Synthesis, structure and luminescence of a new series of rigid–flexible lanthanide coordination polymers constructed from benzene sulfonic acid and glutaric acid

Inorganica Chimica Acta 365 (2011) 269–276

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Synthesis, structure and luminescence of a new series of rigid–flexible lanthanide coordination polymers constructed from benzene sulfonic acid and glutaric acid Ke-Ling Hou a, Feng-Ying Bai a, Yong-Heng Xing a,⇑, Jian-Ling Wang a, Zhan Shi b a b

College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, PR China State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, PR China

a r t i c l e

i n f o

Article history: Received 15 July 2010 Received in revised form 13 September 2010 Accepted 20 September 2010 Available online 29 September 2010 Keywords: Lanthanide complexes Benzene sulfonic acid Glutaric acid Crystal structure Photoluminescent properties

a b s t r a c t A new series of rigid–flexible lanthanide coordination polymers, namely, [Eu(BSA)(glu)(H2O)2]H2O (Ln = Eu(1), Sm(2), Ce(3), Pr(4), Nd(5)); H2glu = glutaric acid, HBSA = benzene sulfonic acid), have been constructed by a solution synthesis method from the self-assembly of the lanthanide ions (Ln3+) with the flexible aliphatic dicarboxylate glutaric and the rigid aromatic benzene sulfonic acid. All of them were characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. X-ray single crystal analyses reveal that they crystallize in monoclinic, space group P21/n, possessing 2D net-structures. 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 2 were investigated in detailed. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Lanthanide metal organic frameworks are one of the topical and active areas of current research. A great deal endeavor has been made to design and construction of functional peculiarity lanthanide MOFs because they exhibit attractive and promising applications in the fields of catalysis, luminescence, magnetism, gas adsorption, sensors, and nonlinear optics (NLO), etc. [1–8]. Encouraged by such engaging application prospects, remarkable accomplishments for creation of desired networks and useful functionalizable MOFs materials have been achieved by pioneers [9–14]. Nevertheless, the design and preparation of coordination polymers with extended structural and specific properties are still one of the challenging tasks in materials chemistry. Generally, the key to the design of lanthanide MOFs holding desired network and outstanding features mainly depends on the judicious and rational choice of the bridging ligand because it greatly influences the molecular packing arrangement of the compound. In fact, rigid aromatic multicarboxylate building blocks with special configurations, such as: benzoic acid [15,16], 1,2-benzene dicarboxylic acid (o-H2BDC) [17], 1,3-benzene dicarboxylic acid (m-H2BDC) [18,19], 1,4-benzene dicarboxylic acid (p-H2BDC) [20,21], 1,2,4,5-benzene-

⇑ Corresponding author. E-mail address: [email protected] (Y.-H. Xing). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.09.034

tetracarboxylic acid (H4BTEC) [22,23], and benzene-1,3,5-tricarboxylic acid (H3BTC) [24] are all most widely used linkers in the construction of lanthanide MOFs with interesting structures and serviceable function. However, benzenesulfonate/its derivative ligands which contain the interesting functional sulfonic group, remain basically less explored in the construction of lanthanide polymers. Due to the inherent chemistry characteristic of benzenesulfonate/its derivatives, they present many virtues as follows: the sulfonic group –SO3 acting as a versatile coordination mode [25,26] can combine to metal ions in a richness of fashions (Scheme S1), resulting in unforeseen structure patterns and packing frameworks. Moreover, it is found that they have an effective biological activity and the complexes have high catalysis for the nitration of toluene, so they have been particularly successfully applied as catalyst for a large number of organic transformations, etc. [27]. Additional, with an eminent p-conjugate system, they behave as the efficient antenna linkers and can be in favor of enhancing the fluorescence emissions of complexes, which are presently of interesting research in the development of fluorescent materials. Nevertheless, to the best of our knowledge, only a few of lanthanide complexes regarding BSA or its derivative ligands have been reported. Such as: [Eu(p-Tos)(H2O)7][p-Tos]2(H2O)2 (p-Tos = toluene-4-sulfonate) [28]; [Ln(SSA)(H2O)2]nnH2O (SSA = 5-sulfosalicylic acid, Ln = Gd, Sm, Nd, Tb, Eu, Yb, and Dy) [25]; Ln(SSA)(H2O)2 (SSA = 5-sulfosalicylic acid, Ln = Ce, Pr, Nd, and Dy) [29]; [Ln2(ad)2.5(BSA)(H2O)2]n (Ln = Sm, Nd; H2ad = adipic acid; BAS =

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benzenesulfonate) [30]. From the above complexes, it is found that lanthanide complexes involving the mixed-ligand of BSA/its derivative ligands and the second liker are extremely rare. Thereupon, developing and expanding the family of lanthanide polymers involving BSA/its derivative with the second liker to extend the structures of the complexes are needed. As known, flexible linkers with –CH2– spacer are usually selected in the building of lanthanide polymers because they possess certain specific features: (a) the presence of two carboxylate groups are potentially capable of producing bidentate and monodentate coordination modes to metal ions. (b) They have a tendency to generate secondary building blocks in the formation of the architectures [31]. (c) They can bend and rotate freely when they coordinate to the metal centers, causing the structural peculiarity and producing useful properties. Considering of the virtues of both rigid and flexible linkers, it seems to be a more effective avenue that introduction of rigid BSA ligand in company with flexible dicarboxylate as mixed-ligand to coordinate with lanthanide ions at one time to construct lanthanide frameworks with interesting structure and functional peculiarity. Although a number of complexes with flexible linkers have been reported (e.g., succinic, glutaric, and adipic acid), complexes with glutaric acid are relatively fewer, especially with lanthanide metal. As far as we know, the related lanthanide complexes with glutarate can be divided into two types in general: (i) Ln–glutarate (or with oxalate ligand), such as: [Nd(H2O)2 (glu)3]4H2O [32]; [Tb4(H2O)2](C2O4)2(glu)4 [33]. These complexes only contain flexible ligand as lanthanide metal linkers. (ii) Ln–glu–aromatic/heterocyclic, such as: [Ln(2,2bipy)(glu)(NO3)] (Ln = Eu, Tb, Sm, and Pr) [34]; Ln(H2O)(ip)0.5(glu2) (Ln = Gd, Dy, and Y; H2ip = m-phthalic acid) [35]; [Ln(glu) (pic)(H2O)2] (Hpic = picolinic acid; Ln = Sm, Tb, and Eu) [36]; Ln(2,5-pydc)(Hglu)(H2O) (Ln = Nd, Pr; 2,5-pydc = 2,5-pyridine dicarboxylic acid) [37]. In these complexes, both rigid and flexible polycarboxylates as mixed linkers connected the lanthanide metals. In our previous work, our group has made great efforts to create several series of unique functional lanthanide organic frameworks with good luminescence properties controlled by rigid and the second linker flexible polycarboxylates and parts of our previous works have been reported [38–40]. Within the aim to have a deep insight of the systematic synthesis regular, further investigate the influence of rigid–flexible ligand on the architectures of lanthanide MOFs and the inherent correlation between the structures and luminescence properties, in our current experiment, flexible glutaric acid was introduced companied with rigid BSA as mixedlinker to develop a new family of lanthanide MOFs. As respected, a new series of rigid–flexible lanthanide complexes (1–5): [Eu(BSA) (glu)(H2O)2]H2O (Ln = Eu(1), Sm(2), Ce(3), Pr(4), and Nd(5)) formed by mixed-ligands of BSA and glutaric acid were synthesized by solution preparation method for the first time. Photoluminescent properties for complexes 1–2 and the thermal stabilities for 1 were examined by using thermogravimetric analysis and luminescent spectra, respectively.

2. Experimental 2.1. Materials and methods 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 and then evaporating at 100 °C until the crystal film formed. The infrared spectra were recorded on a JASCO FT/IR-480 PLUS Fourier Transform spectrometer with pressed KBr pellets in the range 200– 4000 cm1. The luminescence spectra were reported on a JASCO

FP-6500 spectrofluorimeter (solid). The elemental analyses were carried out on a Perkin Elmer 240C automatic analyzer. Thermogravimetric analyses (TGA) were performed under N2 atmosphere at 1 atm with a heating rate of 10 °C/min on a Perkin Elmer Diamond TG/DTA. X-ray powder diffraction (XRD) data were collected on a Bruker Advance-D8 with Cu Ka radiation, 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 the complexes [Eu(BSA)(glu)(H2O)2]H2O (1). EuCl36H2O (0.20 g, 0.55 mmol), benzene sulfonic acid (HBSA, 0.20 g, 1.26 mmol), glutaric acid (0.14 g, 1.06 mmol), were dissolved in 10 mL H2O. To this reaction mixture with stirring, an aqueous solution of potassium hydroxide (1 mol L1) was dropwise added adjusting pH value to 3–4, After stirring for 2 h, it was filtered and the filtrate was allowed to evaporate at room temperature. Colorless single crystals of 1 for X-ray diffraction analysis were obtained in ca. 77% yield based on Eu(III) after 2 weeks. Elemental Anal. Calc. for C11H17O10SEu (Mr = 493.27): C, 26.76; H, 3.45. Found: C, 26.68; H, 3.49%. IR data (KBr pellet, t[cm1]): 3423(s), 2979(w), 2932(w), 1548(s), 1433(s), 1351(m), 1205(s), 1132(s), 1048(m), 1020(m), 996(w), 759(m), 731(m), 697(m), 603(s), 552(m), 533(m), 477(m), 382(m), 329(w). [Sm(BSA)(glu)(H2O)2]H2O (2). The complex was synthesized by a procedure similar to that used for 1 but changing the EuCl36H2O to SmCl36H2O (0.20 g, 0.55 mmol), primrose yellow crystals of 2 were obtained in ca. 75% yield based on Sm(III). Elemental Anal. Calc. for C11H17O10SSm (Mr = 491.66): C, 26.85; H, 3.46. Found: C, 26.90; H, 3.43%. IR data (KBr pellet, t[cm1]): 3407(s), 2979(w), 2929(w), 1546(s), 1432(s), 1304(m), 1202(s), 1132(s), 1047(m), 1019(m), 995(w), 759(m), 732(m), 697(m), 602(s), 551(m), 536(m), 477(m), 382(m), 330(w). [Ce(glu)(BSA)(H2O)2]H2O (3). The complex was synthesized by a procedure similar to that used for 1 but changing the EuCl36H2O to Ce(NO3)36H2O (0.20 g, 0.46 mmol), colorless crystals of 3 were obtained in ca. 77% yield based on Ce(III). Elemental Anal. Calc. for C11H17O10SCe (Mr = 481.43): C, 27.42; H, 3.53. Found: C, 26.36; H, 3.57%. IR data (KBr pellet, m[cm1]): 3434(s), 2978(w), 2930(w), 1540(s), 1425(s), 1350(m), 1203(s), 1131(s), 1045(m), 1019(m), 995(w), 756(m), 729(m), 696(m), 602(s), 550(m), 527(m), 469(m), 384(m), 327(w). [Pr(BSA)(glu) (H2O)2]H2O (4). The complex was synthesized by a procedure similar to that used for 1 but changing the EuCl36H2O to PrCl36H2O (0.2 g, 0.55 mmol), light green crystals of 4 were obtained in ca. 73% yield based on Pr(III). Elemental Anal. Calc. for C11H17O10SPr (Mr = 482.22): C, 27.37; H, 3.53. Found: C, 27.43; H, 3.49%. IR data (KBr pellet, t[cm1]): 3431(s), 2978(w), 2932(w), 1543(s), 1428(s), 1301(m), 1202(s), 1132(s), 1046(m), 1019(m), 995(w), 757(m), 733(m), 696(m), 602(s), 550(m), 531(m), 475(m), 383(m), 328(w). [Nd(BSA)(glu)(H2O)2]H2O (5). The complex was synthesized by a procedure similar to that used for 1 but changing the EuCl36H2O to NdCl36H2O (0.20 g, 0.56 mmol), light purple crystals of 5 were obtained in ca. 78% yield based on Nd(III). Elemental Anal. Calc. for C11H17O10SNd (Mr = 485.55): C, 27.19; H, 3.50. Found: C, 27.26; H, 3.47%. IR data (KBr pellet, t[cm1]): 3419(s), 2977(w), 2929(w), 1544(s), 1430(s), 1350(m), 1202(s), 1132(s), 1047(m), 1019(m), 995(w), 758(m), 732(m), 697(m), 602(s), 551(m), 531(m), 475(m), 381(m), 328(w). 2.3. Single crystal structural determinations Suitable single crystals of two 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

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with graphite monochromatized Mo Ka radiation (k = 0.71073 Å). All absorption corrections were performed using the SADABS program [41]. Crystal structures were solved by the direct method. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms of organic multi-polycarboxylate ligands were fixed at calculated positions with isotropic thermal parameters, while the coordinated water molecules and lattice water molecules were located by difference Fourier map. All calculations were performed using the SHELX-97 program [42]. Crystal data and details of the data collection and the structure refinement of complexes 1–5 are given in Table 1. The selected bond lengths and bond angles of complexes 1 are listed in Table 2 and that of 2–5 are shown in the supplement materials (Tables S2–S5). 3. Results and discussion 3.1. Synthesis By the solution preparation method, a new series of Ln–BSA–glu coordination polymers were successfully generated for the first time. In the reaction system, it is especially crucial to meet the

coordinated conditions of both aromatic (rigid) and aliphatic (flexible) muticarboxylate ligands because the physical and chemical properties of them are apparently different. Herein we have done our endeavor to search for the optimistic reaction conditions in which the two distinct ligands are able to combine together to lanthanide ion at the same time. We have tried to prepare the Ln– BSA–glu system compounds adopting the 1 M L1 potassium hydroxide liquid as template to adjust the pH value to weak acid (3–4). And the finally reaction solution was placed at room temperature after 2 weeks, the expected Ln–BSA–glu crystals with well formed and desired yield were obtained. In the process of synthesis, it is found that the yield and crystal qualities of the complexes were also satisfied when the starting material of lanthanide chloride salts were changed into lanthanide nitrate salts. In order to have a deep insight of the influences of different experimental conditions on the synthesis of lanthanide–BSA–flexible system complexes with both rigid and flexible carboxylate ligands, a comparison of the reaction processes about the title complexes and the complexes [30] of the previous work of our group was given in Scheme 1, which indicates that the different reaction conditions lead to different reaction results.

Table 1 Crystallographic data for complexes 1–5.

a b

Formula

C11H17O10SEu

C11H17O10SSm

C11H17O10SCe

C11H17O10SPr

C11H17O10SNd

M (g mol1) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc Crystal size (mm) F(0 0 0) l (Mo Ka) (mm1) h (°) Reflections collected Independent reflections Parameters D(q) (e Å3) Goodness of fit Ra wR2a

493.27 monoclinic P21/n 9.227(2) 9.410(3) 18.402(5) 90 100.620(3) 90 1570.4(7) 4 2.086 0.19  0.14  0.10 968 4.176 2.25–24.99 7645 2755 232 0.417, 1.258 1.077 0.0241 (0.0320)b 0.0596 (0.0630)b

491.66 monoclinic P21/n 9.220(3) 9.425(4 18.441(7) 90 100.636(5) 90 1575.0(10) 4 2.073 0.63  0.38  0.07 964 3.910 2.25–25.00 6549 2601 209 0.837, 1.898 1.054 0.0375 (0.0458)b 0.0926 (0.0976)b

481.43 monoclinic P21/n 9.2677(19) 9.2623(19) 19.023(4) 90 102.12(3) 90 1596.5(6) 4 2.003 0.17  0.16  0.09 948 3.030 3.10–27.48 15 228 3629 227 0.734, 0.597 1.036 0.0195 (0.0238)b 0.0422 (0.0436)b

482.22 monoclinic P21/n 9.256(6) 9.424(6) 18.703(11) 90 101.339(7) 90 1599.5(17) 4 2.003 0.28  0.24  0.06 952 3.225 2.30–25.00 5730 2604 212 3.587, 5.084 1.219 0.0951 (0.1022)b 0.2628 (0.2824)b

485.55 monoclinic P21/n 9.2407(18) 9.4216(19) 18.566(4) 90 100.97(3) 90 1586.9(5) 4 2.032 0.96  0.69  0.52 956 3.452 3.11–27.48 14 596 3607 232 0.428, 0.885 1.095 0.0206 (0.0258)b 0.0412 (0.0427)b

R ¼ RjjF o j  jF c jj=RjF o j; wR2 ¼ ½RðwðF 2o  F 2c Þ2 =½RðwðF 2o Þ2 Þ1=2 ; ½F o > 4rðF o Þ. Based on all data.

Table 2 Selected bond distances (Å) and angles (deg) of complex 1.* Bond distances Eu–O1 Eu–O7#1 Eu–O3#2 Bond angles O7#1–u–O6 O5#2–Eu–O1 O5#2–Eu–O2W O7#1–Eu–O4 O1–Eu–O4 O1–Eu–O3#2 O7#1–Eu–O1W O1–Eu–O1W O3#2–Eu–O1W O6–Eu–O5 O4–Eu–O5 *

2.447(3) 2.331(3) 2.491(3) 91.94(9) 74.41(10) 143.09(11) 81.89(9) 79.22(10) 137.12(10) 71.35(10) 70.37(10) 124.88(10) 141.16(9) 49.63(8)

Eu–O5#2 Eu–O2W Eu–O1W O5#2–Eu–O6 O6–Eu–O1 O6–Eu–O2W O5#2–Eu–O4 O2W–Eu–O4 O2W–Eu–O3#2 O5#2–Eu–O1W O2W–Eu–O1W O7#1–Eu–O5 O1–Eu–O5 O3#2–Eu–O5

2.365(3) 2.473(3) 2.532(3) 91.73(9) 135.10(9) 75.20(9) 115.44(9) 67.79(10) 70.98(10) 76.29(10) 124.86(10) 125.37(9) 71.60(9) 70.79(9)

Symmetry transformations used to generate equivalent atoms: #1: x, y + 2, z + 1; #2: x, y + 1, z + 1.

Eu–O6 Eu–O4 Eu–O5 O7#1–Eu–O1 O7#1–Eu–O2W O1–Eu–O2W O6–Eu–O4 O6–Eu–O3#2 O4–Eu–O3#2 O6–Eu–O1W O4–Eu–O1W O5#2–Eu–O5 O2W–Eu–O5 O1W–Eu–O5

2.444(2) 2.488(3) 2.695(3) 76.56(9) 73.81(11) 138.02(10) 142.76(9) 72.13(9) 91.61(10) 64.85(10) 143.14(10) 66.24(10) 102.89(9) 132.10(9)

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Additionally, the compositions of 1–5 were confirmed by elementary analysis, IR spectra, and powder X-ray diffraction (PXRD) was used to confirm the phase purity of the bulk samples. As shown in Fig. S1, all the peaks presented in the measured patterns closely match in the simulated patterns generated from single crystal diffraction data. 3.2. Structural description of complexes 1–5 X-ray diffraction determination results reveal that coordination polymers 1–5 are isomorphous, hereby complex 1 is taken as the example to present and describe the structure in detail.

Scheme 1. The comparison of the reaction conditions of the title complexes and that of the complexes reported.

X-ray single crystal analysis indicates that complex [Eu(BSA) (glu)(H2O)2]H2O has a 2D framework, crystallizing in monoclinic, space group P21/n. The asymmetric unit of 1 contains one ninecoordinated europium ion, one benzenesulfonate, one glutarate, two coordinated water molecules and one lattice water molecule. The coordination environment of the europium ion (Eu) is depicted in Fig. 1a. The nine oxygen atoms coordinate to Eu(III) ion to form a slightly distorted tricapped trigonal prism EuO9 polyhedron configuration (Fig. 1b), in which two oxygen atoms are from two different BSA ligands (O1, O3#2), five are from four different glutarate acid ligands (O4, O5, O5#2, O6, and O7#1) and two are from two water molecules(O1W, O2W). The Eu–Osulfonic (from BSA ligand) distance range from 2.447(3) to 2.491(3) Å and Eu–Oglu (from glutaric acid) bond lengths are in range of 2.331(3)–2.695(3) Å, while 2.473(3) and 2.532(3) Å for Eu–Owater, distance, all of which are close to those observed in the related europium–oxygen donor complexes [28,43,44]. The coordination mode of glutarate in the complex is shown in Fig. 4. It acts as a l4-bridging linker with one carboxylate group in a l2–g1–g2 mode and the opposite in a l2–g1–g1-monodentate fashion. Sulfonic group in BSA ligand coordinates to two Eu ions generating a l2–g1–g1 coordination fashion (Fig. 4). (The coordination environments of complexes 2– 5 are shown in Figs. S2–S5).

Fig. 1. (a) The ORTEP view of the coordination environment of Eu in complex 1; (b) the polyhedron structure of the EuO9 unit of complex 1. The lattice water molecule has been omitted for clarity (Symmetry codes: #1: x, y + 2, z + 1; #2: x, y + 1, z + 1).

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With an aim to have a thorough understanding of the structure framework and the molecular conformation, it would be essential to investigate the connection ways of the metal centers and carboxylate ligands. In complex 1, as depicted in Fig 2a, the adjacent two lanthanide metal Eu ions are connected by two sulfonic groups from BSA ligands to bring on a dinuclear unit with eight number ring, in which the EuEu contact is 4.243(1) Å. The dinuclear units are further linked to a 1D wavelike polymeric chain (Fig 2b) viewed along [0 1 0] direction via the bidentate bridging carboxylate groups of glutarate ligands, in which the contact of EuEu connected by glutarate ligands is 5.169(1) Å. The 1D polymeric chains were bridged alternatively by the flexible glutarate ligands, consequently, producing a 2D Ln–BSA–glu network packed parallel to the bc plane (Fig. 2c). The 2D packing architecture is shown in Fig. 3. In addition, numerous O–HO hydrogen bonding interactions involving the coordinated water molecules/sulfonic groups from benzenesulfonate of one layer and the coordinated water molecules/sulfonic groups of the adjacent layer via the bridging lattice water moleculars (O3W) are established. Consequently, these hydrogen bond interactions combine to form a tightly 3D hydrogen bonding network (Fig. S6). Another type of O–HO hydrogen bonds occur between the coordinated water molecules (O2W) and the other coordinated molecular (O1W)/the coordinated oxygen of carboxylate groups from glutarate in one molecular, strengthening the structure through intramolecular hydrogen bonding. Besides the strong O–HO hydrogen bonds, weak C–HO hydrogen bonds exist between the coordinated carboxylate groups and the carbon atoms on the benzenesulfonate/glutarate. This hydrogen bonding interaction further enhances the stability of the crystal structure. The interatomic distances and angles regarding hydrogen bonding are listed in Table S5. In order to understand the structural features of lanthanide–rigid–flexible polymers and the influences of both rigid and flexible

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multicarboxylate acids on the molecular packing configuration of complexes, Fig. 4 gives a comparison of the related lanthanide complexes containing BSA as rigid ligand (1, 6 [30]) or glutaric acid as flexible ligand (1, 7 [37]). X-ray diffraction studies indicate that complexes 6 and 7 are 3D frameworks, while complex 1 exhibits a 2D network. As for complexes 1 and 6, they contain the same rigid BSA ligand, but they show different packing arrangements, which are mainly attributed to the different coordination modes of the flexible dicarboxylate ligands. Herein it seems that the coordination modes of the flexible carboxylate ligands are one of the main factors influencing the structural conformation of complexes when the coordination fashions of rigid ligand are the same. On the other hand, complexes 1 and 7 hold the same flexible ligand, the dimensionality are also different because the variety coordination modes of the flexible ligand and the difference of the rigid ligand. Therefore, in the process of the formation of these complexes, it can be concluded that the dimension of the packing framework is controlled by the two types ligands together. In addition, the variety of coordination modes of flexible glutaric acid ligand also plays the important role in the construction of complexes, and they were summarized and presented in Scheme S2. Among the diverse and various coordination modes, the fashion of k is adopted in the title complexes. 3.3. Thermal properties To examine the thermal stability of the polymer, thermal gravimetric analysis (TGA) was performed on crystalline samples of the compounds in the temperature range of 25–1000 °C. The TGA for complex 1 was determined at a heating rate of 10 °C/min under N2 atmosphere. From the TG–DTA curves (Fig. S7), thermal decomposition process of complex 1 can be divided into two stages. The initial weight loss of 10.96% in the temperature range of 44–176 °C

Fig. 2. (a) A view of a dinuclear unit with eight number ring linked via BSA ligand of complex 1; (b) A 1D wavelike polymeric chain viewed along [0 1 0] direction generated through the bidentate bridging carboxyl groups of glutarate ligands connecting the dinuclear units; (c) The 2D Ln–BSA–glu layer structure in the bc plane formed by glutarate ligands connecting 1D chain.

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176–823 °C, which is ascribed to the release of one glutarate ligand and one SO3 molecule (42.57%, theoretical weight loss). Eventually, it remains a mixture of Ln2O3 and residue of carbon. 3.4. Photoluminescent properties

Fig. 3. The packing structure giving an overall 2D structural architecture of complex 1.

is due to the release of one lattice water molecule and two coordinated water molecules (10.95%, theoretical weight loss). The second weight loss of 42.64% occurs in the temperature range of

The fluorescence on lanthanide inorganic–organic compounds is currently a significant attention in the development of fluorescent materials. Hereupon it is necessary to have a systematic investigation of the photoluminescence with regard to the lanthanide coordination polymers. In the series of Ln–BSA–glu system, BSA ligand is served as a relatively strong absorbing antenna linker due to its eminent p-conjugate system, and herewith the energy transfer from the linker excited state to the relevant metal energy level can be readily accessible. Here, we mainly have an attentive study of polymer 1 and 2 because the compounds involving Eu(III) or Sm(III) have excellent luminescent characteristic .The luminescent properties regarding polymer 1 was studied at the excitation wavelength of 396 nm with a slit width (3:1), giving a bright red sensitized luminescence characteristic of Eu ions. The emission spectrum and the excitation spectrum of polymer 1 are shown in Fig. 5a and b, respectively. The characteristic 5D0 ? 7FJ (J = 1, 2, and 4) transitions of the Eu(III) ions in the region of 591, 616 and 697 nm show well efficient ligand-to-Eu energy transfer. The quite small emission band 5D0 ? 7F0 in the region of 579 nm is attributed to the symmetry-forbidden emission of the Eu(III) ions in the polymer. A broad and especially weak emission band appearing at 650–655 nm corresponds to the transition of 5D0 ? 7F3. The

Fig. 4. The comparison of coordination modes and conformation of three types of structure systems constructed from rigid and flexible polycarboxylate ligands

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Fig. 5. Photoluminescence emission spectrum (a) and the excitation spectrum (b) for complex 1 in the solid state at room temperature.

Fig. 6. Photoluminescence emission spectrum (a) and the excitation spectrum (b) for complex 2 in the solid state at room temperature.

5 D0 ? 7F1 emission band pertains to the prominent magnetic dipole transitions, which are almost uninfluenced by the coordination environment. On the other hand, the outstanding 5D0 ? 7F2 emission bands, possessing strong electric dipole character, are hypersensitive to the coordination environment. Herein luminescence concerning europium polymer can act as a sensitive probe of the lanthanide coordination environment [45,46]. Particularly, the ratio of the intensities of the (5D0 ? 7F2): (5D0 ? 7F1) transition is very sensitive to the symmetry of the Eu(III) centers. The site symmetry of the Eu(III) ions decreases along with the intensity of the (5D0 ? 7F2): (5D0 ? 7F1) transition increasing. From the emission spectrum, it can be obviously seen that the intensity of the electric dipole transitions 5D0 ? 7F2 are much stronger than that of the magnetic dipole transition 5D0 ? 7F1, suggesting that the Eu(III) ions in polymer 1 have a low symmetric coordination environments. This can be confirmed by the result of the single crystal X-ray analysis. The emission spectrum involving polymer 2 was determined on excitation at 402 nm with a slit width (3:3), which was depicted in Fig. 6a and b gave the excitation spectrum of complex 2. As expected, the three emission bonds in the region of 561–564, 596– 603, and 641–650 nm are corresponding to the characteristic emissions of Sm emissive state 4G5/2 to the 4H5/2, 4H7/2, and 4H9/2 levels, respectively. It should be mentioned that a wide emission band appearing at 429–500 nm is assigned to the transition of intraligand of antenna linker benzenesulfonate, implying that the energy

is not fully transferred from the linker BSA to Sm ions. This is different from the luminescent spectrum of the europium polymers in which the characteristic emission bond of linker BSA is not observed, indicating that the more efficient ligand-to-metal energy transfer occur in europium polymers of complex 1. On a careful insight of the related references, it is generally regarded that when the triplet-state energy of ligand is a little greater than the energy gap (DE) between the excited state and ground state of the lanthanide metal ion, efficient luminescence could be accessible [47–49]. Among the emission peaks of complex 2, 4G5/2 ? 4H7/2 transition is most striking, creating the intense pink luminescence.

3.5. IR spectra The IR spectra of complexes 1–5 were examined (Fig. S8). It can be seen clearly that the IR spectral shape of these five complexes are similar. The strong and broad absorption bands appearing in the region of 3474–3346 cm1 indicate the presence of water molecules. The characteristic bands of carboxylate groups are shown in the range of 1580–1516 cm1 for asymmetric stretching vibrations and 1445–1409 cm1 for symmetric stretching vibrations. The features at the region of 995–1205 cm1 and 602–533 cm1 correspond to the strong absorption of sulfonic group –SO3. The bands of 2927–2979 cm1 are characteristics of the mC–H vibration modes of –CH2– groups of the flexible glutarate in the complexes. These

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data were reasonably consistent with the crystallographic analysis results. 4. Conclusion A new series Ln–BSA–glu coordination polymers including 2D frameworks based on the flexible glutaric acid and the rigid BSA ligands, were synthesized and characterized for the first time. In the construction of the networks of lanthanide complexes, flexible linker glutaric acid with –CH2– spacer, is of great interest because it can bend and rotate freely when it coordinate to the metal centers, causing the structural peculiarity and producing useful properties. On the other hand, the rigid BSA ligand with aromatic ring can well control and adjust opening frameworks. The successful preparation of the series of Ln–BSA–glu complexes provides a valuable route for the construction of other novel lanthanide Ln–BSA–flexible MOFs with structural peculiarity and functional characteristic. Further systematic investigations for the design and synthesis lanthanide metal organic frameworks with rigid BSA ligand and other flexible linkers with long spanning are underway in our laboratory. Acknowledgments This work was supported by the grants of the National Natural Science Foundation of China (Grant No. 20771051), the Education Foundation of Dalian city in China (Grant No. 2009J21DW004) for financial assistance and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, PR China (Grant No. 2010-15). Appendix A. Supplementary material CCDC 779948, 779949, 779950, 779951, and 779952 contain the supplementary crystallographic data for 1–5. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010.09.034. References [1] [2] [3] [4] [5] [6] [7] [8]

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