Syntheses, Structures, and Luminescence Properties of a Series of

Aug 7, 2009 - Compound 5a displays a 3D framework, which was constructed through the ... 6 and 6a originate from different amounts of Ba(OH)2 in the s...
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DOI: 10.1021/cg9000818

Syntheses, Structures, and Luminescence Properties of a Series of LnIII-BaII Heterometal-Organic Frameworks

2009, Vol. 9 3948–3957

Xiao-Qing Zhao, Ya Zuo, Dong-Liang Gao, Bin Zhao,* Wei Shi, and Peng Cheng Department of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China Received January 22, 2009; Revised Manuscript Received July 18, 2009

ABSTRACT: Ten novel LnIII-BaII heterometal-organic frameworks, {[Ln2Ba2(PDA)5(H2O)12] 3 mH2O}n (Ln=Pr (1, m=9); Sm (2, m = 6); PDA = pyridine-2,6-dicarboxylic anion), {[LnBa1.5(PDA)3(H2O)8] 3 2H2O}n (Ln = Eu (3); Gd (4); Tb (5)), {[Ln4Ba6(PDA)12(H2O)x] 3 mH2O}n (Ln = Dy (6, x = 27.5, m = 12); Lu (7, x = 27, m = 11.5)), {[Eu4Ba4(PDA)10(H2O)23] 3 16H2O}n (3a), {[TbBa3(PDA)4(NO3)(H2O)6] 3 2H2O}n (5a), and {[DyBa1.5(PDA)3(H2O)7] 3 2H2O}n (6a), have been successfully synthesized under hydrothermal conditions, and the various structures are constructed from 1D chain, 2D layer, to 3D framework. Compounds 1 and 2 exhibit 1D ribbonlike structures. Compounds 3-5 display 2D layers constructed by 1D BaII chains and [Ln(PDA)3] units. Compounds 6 and 7 exhibit complicated 2D structures different from those of 3-5. When the amount of Ba(OH)2 changes during the syntheses of 3, 5, and 6, three novel coordination polymers 3a, 5a, and 6a were obtained. Compound 3a consists of a 1D chain different from those in 1 and 2. Compound 5a displays a 3D framework, which was constructed through the 2D Ba layers and [Tb(PDA)3] linkers. Compound 6a is isostructural to those of 3-5, although synthetic conditions are different from each other. The significant differences in structure from 1 to 7, and from 3a to 6a, may result from the lanthanide contraction effect, whereas the structural divergences between 3 and 3a, 5 and 5a, and 6 and 6a originate from different amounts of Ba(OH)2 in the synthetic process. The luminescence studies of 2, 3, 5, 6, 3a, 5a, and 6a were applied in the solid state at room temperature, showing intense characteristic emission bands of lanthanide ions, and the results reveal that PDA ligand as an “antenna” may effectively sensitize the luminescence of lanthanide ions.

Introduction Lanthanide ions are widespread employed in constructing metal-organic frameworks (MOFs) for their potential to photonic and magnetic applications.1 In the past decade, the exploration of heterometal-organic frameworks containing lanthanide metal ions has attracted much attention for their fascinating topologies with interesting properties, such as luminescence, gas storage, catalysis, and magnets.2 The main synthetic strategy for heterometallic coordination polymers is to employ bridging linkers to bridge two metal ions with significantly different natures. On the basis of this point, there are two general approaches for the preparation of heterometallic networks: (i) self-assembly with the different metal ions and bridging ligands in one-pot reaction, and (ii) using appropriate metal complexes as “ligands” strategy, where one type of metal ion is first assembled with ligands, leaving other coordination sites to bind the second type of metal ions.2a Both of the above processes are facilitated by employing multifunctional ligands containing bonding sites with different affinities to different metal ions. As a result, many heterometal-organic frameworks containing lanthanide ions have been well established, including systems associated with [Ln-M] (M=Cu,3 Mn,4 Fe,5 Co,6 and so on7). However, the reports of heterometal-organic frameworks associated with lanthanide and alkaline earth ions are rather rare so far.8 On the other hand, the complexes containing lanthanide ions, such as SmIII, EuIII, TbIII, and DyIII, usually exhibit intense luminescence arising from f-f transitions generated though the “antenna effect” of organic ligand.9 Especially, due to the long-lived 5D0/5D4 excited states and large Stokes *Corresponding author. E-mail: [email protected]. pubs.acs.org/crystal

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shifts of EuIII/TbIII ions,10 the luminescent studies of coordination polymers comprising these ions are of great current interest. However, the photophysical properties of lanthanide ions mainly depended on their environments, and for occurrence of the emission from symmetry forbidden excited states, it is also found that many complexes including lanthanide ions are only weakly emissive and therefore of limited use. Thus, selecting chromophoric ligands as antennas for collecting light is the better way to transfer adsorbed energy efficiently to the lanthanide ions and generate strong photoluminescence. Pyridine-2,6-dicarboxylate acid (H2PDA) has been wellknown to be an ideal ligand to encapsulated lanthanide ions,11,12 forming coordination compounds with unique optical properties.4b,d,7e,12 As a tridentate ligand, each PDA anion chelated to lanthanide ions possesses free carboxylate oxygen atoms, which can coordinate to other metal ions, such as d-block metal ions, alkali and alkaline earth ions. In our previous work, H2PDA has been employed as a multidentate ligand to fabricate novel functional materials, including porous materials adsorbing radicals, magnetic materials, luminescent probes and so on, which indicates that H2PDA as a bridging ligand is an efficient way to construct luminescent materials.4b-d,13 Inspired by above-mentioned aspects and our previous work, in this contribution, the syntheses, structures, and luminescence properties of 10 novel LnIII-BaII heterometallic coordination polymers, {[Ln2Ba2(PDA)5(H2O)12] 3 mH2O}n (Ln = Pr (1, m = 9); Sm (2, m = 6); PDA = pyridine-2,6dicarboxylic anion), {[LnBa1.5(PDA)3(H2O)8] 3 2H2O}n (Ln= Eu (3); Gd (4); Tb (5)), {[Ln4Ba6(PDA)12(H2O)x] 3 mH2O}n (Ln = Dy (6, x = 27.5, m = 12); Lu (7, x = 27, m = 11.5)), {[Eu4Ba4(PDA)10(H2O)23] 3 16H2O}n (3a), {[TbBa3(PDA)4(NO3)(H2O)6] 3 2H2O}n (5a), and {[DyBa1.5(PDA)3(H2O)7] 3 r 2009 American Chemical Society

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2H2O}n (6a), were systematically investigated. Their structures are various and change from 1D chain to 2D layer to 3D framework. Compounds 1 and 2 exhibit 1D ribbonlike chains, whereas 3-5 display 2D layers constructed by 1D BaII chains and [Ln(PDA)3] units, and compounds 6 and 7 exhibit complicated 2D structures different from those of 3-5. When the amount of Ba(OH)2 changes during the syntheses of 3, 5, and 6, three novel coordination polymers 3a, 5a, and 6a were obtained. Compound 3a consists of a 1D chain different from those in 1 and 2, whereas 5a displays a 3D framework, which was constructed through the 2D Ba layers and [Tb(PDA)3] linkers; interestingly, 6a is isostructural to 3-5, although synthetic conditions are different. The luminescence studies of 2, 3, 5, 6, 3a, 5a, and 6a were applied in the solid state at room temperature, showing intense characteristic emission bands of lanthanide ions. Experimental Section Materials. All reagents and solvents employed were commercially available and used as received without further purification. Elemental analyses for C, H, and N were carried out by using a Perkin-Elmer analyzer. The fluorescent spectra were measured on a Varian Cary Eclipse Fluorescence spectrophotometer. Syntheses of Complexes. {[Ln2Ba2(PDA)5(H2O)12] 3 mH2O}n (Ln=Pr (1, m=9); Sm (2, m=6); PDA=pyridine-2,6-dicarboxylic anion), {[LnBa1.5(PDA)3(H2O)8] 3 2H2O}n (Ln=Eu (3); Gd (4); Tb (5)), {[Ln4Ba6(PDA)12(H2O)x] 3 mH2O}n (Ln=Dy (6, x=27.5, m= 12); Lu (7, x = 27, m = 11.5)): A mixture of H2PDA (0.8 mmol, 0.134 g), Ba(OH)2 3 H2O (0.5 mmol, 0.095 g), Ln(NO3)3 3 6H2O (0.2 mmol), and H2O (10 mL) was sealed in a 25 mL Teflon-lined bomb at 180 °C for 3 days that was cooled to room temperature slowly, resulted in well-shaped crystals; they were washed with distilled water and dried in air with 69, 65, 72, 75, 65, 50, and 53% yields, respectively. Elemental anal. (%) Calcd for 1: C, 23.88; H, 3.26; N, 3.98. Found: C, 23.50; H, 3.46; N, 3.68. Calcd for 2: C, 24.37; H, 2.98; N, 4.06. Found: C, 24.02; H, 3.27; N, 3.94. Calcd for 3: C, 24.41; H, 2.83; N, 4.07. Found: C, 24.12; H, 3.14; N, 4.26. Calcd for 4: C, 24.28; H, 2.81; N, 4.05. Found: C, 23.85; H, 3.11; N, 4.33. Calcd for 5: C, 24.24; H, 2.81; N, 4.04. Found: C, 24.12; H, 3.04; N, 4.38. Calcd for 6: C, 24.21; H, 2.78; N, 4.03. Found: C, 24.46; H, 3.02; N, 4.08. Calcd for 7: C, 24.68; H, 2.69; N, 3.97. Found: C, 24.51; H, 2.64; N, 4.16. {[Eu4Ba4(PDA)10(H2O)12] 3 27H2O}n (3a), {[TbBa3(PDA)4(H2O)6]NO3 3 2H2O}n (5a), and {[DyBa1.5(PDA)3(H2O)7] 3 3H2O}n (6a): Those compounds were obtained through the synthetic method similar to that of corresponding 3, 5, and 6, except for tuning the amount of

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Ba(OH)2 3 H2O from 0.5 to 0.7 mmol with yields 65, 80, and 67%, respectively. Elemental ana. (%) Calcd for 3a: C, 23.95; H, 3.10; N, 3.99. Found: C, 23.91; H, 3.27; N, 3.88. Calcd for 5a: C, 23.39; H, 1.96; N, 4.87. Found: C, 23.24; H, 1.81; N, 5.04. Calcd for 6a: C, 24.58; H, 2.65; N, 4.09. Found: C, 24.44; H, 2.91; N, 3.84. Crystallographic Studies. Single-crystal X-ray diffraction measurements of 1-7 and 3a-6a were carried out with a Bruker Smart CCD diffractometer and an APEX II CCD area detector equipped with a graphite crystal monochromator situated in the incident beam for data collection at 113(2) and 294(2) K. Lorentz polarization and absorption corrections were applied. The structures were solved by direct methods and refined by full-matrix least-squares techniques using the SHELXS-97 and SHELXL-97 programs.14 Anisotropic thermal parameters were assigned to all non-hydrogen atoms. The hydrogen atoms were placed in idealized positions. It should be noted that the hydrogen atoms of all lattice water molecules in these complexes were not located by difference Fourier Map, and thus some A-type errors related to the case in CIF-check files may be observed. Additionally, in 2, the PDA ligand (labeling O17, O18, C29, C30, C31, C32, C33, C34, N5, C35, O19, O20, as shown in the Supporting Information) exists disorder with position occupancy of 0.53, which causes rather larger R1, even if the diffraction data of the single crystal were collected under a low temperature of 113 K; in complexes 6 and 7, the larger R1 value may result from the following aspects: (1) The larger molecule structures in 6 and 7 with high formula weight of 4221.98 for 6 and 4195.82 for 7 make better single-crystal samples difficult to obtain, although much effort to get perfect single crystals has been expended. (2) There are too many lattice water molecules and disorder water molecules. (3) The large number of refinement parameters, 1846 for 6 and 1792 for 7, result in a big refinement matrix and they are refined only by XH rather than the XL program. The crystallographic data and structure refinements for 1-7 and 3a-6a are listed in Tables 1 and 2, respectively.

Results and Discussion Syntheses. The series compounds were generated by the hydrothermal reaction of Ln(NO3)3 3 6H2O, Ba(OH)2, and H2PDA in a mixture of water. The various topological structures of 10 compounds originated from the following two aspects: one depending solely on the size of lanthanide ions, demonstrating the lanthanide contraction effect; another one depending on the amount of Ba(OH)2 used. Hydrothermal reaction of H2PDA (0.8 mmol), Ln(NO3)3 3 6H2O (0.2 mmol) (Ln= Pr, Sm, Eu, Gd, Tb, Dy, Lu), and Ba(OH)2 (0.5 mmol) in a molar ratio of 8:2:5 at 180 °C for 3 days yielded compounds 1-7, which exhibit three different

Table 1. Crystal Data and Structure Refinement Information for Compounds 1-4 formula M (g mol-1) T (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z F (000) Fcalcd (Mg m-3) μ (mm-1) 2θmax (deg) no. of reflns collected/unique GOF on F2 R1/wR2 (I g 2σ(I)) R1/wR2 (all data)

1

2

3

3a

4

C35H57N5O41Ba2Pr2 1760.36 294(2) triclinic P1 13.3845(11) 14.7152(13) 16.7344(13) 70.215(4) 75.210(4) 73.588(4) 2928.1(4) 2 1720 1.997 3.072 54.20 20079/12690 1.068 0.0431/0.1194 0.0511/0.1248

C35H51N5O38Ba2Sm2 1725.19 113(2) triclinic P1 13.676(14) 15.366(15) 16.727(16) 70.543(19) 75.295(17) 74.895(17) 3145(5) 2 1672 1.830 3.172 50.02 15475/10909 0.950 0.1082/0.2251 0.3128/0.3482

C21H29N3O22Ba1.50Eu 1033.44 293(2) monoclinic P21/c 10.2214(12) 21.306(2) 15.5462(18) 90 106.719(2) 90 3242.6(6) 4 1996 2.117 3.813 50.02 16439/5668 1.047 0.0362/0.0863 0.0481/0.0935

C70H108N10O79Ba4Eu4 3510.91 294(2) triclinic P1 13.426(3) 18.161(4) 24.972(5) 94.763(3) 102.297(4) 90.479(4) 5927(2) 2 3412 1.971 3.504 50.04 29462/20711 1.009 0.0582/0.1257 0.1376/0.1632

C21H29N3O22Ba1.50Gd 1038.73 294(2) monoclinic P21/c 10.097(3) 21.140(6) 15.381(5) 90 106.536(4) 90 3147.5(16) 4 2000 2.192 4.042 55.80 23790/7484 1.084 0.0226/ 0.0663 0.0260/0.0678

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Table 2. Crystal Data and Structure Refinement Information for Compounds 5-7 formula M (g mol-1) T (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ deg) V (A˚3) Z F (000) Fcalcd (Mg m-3) μ (mm-1) 2θmax (deg) no. of reflns collected/unique GOF on F2 R1/wR2 (I = 2σ(I)) R1/wR2 (all data)

5

5a

6

6a

7

C21H29N3O22Ba1.50Tb 1040.40 113(2) monoclinic P21/c 10.129(2) 21.070(4) 15.365(3) 90 106.545(3) 90 3143.5(10) 4 1974 2.170 4.184 50.02 23446/5495 1.057 0.0480/0.1101 0.0511/0.1124

C28H28N5O27Ba3Tb 1437.49 294(2) monoclinic P21/n 12.8071(14) 10.7274(12) 29.754(3) 90 99.518(2) 90 4031.6(8) 4 2720 2.368 4.729 50.02 20066/7117 1.020 0.0365/0.0790 0.0589/0.0874

C84H115N12O87.5Ba6Dy4 4167.93 113(2) triclinic P-1 16.182(3) 20.573(4) 20.857(4) 89.774(3) 71.841(3) 88.870(4) 6596(2) 2 4006 2.098 4.112 50.02 33981/22948 1.029 0.0761/0.1877 0.1530/0.2297

C21H27N3O21Ba1.50Dy 1025.97 293(2) monoclinic P21/c 10.1928(12) 21.094(3) 15.4861(19) 90 106.661(2) 90 3189.8(7) 4 1968 2.136 4.248 50.02 15885/5561 1.038 0.0381/0.0934 0.0492/0.0998

C87H113N12O86.5Ba6Lu4 4198.28 113(2) triclinic P-1 16.117(3) 20.318(3) 20.763(4) 89.835(3) 72.005(3) 88.916(3) 6465.4(19) 2 4026 2.157 4.936 50.02 32285/22270 1.029 0.0882/0.2286 0.1320/0.2582

Scheme 1. Synthetic Strategy for 1-7, 3a, 5a, and 6a

kinds of structures resulting from the lanthanide contraction effect; when the amount of Ba(OH)2 increased to 0.7 mmol, the resultant compounds 3a, 5a, and 6a are obtained (Scheme 1). Single-crystal X-ray diffraction analyses reveal that compounds 1-7 and 3a-6a exhibit five types of structures from 1D chains and 2D layers to 3D network, and PDA ligands coordinate to LnIII and BaII with nine types of coordination modes (Scheme 2). Structures of {[Ln2Ba2(PDA)5(H2O)12] 3 mH2O}n (Ln=Pr (1, m=9); Sm (2, m=6). X-ray crystallography reveals that compounds 1 and 2 are isostructural and crystallize in triclinic system, space group P-1. The molecular motifs of two compounds display extreme similarity with slight differences in the number of lattice water molecules. Here, compound 1 is taken as a representation to depict the structure in detail. In the asymmetric unit of 1, there are two characteristic distinct PrIII ions and two BaII ions, as shown in Figure 1. Both Pr1 and Pr2 centers are nine-coordinated to form tricapped trigonal prism geometries. The Pr1 center coordinates to three PDA anions (one with coordination mode C and two with D) with a tridentate mode to form a coordination sphere. The Pr2 chelates only to two tridentate PDA anions (coordination modes A and H), and seven O and two N atoms complete the coordination geometry. Pr1 and Pr2 are linked by one carboxyl bridge, and all Pr-O and Pr-N bond lengths fall in the normal range.10c The coordination numbers of Ba1 and Ba2 ions are ten and nine, respectively. Ba1 coordinates to three OCOO- atoms, two bridging H2O molecules, and five terminal water molecules, with an average Ba1-O bond length of 2.880 A˚, whereas the coordination environment of Ba2 is completed by four OCOO- atoms,

Figure 1. (Top) Coordination environments of PrIII and BaII ions in 1. (Bottom) Repeating unit of [Pr4Ba4].

two bridging H2O molecules, and three terminal water molecules, with an average Ba2-O bond length of 2.838 A˚. Ba1 and Ba2 centers were bridged by two bridging H2O molecules and one μ2-OCOO- to form a [Ba2] motif, and the angle of Ba1-OCOO--Ba2 is 102.71°. Two adjacent [Ba2] motifs were connected by two bridging H2O molecules to give rise to a tetranuclear Ba4 cluster (Figure 1), which further linked four PrIII (Pr1, Pr2, Pr1A, Pr2A) as its nearest neighbors by carboxyl groups or OCOO- bridges, constructing a minimal repeating unit of [Pr4Ba4]. The edge of the

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Figure 2. 1D chain structure in 1 constructed by the [Pr4Ba4] unit. Free water molecules and all H atoms are omitted for clarity. Color codes: green, Pr; purple, Ba; red, O; blue, N; gray, C.

Scheme 2. Coordination Modes of PDA Anions in 1-7, 3a, 5a, and 6a

[Pr4Ba4] unit is four PrIII ions, which link two other [Pr4Ba4] units with Pr-OCO-Pr connectivity as shown in coordination mode C and then assemble into a complicated 1D ribbonlike chain (Figure 2). Structures of {[LnBa1.5(PDA)3(H2O)8] 3 2H2O}n (Ln=Eu, (3); Gd, (4); Tb, (5)). The X-ray structural analyses reveal that 3, 4, and 5 are isostructural and crystallize in the monoclinic system, space group P21/c. The overall structure displays a 2D layer motif fabricated by a 1D BaII chain and a Ln(PDA)3 unit. We take 3 as an example to depict the 2D layer structure. The coordination environments of EuIII and BaII ions are presented in Figure 3. Ba1 is seven-coordinated by three OCOO- atoms (O2, O4, and O12) and four water molecules, with an average Ba1-O bond length of 2.807 A˚, of which coordinated water molecules O13 and O15 are disordered with position occupancy of 0.5; only O13 as a representation was labeled for clarity in Figure 3. Ba2 is coordinated with three OCOO- atoms (O2, O4, and O6A) and six water molecules with an average Ba2-O bond length of 2.845 A˚ to complete the nine-coordination sphere. Ba1 and

Ba2 are linked by two μ2-OCOO- bridges (O2 and O4) with a distance of 4.712 A˚. Interestingly, two adjacent Ba1 (Ba1 and Ba1A) ions formed a dimer-A by two bridging H2O molecules with a Ba1 3 3 3 Ba1A distance of 4.353 A˚, and two neighboring Ba2 (Ba2 and Ba2A) produced a dimer-B through two bridging H2O molecules with a Ba2 3 3 3 Ba2A distance of 4.654 A˚. The dimer-A and -B alternatively arrayed by two μ2-OCOO- bridges along c direction to give a 1D chain structure (Figure 4). Each Eu center coordinated to three PDA anions (two with coordination mode D and one with I), forming a [Eu(PDA)3] unit with a tricapped trigonal prism geometry. The PDA anions in coordination mode D only coordinate to one Ba2þ, whereas that in mode I connects four Ba2þ. As a result of this connection, the chains consisted of dimer-A and -B are further linked by [Eu(PDA)3] units as bridges to form a 2D coordination polymer (Figure 4). Structures of {[Ln4Ba6(PDA)12(H2O)x] 3 mH2O}n (Ln=Dy (6, x=27.5, m=12); Lu (7, x=27, m=11.5)). Single-crystal X-ray analyses reveal that compounds 6 and 7 are isomorphous, and crystallize in triclinic system, space group P-1.

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Figure 3. Coordination environments of EuIII and BaII ions in 3.

Figure 4. (Top) Dimer-A and -B alternatively arrayed by two μ2-OCOO- bridges along the c direction to give a 1D chain structure in 3. (Bottom) 2D layer structure of 3 constructed by a1D chain and [Eu(PDA)3] units. Color codes: purple, Ba; red, O; blue, N; gray, C; green polyhedron, Eu.

In the asymmetric unit, there are four crystallographically independent LnIII ions, six BaII ions and twelve PDA anions. Here, compound 6 is taken as a representation to depict the structure, as shown in Figure 5. Each Dy3þ is nine-coordinated with three tridentate PDA anions (with coordination modes A, D, and G) to form tricapped trigonal prism geometries, constructing a [Dy(PDA)3] unit. Four crystallographically independent Dy3þ in this structure exhibit four kinds of [Dy(PDA)3] motifs. Two of them with coordination modes A, D, and G connect three BaII ions, and the other two with coordination modes D and G connect four BaII ions.

The BaII ions have two types of coordination geometries with eight- and nine-coordination, of which Ba1, Ba3, and Ba6 are eight-coordinated, whereas the remaining ones are ninecoordinated. Ba1, Ba3, and Ba6 are coordinated with three OCOO- atoms and five H2O molecules to form the coordination sphere; Ba2, Ba4, and Ba5 bond to three OCOO- atoms and six H2O molecules. Ba1 and Ba2 are connected by two μ2-OCOO- bridges (O11 and O32), and Ba2 and Ba3 are bridged by three bridging H2O molecules (O56, O58, and O59). As a result, Ba1, Ba2, and Ba3 form a unit-A of [Ba3] cluster with the Ba1 3 3 3 Ba2 separation of 4.559 A˚ and

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Ba2 3 3 3 Ba3 one of 4.302 A˚. Two OCOO- atoms (O40 and O18) bridge Ba4 and Ba5 centers, and two H2O molecules (O72 and O74) bridge Ba5 and Ba6, in which O72 and O74 are disorder with position occupancy of 0.5 and 0.6, respectively. Consequently, Ba4, Ba5, and Ba6 construct a unit-B of [Ba3] cluster with the Ba4 3 3 3 Ba5 separation of 4.619 A˚ and Ba5 3 3 3 Ba6 one of 4.802 A˚. There are five [Dy(PDA)3] units as the neighbors of unit-A or -B. The [Dy(PDA)3] unit containing coordination modes A, D and G connected two unit-A and one unit-B, and that with coordination modes D and G linked one unit-A and one unit-B in the vicinity. As a result of this connection, unit-A, -B and [Dy(PDA)3] units are connected to give a 2D layer in ac plane (Figure 6). Along

a direction, unit-A, -B and PDA anions (with coordination mode G) fabricate a left- or right-hand helical chain with a pitch of about 16.12 A˚, and these left- or right-hand helixes alternatively arrayed in ac plane. This implies achirality of 6, supported by space group of P1. Structure of {[Eu4Ba4(PDA)10(H2O)23] 3 16H2O}n (3a). Single-crystal X-ray analysis reveals that compound 3a consists of a 1D chain with crystallographically independent four EuIII ions and four BaII ions in the asymmetric unit (Figure 7). Eu1 and Eu4 are nine-coordinated by two tridentate PDA anions (with coordination modes A, H, and B), one OCOO- atom and two H2O molecules, whereas

Figure 5. Coordination environments of DyIII and BaII ions in 6, and the motifs of unit-A (consisted of Ba1, Ba2, and Ba3) and unit-B (consisted of Ba4, Ba5, and Ba6). Color codes: green, Dy; purple, Ba; blue, N; red, O; black, C.

Figure 6. 2D layer in the ac plane formed by unit-A, -B, and [Dy(PDA)3] units in 6, displaying alternative left- and right-hand helixes chains along the a direction. Color codes: purple, Ba; blue, N; red, O; gray, C.

Figure 7. Coordination environments of EuIII and BaII ions in 3a.

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Figure 8. 1D chain structure in 3a. Free water molecules and other C atoms are omitted for clarity. Color codes: purple, Ba; green, Eu; blue, N; red, O; gray, C.

both Eu2 and Eu3 coordinated to three tridentate PDA anions (one with mode C and two with mode D), and the overall coordination geometry conforms close to a tricapped trigonal prism. The coordination number of BaII ions is either 9 or 10, of which Ba1 is 10-coordinated, and the remaining Ba centers are 9-coordinated. Ba1 center coordinates with three OCOO- atoms and seven H2O molecules with average Ba-O bond length of 2.907 A˚; Ba2 coordinates to three OCOO- atoms and six H2O molecules with average BaO bond length of 2.851 A˚; the coordinated sphere of Ba3 is similar to that of Ba2 with average Ba-O bond length of 2.866 A˚; Ba4 coordinates to two OCOO- atoms and seven H2O molecules with average Ba-O bond length of 2.873 A˚. Four BaII ions are connected into a [Ba4] cluster by H2O and OCOO- atoms bridges, including two bridging H2O molecules (O48, O49) and one μ2-OCOO- (O7) bridges between Ba1 and Ba2; two bridging H2O molecules (O52, O54) bridges between Ba2 and Ba3; as well as two bridging H2O molecules (O55, O56) and one μ2-OCOO- (O36) bridges between Ba3 and Ba4. Eu3 and Eu4 bridged by carboxyl group of PDA anion with coordination mode C form dimer-A, whereas Eu1 and Eu2 may form dimer-B by a similar bridge mode in the dimer-A. Each [Ba4] cluster connected two dimer-A and two dimer-B, whereas each dimer-A or -B has two [Ba4] clusters in its vicinity. As a result, [Ba4] cluster, dimer-A and -B are assembled into a 1D ribbonlike chain (Figure 8). Structure of {[TbBa3(PDA)4(NO3)(H2O)6] 3 2H2O}n (5a). The X-ray structural analysis reveals that 5a is monoclinic crystal system, space group P21/n. As shown in Figure 9, all TbIII and BaII ions have nine-coordinated environments. Ba1 coordinates with three OCOO- atoms, three H2O molecules together with three O atoms from two NO3-; Ba2 coordinates to four OCOO- atoms and five H2O molecules, whereas Ba3 is coordinated with six OCOO- atoms, two H2O molecules, and one N atom from PDA anion (with coordination mode E). Ba1and Ba2 are bridged by two bridging H2O molecules (O21, O22) and one μ2-OCOO- (O16); Ba2 and Ba3 are connected by two bridging H2O molecules (O24, O25) and one μ2-OCOO- (O13) bridge. As a result, three Ba(II) ions construct a [Ba3] unit, and the distances of Ba1 3 3 3 Ba2 and Ba2 3 3 3 Ba3 are 4.398 and 4.394 A˚, respectively. The adjacent [Ba3] units are further connected into a 2D BaII-layer in bc plane by OCOO- and ONO3- bridges (Figure 10), of which adjacent Ba3 centers are bridged by only one OCOO- bridge along the b direction to give a 1D chain, and along the c direction, two μ2-ONO3- bridges exist between adjacent Ba1 centers from two neighboring [Ba3] units. Considering [Ba3] unit as a node, the 2D layer can be interpreted as a 63-net, as shown in Figure 11. Each TbIII ion

Figure 9. Coordination environments of TbIII and BaII ions in 5a, showing a [Ba3] unit.

is nine-coordinated with three tridentate PDA anions (one with coordination mode D and two with F) to form a tricapped trigonal prism geometry. According to the coordination modes of PDA anions, each [Tb(PDA)3] unit connects five BaII ions. As a result, [Tb(PDA)3] unit acts as a linker to connect the 2D BaII-layers to form a 3D network, as shown in Figure 12. Considering the [Ba3] unit as a node and ignoring the connection between [Ba3] units, the [Ba3] unit and [Tb(PDA)3] unit both are four-connected nodes and this 3D structure can be simplified as a overall 426282net (Figure 13 left). Considering the connection between [Ba3] units, [Ba3] unit becomes a seven-connected node and this structure is a complicated (342526)(3242576872)-net (Figure 13 right). {[DyBa1.5(PDA)3(H2O)7] 3 2H2O}n (6a). Compound 6a is isostructural to those of 3-5, although synthetic conditions are different from each other, displaying a 2D layerlike structure. Here its structure feature is not described in detail. Comparison of Structures. The structures of ten compounds mentioned above are various and change from 1D chain to 2D layer to 3D network. The significant differences in structure from 1 to 7, and from 3a to 6a, maybe result from the lanthanide contraction effect, whereas the structural divergences between 3 and 3a, 5 and 5a, 6 and 6a mainly originate from the different amounts of Ba(OH)2 in the synthetic process. Thermal Gravimetric Analyses (TGA). In these compounds divided into five structural types, 1, 5, 6, 3a, and 5a

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Figure 10. 2D BaII-layer in bc plane fabricated by [Ba3] units, OCOO- and ONO3- bridges. Color codes: cyan, Ba1; green, Ba2; purple, Ba3; blue, N; red, O. Other atoms are omitted for clarity.

Figure 11. 63-topology of the 2D BaII layer considering [Ba3] units as nodes (blue).

are chosen as a representation of each structural type for thermogravimetric analyses. The thermogravemetric analyses were performed under atmosphere in the temperature range 25-700 °C, and the results reveal that all of them possess two steps of weight loss, as shown in Figure S2 in the Supporting Information. For the five compounds, the first weight loss occurs in the range of 25-180 °C, and is about 20.6, 18.0, 15.8, 20.4, and 10.5%, respectively, which corresponds to the loss of all coordinated and lattice water molecules (calcd 21.5, 17.3, 16.2, 20.0, and 10.0%, respectively). Above 400 °C, the frameworks begin to collapse, and those compounds are gradually decomposed to complicated oxides. Luminescence Properties. The emission spectra obtained from seven complexes 2, 3, 5, 6, 3a, 5a, and 6a principally arise from transitions originating at the 4G5/2, 5D0, 5D4, and 4 F9/2 levels for SmIII, EuIII, TbIII, and DyIII ions, respectively, which are depicted in Figure 14. For complex 2, the three intense peaks at 564, 603, and 645 nm correspond to 4 G5/2 f 6F5/2, 4G5/2 f 6F7/2, and 4G5/2 f 6F9/2 transition of Sm3þ ion, respectively,15 and all are made up of a single intense peak. Complexes 3 and 3a emit strong red light when

Figure 12. 3D structure of 5a consisting of 2D Ba layers and [Tb(PDA)3] units. Other atoms are omitted for clarity. Color codes: green, Tb; purple, Ba; blue, N; red, O; gray, C.

excited at 291 and 290 nm, respectively, and exhibit the characteristic transitions of the EuIII ions.16 The spectra of 3 and 3a show two weak bands originated from the 5D1 f 7FJ (J=1, 2) transitions: 538, 559 nm for 3 and 538, 557 nm for 3a. The stronger transitions (594, 595 nm) are attributed to 5D0 f 7F1, and the most intense bands (615, 617 nm) correspond to the 5D0 f 7F2 transition, which belongs to the hypersensitive transition. The bands (651, 650 nm) corresponding to 5D0 f 7F3 are weak but measurable, and the 5 D0 f 7F4 transition around 696 nm consists of an intense peak with one weak shoulder. The symmetric forbidden emission 5D0 f 7F0 is invisible in 3 and 3a, indicating that EuIII ions occupy sites with inversion symmetry.17 The emission spectra investigations for Tb-containing complexes 5 and 5a reveal the green-luminescence with typical emission of TbIII ions18 at 491, 545, 585, 623, 650, 669, 680 nm and 491, 545, 585, 622, 648, 670, 680 nm, respectively, attributing to

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Figure 13. 426282-net ignoring the connection between [Ba3] clusters (left) and (342526)(3242576872) net considering the connection between [Ba3] clusters (right). Color codes: green, Tb; blue, [Ba3]; red lines, connection around Tb; orange lines, connection around [Ba3].

Figure 14. Solid-state emission spectra of 2 (λex = 300 nm), 3 (λex = 291 nm), 5(λex = 296 nm), 6 (λex = 290 nm), 3a (λex = 290 nm), 5a (λex = 290 nm), and 6a (λex = 290 nm) at room temperature.

D4 f 7FJ (J=6-0) transitions. The dominant band is the hypersensitive transition 5D4 f 7F5 of Tb3þ ions in compounds 5 and 5a, and is made up of a single intense peak. The stronger luminescent band corresponds to 5D4 f 7F6 transition and two less intense bands ascribe to 5D4 f 7F4 and 5 D4 f 7F3 transitions. The 5D4 f 7FJ (J=2-0) transitions are measured with weak intensity. The dysprosium com5

plexes 6 and 6a exhibit two apparent emission bands under the excitation of 290 nm with the maximum emission wavelengths of 483, 573 nm and 482, 574 nm, respectively, which are ascribed to the characteristic emission 4F5/2 f 6H15/2 and 4 F5/2 f 6H13/2 transitions of Dy3þ ions. The weak intense bands at 655 and 657 nm for complexes 6 and 6a correspond to 4F5/2 f 6H11/2.19 It is obvious that the intensity of the

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yellow emission corresponding to 4F5/2 f 6H13/2 is much stronger than that of the blue one (4F5/2 f 6H15/2). The luminescence investigations on seven complexes mentioned above suggested that the PDA ligand may effectively sensitize the luminescence of Sm3þ, Eu3þ, Tb3þ, Dy3þ ions.

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Conclusion In summary, a series of novel LnIII-BaII heterometalorganic frameworks were obtained successfully by tuning the amount of Ba(OH)2 and using the lanthanide contraction effect under hydrothermal condition, displaying 1D chains, 2D layers and 3D network. Five kinds of structures and nine types of coordination modes of PDA ligand were observed in these complexes. Although all Ln3þ in these frameworks are nine-coordinated, the average Ln-O bond lengths slowly decrease from 2.507 A˚ (Pr-O in 1) to 2.359 A˚ (Lu-O in 7) with increasing atomic number of Ln3þ, exhibiting the lanthanide contraction effect, which gives rise to the structural divergences among complexes 1-7 and 3a-6a. The significant structure changes between 3 and 3a, 5 and 5a, and 6 and 6a mainly result from different amounts of Ba(OH)2. The results of luminescence investigations show intense and characteristic photoluminescence for samarium, europium, terbium and dysprosium, respectively, implying PDA ligand may effectively sensitize the luminescence of Sm3þ, Eu3þ, Tb3þ, Dy3þ ions. This work was hoped to provide a rational synthetic strategy for the construction of novel heterometallic luminescent materials. Acknowledgment. This work was supported by NSFC (20501012), FANEDD (200732), NCET-07-0463, NSF of Tianjin (07JCYBJC02000), and 973 Program (2005CB623607). Supporting Information Available: X-ray crystallographic files in CIF format for the ten compounds presented in this work; the disorder structure of PDA ligand in 2 and TGA curves for complexes 1, 5, 6, 3a, and 5a (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

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