English

• 0.   Introduction

  Lanthanide coordination polymers are a unique class of crystalline materials that are widely used in many fields, such as luminescence, sensors, singlemolecular magnet, storage and separation of small molecules, catalysis^[1-10]. Recently, lanthanide elements have been extensive used as luminescent materials for their fascinating optical properties. Since the 4f electron layer is shielded by the filled 5p⁶6s² orbitals, lanthanide ions have the advantages of high luminescence intensity, good color purity and long lifetimes^[11-12]. It is well known that the molar absorption coefficient of direct excitation of trivalent metal ions is very low, so we need to introduce aromatic carboxylic acid ligands and neutral ligands as antenna ligands to enhance light emission^[13]. The introduction of halogenated aromatic carboxylic acid ligands and bipyridine ligands not only serves as antenna ligands to increase the luminescence intensity of lanthanide ion, but also enhances the stability of lanthanide complex. The carboxyl group of aromatic carboxylic acid ligand can bond to the lanthanide ion by multitudes of coordination modes, thus forming lanthanide complexes with various structures^[14-15]. In general, the research on lanthanide complexes mainly focuses on the construction of compounds with various topological structures. However, most of the assembly is done by covalent coordination ions with ligands. What we are exploring is another model for generating extended structures through noncovalent supramolecules^[16-18].

  Therefore, we chose 3, 4-dichlorobenzoic acid (3, 4-HDClBA) and 3, 5-dichlorobenzoic acid (3, 5-HDClBA=3, 5 - dichlorobenzoic acid) as carboxylic acid ligands, and 5, 5′-dimethyl-2, 2′-bipyridine(5, 5′-DM-2, 2′-bipy) as auxiliary ligands to assemble four novel complexes by different synthesis methods. The one-dimensional and two - dimensional structures of the complexes are also assembled by C-H…Cl hydrogen bonding and π-π interactions. The pyrolysis process of the complexes has been studied by the TG-FTIR technology. Further- more, the fluorescence spectra of 2 and 4 were studied at room temperature.

  1.   Experimental

  1.1   Materials and methods

  3, 4 - HDClBA (Alfa Aesar, 99%), 3, 5 - HDClBA (Alfa Aesar, 99%), Ln(NO₃)₃·6H₂O (Ln=Sm, Eu) (Alfa Aesar, 99.9%), 5, 5′-DM-2, 2′-bipy (Alfa Aesar, 98%) were used without any treatment. Elemental analysis of C, H and N were measured on a Vario-EL Ⅱ element analyzer. The powder X-ray diffraction patterns (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. In the atmosphere of simulated air, TG/FTIR spectra were recorded on a NETASCH STA 449 F3 instrument with a Bruker TENSOR 27 FTIR with approximately 3 mg compounds. Fluorescence spectra of complexes 2 and 4 were studied on a Fluorescence spectrum (FS5) spectrofluorophotometer.

  1.2   Synthesis of the complexes

  1.2.1   Synthesis of 1 and 2 (Ln=Sm (1), Eu (2))

  The pH value of the mixture of 3, 4-HDClBA (0.6 mmol) and 5, 5′-DM-2, 2′-bipy (0.2 mmol) in 8 mL ethanol was adjusted to 5~7 by 1.0 mol·L-1 NaOH. This mixture was mixed with an aqueous solution of lanthanide nitrate for 40 min, and then filled into an autoclave and heated at 393 K for a week, then cooled to 298 K gradually. The resulting translucent crystal were obtained. Elemental analyses Calcd. for C₆₈H₅₀Cl₁₂N₄O₁₄Sm₂(%): C, 43.60; N, 2.99; H, 2.69. Found(%): C, 43.62; N, 2.97; H, 2.68. Calcd. for C₆₈H₅₀Cl₁₂N₄O₁₄Eu₂(%): C, 43.52; N, 2.99; H, 2.69. Found(%): C, 43.50; N, 2.98; H, 2.67.

  1.2.2   Synthesis of 3 and 4 (Ln=Sm (3), Eu (4))

  The pH value of the mixture of 0.6 mmol 3, 5-HDClBA and 0.2 mmol 5, 5′-DM-2, 2′-bipy in 8 mL ethanol was adjusted to 5~7 with 1.0 mol·L-1 NaOH. This mixture was mixed with an aqueous solution of lanthanide nitrate for 6 h and held for 12 h, then the powder was filtered to obtain the filtrate. The crystals of 3 were acquired after about a week. Elemental analyses Calcd. for C₆₆H₄₂Cl₁₂N₄O₁₂Sm₂(%): C, 43.82; N, 3.10; H, 2.34. Found(%): C, 43.85; N, 3.08; H, 2.35. Calcd. for C₆₆H₄₂Cl₁₂N₄O₁₂Eu₂(%): C, 43.74; N, 3.09; H, 2.34. Found(%): C, 43.75; N, 3.08; H, 2.31.

  1.3   Crystal structure determination

  The diffraction of the complexes was performed on a Smart-1000 diffractometer using graphite-monochromated with Mo Kα radiation (λ =0.071 073 nm). The data of complexes 1~3 was collected at 298(2) K and solved by direct methods. All crystal structures were refined using SHELXL-97 program. Data collection and refinements of 1~3 are shown in Table 1 and primary bond length parameters are presented in Table S1 (Supporting information).

  Table 1

  

  Table 1.  Crystal data and structure refinement for complexes 1~3

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  Complex	1	2	3
  Empirical formula	C68H50Cl12N4O14Sm2	C68H50Cl12N4O14Eu2	C66H42Cl12N4O12Sm2
  Formula weight	1 873.22	1 876.44	1 809.14
  Crystal system	Triclinic	Triclinic	Triclinic
  Space group	P1	P1	P1
  a/nm	1.266 00(11)	1.260 68(12)	1.164 60(11)
  b/nm	1.392 01(12)	1.383 31(12)	1.214 30(12)
  c/nm	2.354 0(2)	2.340 4(2)	1.340 00(13)
  α/(°)	90.850 0(10)	90.707 0(10)	104.511(3)
  β/(°)	91.270 0(10)	91.398 0(10)	92.930 0(10)
  γ/(°)	113.210(3)	113.189(4)	98.252(2)
  Volume/nm3	3.810 5(6)	3.749 5(6)	1.808 0(3)
  Z	2	2	1
  Dc/(g·cm-3)	1.633	1.662	1.662
  Absorption coefficient/mm-1	2.009	2.149	2.112
  F(000)	1 852	1 856	890
  Crystal size/mm	0.25×0.13×0.11	0.17×0.12×0.10	0.16×0.12×0.10
  θ range for data collection/(°)	2.32~25.02	2.34~25.02	2.26~25.02
  Limiting indices	-14 ≤ h ≤ 14,	-14 ≤ h ≤ 13,	-13 ≤ h ≤ 13,
  	-16 ≤ k ≤ 15,	-16 ≤ k ≤ 13,	-14 ≤ k ≤ 12,
  	-28 ≤ l ≤ 23	-27 ≤ l ≤ 27	-15 ≤ l ≤ 15
  Reflection collected, unique Completeness to θ=25.02°/%	19 489, 13 257(Rint=0.038 9)	19 159, 13 034(Rint=0.037 5)	9 237, 6 291(Rint=0.028 8)
  	98.5	98.5	98.5
  Max. and min. transmission	0.809 2 and 0.633 5	0.813 8 and 0.711 5	0.816 6 and 0.728 7
  Data, restraint, parameter	13 257, 2, 906	13 034, 2, 906	6 291, 0, 435
  Goodness-of-fit on F2	1.021	1.033	1.018
  Final R indices [I > 2σ(I)]	R1=0.057 4, wR2=0.138 5	R1=0.048 7, wR2=0.091 5	R1=0.037 5, wR2=0.060 7
  R indices (all data)	R1=0.089 5, wR2=0.151 8	R1=0.089 0, wR2=0.101 3	R1=0.051 3, wR2=0.064 0
  Largest diff. peak and hole/(e·nm-3)	1 570 and -1 728	1 394 and -696	1 159 and -540

  CCDC: 1939324, 1; 1939325, 2; 1939326, 3.

  2.   Results and discussion

  2.1   Structure description of [Ln₂(5, 5′ -DM- 2, 2′ - bipy)₂(3, 4 - DClBA)₆(H₂O) (C₂H₅OH)] (Ln=Sm (1), Eu (2))

  The crystal diffraction data indicate that 1 and 2 are isostructural and crystallize in space group P1. The structure of 2 is described in detail as an example. Complex 2 contains two eight - coordinated Eu³⁺ ions, each of which is coordinated with two nitrogen atoms and six oxygen atoms. Among the oxygen atoms coordinated with Eu1, five are from 3, 4-DClBA^- anions and one is from water molecule. Among the oxygen atoms coordinated with Eu2, five are from 3, 4-DClBA^- anions and one is from ethanol (Fig. 1a). Each Eu³⁺ adopts a distorted square antiprismatic molecular geometry (Fig. 1b). The average values of Eu-O distances and EuN distances of complex 2 are 0.238 3 and 0.263 7 nm, respectively. The average Eu-N distances is longer than Eu-O distances in the binuclear complex, which is consistent with the previously reported Eu complexes[20-21]. The adjacent molecules are connected together by π-π stacking interactions^[22] of bipyridine ligands with a distance of 0.373 5 nm, resulting in a four nuclear unit. Then the unit is linked by the C-H…Cl hydrogen bonding^[23] with a distance of 0.353 6 nm forming a 1D supramolecular structure (Fig. 2a). Then the 1D chains are assembled to 2D supramolecular network frameworks along b and c axes by C-H…O hydrogen bonding with a distance of 0.340 2 nm between two 3, 4- DClBA ligands (Fig. 2b).

  Figure 1

  

  Figure 1.  (a) Crystal structure of 1; (b) Coordination geometry of Eu³⁺ ion

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  Figure 2

  

  Figure 2.  (a) View of 1D chain of 2 along c axis; (b) 2D layered of 2 along b and c axes

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  2.2   Crystal structure description of 3

  The crystal diffraction data reveal that complex 3 is the triclinic system with a binuclear structure. The asymmetric part of contains one Sm3+ ion, three 3, 5-DClBA^- anions and one 5, 5′-DM-2, 2′-bipy molecule (Fig. 3a). Each Sm³⁺ ion is bonded with seven oxygen atoms from five 3, 5-DClBA^- anions, and two nitrogen atoms from one bipyridine. The coordination geometry of Sm³⁺ ion is a distorted monocapped square antiprismatic (Fig. 3b). The average values of Sm-O and Sm-N distances are 0.248 1 and 0.261 9 nm, respectively. The adjacent molecules are interconnected with each other through π-π interactions with 0.350 8 nm between 3, 5-DClBA^- anions, forming a 1D chain structure (Fig. 4a). The adjacent two chains are extended via another π-π interactions with 0.378 7 nm between bipyridine ligands to come into being a 2D layer (Fig. 4b).

  Figure 3

  

  Figure 3.  (a) Crystal structure of 3; (b) Coordination geometry of Sm³⁺ ion

  Symmetry code: #1:-x+1, -y+2, -z

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  Figure 4

  

  Figure 4.  (a) View of 1D chain structure of 3 along a axis; (b) 2D layered of 3 along a and b axes

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  Compared with the samarium complex (the coordi- nation number is 8) synthesized by Carter et al.^[17] With 3, 5 - dichlorobenzoic acid and tripyridine, the coordination number of 3 is 9. In addition to bidentate chelation and bridging bidentate, complex 3 also has a tridentate bridging coordination mode. The reason may be related to the steric hindrance of the auxiliary ligand. The auxiliary ligand of complex 3 is dipyridine with smaller steric hindrance. Therefore, in order to meet the characteristics of high coordination number of rare lanthanide ions, it is easier to form 9-coordination complex.

  2.3   Powder X-ray diffraction

  At 298 K, PXRD patterns of all complexes were measured. As shown in Fig. 5, the PXRD data of synthesized samples of complexes 1 and 2 were essentially close to the simulated pattern of the crystal, indicating that complexes 1 and 2 are isostructural. No single crystals of complex 4 was obtained, but the XRD pattern of its powder was consistent with that of complex 3, indicating that complex 4 may be isostructural to complex 3. The simulated PXRD patterns of complex 2 are shown in Fig.S1.

  Figure 5

  

  Figure 5.  PXRD patterns of complexes 1~4 and simulated PXRD patterns of complexes 1 and 3

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  2.4   Thermal analysis

  As shown in Fig. 6a and 6b, TG-DTG-DSC curves of 2 and 3 were obtained under a simulated air atmosphere. The TG-DTG-DSC curves of 1 and 4 are shown in Fig. S2a and S2b. Thermoanalysis data at different temperature stages are presented in Table 2. Pyrolysis process of 2 and 3 were investigated thoroughly.

  Figure 6

  

  Figure 6.  TG-DTG/DSC curves of complexes 2 (a) and 3 (b)

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  As shown in Fig. 6a, there are four platforms on the TG curve of complex 2. At 374~423 K, the weight loss was about 3.4%, which is equivalent to the removal of one molecule of water and ethanol (Calcd. 3.4%). A small endothermic peak was observed on DSC curve. The weight loss at 423~662 K was 18.6%, indicating that 5, 5′ - DM - 2, 2′ - bipy ligand began to decompose (Calcd. 19.6%). The remaining step (third, fourth) weight loss of 57.5% at 622~1267 K are attributed to the loss of 3, 4-DClBA-ligands (Calcd. 58.2%). Finally, the complex entirely collapsed into the Eu₂O₃.

  Table 2

  

  Table 2.  Pyrolysis data for complexes 1~4

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  Complex	Step	Temperature range/K	Tp of DTG/K	Weight loss/%		Probable expelled groups	Intermediate and residue
  				Found	Calcd.
  1	Ⅰ	368~432	400	3.8	3.4a	C2H5OH+H2O	[Sm2(3, 4-DClBA)6(5, 5′-DM-2, 2′-bipy)2]
  	Ⅱ	432~658	474	19.4	19.7b	2(5, 5′-DM-2, 2′-dipy)	[Sm2(3, 4-DClBA)6]
  	Ⅲ	658~819	792	38.9		x(3, 4-DClBA)	[Sm2(3, 4-DClBA)6-x]
  	Ⅳ	819~1 266	836	19.2	58.3c	(6-x)(3, 4-DClBA)	Sm2O3
  				81.3	81.4e
  2	Ⅰ	374~423	401	3.4	3.4a	C2H5OH+H2O	[Eu2(3, 4-DClBA)6(5, 5′-DM-2, 2′-bipy)2]
  	Ⅱ	423~662	479	18.6	19.6b	2(5, 5′-DM-2, 2′-dipy)	[Eu2(3, 4-DClBA)6]
  	Ⅲ	662~803	782	32.5		x (3, 4-DClBA)	[Eu2(3, 4-DClBA)6-x]
  	Ⅳ	803~1 267	823	25.0	58.2c	(6-x)(3, 4-DClBA)	Eu2O3
  				79.5	81.2e
  3	Ⅰ	492~550	540	9.4		x (5, 5′-DM-2, 2′-dipy)	[Sm2(3, 5-DClBA)6(5, 5′-DM-2, 2′-bipy)2-x]
  	Ⅱ	550~596	566	10.4	20.4b	(2-x) (5, 5′-DM-2, 2′-bipy)	[Sm2(3, 5-DClBA)6]
  	Ⅲ	596~816	802	41.7		y (3, 5-DClBA)	[Sm2(3, 5-DClBA)6-y]
  	Ⅳ	816~1 223	827	18.5	60.4d	(6-y) (3, 5-DClBA)	Sm2O3
  				80	80.8e
  4	Ⅰ	490~546	541	8.2		x(5, 5′-DM-2, 2′-dipy)	[Eu2(3, 5-DClBA)6(5, 5′-DM-2, 2′-bipy)2-x]
  	Ⅱ	546~590	562	11.7	20.3b	(2-x) (5, 5′-DM-2, 2′-bipy)	[Eu2(3, 5-DClBA)6]
  	Ⅲ	590~807	798	37.1		y (3, 5-DClBA)	[Eu2(3, 5-DClBA)6-y]
  	Ⅳ	807~1 266	816	22.3	60.3d	(6-y) (3, 5-DClBA)	Eu2O3
  a Theoretical total weight loss of C2H5OH and H2O; b Theoretical total weight loss of two 5, 5′-DM-2, 2′-bipy; c Theoretical total weight loss of six 3, 4-DClBA; d Theoretical total weight loss of six 3, 5-DClBA; e Total weight loss.

  Compared to complexes 1 and 2, complexes 3 and 4 have higher thermal stability due to the absence of coordination water. According to Fig. 6b, the decomposition of complex 3 was observed over 492 K. In the first two consecutive steps, the total weight loss was 19.8%, which is attributed to the removal of neutral 5, 5′-DM-2, 2′-bipy (Calcd. 20.4%). This process occurred at 492~596 K. There was no weight loss at the second endothermic peak, and phase transition might occur. The weight loss of the last two steps was 60.2%, which is attributed to the abscission of six 3, 5-DClBA^- anions at 596~1223 K (Calcd. 60.4%). Finally, complex 3 completely collapsed into Sm₂O₃.

  2.5   TG-FTIR analysis

  In order to further study the pyrolysis mechanism of the whole complex, the 3D-FTIR spectrum of the gas escaping from the pyrolysis process was obtained by TG/FTIR system. The 3D plots and 2D IR spectra of complexes 2 and 3 are shown in Fig. 7 and 8, respectively. The 3D plots and 2D IR spectra of complexes 1 and 4 are shown in Fig. S3 and S4, respectively. We chose complexes 2 and 3 as the examples to explain in detail. In Fig. 7a, there are four peaks in the 3D diagram of complex 2, corresponding to four-step decomposition in TG curve. In the 2D IR spectra of 401 K, we can observe the weak absorption peaks of H₂O (3 560~3 797 cm^-1), and the characteristic peaks of ethanol, such as ν_C-O (1 065 cm^-1), ν_C-H (2 890~2 994 cm^-1), δ_C-H (1 393 cm^-1) ^[24]. The existence of these characteristic bands indicates that the coordination of ethanol and water molecules has been removed in this step. On the 2D IR spectra of 485 K, we could observe the weak characteristic peaks of CO₂ (2 294~2 395 cm^-1) and some characteristic peaks including ν_C=C, ν_C=N (1 600, 1 563, 1 469 cm^-1) and ν_C-N (1 218 cm^-1)^[25], which leads to the conclusion that neutral 5, 5′-DM-2, 2′-bipy ligands are removed in this step. On the 2D IR spectra of 788 K (Fig. 8a), the characteristic peaks of CO₂ (2 287~2 359 cm^-1 and 669 cm^-1) and H₂O (3 560~3 751 cm^-1) could be observed, and we could also find some absorption peaks such as ν_C=O (1 767 cm^-1) and ν_C=C (1 461 cm^-1) ^[26]. The carboxylic acid ligand began to lose in this step. In the IR spectra of the last step at 829 K, only the peaks of CO₂ (2 310~2 360 cm^-1), CO (2 114, 2 181 cm^-1) and H₂O (3 594~3 734 cm^-1) could be found, which indicates that carboxylic ligands have been completely decomposed.

  Figure 7

  

  Figure 7.  Three-dimensional IR plots during pyrolysis of 2 (a) and 3 (b)

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  Figure 8

  

  Figure 8.  Two-dimensional IR spectra of 2 (a) and 3 (b)

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  For complex 3, similar absorption peaks appeared in the IR spectra at 542 and 573 K. The absorption bands at 1 469, 1 557 and 1 600 cm^-1 belong to the ν_C=C and ν_C=N; the weak absorption peaks at 2 899~3 037 and 826 cm^-1 belong to the ν_C-H and γ_=C-H, indicating that neutral bipy ligands have been removed. At 803 K, the characteristic peaks of CO₂(2 310~2 360 and 669 cm^-1) and H₂O (3 562~3 738 cm^-1) could be observed^[27], while the absorption bands ν_C=O (1 770 cm^-1) and ν_C=C (1 572, 1 420 cm^-1) could also be found. The results show that the products of gas phase include the decomposed and undifferentiated 3, 5-DClBA ligands. In the final infrared spectrum of 824 K, only the bands of CO₂ (2 312~2 365 cm^-1) and H₂O (3 544~3 752 cm^-1) could be observed, indicating that the carboxyl ligand has been completely decomposed^[28].

  2.6   Luminescence properties

  The solid-state photoluminescent of complex 2 and complex 4 were investigated in detail at 298 K. The excitation (Inset) and emission spectra of 2 and 4 are presented in Fig. 9a and 10a, respectively. The excitation spectra of two complexes were recorded at the maximum emission wavelength of 615 nm. In the excitation spectra of the two complexes, the strong absorption band of 230~350 nm is caused by the ligand metal electron transfer band^[29]. The emission spectra of complexes 2 and 4 were recorded upon excitation at 329 and 325 nm, respectively. In the emission spectra of the two complexes, five characteristic peaks can be seen at 581, 594, 614, 652, 701 nm and 581, 592, 615, 651, 701 nm, respectively. These characteristic emission peaks are assigned to the ⁵D₀→⁷F_j (j=0~4) of Eu³⁺, severally^[30-31]. Among these peaks, the strongest peak was ⁵D₀→⁷F₂ at 615 nm, which produces red emission. Eu³⁺ ions occupy a non-symmetry site in two complexes, because the magnetic dipole transition ⁵D₀→⁷F₀ is totally prohibited in symmetry site^[32]. The photoluminescent intensity of 4 was stronger than that of 2, probably owing to that complex 2 contains a coordination water, which can easily cause fluorescence quenching.

  Figure 9

  

  Figure 9.  (a) Excitation (Inset) and emission spectra of 2 at 298 K; (b) Fluorescence decay curve of 2

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  Figure 10

  

  Figure 10.  (a) Excitation (Inset) and emission spectra of 4 at 298 K; (b) Fluorescence decay curve of 4

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  The fluorescence decay curves and fitting curves of two Eu³⁺ complexes were also given in Fig. 9b and 10b, respectively. The fluorescence lifetime values were calculated according to the following equation^[33]:

  $\left.\tau=\left(C_{1} \tau_{1}^{2}+C_{2} \tau_{2}^{2}\right)\right) /\left(C_{1} \tau_{1}+C_{2} \tau_{2}\right)\\ I(t)=C_{1} \exp \left(-t / \tau_{1}\right)+C_{2} \exp \left(-t / \tau_{2}\right) $

  where I(t) is the fluorescence intensity varying with time t; C₁ and C₂ are coefficient; τ₁ and τ₂ are the fall times. The fluorescence lifetime τ of 2 and 4 are 1.00 and 1.48 ms, respectively.

  3.   Conclusions

  Four novel lanthanide coordination complexes have been successfully synthesized under solvothermal or conventional solution method, namely [Ln₂(5, 5′-DM-2, 2′-bipy)2(3, 4 - DClBA)₆(H₂O)(C₂H₅OH)] (Ln=Sm (1), Eu(2)) and [Ln(5, 5′-DM-2, 2′-bipy)(3, 5-DClBA)₃]₂ (Ln=Sm (3), Eu (4)). Complexes 1 and 2 are isostructural and each metal center is eight-coordinated, while the coordination number of Sm³⁺ ion of 3 is nine. Complexes 1 and 2 are connected to form 2D supermolecular structure by C-H…Cl hydrogen bonding and π-π interactions, while complex 3 is connected to form 2D supermolecular framework by different π-π interactions. TG/FTIR analysis reveals the pyrolysis mechanism of complexes 1~4, and complexes 3 and 4 have good thermal stability. Complexes 2 and 4 can emit intense red light and have long fluorescence lifetimes.

  Acknowledgements

  The work is supported by the National Natural Science Foundation of China (Grant No.21803016).

  Supporting information is available at http://www.wjhxxb.cn

  
  
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  Figure 1  (a) Crystal structure of 1; (b) Coordination geometry of Eu³⁺ ion

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  Figure 2  (a) View of 1D chain of 2 along c axis; (b) 2D layered of 2 along b and c axes

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  Figure 3  (a) Crystal structure of 3; (b) Coordination geometry of Sm³⁺ ion

  Symmetry code: #1:-x+1, -y+2, -z

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  Figure 4  (a) View of 1D chain structure of 3 along a axis; (b) 2D layered of 3 along a and b axes

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  Figure 5  PXRD patterns of complexes 1~4 and simulated PXRD patterns of complexes 1 and 3

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  Figure 6  TG-DTG/DSC curves of complexes 2 (a) and 3 (b)

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  Figure 7  Three-dimensional IR plots during pyrolysis of 2 (a) and 3 (b)

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  Figure 8  Two-dimensional IR spectra of 2 (a) and 3 (b)

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  Figure 9  (a) Excitation (Inset) and emission spectra of 2 at 298 K; (b) Fluorescence decay curve of 2

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  Figure 10  (a) Excitation (Inset) and emission spectra of 4 at 298 K; (b) Fluorescence decay curve of 4

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  Table 1.  Crystal data and structure refinement for complexes 1~3

  Complex	1	2	3
  Empirical formula	C68H50Cl12N4O14Sm2	C68H50Cl12N4O14Eu2	C66H42Cl12N4O12Sm2
  Formula weight	1 873.22	1 876.44	1 809.14
  Crystal system	Triclinic	Triclinic	Triclinic
  Space group	P1	P1	P1
  a/nm	1.266 00(11)	1.260 68(12)	1.164 60(11)
  b/nm	1.392 01(12)	1.383 31(12)	1.214 30(12)
  c/nm	2.354 0(2)	2.340 4(2)	1.340 00(13)
  α/(°)	90.850 0(10)	90.707 0(10)	104.511(3)
  β/(°)	91.270 0(10)	91.398 0(10)	92.930 0(10)
  γ/(°)	113.210(3)	113.189(4)	98.252(2)
  Volume/nm3	3.810 5(6)	3.749 5(6)	1.808 0(3)
  Z	2	2	1
  Dc/(g·cm-3)	1.633	1.662	1.662
  Absorption coefficient/mm-1	2.009	2.149	2.112
  F(000)	1 852	1 856	890
  Crystal size/mm	0.25×0.13×0.11	0.17×0.12×0.10	0.16×0.12×0.10
  θ range for data collection/(°)	2.32~25.02	2.34~25.02	2.26~25.02
  Limiting indices	-14 ≤ h ≤ 14,	-14 ≤ h ≤ 13,	-13 ≤ h ≤ 13,
  	-16 ≤ k ≤ 15,	-16 ≤ k ≤ 13,	-14 ≤ k ≤ 12,
  	-28 ≤ l ≤ 23	-27 ≤ l ≤ 27	-15 ≤ l ≤ 15
  Reflection collected, unique Completeness to θ=25.02°/%	19 489, 13 257(Rint=0.038 9)	19 159, 13 034(Rint=0.037 5)	9 237, 6 291(Rint=0.028 8)
  	98.5	98.5	98.5
  Max. and min. transmission	0.809 2 and 0.633 5	0.813 8 and 0.711 5	0.816 6 and 0.728 7
  Data, restraint, parameter	13 257, 2, 906	13 034, 2, 906	6 291, 0, 435
  Goodness-of-fit on F2	1.021	1.033	1.018
  Final R indices [I > 2σ(I)]	R1=0.057 4, wR2=0.138 5	R1=0.048 7, wR2=0.091 5	R1=0.037 5, wR2=0.060 7
  R indices (all data)	R1=0.089 5, wR2=0.151 8	R1=0.089 0, wR2=0.101 3	R1=0.051 3, wR2=0.064 0
  Largest diff. peak and hole/(e·nm-3)	1 570 and -1 728	1 394 and -696	1 159 and -540

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  Table 2.  Pyrolysis data for complexes 1~4

  Complex	Step	Temperature range/K	Tp of DTG/K	Weight loss/%		Probable expelled groups	Intermediate and residue
  				Found	Calcd.
  1	Ⅰ	368~432	400	3.8	3.4a	C2H5OH+H2O	[Sm2(3, 4-DClBA)6(5, 5′-DM-2, 2′-bipy)2]
  	Ⅱ	432~658	474	19.4	19.7b	2(5, 5′-DM-2, 2′-dipy)	[Sm2(3, 4-DClBA)6]
  	Ⅲ	658~819	792	38.9		x(3, 4-DClBA)	[Sm2(3, 4-DClBA)6-x]
  	Ⅳ	819~1 266	836	19.2	58.3c	(6-x)(3, 4-DClBA)	Sm2O3
  				81.3	81.4e
  2	Ⅰ	374~423	401	3.4	3.4a	C2H5OH+H2O	[Eu2(3, 4-DClBA)6(5, 5′-DM-2, 2′-bipy)2]
  	Ⅱ	423~662	479	18.6	19.6b	2(5, 5′-DM-2, 2′-dipy)	[Eu2(3, 4-DClBA)6]
  	Ⅲ	662~803	782	32.5		x (3, 4-DClBA)	[Eu2(3, 4-DClBA)6-x]
  	Ⅳ	803~1 267	823	25.0	58.2c	(6-x)(3, 4-DClBA)	Eu2O3
  				79.5	81.2e
  3	Ⅰ	492~550	540	9.4		x (5, 5′-DM-2, 2′-dipy)	[Sm2(3, 5-DClBA)6(5, 5′-DM-2, 2′-bipy)2-x]
  	Ⅱ	550~596	566	10.4	20.4b	(2-x) (5, 5′-DM-2, 2′-bipy)	[Sm2(3, 5-DClBA)6]
  	Ⅲ	596~816	802	41.7		y (3, 5-DClBA)	[Sm2(3, 5-DClBA)6-y]
  	Ⅳ	816~1 223	827	18.5	60.4d	(6-y) (3, 5-DClBA)	Sm2O3
  				80	80.8e
  4	Ⅰ	490~546	541	8.2		x(5, 5′-DM-2, 2′-dipy)	[Eu2(3, 5-DClBA)6(5, 5′-DM-2, 2′-bipy)2-x]
  	Ⅱ	546~590	562	11.7	20.3b	(2-x) (5, 5′-DM-2, 2′-bipy)	[Eu2(3, 5-DClBA)6]
  	Ⅲ	590~807	798	37.1		y (3, 5-DClBA)	[Eu2(3, 5-DClBA)6-y]
  	Ⅳ	807~1 266	816	22.3	60.3d	(6-y) (3, 5-DClBA)	Eu2O3
  a Theoretical total weight loss of C2H5OH and H2O; b Theoretical total weight loss of two 5, 5′-DM-2, 2′-bipy; c Theoretical total weight loss of six 3, 4-DClBA; d Theoretical total weight loss of six 3, 5-DClBA; e Total weight loss.

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