Inorganica Chimica Acta 363 (2010) 669–675

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Inorganica Chimica Acta

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Synthesis and luminescent properties of the first series of lanthanidecomplexes based on sebacate and 2,5-pyridinedicarboxylate

Zhuo Wang a, Feng-Ying Bai a, Yong-Heng Xing a,*, Yan Xie a, Mao-Fa Ge b, Shu-Yun Niu a

a College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, PR Chinab Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 18 September 2009Received in revised form 11 November 2009Accepted 13 November 2009Available online 22 November 2009

Keywords:Lanthanide complexesLuminescent propertiesSebacate acid2,5-Pyridinedicarboxylic acidSynthesis

0020-1693/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.ica.2009.11.021

* Corresponding author.E-mail address: yhxing2000@yahoo.com (Y.-H. Xin

By using 2,5-pyridinedicarboxylate and sebacate as rigid and flexible mixed carboxylate linkers, five new3D lanthanide complexes, [Ln(seb)0.5(2,5-pydc)(H2O)] (Ln = Eu (1), Nd (2), Sm (3), Pr (4) and Tb (5),H2pydc = 2,5-pyridinedicarboxylic acid, H2seb = sebacate acid) with macroporous structures, have beensynthesized. Complexes 1–5 were characterized by elemental analysis, ICP spectrometer and IR spectros-copy. In particular, the structures of 1–3 were further determined by single-crystal X-ray diffraction.Structural analyses reveal that complexes 1–3 have intricate 3D frameworks, which are constructed by2,5-pyridinedicarboxylate and sebacate ligands. In addition, the thermogravimetric analysis of 1–3 andphotoluminescent properties of 1 and 5 are also discussed in detail.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

In recent years, more and more concern has been paid to themetal coordination polymers (CPs), which can be seen as an exten-sion of functional materials and also have potential applicationsparticular as liquid crystalline materials, optical fiber lasers andamplifiers, luminescent label design for specific bimolecular inter-actions, magnetic molecular materials and electroluminescentmaterials [1–9]. Although the potential applications of CPs areinspiring, contribution to the fundamental understanding of theformation of these materials, as well as an expansion of the CPscontaining both rigid and flexible carboxylate are needed [10].

CPs consist of a metal center or multi-nuclear cluster bonded tomultifunctional organic linkers, which in turn assembled into largemicro-porous to produce considerable properties. CPs take advan-tages of both the diversity and functionalities of the coordinationsphere of the metal atoms and the steric of organic polycarboxylatespecies. As for the metal atoms, rare earth ions have high affinityfor hard donor atoms, eg. ligands containing oxygen or hybrid oxy-gen–nitrogen atoms, especially multi-carboxylate ligands are usu-ally employed in the architectures for lanthanide coordinationpolymers [11]. While for the rigid acids, such as aromatic acids[12], pyridinecarboxylic acids [13–15] and so on, have been inves-tigated widely. In particular, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-pyr-

ll rights reserved.

g).

idinedicarboxylic isomers, which contain a pyridine ring and twocarboxylate groups, can form various coordinated geometries[16], among them, 2,5-pydc is more easily coordinated to metalatoms to form an infinite structure, because two carboxyl groupswith a 180� angle may be helpful to reduce the space hindranceand form rigid frameworks with macro porous structure.

Recently, there has been much research on the coordinationchemistry of 2,5-pyridinedicarboxylic acid, including (i) complexesof lanthanide [15,17–19]; (ii) mixed ligand complexes of lantha-nide pydc and another ligand such as benzoic acid or nicotinic acid[15,17,18,20–21]; (iii) complexes with lanthanides and a secondmetal such as copper or zinc [22–23]. However, they are all com-plexes containing just one type of ligand (rigid). In order to furtherextend structures of the new complexes and investigate coordina-tion modes of mixed carboxylate group (rigid and flexible), ourgroup have been dedicated ourselves on synthesizing complexeswith both rigid and flexible as mixed ligands, and part works havebeen reported: eg. (I) [Ln2 (Suc)0.5(BC)3(H2O)2] (Ln = Tb, Eu, Sm, Pr;H2Suc = succinic acid; HBC = benzoic acid) [24]; (II) [Ln (Suc)0.5(p-BDC)] (Ln = Eu, Sm, Nd, Pr; H2Suc = succinic acid; p-H2BDC = 1,4-benzenedicarboxylic acid) [25]. [Ln(ad)0.5(2,5-pydc)(H2O)] (Ln =Eu, Pr, Nd, Sm, Tb; H2ad = adipic acid; 2,5-H2pydc = 2,5-pyridinedi-carboxylic acid) [26]. In addition, it is found that short-spanningaliphatic acids used as flexible ligands are well developed, suchas: succinic acid, glutaric acid, adipic acid, etc., however, lantha-nide or transition complexes containing long-spanning aliphaticacid as ligands are rare, especially coordination polymers withsebacate acid as a kind of flexible acids are less developed. To the

670 Z. Wang et al. / Inorganica Chimica Acta 363 (2010) 669–675

best of our knowledge, only few papers about sebacate complexeshave been reported: [Cu2(phen)2L4/2](H2O)6, [(phen)2Cu(l-L)-Cu(phen)2](HL)2(H2L)(H2O)4 (H2L = sebacate acid) [27], UO2(L)[28], (UO2)2(L)2(C10H8N2) [29], [(UO2)2(CB6)3(H2O)6][(UO2)2(NO3)4-(L)]2�CB6�8H2O (CB6 = cucurbit[n]urils, n = 6) [30], [Ni(phen)3](L)(-H2L)0.5�11H2O[31], [Zn2(atz)2(L)](atz = 3-amino-1H-1,2,4-triazole)[32], and [Nd(L)(C10H17O4)(H2O)] [33], etc. Compared with short-spanning aliphatic acid, it is found that synthesis of complexeswith sebacate as ligand is difficult and less developed. So our grouphas been attempted to explore lanthanide complexes containinglonger aliphatic dicarboxylate linkers, both with the aim of under-standing the crystal chemical systematic of this family of com-pounds and also as a precursor study of lanthanide coordinationpolymers with long-spanning flexible acid. Herein, we choosesebacate acid as the flexible ligand, 2,5-pyridinedicarboxylic acidas a rigid ligand, and the first series of Ln–pydc–seb coordinationpolymers, [Ln(seb)0.5(2,5-pydc)(H2O)] (Ln = Eu (1), Nd (2), Sm (3),Pr(4) and Tb(5)) are reported. Among them, 1–3 are crystals suit-able for single-crystal X-ray diffraction; however, 4 and 5 are ob-tained in the form of the microcrystals. Except the spectra andthe crystal structures; the thermal stability and luminescent prop-erties have also been investigated.

2. Experimental section

2.1. Materials and methods

All chemicals purchased were of reagent grade or better andwere used without further purification. Lanthanide chloride saltswere prepared by dissolving lanthanide oxides with 12 M HClwhile adding a bit of H2O2 for Tb4O7, and then evaporating at100 �C until the crystal film formed; lanthanide nitrate salts wereprepared the same procedure as the chloride salts. The infraredspectra were recorded on a JASCO FT/IR-480 PLUS Fourier Trans-form spectrometer with pressed KBr pellets in the range 200–4000 cm�1. The luminescence spectra were reported on a JASCOFP-6500 spectrofluorimeter (solid). The elemental analyses werecarried out on a Perkin–Elmer 240C automatic analyzer. Contentof lanthanide was analyzed on a Plasma-Spec(I)-AES model ICPspectrometer. Thermogravimetric analyses (TGA) were performedunder N2 atmosphere at 1 atm with a heating rate of 10 �C/minon a Perkin Elmer Diamond TG/DTA. X-ray powder diffraction(XRD) data were collected on a Bruker Advance-D8 with Cu Karadiation, in the range 5� < 2h < 60�, with a step size of 0.02� (2h)and an acquisition time of 2 s per step.

2.2. Synthesis of complexes

2.2.1. Synthesis of [Eu(seb)0.5(2,5-pydc)(H2O)] (1)The complex was prepared by hydrothermal reaction. Eu-

Cl3�6H2O (0.12 g, 0.33 mmol), 2,5-pyridinedicarboxylic acid(H2pydc, 0.10 g, 0.06 mmol), sebacate (0.10 g, 0.05 mmol), andH2O (12 mL) were mixed in 25 mL beaker. The pH value was ad-justed to 5 with triethylamine. After stirring for 2 h, the mixturewas sealed in the bomb and heated at 180 �C for three days, thencooled at 10 �C/3 h to 100 �C, followed by slowly cooling to roomtemperature. After filtration, the product was washed with dis-tilled water and then dried at room temperature. White crystalssuitable for X-ray diffraction analysis were obtained in ca. 54.32%yield based on Eu(III). Elemental analysis results Anal. Calc. forC12H13NO7Eu (Mr = 435.19): C, 33.12; H, 2.99; N, 3.22; Eu, 34.92.Found: C, 33.47; H: 2.96; N, 3.18; Eu, 34.35%. IR data (KBr pellet,m[cm�1]): 3631, 3432, 2924, 2852, 1579, 1396, 1280, 1239, 1178,770, 648, 577, 515.

2.2.2. Synthesis of [Nd(seb)0.5(2,5-pydc)(H2O)] (2)An identical procedure with 1 was followed to prepare 2 except

EuCl3�6H2O was replaced by NdCl3�6H2O. Lilac single crystals wereobtained for 2 (56.53%) Elemental analysis results Anal. Calc. forC12H13NO7Nd (Mr = 427.47): C, 33.72; H, 3.04; N, 3.27; Nd, 33.74.Found: C, 33.21; H, 2.84; N, 2.98; Nd, 34.28%. IR data (KBr pellet,m[cm�1]): 3633, 3417, 2925, 2853, 1580, 1395, 1280, 1239, 1178,770, 648, 583, 514.

2.2.3. Synthesis of [Sm(seb)0.5(2,5-pydc)(H2O)] (3)An identical procedure with 1 was followed to prepare 3 except

EuCl3�6H2O was replaced by SmCl3�6H2O. Yellow single crystalswere obtained for 3 (49.87%) Elemental analysis results Anal. Calc.for C12H13NO7Sm (Mr = 433.58): C, 33.72; H, 3.04; N, 3.23; Sm,34.68. Found: C, 33.21; H, 2.84; N, 2.97; Sm, 34.02%. IR data (KBrpellet, m[cm�1]): 3631, 3432, 2925, 2852, 1579, 1396, 1280, 1239,1178, 770, 648, 577, 515.

2.2.4. Synthesis of [Pr(seb)0.5(2,5-pydc)(H2O)] (4)An identical procedure with 1 was followed to prepare 4 except

EuCl3�6H2O was replaced by PrCl3�6H2O. Green single crystals wereobtained for 4 (50.22%) Elemental analysis results Anal. Calc. forC12H13NO7Pr (Mr = 424.14): C, 33.98; H, 3.09; N, 3.30; Pr, 33.22.Found: C, 33.44; H, 3.01; N, 3.38; Pr, 33.15%. IR data (KBr pellet,m[cm�1]): 3632, 3423, 2918, 2851, 1579, 1396, 1281, 1240, 1189,770, 648, 577, 516.

2.2.5. Synthesis of [Tb(seb)0.5(2,5-pydc)(H2O)] (5)An identical procedure with 1 was followed to prepare 5 except

EuCl3�6H2O was replaced by TbCl3�6H2O. White single crystalswere obtained for 5 (51.13%) Elemental analysis results Anal. Calc.for C12H13NO7Tb (Mr = 444.16): C, 32.60; H, 2.96; N, 3.15; Tb, 35.78.Found: C, 31.86; H, 3.11; N, 3.01; Tb, 35.11%. IR data (KBr pellet,m[cm�1]): 3593, 3414, 2929, 2857, 1587, 1401, 1282, 1238, 1183,766, 650, 581, 523.

2.3. X-ray crystallographic determination

Suitable single crystals of three complexes were mounted onglass fibers for X-ray measurement. Reflection data were collectedat room temperature on a Bruker AXS SMART APEX II CCD diffrac-tometer with graphite monochromatized Mo Ka radiation(k = 0.71073 Å). All absorption corrections were performed usingSADABS program [34]. Crystal structures were solved by the directmethod. All non-hydrogen atoms were refined anisotropically. Allhydrogen atoms were fixed at calculated positions with isotropicthermal parameters. All calculations were performed using SHELX-97 program [35]. Crystal data and details of the data collectionand the structure refinement are given in Table 1. The selectedbond lengths and bond angles of complexes 1–3 are listed in Table2. Structure of complex 1 contains disordered sebacate groups thatwas ultimately deemed the result of nonmeroheral twinning. Thecenter of the sebacate ligand has four positions (C9 and C9#1,C10 and C10#1) where the atom is likely to be found. Each of thedisorder sites has a 50% probability of being occupied, which al-lows for a more reasonable C–C bond distance of 1.514 Å. Similartrends have been found in complexes 2 and 3, too.

2.4. Thermal analysis

Thermogravimetric analyses (TGA) experiments were carriedout on a Perkin Elmer Diamond TG/DTA instrument. The samplesare initially heated for 1 h at 50 �C to remove the rudimental air.During the simple ramping experiment, weight changes were re-corded as a function of temperature for a 10 �C min�1 temperaturegradient between 50 and 800 �C in nitrogen environments.

Table 2Selected bond distances (Å) and angles (�) for complexes 1–3a.

Complex 1Eu1–O3 2.327(3) Eu1–O7 2.413(3) Eu1–O6 2.418(3)Eu1–O2 2.424(3) Eu1–O4 2.427(3) Eu1–O1 2.458(3)Eu1–O5 2.531(4) Eu1–N1 2.647(3) Eu1–O3#1 2.652(3)O3–Eu1–O7 144.58(10) O3–Eu1–O1 123.70(10) O7–Eu1–O6 137.22(9)O3–Eu1–O2 77.12(10) O2–Eu1–O4 139.34(10) O6–Eu1–O2 134.46(9)O7–Eu1–O1 72.19(10) O1–Eu1–O5 134.39(12) O7–Eu1–N1 63.23(9)O2–Eu1–N1 134.41(10) O3–Eu1–N1 148.24(10) O1–Eu1–N1 71.07(10)

Complex 2Nd–O3 2.375(3) Nd–O7 2.449(3) Nd–O2 2.456(3)Nd–O4 2.466(3) Nd–O6 2.468(2) Nd–O1 2.512(3)Nd–O5 2.574(3) Nd–O3#1 2.657(3) Nd–N1 2.683(3)O3–Nd–O7 145.08(9) O3–Nd–O2 78.23(9) O7–Nd–O2 136.44(8)O3–Nd–O6 76.69(9) O7–Nd–O6 77.73(8) O2–Nd–O6 134.74(9)O3–Nd–O5 78.12(10) O3–Nd–O1 123.44(9) O1–Nd–O5 133.93(10)O2–Nd–N1 75.19(9) O4–Nd–N1 70.31(9) O6–Nd–N1 134.24(9)

Complex 3Sm1–O3 2.3395(19) Sm1–O7 2.4233(19) Sm1–O2 2.4292(18)Sm1–O6 2.4377(19) Sm1–O4 2.4416(19) Sm1–O1 2.473(2)Sm1–O5 2.552(2) Sm1–O3#1 2.646(2) Sm1–N1 2.660(2)O3–Sm1–O7 144.74(7) O3–Sm1–O2 78.13(7) O7–Sm1–O2 136.92(6)O6–Sm1–O4 139.49(7) O3–Sm1–O1 123.55(7) O7–Sm1–O1 72.22(7)O2–Sm1–N1 74.98(7) O6–Sm1–N1 134.32(7) O1–Sm1–O5 134.30(8)O1–Sm1–N1 71.07(7) O5–Sm1–N1 113.03(8) O4–Sm1–N1 70.38(7)

a Symmetry codes: #1�x+1, �y+2, �z for 1, #1�x, �y+1, �z for 2, #1�x+1, �y, �z+1 for 3.

Table 1Crystallographic data for complexes 1–3.

Complexes 1 2 3

Formula C12H13NO7Eu C12 H13NO7Nd C12H13NO7SmM (g mol�1) 435.19 427.47 433.58Crystal system monoclinic monoclinic monoclinicSpace group P21/c P21/c P21/ca (Å) 9.3805(7) 9.4528(9) 9.403(7)b (Å) 14.6598(10) 14.717(1) 14.683(1)c (Å) 9.6699(7) 9.7420(9) 9.6860(7)a (�) 90 90 90b (�) 92.665(1) 92.799(1) 92.670(1)c (�) 90 90 90V (Å3) 1328.3(2) 1353.6(2) 1335.8(2)Z 4 4 4Dcalc 2.176 2.098 2.156Crystal size (mm) 0.170 � 0.113 � 0.096 0.140 � 0.107 � 0.097 0.247 � 0.140 � 0.062F(0 0 0) 844 832 840l (Mo Ka) (mm�1) 4.756 3.869 4.430h (�) 2.53–28.90 2.16–25.00 2.52–25.00Reflections collected 8209 6666 6580Independent reflections(I > 2r(I)) 3254 2380 2340Parameters 211 203 203D (q) (e Å�3) 1.082 and �0.589 0.583 and �0.383 0.661 and �0.334Goodness of fit 1.011 1.034 1.074Ra 0.0269 (0.0369)b 0.0230 (0.0281)b 0.0164 (0.0177)b

wR2a 0.0600 (0.0653)b 0.0527 (0.0546)b 0.0424 (0.0431)b

a R = R||Fo| � |Fc||/R|Fo|, wR2 = {R[w(F2o � F2

c )2]/R[w(F2o )2]}1/2; [Fo > 4r(Fo)].

b Based on all data.

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3. Results and discussion

3.1. Synthesis

Hydrothermal reaction of sebacate acid, EuCl3�6H2O, 2,5-pyri-dinedicarboxylate acid in an aqueous solution at 180 �C for 3 daysproduced white block crystals. In the reaction, it is found that thestarting materials and the template reagents adjusting the pH valueaffect the reaction results to some extent, and using organic alkalias template reagents is more favor to produce the title compoundsin the reaction system than inorganic alkali (Scheme 1).

Additionally, the compositions of 1–5 were confirmed by ele-mentary analysis, IR spectra, ICP spectrometer and the phase puri-ties of the bulk samples were identified by X-ray powderdiffraction. (Fig. S1).

3.2. Structural description of complexes 1–3

Single-crystal X-ray structure analyses revealed that the frame-works of 1–3 are isomorphous. Therefore, complex 1 is taken as anexample to present and discuss the structure in detail. (The struc-tures of complexes 2 and 3 are shown in Figs. S2–S7).

Scheme 1. The effects of different starting materials and templates.

Fig. 1. The coordination environment of Eu in complex 1 (symmetry codes: #1:1 � x, 2 � y, �z).

672 Z. Wang et al. / Inorganica Chimica Acta 363 (2010) 669–675

Complex 1 has a three-dimensional framework, crystallizing inmonoclinic space group P21/c. The asymmetric unit of 1 containsone nine-coordinated europium atom, half a seb2� ligand, a 2,5-pydc2� ligand and a coordinated water molecule. The coordinationmode of the europium atom (Eu) is shown in Fig. 1. The eight oxy-gen atoms coordinated with Eu are from one chelating bidentatecarboxyl group (O1 and O3#1, (#1:1 � x, 2 � y, �z)) and one dimo-nodentate carboxyl group (O3) from seb2– anions, and four dimo-nodentate carboxyl groups (O2, O4, O6, and O7) from 2,5-pydc2�

ligands. The Eu-Oseb (from sebacate acid) and Eu-Opydc (from 2,5-pyridinedicarboxylic acid) bond lengths are in the range of2.327(3)–2.652(3) Å and 2.413(3)–2.427(3) Å, respectively. All ofthem are similar to those found in the related europium–oxygendonor complexes [24–26]. Each 2,5-pydc2� ligand acts as a l4-

Scheme 2. Coordination modes of the 2,5-pydc2� (a) and Seb2� anionic ligands (b).

bridge to link four EuIII ions as shown in Scheme 2a, in which thenitrogen and one oxygen atom of the 2-carboxylate chelated onemetal atom, the other one ligates another metal atom in monoden-tate mode; and 5-carboxyl group ligates two metal atoms in dimo-nodentate fashion. Both carboxylate groups of each seb2� ligandexhibit only one kind of coordination mode: l2-g1-g2-bridging(namely one oxygen atom of the carboxylate group connects onemetal ion, the other one connects two metal ions and the carbox-ylate group coordinates to two metal ions) (Scheme 2b).

It is necessary to explore the connection fashions of the metalcenters and organic ligands for understanding the structure ofthe framework. In the framework, the nearest two lanthanide me-tal center atoms are linked by two oxygen atoms from the carbox-ylate groups of the two seb ligands to form a binuclear unit. Andthese binuclear units are further linked via 2-carboxylateroups of2,5-pydc ligands to form a chain structure in the [1 0 0] direction(Fig. 2a). These chains are further connected by the nitrogen atomsand the oxygen atoms of 5-carboxylate groups from 2,5-pyridine-dicarboxylic acids to form a 2D Ln–pydc planar structure with par-allel helical chains along [0 1 0] direction (Fig. 2b). Along [1 0 0]direction the 2D structure are further connected by 2,5-pydc li-gands to form a 3D structure (Fig. 2c), moreover sebacate ligandsinserted in the structure to amplify the construction of the 3D

Fig. 2. (a) 1D Ln–pydc double chain structure; (b) 2D Ln–pydc layer structure; (c) 3D Ln–pydc network.

Z. Wang et al. / Inorganica Chimica Acta 363 (2010) 669–675 673

structure (Fig. 3). So the structural forming of the complex could besummarized as from 1D Ln-carboxylate (from pydc) chain motif(Fig. 2a), to 2D Ln–pydc layer motif (Fig. 2b), and then to 3D Ln–

Fig. 3. The 3D framework of complex 1.

pydc framework (Fig. 2c), and finally to the 3D Ln–pydc–sebacateframework (Fig. 3) structure.

3.3. Photoluminescent properties

The solid-state luminescent properties of complexes 1 and 5were investigated at room temperature. When excited at 396 nmfor 1 and 352 nm for 5, they emit red (1) and green luminescence(5) at room temperature, respectively (Fig. 4). The emission peaksof the complexes correspond to the transitions from 5D0 ?

7Fn

[n = 1 (591 nm), 2 (611 nm), 3 (650 nm) and 4 (700 nm)] for theEu (III) ion in 1; while the four peaks at 490, 543, 585, and619 nm are assigned to 5D4 ?

7Fn (n = 6, 5, 4 and 3) transitionsfor Tb (III) ion in 5. Among these emission peaks, the most strikingred luminescence 5D0 ?

7F2 for complex 1 and green emission5D4 ?

7F5 for complex 5 were observed in their emission spectra.

3.4. Thermal properties

To examine the thermal stability of the polymer, thermal gravi-metric analysis (TGA) was performed on crystalline samples of thecompound in the range of 50–1000 �C. As shown in Fig. 5, thermaldecomposition process of complex 1 can be divided into twostages. The first weight loss occurs in the temperature range of125–219 �C and corresponds to the release of the one-coordinatedwater molecule. The weight loss for the one-coordinated watermolecule is 4.68% (calc 4.14%). In the temperature range of 219–694 �C, a 42.55% weight loss is observed, which may correspondto the release of 0.5 sebacate ligand and two CO2 molecules (calc43.23%). The remaining product (52.77%) is due to the oxidationcompound of Eu with the residue of part carbon (calc 52.83%).Complexes 2 and 3 show similar courses of thermal decompositionto complex 1. (Shown in Figs. S8 and S9.)

Fig. 4. Room-temperature solid-state photoluminescence spectra of 1 and 5.

Fig. 5. The TG diagrams of complex 1

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4. Conclusions

In summary, five new 3D isostructural complexes[Ln(seb)0.5(2,5-pydc)(H2O)] (Ln = Eu (1), Nd (2), Sm (3), Pr (4), Tb(5)) have been synthesized under hydrothermal conditions. It isthe first series of lanthanide complexes with sebacate acid and2,5-pydc as mixed ligands. In the reaction process, it is found thatthe template and the starting material are important factors for thesuccessful introduction of flexible dicarboxylate ligands on basis oflanthanide complexes with rigid dicarboxylate ligands. X-ray dif-fraction analyses reveal that they exhibit the same three-dimen-sional (3D) architecture. Furthermore by comparison of theluminescence property of lanthanide complexes with 2,5-pydcand adipic acid, ([Ln(ad)0.5(2,5-pydc)(H2O)] (Ln = Eu, Pr, Nd, Sm,Tb) [26], it is found that the flexible acids have impact on it obvi-ously. The thermal stability of complexes 1–3 have been investi-gated and it reveals that the thermal stability behaviors of themare analogical.

Acknowledgments

This work was supported by the grant of the National NaturalScience Foundation of China (Grant No. 20771051), and the Educa-tion Foundation of Liaoning Province in China (Grant No.2007T093) for financial assistance.

Appendix A. Supplementary material

CCDC 735967, 735968 and 735969 contain the supplementarycrystallographic data for compounds (1), (2) and (3) respectively.These data can be obtained free of charge from The CambridgeCrystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-quest/cif. Supplementary data associated with this article can befound, in the online version, at doi:10.1016/j.ica.2009.11.021.

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