was stirred for 7 h and allowed to stand for 12 h. The obtained mother liquor was allowed to stand for 7 d to obtain crystals.

  Elemental analysis Calcd. for C₆₆H₄₂Cl₆F₆N₄O₁₂Pr₂(%): C, 46.86; H, 2.50; N, 3.31; Pr, 16.66. Found(%): C, 46.70; H, 2.63; N, 3.17; Pr, 16.61. Elemental analysis Calcd. for C₈₀H₅₀Cl₈Dy₂F₈N₄O₁₆(%): C, 46.11; H, 2.42; N, 2.69; Dy, 15.60. Found(%): C, 46.08; H, 2.43; N, 2.67; Dy, 15.58.

  1.3   X-ray single crystal structure determination

  The single crystal data of the complexes were collected on a Bruker Smart-1000 single crystal diffractometer with the emission source of Mo Kα (λ=0.071 073 nm) monochromatized by the graphite. At the same time, the obtained data were improved and refined by the SHELXS-2019/2 program. The non-hydrogen atomic coordinates were corrected by full matrix least squares. All non-hydrogen atoms were redefined using anisotropic thermal parameters.

  2.   Results and discussion

  2.1   Infrared and Raman spectroscopy

  Infrared and Raman spectroscopy were collected to detect and characterize the functional groups of ligands and complexes (Table 1). After forming the complexes, the absorption peaks of ν_C=O at 1 696 cm^-1 (IR) and 1 653 cm^-1 (Raman) in 2-Cl-4-FHBA were replaced by ν_as(COO^-) and ν_s(COO^-) of carboxyl groups. They occurred in the vicinity of 1 626-1 636 cm^-1 (IR), 1 600-1 603 cm^-1 (Raman), 1 402-1 405 cm^-1 (IR), and 1 415-1 425 cm^-1 (Raman), respectively. At 415-418 cm^-1 (IR) and 420 cm^-1 (Raman), a new Ln—O bond tensile vibration characteristic absorption band appeared in the complex. All the above changes indicated that the oxygen atoms coordinated with Ln(Ⅲ) cation. Furthermore, the ν_C=N peak in 5, 5′-DM-2, 2′-bipy was shifted toward higher wavenumbers in the complexes (IR: 1 483-1 484 cm^-1, Raman: 1 509-1 510 cm^-1). In addition, the absorption of Ln—N at 204-208 cm^-1 also appeared in the Raman spectrum. These facts indicate that the nitrogen atoms coordinate with Ln(Ⅲ) cation^[19]. It is speculated that new products are formed.

  Table 1

  

  Table 1.  IR and Raman spectra of the complexes and ligands

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  Compound	νC=N			δC—H		νC=O			νas(COO-)			νs(COO-)			νLn—O			νLn—N
  	IR	Raman		IR		IR	Raman		IR	Raman		IR	Raman		IR	Raman		Raman
  2-Cl-4-FHBA						1 696	1 653
  5, 5′-DM-2, 2′-bipy	1 467	1 503		827, 736
  1	1 484	1 510		862, 788					1 626	1 600		1 402	1 415		415	420		204
  2	1 483	1 509		861, 788					1 636	1 603		1 405	1 425		418	420		208

  2.2   Description of crystal structure

  Table 2 lists the single crystal structure data of complexes 1 and 2. Table 3 lists the data of selected bond lengths for complexes 1 and 2. Analyzing the single crystal diffraction data in Table 2 shows that complexes 1 and 2 have completely different structures. Next, the crystal structures of complexes 1 and 2 will be discussed separately.

  Table 2

  

  Table 2.  Crystal and structure refinement data for complexes 1 and 2

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  Parameter	1	2
  Empirical formula	C66H42Cl6F6N4O12Pr2	C80H50Cl8Dy2F8N4O16
  Formula weight	1 691.55	2 083.84
  Temperature / K	298.15	298.15
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a / nm	1.119 33(11)	1.270 20(11)
  b / nm	1.238 45(12)	1.297 59(12)
  c / nm	1.316 93(14)	1.405 71(13)
  α / (°)	87.837(2)	112.761(4)
  β / (°)	89.275(2)	96.631(2)
  γ / (°)	72.148 0(10)	102.695(3)
  Volume / nm3	1.736 4(3)	2.031 8(3)
  Z	1	2
  Dc / (g·cm-3)	1.618	1.703
  Absorption coefficient / mm-1	1.695	2.175
  F(000)	836	1 026
  Crystal size / mm	0.40×0.18×0.07	0.30×0.11×0.07
  θ range for data collection / (°)	4.558-56.55	5.158-50.36
  Limiting indices	-14 ≤ h ≤ 14, -15 ≤ k ≤ 16, -17 ≤ l ≤ 10	-15 ≤ h ≤ 14, -15 ≤ k ≤ 13, -9 ≤ l ≤ 16
  Reflection collected, unique	10 893, 7 996 (Rint=0.062 3)	10 328, 7 033 (Rint=0.030 5)
  Completeness to θ=25.02° / %	98.1	98.1
  Max. and min. transmission	0.890 6 and 0.550 5	0.862 7 and 0.561 5
  Data, restraint, parameter	7 996, 0, 424	7 033, 24, 530
  Goodness-of-fit on F 2	1.001	0.991
  Final R indices [I > 2σ(I)]	R1=0.077 9, wR2=0.191 4	R1=0.038 1, wR2=0.086 2
  R indices (all data)	R1=0.107 4, wR2=0.216 0	R1=0.048 9, wR2=0.092 4
  Largest diff. peak and hole / (e·nm-3)	1 830 and -1 640	1 830 and -910

  Table 3

  

  Table 3.  Selected bond lengths (nm) for complexes 1-2

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  1
  Pr1—O4#1	0.230 4(7)	Pr1—O3	0.236 7(7)	Pr1—O1	0.236 2(6)
  Pr1—O2#1	0.238 2(6)	Pr1—O6	0.242 4(7)	Pr1—O5	0.243 2(7)
  Pr1—N1	0.255 6(8)	Pr1—N2	0.259 9(8)
  2
  Dy1—O4#1	0.231 7(3)	Dy1—O3	0.233 2(3)	Dy1—O2#1	0.234 1(3)
  Dy1—O5	0.239 4(3)	Dy1—O1	0.239 9(3)	Dy1—O6	0.251 4(4)
  Dy1—N2	0.253 9(4)	Dy1—N1	0.257 4(3)	Dy1—O2	0.270 8(3)
  Symmetry codes: #1: 1-x, 1-y, 1-z for 1; #1: 1-x, -y, 1-z for 2.

  2.2.1   Structure of complex 1

  Complex 1 contains one kind of Pr³⁺, three 2-Cl-4-FBA ligands, and one 5, 5′-DM-2, 2′-bipy ligand (Fig. 1a). The coordination with oxygen and nitrogen atoms is carried out with eight-coordinated Pr³⁺ ion as the center (Fig. 1b), which belong to the 2-Cl-4-FBA ligand of the bridged and chelated di-dentate and the 5, 5′-DM-2, 2′-bipy ligand of the chelated di-dentate, respectively, shows a distorted dodecahedral coordination sphere^[20]. The Pr—O distance (0.230 4-0.242 7 nm) is within the previously reported Pr—O bond length range^[21]. In addition, the Pr—N distance is 0.255 6-0.259 9 nm. The average distance of Pr—O (0.237 9 nm) is significantly shorter than Pr—N (0.2578 nm), and it has been confirmed that neutral ligands are first lost during thermal decomposition^[22].

  Figure 1

  

  Figure 1.  (a) ORTEP diagram of complex 1 with a 50% probability; (b) Coordination polyhedron of the Pr3+ ion in 1

  Symmetry codes: #1: 1-x, 1-y, 1-z.

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  Along the a-axis, the adjacent binuclear molecules are linked by C—H…F weak hydrogen bonds (Fig. 2a) to form a 1D supramolecular in complex 1. Then, the adjacent 1D chains extend to the a- and c-axis directions through π-π stacking to form a 2D thin-section structure (Fig. 2b).

  Figure 2

  

  Figure 2.  (a) One-dimensional chain structure of complex 1 viewed along the a-axis; (b) 2D structure of 1 viewed from the a- and c-axis directions

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  2.2.2   Structure of complex 2

  The complex consists of two Dy³⁺ ions, two 5, 5′-DM-2, 2′-bipy ligands, six 2-Cl-4-FBA ligands, and two free 2-Cl-4-FHBA molecules, as illustrated in Fig. 3a (To make the structure clear, two free 2-Cl-4-FHBA molecules are omitted). A twisted triple prism geometry is formed with a nine-coordinated Dy³⁺ as the central ion (Fig. 3b)^[23]. Dy³⁺ ion chelates with acid and neutral ligands: they contribute nitrogen atoms (N1, N2) and oxygen atoms (O5, O6), respectively. The average bond lengths of Dy—N and Dy—O are 0.255 7 and 0.245 4 nm, respectively. Three (O1, O2, O2#1) of these are from bridging tridentate 2-Cl-4-FBA ligands with an average Dy—O length of 0.248 3 nm. The other oxygen atoms (O3, O4) come from two different bridging bidentate 2-Cl-4-FBA ligands with an average length of 0.232 5 nm.

  Figure 3

  

  Figure 3.  (a) ORTEP diagram of complex 2 with a 50% probability; (b) Coordination polyhedron of the Dy³⁺ion in 2

  Symmetry codes: #1: 1-x, -y, 1-z.

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  Further, along the c-axis, the adjacent binuclear molecules are linked by C—H…F weak hydrogen bonds (Fig. 4a) to form a 1D supramolecular in complex 2. Then, the adjacent 1D chains extend to the a- and c-axis directions through π-π stacking to form a 2D thin-section structure (Fig. 4b).

  Figure 4

  

  Figure 4.  (a) One-dimensional chain structure of complex 2viewed along the a-axis; (b) 2D structure of 2 viewed from the a- and b-axis directions

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  2.3   PXRD analysis

  The ligands and complexes were subjected to PXRD to determine their purity and structure (Fig. 5). However, from the PXRD patterns of complexes 1 and 2, it is found that the position and number of peaks were different, which shows that complexes 1 and 2 have different crystal structures. The diffraction patterns simulated by the single crystal data had a good similarity with the observed results, confirming their excellent phase purity. We could also find that the complexes were not the result of the addition of raw materials, indicating that the synthesized complexes have a new phase structure.

  Figure 5

  

  Figure 5.  Experimental and simulated PXRD patterns of theligands and complexes

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  2.4   Thermal analysis

  Thermal stability is an important parameter in material application. TG-DSC method was used to characterize the thermal stability of the complexes, and the results are shown in Fig. 6, respectively. The thermal behavior of the two complexes was studied. Table 4 gives the TG-DSC analysis results of the complexes^[24].

  Figure 6

  

  Figure 6.  TG-DTG/DSC curves of complexes 1 (a) and 2 (b)

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  Table 4

  

  Table 4.  Thermal analysis data of complexes 1 and 2

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  Complex	Step	Temperature range / K	Tp of DTG / K	Mass loss rate / %		Probably expelled groups	Intermediate and residue
  				Found	Calcd.
  1	Ⅰ	438.15-599.15	501.45	21.53	21.78	2(5, 5′-DM-2, 2′-bipy)	[Pr2(2-Cl-4-FBA)6]
  	Ⅱ	599.15-801.15	780.15	42.06	58.04	6(2-Cl-4-FBA)	Pr6O11
  	Ⅲ	801.15-1 260.65	829.05	15.21
  2	Ⅰ	410.15-476.15	461.15	1.91		x(2-Cl-4-FHBA)	[Dy2(2-Cl-4-FBA)6(5, 5′-DM-2, 2′-bipy)2]·(2-x)(2-Cl-4-FHBA)
  	Ⅱ	476.15-632.15	515.15	20.41		(2-x)(2-Cl-4-FHBA)+ y(5, 5′-DM-2, 2′-bipy)	[Dy2(2-Cl-4-FBA)6(5, 5′-DM-2, 2′-bipy)2-y]
  	Ⅲ	632.15-792.25	766.15	39.41		(2-y)(5, 5′-DM-2, 2′-bipy)+z(2-Cl-4-FBA)	[Dy2(2-Cl-4-FBA)6-z]
  	Ⅳ	792.15-1 260.25	822.15	17.62		(6-z)2-Cl-4-FBA	Dy2O3

  As shown in Fig. 6a, for complex 1, In the first stage (438.15-599.15 K), all neutral ligands were lost. The mass loss rate at this stage was 21.53% (Calcd. 21.78%). In a range of 599.15-1 260.15 K, the mass loss rate of step Ⅱ and step Ⅲ were 57.27%, which is the elimination of all 2-Cl-4-FBA ligands. One upward endothermic peak and two downward exothermic peaks were observed on the corresponding DSC curve (T₁=503.55 K; H₁=69.8 J·g^-1; T₂=786.05 K, H₂=91.33 J·g^-1; T₂=830.45 K, H₃=1534 J·g^-1). Finally, complex 1 was degraded to Pr₆O₁₁, and the total mass loss was 78.80% (Calcd. 79.82%).

  As shown in Fig. 6b, for complex 2, the first stage of decomposition (410.15-476.15 K) can be attributed to the loss of some free 2-Cl-4-FBA molecules. The second step occurred in a range of 476.15-632.15 K with a mass loss rate of 20.41%, belonging to the decomposition of the rest free 2-Cl-4-FHBA molecules and part of 5, 5′-DM-2, 2′-bipy molecules. The third and fourth steps occurred in the ranges of 632.15-792.25 K and 792.15-1 260.25 K, which eliminates all ligands. Finally, complex 2 was degraded to Dy₂O₃, and the total mass loss rate was 79.35% (Calcd. 82.10%).

  2.5   Evolved gas analysis

  To further determine the stability of the complexes in the air and the gas products produced during thermal decomposition, the 3D infrared spectra (Fig. 7a and 7b) of complexes 1 and 2 were measured by TG-DSC/FTIR system. The 2D infrared spectra (Fig. 8a and 8b) were analyzed by FTIR.

  Figure 7

  

  Figure 7.  Three-dimensional FTIR stacking diagrams of gas escaping of complexes 1 (a) and 2 (b)

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  Figure 8

  

  Figure 8.  FTIR spectra of the evolved gases for complexes 1 (a) and 2 (b)

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  For complex 1, at 501.42 K, the characteristic absorption bands of H₂O and CO₂ can be seen in the wavenumber ranges of 3 358-3 840 cm^-1 and 2 336-2 414 cm^-1, and 653 cm^-1. Besides, the absorption peaks ν_C=N (1 468 cm^-1), ν_C—N (1 131, 1 217 cm^-1), ν_C=C (1 551, 1 572, 1 599 cm^-1), ν_C—H (2 880-3 012 cm^-1), γ_=C—H (1 060, 1 028, 863 cm^-1) were observed. This matches the removal of 5, 5′-DM-2, 2′-bipy. At 771.24 K, characteristic absorption peaks of CO₂ (2 330-2 358 cm^-1, 648 cm^-1) and H₂O (3 425-3 962 cm^-1) were found. And some important characteristic bands were observed: ν_C=O (1 758 cm^-1), ν_C=C (1 486, 1 600 cm^-1), γ_C—H (885 cm^-1). All of these indicate that the 2-Cl-4-FBA ligands have been destroyed. At 826.59 K, the absorption peaks of CO₂ (2 330-2 359, 668 cm^-1) and H₂O (3 604-3 901 cm^-1) were detected in the infrared spectrum, indicating that the acid ligand has been completely decomposed.

  For complex 2, at 416.87 K, the characteristic absorption bands of H₂O and CO₂ could be seen in the wavenumber ranges of 3 243-3 926 cm^-1 and 2 318-2 367 cm^-1, and 668 cm^-1. Besides, the absorption peaks ν_C=O (1 775 cm^-1), ν_C=C (1 468, 1 492, 1 602 cm^-1), and γ_=C—H (1 094, 1 036, 914 cm^-1) were observed. The above shows that free 2-Cl-4-FHBA molecules have started to decompose. At 515.30 K, the absorption bands CO₂ (2 371-2 358 cm^-1) and H₂O (3 400-3 953 cm^-1) are found. And some characteristic bands are observed: ν_C=C (1 599, 1 563, 1 536 cm^-1), ν_C—H (2 875-3 037 cm^-1), γ_C—H (1 060, 1 028, 825 cm^-1), ν_C=N (1 468 cm^-1), ν_C—N (1 236, 1 129 cm^-1). This indicates that the remaining free 2-Cl-4-FHBA molecules and some 5, 5′-DM-2, 2′-bipy molecules decompose in the second step. At T=771.33 and 826.68 K, the bands were the strongest absorptions of the third and fourth step decomposition. We have observed not only the absorption of CO₂ and H₂O but also the characteristic absorption of C=N, C—N, C=C, C—H, and C=O. It indicates that the remaining 5, 5′-DM-2, 2′-bipy and 2-Cl-4-FBA ligands are decomposed. The results are consistent with the thermogravimetric analysis.

  2.6   Fluorescence property

  It is obtained from the excitation spectrum in Fig. 9a that there was a strong excitation-wide peak in a range of 240-400 nm, which is mainly due to the absorption peak generated by electron transfer from the ligand to the central ion. After excitation at 329 nm, the ligand-mediated emission spectra of complex 2 showed two characteristic emission bands of Dy³⁺ at 482 and 576 nm^[25-26]. The reason why the Dy complex sensitized by 2-Cl-4-FBA ligand has yellow light is that the transition intensity of ⁴F_9/2 → ⁶H_13/2 (yellow) is greater than that of ⁴F_9/2 → ⁶H_15/2 (blue) (Fig. 9b)^[27-28].

  Figure 9

  

  Figure 9.  Solid-state excitation (a) and emission (b) spectra ofcomplex 2

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  3.   Conclusions

  In summary, we have successfully assembled 5, 5′-DM-2, 2′-bipy, 2-Cl-4-FBA, and lanthanide nitrate into two novel one- and two-dimensional lanthanide complexes, and carried out a series of characterization for them. Although the two complexes have different structures, they all form a 1D chain and 2D planar structures. Each stage of the thermal decomposition behavior of the two complexes was described by TG-DSC/ FTIR technology. In addition, the fluorescence spectra of solid complex 2 showed the luminescence characteristics of Dy³⁺ ions.

  
  Acknowledgments: The research work was supported by the National Natural Science Foundation of China (Grant No.22273015).
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  Figure 1  (a) ORTEP diagram of complex 1 with a 50% probability; (b) Coordination polyhedron of the Pr3+ ion in 1

  Symmetry codes: #1: 1-x, 1-y, 1-z.

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  Figure 2  (a) One-dimensional chain structure of complex 1 viewed along the a-axis; (b) 2D structure of 1 viewed from the a- and c-axis directions

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  Figure 3  (a) ORTEP diagram of complex 2 with a 50% probability; (b) Coordination polyhedron of the Dy³⁺ion in 2

  Symmetry codes: #1: 1-x, -y, 1-z.

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  Figure 4  (a) One-dimensional chain structure of complex 2viewed along the a-axis; (b) 2D structure of 2 viewed from the a- and b-axis directions

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  Figure 5  Experimental and simulated PXRD patterns of theligands and complexes

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  Figure 6  TG-DTG/DSC curves of complexes 1 (a) and 2 (b)

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  Figure 7  Three-dimensional FTIR stacking diagrams of gas escaping of complexes 1 (a) and 2 (b)

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  Figure 8  FTIR spectra of the evolved gases for complexes 1 (a) and 2 (b)

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  Figure 9  Solid-state excitation (a) and emission (b) spectra ofcomplex 2

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  Table 1.  IR and Raman spectra of the complexes and ligands

  Compound	νC=N			δC—H		νC=O			νas(COO-)			νs(COO-)			νLn—O			νLn—N
  	IR	Raman		IR		IR	Raman		IR	Raman		IR	Raman		IR	Raman		Raman
  2-Cl-4-FHBA						1 696	1 653
  5, 5′-DM-2, 2′-bipy	1 467	1 503		827, 736
  1	1 484	1 510		862, 788					1 626	1 600		1 402	1 415		415	420		204
  2	1 483	1 509		861, 788					1 636	1 603		1 405	1 425		418	420		208

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  Table 2.  Crystal and structure refinement data for complexes 1 and 2

  Parameter	1	2
  Empirical formula	C66H42Cl6F6N4O12Pr2	C80H50Cl8Dy2F8N4O16
  Formula weight	1 691.55	2 083.84
  Temperature / K	298.15	298.15
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a / nm	1.119 33(11)	1.270 20(11)
  b / nm	1.238 45(12)	1.297 59(12)
  c / nm	1.316 93(14)	1.405 71(13)
  α / (°)	87.837(2)	112.761(4)
  β / (°)	89.275(2)	96.631(2)
  γ / (°)	72.148 0(10)	102.695(3)
  Volume / nm3	1.736 4(3)	2.031 8(3)
  Z	1	2
  Dc / (g·cm-3)	1.618	1.703
  Absorption coefficient / mm-1	1.695	2.175
  F(000)	836	1 026
  Crystal size / mm	0.40×0.18×0.07	0.30×0.11×0.07
  θ range for data collection / (°)	4.558-56.55	5.158-50.36
  Limiting indices	-14 ≤ h ≤ 14, -15 ≤ k ≤ 16, -17 ≤ l ≤ 10	-15 ≤ h ≤ 14, -15 ≤ k ≤ 13, -9 ≤ l ≤ 16
  Reflection collected, unique	10 893, 7 996 (Rint=0.062 3)	10 328, 7 033 (Rint=0.030 5)
  Completeness to θ=25.02° / %	98.1	98.1
  Max. and min. transmission	0.890 6 and 0.550 5	0.862 7 and 0.561 5
  Data, restraint, parameter	7 996, 0, 424	7 033, 24, 530
  Goodness-of-fit on F 2	1.001	0.991
  Final R indices [I > 2σ(I)]	R1=0.077 9, wR2=0.191 4	R1=0.038 1, wR2=0.086 2
  R indices (all data)	R1=0.107 4, wR2=0.216 0	R1=0.048 9, wR2=0.092 4
  Largest diff. peak and hole / (e·nm-3)	1 830 and -1 640	1 830 and -910

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  Table 3.  Selected bond lengths (nm) for complexes 1-2

  1
  Pr1—O4#1	0.230 4(7)	Pr1—O3	0.236 7(7)	Pr1—O1	0.236 2(6)
  Pr1—O2#1	0.238 2(6)	Pr1—O6	0.242 4(7)	Pr1—O5	0.243 2(7)
  Pr1—N1	0.255 6(8)	Pr1—N2	0.259 9(8)
  2
  Dy1—O4#1	0.231 7(3)	Dy1—O3	0.233 2(3)	Dy1—O2#1	0.234 1(3)
  Dy1—O5	0.239 4(3)	Dy1—O1	0.239 9(3)	Dy1—O6	0.251 4(4)
  Dy1—N2	0.253 9(4)	Dy1—N1	0.257 4(3)	Dy1—O2	0.270 8(3)
  Symmetry codes: #1: 1-x, 1-y, 1-z for 1; #1: 1-x, -y, 1-z for 2.

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  Table 4.  Thermal analysis data of complexes 1 and 2

  Complex	Step	Temperature range / K	Tp of DTG / K	Mass loss rate / %		Probably expelled groups	Intermediate and residue
  				Found	Calcd.
  1	Ⅰ	438.15-599.15	501.45	21.53	21.78	2(5, 5′-DM-2, 2′-bipy)	[Pr2(2-Cl-4-FBA)6]
  	Ⅱ	599.15-801.15	780.15	42.06	58.04	6(2-Cl-4-FBA)	Pr6O11
  	Ⅲ	801.15-1 260.65	829.05	15.21
  2	Ⅰ	410.15-476.15	461.15	1.91		x(2-Cl-4-FHBA)	[Dy2(2-Cl-4-FBA)6(5, 5′-DM-2, 2′-bipy)2]·(2-x)(2-Cl-4-FHBA)
  	Ⅱ	476.15-632.15	515.15	20.41		(2-x)(2-Cl-4-FHBA)+ y(5, 5′-DM-2, 2′-bipy)	[Dy2(2-Cl-4-FBA)6(5, 5′-DM-2, 2′-bipy)2-y]
  	Ⅲ	632.15-792.25	766.15	39.41		(2-y)(5, 5′-DM-2, 2′-bipy)+z(2-Cl-4-FBA)	[Dy2(2-Cl-4-FBA)6-z]
  	Ⅳ	792.15-1 260.25	822.15	17.62		(6-z)2-Cl-4-FBA	Dy2O3

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