A Series of Three-Dimensional Lanthanide-Rigid-Flexible Frameworks

A Series of Three-Dimensional Lanthanide-Rigid-Flexible Frameworks: Synthesis, Structure, and Luminescent Properties of Coordination Polymers with 2,5-Pyridine Dicarboxylic Acid and Adipic Acid

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 3 1525–1530

Chun-Guang Wang,† Yong-Heng Xing,*,† Zhang-Peng Li,† Jing Li,† Xiao-Qing Zeng,‡ Mao-Fa Ge,‡ and Shu-Yun Niu† College of Chemistry and Chemical Engineering, Liaoning Normal UniVersity, Dalian 116029, P. R. China, and Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China ReceiVed October 16, 2008; ReVised Manuscript ReceiVed December 28, 2008

ABSTRACT: A new series of lanthanide coordination polymers, namely, [Ln(ad)0.5(2,5-pydc)(H2O)] (Ln ) Eu (1), Pr (2), Nd (3), Sm (4), Tb(5); H2ad ) adipic acid; 2,5-H2pydc ) 2,5-pyridine dicarboxylic acid), have been synthesized hydrothermally from the self-assembly of the lanthanide ions (Ln3+) with the flexible adipic dicarboxylate ligand and the rigid 2,5-pyridine dicarboxylic acid ligand. All of them were characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Structural analyses reveal that all five complexes have intricate three-dimensional net-structures, and in these complexes, they were crystallized in monoclinic space group P21/c. In addition, the phase purities of the bulk samples were identified by X-ray powder diffraction. The thermogravimetric analysis of 1 and photoluminescent properties of 1 and 5 are discussed in detail. Introduction In recent years, the design and synthesis of novel lanthanideorganic frameworks have developed into a significant area of research. Their intriguing frameworks and potential applications in luminescence, sensors, liquid crystalline materials, optical fiber lasers and amplifiers, luminescent label design for specific biomolecule interactions, magnetic molecular materials, and electroluminescent materials have received increasing attention.1 Many different kinds of multicarboxylate ligands have been widely used in this aspect. Thereinto, the long-carbon-chain is characteristic of flexible multicarboxylate ligands, which may bend and rotate to coordinate to metal centers, such as succinic acid, glutaric acid, adipic acid, etc. Using lanthanide ions and flexible multicarboxylate ligands usually results in robust microporous coordination polymers. By far, only a few kinds of coordination polymers of Ln-ad (H2ad ) adipic acid) have been synthesized, such as [Ln2(ad)3(H2O)2] · xH2O (Ln ) La3+, Pr3+; x ) 0.1);2a [Ln2(ad)3(H2O)4] · xH2O (Ln ) La3+, Ce3+, Pr3+, Nd3+, Sm3+, Gd3+, Er3+, Yb3+; x ) 4, 6);2b [Ln2(ad)3(H2O)2] · (4,4′bipy) (Ln ) Pr, Eu, Tb); 2a,c-e Er(H2O)2(ip)(ad)0.5 (H2ip ) m-phthalic acid).2f On the other hand, the rigid multicarboxylatecontaining ligands with aromatic rings have been used to control and adjust open and stable frameworks. At present, pyridine dicarboxylic acid (H2pydc) seems to be a potential rigid ligand in some complexes reported. O- and N-donors of H2pydc allow it to result in many different kinds of interesting 3D structures of transition metal and lanthanide complexes.3 Compared with other pyridine dicarboxylic acids, 2,5-H2pydc seems to easily coordinate to metal to form an infinite structure, because two carboxyl groups with a 180° angle may lead to a more stable framework. In the reported lanthanide complexes with 2,5H2pydc ligand, there are mainly three types, as follows: (i) Ln-pydc;4a-d (ii) Ln-pydc-L (L ) benzoic acid, phen, nicotinic acid, Ac-, 1,4-phenylenediacetic acid);4a-c,e,f (iii) Ln-pydc-M (M ) Zn).4g It is mostly three-dimensional (3D) * Corresponding author: E-mail: [email protected]. † Liaoning Normal University. ‡ Institute of Chemistry, Chinese Academy of Sciences.

open frameworks for them except that type (ii) (when L ) phen) and (iii) are one-dimensional (1D) chains and two-dimensional (2D) layers structures, respectively. These complexes are all synthesized under hydrothermal conditions at different temperatures (130, 140, 160 °C). It is to be noted that nicotinic acid (in type (ii)) is not present in the starting reaction mixture, which may be derived from 2,5-H2pydc via in situ decarboxylation under hydrothermal conditions (180 °C).4c By contrast with a large number of lanthanide complexes containing only rigid or flexible multicarboxylate ligands, studies on designing and investigating the influence of the mixed multicarboxylate ligands (rigid and flexible) to the structure and character of the coordination polymers are still rare. Our group has been applying ourselves to synthesize a series of lanthanide coordination polymers with two types of carboxylates: (I) [Ln2 (Suc)0.5(BC)3(H2O)2] (Ln ) Tb, Eu, Sm, Pr; H2Suc ) succinic acid; HBC ) benzoic acid);5 (II) [Ln (Suc)0.5(p-BDC)] (Ln ) Eu, Sm, Nd, Pr; H2Suc ) succinic acid; p-H2BDC ) 1,4benzene dicarboxylic acid).6 In order to further understand the influence of the flexible multicarboxylate ligands with different carbon chains and the rigid ones with diverse coordination modes, adipic acid (with longer carbon chain) and 2,5-H2pydc (with N donor) were chosen as mixed multicarboxylate ligands, and a new series of Ln-pydc-ad coordination polymers, [Ln(ad)0.5(2,5-pydc)(H2O)] (Ln ) Eu (1), Pr (2), Nd (3), Sm (4), Tb(5)), is reported in this paper. The thermal stability and luminescent properties have also been investigated. Experimental Section All chemicals purchased were of reagent grade or better and were used without further purification. Lanthanide chloride salts were prepared via dissolving lanthanide oxides with 12 M HCl while adding a bit of H2O2 for Tb4O7 and then evaporating at 100 °C until the crystal film formed. C and H analyses were made on a Perkin-Elmer 240C automatic analyzer at the analysis center of Liaoning Normal University. Infrared (IR) spectra were recorded on JASCO FT/IR-480 PLUS Fourier transform spectrophotometer with pressed KBr pellets in the range 200-4000 cm-1. The luminescence spectra were reported on a JASCO FP-6500 spectrofluorimeter (solid) in the range of 200-850 nm.

10.1021/cg801157k CCC: $40.75  2009 American Chemical Society Published on Web 01/30/2009

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Table 1. Crystallographic Data for Complexes 1-5 formula

C10H9NO7Eu

M (g mol-1) 407.14 crystal system monoclinic space group P21/c a (Å) 9.1370(2) b (Å) 15.484(3) c (Å) 8.8238(2) R (deg) 90 β (deg) 98.68(3) γ (deg) 90 V (Å3) 1234.1(4) Z 4 Dcalc 2.191 crystal size (mm) 0.311 × 0.221 × 0.133 F(000) 780 µ (Mo KR) /mm-1 5.111 θ (deg) 3.27-27.47 reflections collected 11882 independent reflections (I > 2σ(I)) 2817 parameters 172 ∆(F) (e Å-3) 1.230 and -1.136 goodness of fit 1.079 0.0352 Ra (0.0497)b 0.0638 wR2a (0.0683)b a

C10H9NO7Pr

C10H9NO7Nd

C10H9NO7Sm

C10H9NO7Tb

396.09 monoclinic P21/c 9.2092(2) 15.768(3) 8.8739(2) 90 98.31(3) 90 1275.1(4) 4 2.063 0.324 × 0.236 × 0.142 764 3.848 3.25-27.48 12361 2917 172 1.131 and -0.548 1.131 0.0161 (0.0179)b 0.0377 (0.0383)b




R ) Σ|Fo| - |Fc||/Σ|Fo|, wR2 ) [Σ(w(Fo2 - Fc2)2/[Σ(w(Fo2)2]1/2; [Fo > 4σ(Fo)]. b Based on all data.

Thermogravimetric anaylses (TGA) were performed under N2 atmosphere at 1 atm with a heating rate of 10 °C/min on a Perkin-Elmer Diamond TG/DTA. Content of lanthanide was analyzed on a PlasmaSpec (I)-AES model ICP spectrometer. X-ray powder diffraction (XRD) data were collected on a Bruker Advance-D8 with Cu KR radiation, in the range 5° < 2θ < 60°, with a step size of 0.02° (2θ) and an acquisition time of 2 s per step. Synthesis of [Eu(ad)0.5(2,5-pydc)(H2O)] (1). The complex was prepared by hydrothermal reaction. EuCl3 · 6H2O (0.20 g, 0.56 mmol), 2,5-pyridinedicarboxylic acid (H2pydc, 0.10 g, 0.60 mmol), adipic acid (0.05 g, 0.34 mmol), and H2O (10 mL) were mixed in a 25 mL beaker. The pH value was adjusted to 6 with ethylenediamine. After being stirred for 2 h, the mixture was sealed in the bomb and heated at 160 °C for 3 days, then cooled at 10 °C/3 h to 100 °C, followed by slow cooling to room temperature. After filtration, the product was washed with distilled water and then dried at room temperature. White crystals suitable for X-ray diffraction analysis were obtained in ca. 54.32% yield based on Eu (III). Elemental analysis results for C10H9NO7Eu (Mr ) 407.14), calcd: C, 29.50; H, 2.23; N, 3.44; Eu, 37.33. Found: C, 29.47; H: 2.26; N, 3.40; Eu, 37.35. IR data (KBr pellet, ν[cm-1]): 3318(νsOH), 3074(νs(C-H)aromatic), 2988(νs(C-H)CH2), 1590(νsCdO), 1389(νasCdO), 1134(δ(CHaromatic)in-plane), 821 and 767(δ(CHaromatic)out-of-plane). Synthesis of [Pr(ad)0.5(2,5-pydc)(H2O)] (2). Complex 2 was synthesized by a method similar to that of complex 1 except that EuCl3 · 6H2O was replaced by PrCl3 · 6H2O. Light green crystals were obtained in a 56.57% yield based on Pr (III). Elemental analysis results for C10H9NO7Pr (Mr ) 396.09), calcd: C, 30.32; H, 2.29; N, 3.54; Pr, 35.58. Found: C, 30.35; H: 2.27; N, 3.52; Pr, 35.56. IR data (KBr pellet, ν[cm-1]): 3328(νsOH), 3072(νs(C-H)aromatic), 2983(νs(C-H)CH2), 1587(νsCdO), 1395(νasCdO), 1135(δ(CHaromatic)in-plane), 820 and 767(δ(CHaromatic)out-of-plane). Synthesis of [Nd(ad)0.5(2,5-pydc)(H2O)] (3). Complex 3 was synthesized by a method similar to that of complex 1 except that EuCl3 · 6H2O was replaced by NdCl3 · 6H2O. Light purple crystals were obtained in a 52.15% yield based on Nd (III). Elemental analysis results for C10H9NO7Nd (Mr ) 399.42), calcd: C, 30.07; H, 2.27; N, 3.51; Nd, 36.11. Found: C, 30.05; H: 2.28; N, 3.48; Nd, 36.14. IR data (KBr pellet, ν[cm-1]): 3326(νsOH), 3073(νs(C-H)aromatic), 2984(νs(C-H)CH2), 1587(νsCdO), 1395(νasCdO), 1135(δ(CHaromatic)in-plane), 820 and 767(δ(CHaromatic)out-of-plane). Synthesis of [Sm(ad)0.5(2,5-pydc)(H2O)] (4). Complex 4 was synthesized by a method similar to that of complex 1 except that EuCl3 · 6H2O was replaced by SmCl3 · 6H2O. Light yellow crystals were obtained in a 54.26% yield based on Sm (III). Elemental analysis results for C10H9NO7Sm (Mr ) 405.53), calcd: C, 29.62; H, 2.24; N, 3.45; Sm, 37.08. Found: C, 29.64; H: 2.21; N, 3.42; Sm, 37.11. IR data (KBr pellet, ν[cm-1]): 3332(νsOH), 3074(νs(C-H)aromatic), 2987(νs(C-H)CH2),

1589(νsCdO), 1389(νasCdO), 1134(δ(CHaromatic)in-plane), 821 and 767(δ(CHaromatic)out-of-plane). Synthesis of [Tb(ad)0.5(2,5-pydc)(H2O)] (5). Complex 5 was synthesized by a method similar to that of complex 1 except that EuCl3 · 6H2O was replaced by TbCl3 · 6H2O and the reaction was heated at 180 °C for 3 days. Light brown crystals were obtained in a 50.28% yield based on Tb (III). Elemental analysis results for C10H9NO7Tb (Mr ) 414.10), calcd: C, 29.01; H, 2.19; N, 3.38; Tb, 38.38. Found: C, 29.04; H: 2.17; N, 3.35; Tb, 38.36. IR data (KBr pellet, ν[cm-1]): 3423(νsOH), 3082(νs(C-H)aromatic), 2926(νs(C-H)CH2), 1587(νsCdO), 1400(νasCdO), 1147(δ(CHaromatic)in-plane), 827 and 770(δ(CHaromatic)out-of-plane). Crystal Structure Determinations. Suitable single crystals of five complexes were mounted on glass fibers for X-ray measurement. Reflection data were collected at room temperature on a Rigaku R-AXIS RAPID IP diffractometer with graphite monochromatized Mo KR radiation (λ ) 0.71073 Å). All absorption corrections were performed using the SADABS program.7a Crystal structures were solved by the direct method. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were fixed at calculated positions with isotropic thermal patameters. All calculations were performed using the SHELX97 program.7b Crystal data and details of the data collection and the structure refinement are given in Table 1. Selected bond lengths of complexes 1-5 are listed in Table 2.

Results and Discussion Syntheses. To our knowledge, although there are various lanthanide coordination polymers with binary mixed dicarboxylate ligands reported, those with rigid and flexible dicarboxylate as mixed ligands are still rare. In the reaction system, it is required to meet the coordinated conditions of aromatic (rigid) and aliphatic (flexible) dicarboxylate ligands at one time, and the physical and chemical properties of them are obviously different, so we have been trying our best to find the optimal conditions to make them coordinate together to Ln3+. By a hydrothermal method, we have obtained complexes 1-4 at 160 °C and 5 at 180 °C under a similar reaction system. Originally, we tried to synthesize these complexes without adjusting the pH value, but only Ln-2,5-pydc complexes were obtained. So it is crucial to find the suitable reaction conditions to make the adipic acid ligand coordinate to Ln3+. After referring to the synthesis method of Ln-ad complexes reported previously, it is found that the pH values of reaction mixture are all adjusted

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Crystal Growth & Design, Vol. 9, No. 3, 2009 1527

Table 2. Selected Bond Lengths (Å) for Complexes 1-5a Complex 1 Eu-O4A Eu-O1 Eu-O5

2.375(4) 2.429(4) 2.526(4)

Eu-O3 Eu-O7 Eu-O4

Pr-O3 Pr-O6 Pr-O4

2.4429(18) 2.4866(16) 2.5809(19)

Pr-O5A Pr-O7 Pr-O5

Nd-O5A Nd-O6 Nd-O4

2.4278(16) 2.4702(15) 2.5680(18)

Nd-O3 Nd-O7 Nd-O5

Sm-O5A Sm-O1 Sm-O4

2.396(3) 2.445(3) 2.549(3)

Sm-O3 Sm-O7 Sm-O5

Tb-O4 Tb-O3 Tb-O2

2.303(4) 2.395(4) 2.466(5)

Tb-O6 Tb-O5 Tb-O4A

2.395(4) 2.448(4) 2.589(4)

Eu-O6 Eu-O2 Eu-N1

2.423(4) 2.453(4) 2.711(4)

Pr-O1 Pr-O2 Pr-N1

2.4805(17) 2.5128(17) 2.744(2)

Nd-O1 Nd-O2 Nd-N1

2.4661(16) 2.4969(16) 2.733(2)

Sm-O6 Sm-O2 Sm-N1

2.441(3) 2.469(3) 2.723(4)

Tb-O1 Tb-O7 Tb-N1

2.390(4) 2.432(4) 2.570(5)

Complex 2 2.4442(16) 2.5011(17) 2.6228(18)

Complex 3 2.4288(17) 2.4858(16) 2.6081(17)

Complex 4 2.410(3) 2.464(3) 2.5983

Complex 5 2.365(4) 2.417(5) 2.719(5)

a Symmetry transformations used to generate equivalent atoms: A: -x + 1, -y, -z + 1 for 1; A: -x + 2, -y, -z for 2 and 4; A: -x + 1, -y, -z for 3; A: -x + 1, -y, -z + 2 for 5.

Figure 2. XRD powder patterns: (a) the simulated XPRD pattern calculated from single-crystal structure of complex 1; (b) experimental XPRD for complex 1; (c) experimental XPRD for complex 2; (d) experimental XPRD for complex 3; (e) experimental XPRD for complex 4; (f) experimental XPRD for complex 5.

Figure 3. Coordination environment of Eu in complex 1 with nonhydrogen atoms drawn by diamond. Symmetry codes: A: -x + 1, -y, -z + 1. Figure 1. XRD powder patterns of samples, for which the pH value are adjusted by different reagents: (a) KOH; (b) NaOH; (c) ethylenediamine.

to 6 by sodium silicate or ammonium hydroxide.2a-e Hence, we tried to adopt different reagents to adjust the pH to 6, such as ethylenediamine, potassium hydroxide, and sodium hydroxide, etc. However, good crystals of 1-5 are obtained only by using ethylenediamine, which is also an organic structuredirecting agent in the synthesis reaction. As shown in Figure 1, comparing the powder X-ray diffraction data of samples, it is found that the differences in intensity in the region of 9-12° are due to the differences in quality of the crystals, which further indicates that it is the best choice to use ethylenediamine for making good crystals. It should be noteworthy that, for a series of [Ln2(Suc)0.5(BC)3(H2O)2] complexes (Ln ) Tb, Eu, Sm, Pr; H2Suc ) succinic acid; HBC ) benzoic acid) reported, the researchers also adopted ethylenediamine to adjust the pH value to 6.5 On the basis of the results above, we think that adjusting the pH value to neutral by ethylenediamine is an important factor for the introduction of flexible dicarboxylate ligands into the system of rigid dicarboxylate ligands plus lanthanide ions.

Additionally, the compositions of 1-5 were confirmed by elementary analysis, IR spectra, and the phase purities of the bulk samples were identified by X-ray powder diffraction (Figure 2). Single-Crystal X-ray Structures of 1-5. Single-crystal X-ray structure analyses revealed that the frameworks of 1-5 are isostructural. Therefore, complex 1 is taken as an example to present and discuss the structure in detail. Complex 1 has a three-dimensional framework, crystallizing in monoclinic space group P21/c. The asymmetric unit of 1 contains one nine-coordinated europium ion, half an ad2- ligand, a 2,5-pydc2- ligand, and a coordinated water molecule. The coordination mode of the europium ions (Eu) is shown in Figure 3. The eight oxygen atoms coordinated with Eu are from one chelating bidentate carboxyl group (O4 and O5) and one dimonodentate carboxyl group (O4A) from ad2- anions, and four dimonodentate carboxyl groups (O1, O3, O6, and O7) from 2,5-pydc2- ligands. The Eu-Oad (from adipic acid) and Eu-Opydc (from 2,5-pyridinedicarboxylic acid) bond lengths are in the range of 2.375(4)-2.589(4) and 2.395(4)-2.448(4) Å, respectively. However, the Eu-N bond length is rather longer,


Wang et al.

Figure 4. Coordination modes of the (a) 2,5-pydc2- and (b) ad2- anionic ligands.

2.711(4) Å. Similar trends are observed for 2-4, except for 5. The O-Eu-O bond angles vary from 50.54(12) to 144.44(13)°. All of them are similar to those found in the related europium-oxygen donor complexes.8 Each 2,5-pydc2- ligand acts as a µ4-bridge to link four EuIII ions as shown in Figure 4a, in which the nitrogen and one of the 2-carboxylate oxygen atoms chelate one metal ion, another 2-carboxylate oxygen atom ligates a metal ion in monodentate fashion, and 5-carboxyl group ligates two metal ions in dimomodentate fashion. Both carboxylate groups of each ad2- ligand exhibit only one kind of coordination mode: µ2-η1-η2-bridging (namely, one oxygen atom of the carboxylate group connects one metal ion, the other one connects two metal ions and the carboxylate group coordinates to two metal ions) (Figure 4b). Lanthanide metal center atoms (Eu) and its corresponding centrosymmetric atoms are interconnected through 2,5-pydc2ligands and ad2- ligands to be assembled into a complicated three-dimensional (3D) structure. Here after, we describe it step by step. Two EuIII ions are linked through bridging tridentate carboxyl groups of ad2- ligands to generate a dinuclear unit, and these dinuclear units are further linked to a 1D infinite chain via the carbon chains of ad2- ligands along the [001] direction (Figure 5a). These chains appear inverted alternately along the [010] direction and they are linked through 2-carboxylate groups of 2,5-pydc2- ligands to form a sheet on the [011] plane (Figure 5b). Along the [100] direction, two dinuclear units of the adjacent two sheets are connected by 5-carboxylate groups of 2,5-pydc2- and pyridyl nitrogen atoms to generate the 3D framework (Figure 5c). To deeply understand the framework of 1, we find it has nanotubular structure, which is made up of one-dimensional channels (along [100] direction) with walls of EuIII ions and 2,5-pydc2- ligands being divided into two parts by the ad2- ligands (Figure 6). The structures of complexes 2-5 are similar to that of 1. Comparing the structures of complexes with the mixed multicarboxylate ligands (rigid and flexible) obtained in Table 3, it is found that the rigid and the flexible ligands have different effects on the conformation of the frameworks packing. The rigid decide the type of frameworks, because they can adopt different coordination modes to lead to a different arrangement of frameworks’ packing. For example, for a and b, with an

Figure 5. (a) Dinuclear chain linked through ad2- ligands; (b) the sheet formed by 2-carboxylate groups of 2,5-pydc2- bridging the dinuclear units chains; (c) the three-dimensional networks formed by 5-carboxylate groups of 2,5-pydc2- and pyridyl nitrogen atoms connecting the sheets.

increasing number of carboxylate groups, the dimension of the structures change from 2D to 3D. On the other hand, the flexible decide the type of the conformation units to make the whole framework more stable. Even as b and c, with an increasing number of -CH2- in the flexible, and a decreasing number of Ln3+ connected by the flexible, the conformation units formed by the flexible connecting Ln3+ change from 2D to 1D. In general, the rigid are primary for the conformation of the frameworks’ packing, and the flexible can adjust the size of the channel to further reinforce the frameworks. Thermal Properties. The isostructural frameworks lead to the similar thermal decomposition processes, so we took complex 1 as a representative example for thermogravimetric analysis. As shown in Figure S1, Supporting Information, the thermal decomposition process of complex 1 can be divided into three stages. The first weight loss corresponds to the release of the one coordinated water molecule and occurs in the temperature range of 120-168 °C. The weight loss for the one

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Crystal Growth & Design, Vol. 9, No. 3, 2009 1529

Figure 6. Perspective view of the three-dimensional framework with nanotubular structure of complex 1. Table 3. Comparison of the Structures of Complexes with the Mixed Multicarboxylate Ligands

Figure 7. Room-temperature solid-state photoluminescence spectra of complexes 1 (bottom) and 5 (top).

luminescence 5D0 f 7F2 for complex 1 and red emissions D4 f 7F5 for complex 5 were observed in their emission spectra. IR Spectrum. The IR spectral shape of complexes 1-5 are similar. The characteristic bands of carboxyl groups are shown in the range of 1540-1637 cm-1 for asymmetric stretching and 1365-1477 cm-1 for symmetric stretching. The bands in the region ca. 640-1306 cm-1 are attributed to the -CH- in-plane or out-of-plane bend, ring breathing, and ring deformation absorptions of pyridine ring, respectively. The bands of 2854 to 2988 cm-1 are characteristic of the νC-H vibration modes of -CH2- groups within the carbon chain of adipic acid. Weak absorptions observed at 3072-3074 cm-1 can be attributed to νC-H of the pyridyl. The broad bands at ca. 3325 cm-1 are attributed to the vibrations of coordination water. 5

coordinated water molecule is 5.02% (calcd 4.42%). In the temperature range of 374-472 °C, about a 13.21% weight loss is observed, which may correspond to the release of 0.5 adipic acid molecule (calcd 13.75%). In the third stage, it experiences a 21.00% weight loss in the range of 472-790 °C, which is attributed to the release of two CO2 molecules (calcd 21.61%). This suggests that the decarboxylate reaction of the 2,5-pydc2ligands takes place due to the comparatively weak bonding to Eu ions. Eu2O3C5N are assumed to be the final residual product (61.01% weight containing), supported by the expected value of 61.40%. Photoluminescent Properties. The solid-state luminescent properties of complexes 1 and 5 were investigated at room temperature. When excited at 395.5 nm for 1 and 312 nm for 5, they emit red light (1) and green luminescence (5) at room temperature (Figure 7). The emission peaks of the complexes correspond to the transitions from 5D0 f 7Fn (n ) 1, 2, 3, and 4) transitions at 594, 613, 652, and 698 nm for the Eu(III) ion in 1 and 5D4 f 7Fn (n ) 6, 5, 4, and 3) transitions at 489, 544, 583, and 621 nm for Tb(III) ion in 5. Among these emission lines, the most striking green

Conclusions Five new 3D isostructural complexes [Ln(ad)0.5(2,5-pydc)(H2O)] (Ln ) Eu (1), Pr (2), Nd (3), Sm (4), Tb(5)) have been synthesized under hydrothermal conditions. In the reaction process, it is found that adjusting the pH value to neutral by ethylenediamine is an important factor for the introduction of flexible dicarboxylate ligands on the basis of lanthanide complexes with rigid dicarboxylate ligands. For complexes 1-5, the 3D frameworks with nanotubular structure are composed of one-dimensional channels with walls of EuIII ions and 2,5pydc2- ligands which are divided into two parts by the ad2ligands. By comparing the structures of complexes with the mixed multicarboxylate ligands (rigid and flexible) obtained, it is found that the rigid and the flexible ligands have different effects on the conformation of the frameworks packing: the former are primary for the conformation of the frameworks


packing, and the later can adjust the size of the channel to further reinforce the frameworks. In addition, complexes 1 and 5 emit red and green luminescence at room temperature, respectively, and they could be anticipated as potential fluorescent materials. Acknowledgment. This work was supported by the grants of the National Natural Science Foundation of China (Grant Nos. 20771051 and 20633050), and the Education Foundation of Liaoning Province in China (Grant No. 2007T093) for financial assistance.

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(2)

(3)

Supporting Information Available: Figure showing TGA diagram of complex 1. This material is available free of charge via the Internet at http://pubs.acs.org. Tables of atomic coordinates, isotropic thermal parameters, and complete bond distances and angles have been deposited with the Cambridge Crystallographic Data Center. Copies of this information may be obtained free of charge, by quoting the publication citation and deposition numbers CCDC 691201 (1), 691202 (2), 691203 (3), 691204 (4), and 691205 (5), from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax+44-1223-336033; e-mail [email protected]; http://www.ccdc.cam.ac.uk).

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