4f-Block Metal Complexes as Secondary Building Units in Preparing

Article pubs.acs.org/crystal

4f-Block Metal Complexes as Secondary Building Units in Preparing 4d−4f Coordination Polymers: Preparation, Structures, and Luminescent Properties of [Ln2L6(H2O)4]·{[Ln2L4(H2O)6](NO3)2} and {[AgLnL2(H2O)3](NO3)2(H2O)4} (L = 3-Pyridinepropinoate, Ln = Eu, Tb, Nd) Zhen Nu Zheng, Young Ok Jang, and Soon W. Lee* Department of Chemistry (BK21), Sungkyunkwan University, Natural Science Campus, Suwon 440-746, Republic of Korea S Supporting Information *

ABSTRACT: Three new 4d−4f metal−organic coordination polymers were prepared by using 4f-block metal complexes as secondary building units. Discrete 4f complexes, [Ln2L6(H2O)4]·{[Ln2L4(H2O)8](NO3)2} {Ln = Eu (1), Tb (2), Nd (3)}, were prepared by microwave-heating a mixture of Ln(NO3)3·nH2O, 3-pyridinepropionic acid (HL), and NaOH in water for 1 min. Compounds 1−3 were subsequently treated with AgNO3 to form three-dimensional Ag−Ln coordination polymers, [AgLnL2(H2O)3](NO3)2(H2O)4 {Ln = Eu (4), Tb (5), Nd (6)}. Compounds 1−3 are isostructural and consist of two dimers: a neural dimer and an ionic dimer. In these compounds, the pyridyl N atoms of ligands do not coordinate to the Ln3+ ions. In isostructural coordination polymers 4−6, the pyridyl N atoms are bonded to soft Ag+ ions, and carboxylate oxygen atoms are bonded to hard Ln3+ ions. Compounds 1 and 4 exhibit practically the same red luminescence in the solid state, and compounds 2 and 5 exhibit the green luminescence, but compounds 3 and 6 do not exhibit photoluminescence in the visible region.

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INTRODUCTION Coordination polymers, also known as metal−organic frameworks (MOFs) or hybrid inorganic−organic materials, consist of metal atoms as nodes and linking ligands as spacers. They continuously receive much attention due to their various topologies, intriguing structures, and useful properties that can apply in a wide variety of fields.1−5 Almost all known coordination polymers contain either d- or f-block metals. On the other hand, those containing both kinds of metals in the coordination frameworks are rare.6−8 Dipyridyl- and multicarboxylate-type linking ligands are commonly used for the preparation of coordination polymers. In particular, multicarboxylates are typically employed for the construction of coordination polymers of f-block metals.9−11 Nitrogen-donor atoms in dipyridyl-type ligands are softer than oxygen-donor atoms in multicarboxylate-type ligands. Several research groups recently succeeded to prepare coordination polymers of (d-block)−(f-block) metals by utilizing linking ligands that possess both nitrogen- and oxygen-donor atoms.12−18 In these coordination polymers, carboxylate oxygen atoms are coordinated to f-block metals, and pyridyl nitrogen atoms to d-block metals. In particular, a soft Ag+ ion exhibits a high preference to bonding to the pyridyl nitrogen atom.15−17 © 2012 American Chemical Society

The coordination modes of metal−ligands in such coordination polymers are basically consistent with the well-known hard− soft acid−base (HASB) concept.19 3-Pyridinepropinoic acid (HL) is a rather long and flexible multifunctional ligand that contains a terminal carboxylate and a terminal pyridyl groups. LaDuca and Wang groups independently reported the preparation and structures of coordination polymers by employing this compound as a linking ligand.20,21 Our research group also prepared a twodimensional (2-D) cadmium−(L) coordination polymer, [CdL2(H2O)2].22 All of the coordination polymers mentioned above contain only d-block metals. Moreover, this ligand (L) has never been used for the preparation of d−f coordination polymers. From the standpoint of the HSAB theory, the L ligand is expected to serve as a linking ligand that would enable us to prepare d−f coordination polymers. Hydrothermal, hydro(solvo)thermal, and solvothermal methods are commonly used for the preparation of coordination polymers.4 These methods typically require long reaction times and high temperatures. To overcome such vigorous conditions, Received: February 21, 2012 Published: April 17, 2012 3045

dx.doi.org/10.1021/cg300256k | Cryst. Growth Des. 2012, 12, 3045−3056

Crystal Growth & Design

Article

mmol), HL (0.14 g, 0.93 mmol), NaOH (0.93 mmol), and water (3.5 mL) were added to a 23 mL Teflon-lined autoclave vessel. A resulting mixture was heated for 1 min in a microwave oven, and then air-cooled slowly at room temperature. After 24 h, the resulting colorless crystals were isolated by filtration, washed with water (10 mL × 3) and ethanol (10 mL × 3), and then air-dried. Data for compound 1: 53% yield. mp: 99−101 °C. Anal. Calc. for C80H104N12O38Eu4 (Mr = 2449.59): C, 39.23; H, 4.28; N, 6.86. Found: C, 40.16; H, 4.04; N, 7.04. IR (KBr, cm−1): 3433 (s), 2915 (w), 2337 (w), 1560 (s), 1436 (s), 1246 (w), 1039 (w), 939 (w), 812 (w), 717 (m), 635 (w), 493 (m). Compounds 2 and 3 were prepared similarly to compound 1. For the preparation of compounds 2 and 3, Eu(NO3)3·5H2O and Nd(NO3)3·6H2O were used, respectively. Data for compound 2: 45% yield. mp: 110−112 °C. Anal. Calc. for C80H104N12O38Tb4 (Mr = 2477.44): C, 38.78; H, 4.23; N, 6.78. Found: C, 38.44; H, 4.50; N, 6.61. IR (KBr, cm−1): 3441 (s), 2928 (w), 2358 (w), 1575 (s), 1439 (s), 1247(w), 1190 (w), 945 (w), 812 (w), 719 (m), 636 (w), 525 (m). Data for compound 3: 50% yield. mp: 93−95 °C. Anal. Calc. for C80H104N12O38Nd4 (Mr = 2418.71): C, 37.85; H, 3.97; N, 7.72. Found: C, 37.90; H, 4.58; N, 7.88. IR (KBr, cm−1): 3402 (s), 2948 (w), 2339 (w), 1589 (s), 1429 (s), 1245(w), 1189 (w), 941 (w), 811 (w), 718 (m), 636 (w), 520 (m). Synthesis of Ag−Ln Coordination Polymers, [AgLnL2(H2O)3](NO3)2(H2O)4 {Ln = Eu (4), Tb (5), Nd (6)}. Compounds 4−6 were prepared in the same way. Compound 4 was prepared in the dark because the Ag(I) ion may reduce to the Ag(0) metal. After compound 1 was prepared, it was cooled for 2 h without isolation. Onto the top of the resulting solution was layered AgNO3 (0.04 g, 0.234 mmol) in methanol (2 mL) in the dark. After 48 h, colorless crystals were isolated by filtration, washed with water (10 mL × 3) and ethanol (10 mL × 3), and then dried under a vacuum. Data for compound 4: 38% yield. mp: 212−214 °C, Anal. Calc. for C16H30N4O17AgEu (Mr = 810.27): C, 23.72; H, 3.73; N, 6.91. Found: C, 23.47; H, 3.46; N, 6.78. IR (KBr, cm−1): 3374 (w), 1542 (s), 1402 (s), 1328 (w), 1257 (w), 1178 (w), 1111 (w), 1040 (w), 933 (w), 811 (s), 708 (m), 649 (w). For the preparation of compounds 5 and 6, Tb(NO3)3·5H2O and Nd(NO3)3·6H2O were employed, respectively. Data for compound 5: 36% yield. mp: 213−215 °C, Anal. Calc. for C16H30N4O17AgTb (Mr = 817.23): C, 23.52; H, 3.70; N, 6.86. Found: C, 24.31; H, 4.27; N, 7.61. IR (KBr, cm−1): 3415 (w), 1554 (s), 1407 (s), 1376 (w), 1255 (w), 1182 (w), 1127 (w), 1044 (w), 974 (w), 812 (s), 720 (m), 639 (w). Data for compound 6: 39% yield. mp: 90−92 °C, Anal. Calc. for C16H30N4O17AgNd (Mr = 802.55): C, 23.95; H, 3.77; N, 6.98. Found: C, 24.59; H, 4.16; N, 6.83. IR (KBr, cm−1): 3343 (w), 1608 (s), 1409 (s), 1310 (w), 1272 (w), 1190 (w), 1104 (w), 1036 (w), 944 (w), 811 (s), 714 (m), 641 (w). X-ray Structure Determination. All X-ray data were collected on a Bruker Smart APEX2 diffractometer (CCRF) equipped with a Mo Xray tube (CCRF). Absorption corrections based on the Laue symmetry of equivalent reflections were made with SADABS programs.37 All calculations were carried out with SHELXTL programs.38 All structures were solved by direct methods. All nonhydrogen atoms were refined anisotropically. All C−H hydrogen atoms were generated in idealized positions and refined in a riding model. The hydrogen atoms in the aqua ligands could be located and refined freely, but those in the lattice waters (compounds 4−6) could not be located. A colorless crystal of compound 1, shaped as a block of approximate dimensions 0.48 × 0.34 × 0.28 mm3, was used for crystal- and intensity-data collection. A colorless crystal of compound 2 (block, 0.28 × 0.20 × 0.06 mm3), a violet crystal of compound 3 (block, 0.28 × 0.20 × 0.10 mm3), a colorless crystal of compound 4 (a block, 0.42 × 0.18 × 0.14 mm), a colorless crystal of compound 5 (block, 0.28 × 0.20 × 0.16 mm3), and a violet crystal of compound 6 (block, 0.22 × 0.16 × 0.10 mm3) were used. Details on crystal data, intensity collection, and refinement details are given in Table 1. Selected bond lengths and angles are given in Tables 2 and 3.

microwave was recently employed, which creates high heating effects in a short time.9,23−29 For example, Filipe and coworkers (2010) prepared lanthanide coordination polymers under microwave-heating conditions.9 In addition, Zheng’s group utilized microwave-assisted reactions to prepare 3d−4f polynuclear metal clusters.26 However, to the best of our knowledge, no d−f coordination polymers have been prepared under microwave heating conditions. Secondary building units (SBUs) are rigid molecular complexes or metal clusters, in which ligand-coordination modes and metal-coordination environments are utilized to incorporate these fragments into extended networks through polytopic organic linking ligands.30−33 Examples of prototypal SBUs commonly used in the construction of coordination polymers are (a) a dimetal tetracarboxylate square-paddlewheel cluster [M2(O2CR)4L2] (M = transition metal, L = axial ligand), (b) a μ3-oxo trimetallic hexacarboxylate cluster [M3O(O2CR)6L3], and (c) a μ4-oxo tetrametallic hexacarboxylate cluster [M4 O(O 2 CR) 6].31 SBUs have long been fundamental concepts in zeolite chemistry34−36 and are now essential for constructing coordination polymers. Recently, Fan and co-workers prepared a 3d−4f coordination polymer by utilizing a d-block metal complex as a SBU. In this case, they prepared the [Co(3,5-pdc)(H2O)5]·(H2O) complex (3,5-pdc = 3,5-pyridine dicarboxylate) first and then treated it with lanthanide oxide (Ln2O3: Ln = Gd, La) to convert it into the coordination polymer.14 In the cobalt complex, the two carboxylate groups in the 3,5-pdc ligand do not coordinate to the Co metal. However, cases in which an f-block metal complex is prepared first and then used as a SBU to prepare a d−f coordination polymer have not been reported yet. In this study, we prepared lanthanide complexes by microwave-assisted reactions in the first step, and then converted them into d−f coordination polymers by layer diffusion, a two-step reaction by using an f-block metal complex as a SBU. We herein report the preparation, structures, and solid-state photoluminescent properties of [Ln2L6(H2O)4]·{[Ln2L4(H2O)6](NO3)2} (1−3), three discrete complexes, and {[AgLnL2(H2O)3](NO3)2(H2O)4} (4−6), the corresponding three-dimensional (3-D) 4d−4f coordination polymers.

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EXPERIMENTAL SECTION

Solid reactants were purified by recrystallization, and solvents were distilled and stored over molecular sieves. 3-Pyridinepropionic acid (HL) was purchased. Infrared (IR) samples were prepared as KBr pellets, and their spectra were obtained in the range of 400−4000 cm−1 on a Nicolet 320 FTIR spectrophotometer. Mirowave-heating experiments were performed with a household mirowave oven (Samsung RE-C23RW, 700 W). The analytical laboratories at the Basic Science Institute of Kangneung−WonJu National University carried out elemental analyses. Solid-state luminescent spectra were obtained with an Aminco·Bowman Series2 (Xenon lamp, 150 W). Thermogravimetric analysis (TGA) was performed on a TA4000/SDT 2960 instrument at the Cooperative Center for Research Facilities (CCRF) in Sungkyunkwan University. X-ray powder diffraction (XRPD) data were obtained with a Rigaku D/Max-RC diffractometer. Synthesis of [Ln2L6(H2O)4]·{[Ln2L4(H2O)8](NO3)2} {Ln = Eu (1), Tb (2), Nd (3)}. At room temperature, Eu(NO3)3·5H2O (0.10 g, 0.234 3046



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Table 1. X-ray Data Collection and Structure Refinement Details compound

1

2

3

empirical formula formula weight temperature, K crystal system space group crystal size crystal shape a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z Dcal, g cm−3 μ, mm F(000) θ range (°) Tmin Tmax no. of reflns measured no. of reflns unique no. of reflns with I > 2σ(I) no. of params max, in Δρ (e Å−3) min, in Δρ (e Å−3) GOF on F2 R1a wR2b compound

C80H104N12O38Eu4 2449.59 296(2) triclinic P1̅ 0.48 × 0.34 × 0.28 block 11.8853(3) 15.1757(3) 16.3121(4) 117.609(1) 101.656(1) 98.593(1) 2451.2(2) 1 1.659 2.613 1224 1.82−28.48 0.3669 0.5282 33482 12098 10446 688 1.517 −0.645 1.047 0.0244 0.0610 4

C80H104N12O38Tb4 2477.43 296(2) triclinic P1̅ 0.28 × 0.20 × 0.06 block 11.8824(8) 15.1316(4) 16.2650(4) 117.587(1) 101.609(1) 98.559(1) 2438.3(2) 1 1.687 2.955 1232 1.82−28.38 0.4917 0.8426 69723 11782 10366 688 1.374 −0.713 1.047 0.0241 0.0591 5

C80H104N12O38Nd4 2418.71 296(2) triclinic P1̅ 0.28 × 0.20 × 0.10 block 11.9347(13) 15.2341(7) 16.4153(8) 117.624(1) 101.559(2) 98.735(2) 2485.6(3) 1 1.616 2.143 1212 1.82−28.53 0.5853 0.8143 38715 12249 10623 688 1.472 −0.692 1.042 0.0251 0.0626 6

empirical formula formula weight temperature, K crystal system space group crystal size crystal shape a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z Dcal, g cm−3 μ, mm F(000) θ range (°) Tmin Tmax no. of reflns measured no. of reflns unique no. of reflns with I > 2σ(I) no. of params max, in Δρ (e Å−3) min, in Δρ (e Å−3) GOF on F2 R1a

C16H30N4O17AgEu 810.27 296(2) monoclinic P21/c 0.42 × 0.18 × 0.14 block 7.8102(2) 19.4048(5) 17.9157(5) 90 100.225(1) 90 2672.1(1) 4 2.014 3.143 1600 1.56−28.38 0.3520 0.6674 43939 6639 5845 376 0.667 −0. 586 1.039 0.0236

C16H30N4O17AgTb 817.23 296(2) monoclinic P21/c 0.28 × 0.20 × 0.16 block 7.630(3) 19.3892(9) 17.8634(9) 90 100.466(2) 90 2644.0(2) 4 2.053 3.479 1608 2.10−28.38 0.4426 0.6060 69234 6562 5885 376 0.683 −0.619 1.040 0.0226

C16H30N4O17AgNd 802.55 296(2) monoclinic P21/c 0.22 × 0.16 × 0.10 block 7.8624(2) 19.4751(4) 17.7244(4) 90 100.047(1) 90 2672.4(1) 4 1.995 2.738 1588 2.09−28.43 0.5841 0.7714 36541 6662 5109 376 0.852 −0.649 1.004 0.0330

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Table 1. continued compound

4

wR2b a

5

0.0558

6

0.0545

0.0716

R1 = Σ[|Fo| − |Fc|]/Σ|Fo|]. bwR2 = Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]1/2.

Table 2. Selected Bond Lengths (Å) and Bond Angles (°) for Compounds 1−3a Compound 1 Eu1−O12 Eu1−O5#1 Eu1−O2 Eu2−O13 Eu2−O15 Eu2−O8 O1−Eu1−O4 O13−Eu2−O16

2.349(2) 2.428(2) 2.506(2) 2.373(2) 2.425(2) 2.486(2) 131.01(6) 96.19(9)

Eu1−O11 2.385(2) Eu1−O1 2.487(2) Eu1−O6 2.514 (2) Eu2−O16 2.381(2) Eu2−O14 2.449(2) Eu2−O7 2.503(2) O4−Eu1−O2 122.51(7) O13−Eu2−O9 147.18(8) Compound 2

Eu1−O3 Eu1−O4 Eu1−O5 Eu2−O10#2 Eu2−O9 Eu2−O10 Eu1#1−O5−Eu1 Eu2#2−O10−Eu2

2.424(2) 2.488(2) 2.557(2) 2.417(2) 2.592(2) 2.593(2) 114.07(7) 115.41(7)

Tb1−O8 Tb1−O5#3 Tb1−O4 Tb2−O16 Tb2−O14 Tb2−O11 O1−Tb1−O4 O13−Tb2−O16

2.318(2) 2.401(2) 2.484(2) 2.349(2) 2.395(2) 2.467(2) 76.06(7) 74.64(8)

Tb1−O7 2.356(2) Tb1−O3 2.463(2) Tb1−O6 2.495(2) Tb2−O15 2.352(2) Tb2−O13 2.427(2) Tb2−O12 2.479(2) O2−Tb1−O4 122.56(7) O13−Tb2−O9 110.94(7) Compound 3

Tb1−O1 Tb1−O2 Tb1−O5 Tb2−O9#4 Tb2−O10 Tb2−O9 Tb1#3−O5−Tb1 Tb2#4−O9−Tb2

2.399(2) 2.465(2) 2.535(2) 2.383(2) 2.441(2) 2.603(2) 114.40(6) 115.88(8)

Nd1−O8 Nd1−O5#5 Nd1−O2 Nd2−O13 Nd2−O14 Nd2−O11 O8−Nd1−O7 O13−Nd2−O16

2.387(2) 2.471(2) 2.544(2) 2.423(2) 2.469(2) 2.525(2) 80.59(9) 97.12(9)

Nd1−O7 Nd1−O4 Nd1−O6 Nd2−O16 Nd2−O15 Nd2−O12 O7−Nd1−O3 O13−Nd2−O9

Nd1−O3 Nd1−O1 Nd1−O5 Nd2−O9#6 Nd2−O10 Nd2−O9 O8−Nd1−O4 Nd2#6−O9−Nd2

2.465(2) 2.528(2) 2.593(2) 2.460(2) 2.524(2) 2.606(2) 79.29(8) 114.95(7)

2.429(2) 2.521(2) 2.557(2) 2.427(2) 2.495(2) 2.540(2) 124.07(7) 141.51(7)

a Symmetry transformations used to generate equivalent atoms: #1= −x + 1, −y + 1, −z + 1; #2 = −x + 1, −y + 1, −z; #3 = −x, −y + 1, −z + 1; #4 = −x, −y + 1, −z; #5 = −x, −y, −z + 1: #6 = −x, −y, −z.

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RESULTS AND DISCUSSION Preparation of Discrete f-Block Metal Complexes (1− 3). Three isostructural lanthanide complexes, [Ln2L6(H2O)4]·{[Ln2L4(H2O)8](NO3)2} {Ln = Eu (1), Tb (2), Nd (3)}, were prepared from HL, Ln(NO3)3·nH2O, and NaOH in water under microwave-heating conditions. Each complex consists of a neural dimer and an ionic dimer, and therefore it contains a total of four Ln3+ ions. NaOH was added to the reaction mixture to deprotonate the terminal carboxylate group of HL. The reaction is completed in 1 min because of high microwave power (700 W). Although the reaction time is very short, the preparation is reproducible. When a glass pressure tube was used instead of a Teflon-lined autoclave vessel, noncrystalline species was produced. All products were characterized by IR spectroscopy, elemental analysis, and X-ray diffraction. The IR spectra of compounds 1−3 displays two strong absorption bands at 1560−1589 and 1429−1439 cm−1, assignable to the CO bands.39,40 Preparation of 4d−4f Coordination Polymers (4−6). Three 4d−4f (Ag−Ln) coordination polymers (4−6) were prepared by using f-block metal complexes as SBUs (Scheme 1). After microwave-heating a mixture of HL, Ln(NO3)3·nH2O, and NaOH in water for 1 min, the reaction mixture was aircooled for 2 h. Without the isolation of the products (1−3), a

methanol solution containing AgNO3 was layered onto the top of the resulting solution. The mixed solution was allowed to stand in the dark for 48 h to produce the crystals of coordination polymers. Compounds 4−6 were also characterized by IR, elemental analysis, and X-ray diffraction. The phase purity of the crystals of all compounds (1−6) was confirmed by X-ray powder diffraction. It is worth noting that the hydrothermal treatment of a reaction mixture (HL, Eu(NO3)3, and AgNO3) gives a known one-dimensional (1-D) Ag coordination polymer, [Ag(L)·(H2O)]n,21 whereas the corresponding microwave treatment produces compound 1 (Scheme 2). In other words, the Ag−L formation dominates under hydrothermal conditions, whereas the Eu−L formation is favorable under microwaveheating conditions. As a result, compound 4 could not be prepared when the reaction mixture was treated under either hydrothermal or microwave-heating conditions. For this reason, we tried a combination of microwave heating and layer diffusion to synthesize compounds 4−6 (Scheme 1). Because the pyridyl nitrogen atoms are not bonded to the Ln3+ ions in compounds 1−3 (complexes), these compounds could be used as SBUs to produce compounds 4−6 (coordination polymers).14 Heterometallic coordination polymers are typically prepared in an autoclave under hydrothermal conditions for long reaction times.12−18 Such coordination 3048



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Table 3. Selected Bond Lengths (Å) and Bond Angles (°) for Compounds 4−6a Compound 4 Eu1−O1#1 Eu1−O5 Eu1−O3 Ag1−Ag1#4 O1#1−Eu1−O4#2 O6−Eu1−O7 N1−Ag1−Ag1#4

2.324(2) 2.444(3) 2.480(2) 3.3699(7) 159.77(6) 71.23(11) 82.28(7)

Eu1−O4#2 Eu1−O7 Eu1−O4 Ag1−N1 O4#2−Eu1−O6 O6−Eu1−O2 N2#3−Ag1−Ag1#4 Compound 5

Tb1−O1#5 Tb1−O6 Tb1−O3 Ag1−Ag1#8 O1#5−Tb1−O4#6 O6−Tb1−O7 N1−Ag1−Ag1#8

2.294(2) 2.414(3) 2.451(2) 3.3584(7) 159.70(6) 70.47(11) 82.66(7)

Tb1−O4#2 Tb1−O5 Tb1−O4 Ag1−N1 O4#6−Tb1−O6 O6−Tb1−O2

Nd1−O2#1 Nd1−O5 Nd1−O3 Ag1−Ag1#4 O2#1−Nd1−O4#2 O6−Nd1−O7 N1−Ag1−Ag1#4

2.364(2) 2.495(4) 2.525(3) 3.3756(10) 160.43(9) 72.00(15) 82.76(10)

Nd1−O4#2 Nd1−O7 Nd1−O4 Ag1−N1 O4#2−Nd1−O6 O6−Nd1−O2

2.339(2) 2.449(2) 2.603(2) 2.129(3) 80.87(9) 139.58(9) 103.92(8)

Eu1−O6 Eu1−O2 Eu1−O1 Ag1−N2#3 O6−Eu1−O5 N1−Ag1−N2#3

2.414(3) 2.468(2) 2.653(2) 2.136(3) 70.64(11) 170.73(10)

2.306(2) 2.422(2) 2.592(2) 2.129(3) 86.94(8) 74.59(9)

Tb1−O7 Tb1−O2 Tb1−O1 Ag1−N2#7 O6−Tb1−O5 N1−Ag1−N2#7

2.391(2) 2.439(2) 2.654(2) 2.130(3) 141.87(10) 170.48(10)

2.376(2) 2.501(3) 2.618(3) 2.124(4) 81.54(13) 129.33(14)

Nd1−O6 Nd1−O1 Nd1−O2 Ag1−N2#3 O6−Nd1−O5 N1−Ag1−N2#3

2.457(4) 2.516(3) 2.655(2) 2.131(4) 71.04(16) 170.67(15)

Compound 6

Symmetry transformations used to generate equivalent atoms: #1 = −x, −y + 1, −z + 1; #2 = −x + 1, −y + 1, −z + 1; #3 = −x + 1, y − 1/2, −z + 3/ 2; #4 = −x, −y, −z +1; #5 = −x + 1, −y + 1, −z; #6 = −x, −y + 1, −z; #7 = −x, y + 1/2, −z − 1/2; #8 = −x + 1, −y + 2, −z. a

Scheme 1. Synthetic Route to Compounds 4−6

Scheme 2. Different Product Formation Depending on Synthetic Methods

distances, represented by dashed bonds, are 4.1822(2) and 4.2355(2) Å, respectively. These distances indicate elongated Eu−Eu bonds, considering the covalent radius of Eu (1.99 Å). All of the aqua H atoms participate in hydrogen bonding of the type O−H···O or O−H···N. Figure 1 shows that the neutral dimer has two Eu3+ ions, six L ligands, and four aqua ligands. Two out of the six L ligands act as both bridging and chelating ligands, whereas the others act as simple bidentate (chelating) ligands. As can be seen in Figure 2, the ionic dimer consists of two Eu3+ ions, four L ligands, eight aqua ligands, and two nitrate (NO3−) counterions. In the ionic species, two ligands act as simple bidentate

polymers, however, have not been prepared under microwaveheating conditions yet. Therefore, our combination method may provide an efficient way of preparing d−f coordination polymers in relatively short reaction times. Structure of Compounds 1−3. Compounds 1−3 are isostructural, and therefore only the structure of compound 1 will be discussed in detail. Compound 1 consists of two dimers: a neural species and an ionic species. The structures of the neutral and ionic components are given in Figures 1 and 2, respectively. Both dimers have a center of symmetry, which is located midway between two Eu3+ ions. All Eu3+ ions are coordinated to nine O atoms. The Eu1···Eu1A and Eu2···Eu2A 3049



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Figure 1. Ortep drawing of one component (neutral) of compound 1.

Figure 2. Ortep drawing of the other (ionic) component of compound 1.

ligands, whereas the other two ligands act as both bridging and chelating ligands. In compound 1, the carboxylate groups of the ligand coordinate to Eu3+ ions, whereas the pyridyl groups remain uncoordinated. The ligands exhibit two bonding modes: a bridging−chelating mode (μ:κ3O:O,O′) and a chelating mode (κ2O,O′). In the mode A, the ligand acts as both a chelating ligand and a bridging ligand to link two Eu3+ ions. On the other hand, it behaves as a simple chelating ligand in the mode B (Scheme 3). As expected, in the neutral component, the Eu1− O5 bond (2.558(2) Å) is longer than the Eu1−O6 bond (2.512(2) Å), where the O5 and O6 atoms are in the same carboxylate group. Whereas the O5 atom links two Eu3+ ions, the O6 atom is bonded to a single Eu3+ ion. Such bond-length differences are more significant in the ionic component: Eu2− O10 = 2.593(2) Å; Eu2−O9 = 2.475(2) Å).

Scheme 3. Bonding Modes of the Ligand in Compounds 1− 3

The structures of compounds 2 are presented Figure 3, in which Tb1···Tb1A and Tb2···Tb2A distances are 4.1498(2) and 4.2273(2) Å, respectively. Figure 4 shows the structure of compound 3, and Nd1··· Nd1A and Nb2···N2A distances are 4.2418(3) and 4.2726(3) Å, respectively. Structures of Coordination Polymers (4−6). Whereas compounds 1−3 are molecular species, compounds 4−6 are 4d−4f bimetallic coordination polymers. Like compounds 1−3, compounds 4−6 are isostructural, and therefore the structural 3050



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Figure 4. Ortep drawing of compound 3: (top) the neutral component; (bottom) the ionic component. Figure 3. Ortep drawing of compound 2: (top) the neutral component; (bottom) the ionic component.

the same (Scheme 4). Consistent with the HSAB theory,19 the softer Ag+ ion is coordinated to the pyridyl group, and the harder Eu3+ ion is bonded to the carboxylate group. Two carboxylate oxygen atoms behave differently; that is, one oxygen atom is bonded to one Eu3+ ion, and the other to two Eu3+ ions. The Eu3+ ions are linked by the ligand carboxylate groups to form a 1-D chain along the a-axis, in which there are two distinct Eu3+···Eu3+ distances (4.0991(2) and 4.1369(2) Å) due to the two distinct ligands (Figure 6). For the same reason, there are two distinct Ag+···Eu3+ separations: 9.9147(4) and 10.4224(4) Å. The linking patterns of the ligands are given in Figure 7. The Ag+ ions are linked by the ligands to form a 2-D layer approximately parallel to the bc-plane, in which the pyridyl rings appear to be π-stacked with the dihedral angle of 4.6(1)° and the separation of their centroids of 3.76 Å. A basic repeat unit, a 37-membered ring, consists of four ligands, three Ag+ ions, and two Eu3+ ions (Figure 8). The combination of the

description of these compounds will be focused on compound 4. The local coordination environment around the Ag+ and Eu3+ ions is shown in Figure 5. An asymmetric unit consists of one Ag+ ion, one Eu3+ ion, two ligands, three aqua ligands, two NO3− counterions, and four crystalline water molecules. The coordination sphere of the Ag+ can be described as “T-shaped“ with the Ag−Ag bond (3.3699(7) Å), and the N−Ag−N bond angle (170.73(10)°) is considerably deviated from the ideal value (180°) for the linear geometry. The Ag−Ag bond in compound 4 is significantly longer than twice the covalent radius (1.59 Å) of the Ag atom, and therefore can be described as a weak bond. The Eu3+ ion is coordinated to nine oxygen atoms: six oxygen atoms from four ligands and three oxygen atoms from three aqua ligands. The Eu−O bond lengths range from 2.324(2) to 2.653(2) Å. There are two crystallographically independent ligands, but their bonding modes are essentially 3051



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Figure 5. Local coordination environments around Eu and Ag metals in compound 4.

Scheme 4. Bonding Modes of the Ligand in Compounds 4− 6

Figure 6. 1-D chain of europium metals connected by the carboxylate groups along the a-axis.

Figure 8. A 37-membered ring unit consisting of 32 ligand atoms, three Ag+ atoms, and two Eu3+ ions.

Figure 7. Ligand connectivity in compound 4. Two distinct ligands around the Ag+ ions are denoted by solid and dashed lines.

aforementioned 1-D chain and 2-D layer completes a 3-D framework of compound 4 (Figure 9). The major channel along the a-axis is occupied by the counterions and lattice water molecules. The structure of compound 5 is given in Figure 10, which contains two distinct Tb3+···Tb3+ distances (4.0692(2) and 4.1172(2) Å) and two distinct Ag+··· Tb3+ separations (9.8472(6) and 10.4123(6) Å) because of two distinct ligands. Figure 11 shows the structure of compound 6, which also has two distinct Nd3+···Nd3+ distances (4.1352(4) and 4.1688(4) Å) and two distinct Ag+··· Nd3+ separations (9.8705(5) and 10.4739(5) Å). Consistent with the relative sizes of three Ln3+ ions (Nd > Eu > Tb), the Ln3+··· Ln3+ distances are in the order of Nd3+···Nd3+ > Eu3+···Eu3+ > Tb3+···Tb3+ distances in compounds 4−6. Most heterometallic coordination polymers are 3d−4f coordination polymers.12−14,18 However, several Ag−Ln (4d− 4f) coordination polymers were recently reported,15−17 in which the Ag+ ion exhibits coordination numbers from 2 to 4 and is bonded to the nitrogen atom. For example, Deng’s group prepared the Ag−Eu coordination polymer {[Ag 2 Eu3052



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the opportunity to develop solid-state luminescent materials.6 The Eu3+ and Tb3+ ions are known to exhibit excellent luminescent properties, and therefore the luminescence of compounds 4 and 5 was examined in the solid state at room temperature. In order to check the effects of the ligand (antenna effects) and the Ag+ ion, UV−Vis (absorption) spectra of the free ligand (Figure 12) and those of Eu(NO3)3,

Figure 9. Packing diagram of compound 4 along the a-axis, in which dotted lines represent hydrogen bonds.

Figure 12. Solid-state UV−vis spectrum of the free ligand.

Figure 10. Local coordination environments around Tb and Ag metals in compound 5.

Figure 13. Solid-state UV−vis spectra of Eu(NO3)3, compound 1, and compound 4.

compound 1, and compound 4 (Figure 13) were obtained. The free ligand absorbs the UV region, which is free from the absorptions of Eu(NO3)3, compound 1, and compound 4. The UV spectrum of Eu(NO3)3 displays more well-defined, stronger peaks than those of compounds 1 and 4. In addition, the UV spectra of compounds 1 and 4 appear to be practically the same. Figures 12 and 13 indicate that both the ligand and Ag+ ion have negligible contribution to the excitation spectrum of Eu(NO3)3. Figure 14 shows the emission spectra of compounds 1 and 4 upon excitation at 395 nm. Because both compounds exhibit practically the same emission pattern (intense red luminescence), the discussion will be focused on the photoluminescence of compound 1. The emission spectrum of

Figure 11. Local coordination environments around Nd and Ag metals in compound 6.

(nic)4(H2O)4]·(ClO4)·H2O} by heating a mixture of nicotinic acid (nicH), AgNO3, Eu2O3, HClO4, and H2O at 150 °C for 50 h.15 In this polymer, each Ag+ ion is bound to two pyridyl nitrogen atoms in the nicotinato ligands, another Ag+ ion, and the perchlorate oxygen atom; that is, the Ag+ ion has a coordination number of 4. By contrast, the Ag+ ion is 3coordinate in compounds 4−6. Photoluminescent Properties. Coordination polymers are currently under intensive study, because they may provide 3053



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Figure 14. Solid-state emission spectra of compounds 1 (1) and 4 (2) at room temperature.

Figure 15. Solid-state emission spectra of compounds 2 (1) and 5 (2).

compound 1 displays the characteristic transitions of 5D0 → 7Fn (n = 1−4) at 590, 616, 651, and 695 nm, respectively, which can be explained basically on the basis the Eu3+ energy-level structure.41−44 The fact that no emission peaks other than the characteristic emission peaks of Eu3+ ions appear in the emission spectrum indicates that ligand-to-europium energy transfer is inefficient. Moreover, the Ag+ ion also has negligible effects on the emission spectrum of compound 1. This type of phenomenon (poor antenna effect) was also observed in the 3dimensional 4d−4f coordination polymer [AgEu(PDC)2] (H2PDC = pyridine-3,5-dicarboxylic acid).45 The 5D0 → 7F1 emission peak at 590 nm can be ascribed to a magnetic dipole transition, and its intensity should vary with the crystal-field strength acting on the Eu3+ ion. The strongest band at 616 nm can be assigned to an electric-dipolar 5D0 → 7 F2 transition, and it is absent if the Eu3+ ion lies on an inversion center. This observation is consistent with the results of the X-ray diffraction analysis of compound 1. In fact, the intensity of this transition is known to increase as the site symmetry of the Eu3+ ions decreases. The intensity of 5D0 → 7 F2 transition is stronger than that of 5D0 → 7F1 transition, which suggests the acentric coordination environment of Eu3+ ions in compound 1.46−49 The emission spectra of compounds 2 and 5 upon excitation at 410 nm are presented in Figure 15. Like compounds 1 and 4, these compounds exhibit practically the same intense green luminescence. These results indicate that the ligand does not sensitize the emission of the Tb3+ ion. Compound 2 emits green light and exhibits the characteristic transitions of 5D4 → 7 FJ (J = 6−2) of the Tb3+ ion at 489, 544, 584, 621, and 654 nm.46 Two intense emission bands at 489 and 544 nm correspond to 5D4 → 7F6 and 5D4 → 7F5, respectively, whereas the weaker emission band at 584 nm originates from 5D4 → 7 F4. Thermogravimetric Analysis. The TGA curves of compounds 1−3 display practically the same pattern, that is, two well-defined weight losses and additional ill-defined weight losses (Figure 16). Compound 1 is stable up to 80 °C, and its first weight loss occurs at 80−106 °C, which corresponds to the loss of the two NO3− counterions (observed: 5.3%, calculated: 5.1%). The second weight loss in the range of 237−274 °C can be attributed to the elimination of eight aqua ligands (observed:

Figure 16. TGA curves of compounds 1−3.

5.6%, calculated: 5.9%). Above 274 °C, compound 1 decomposes gradually. Compound 2 shows the first weight loss at 80−124 °C due to the loss of two counterions NO3− (observed: 5.0%, calculated: 4.8%). Eight aqua ligands are eliminated in the second step at 240−289 °C (observed: 5.6%, calculated: 5.5%). Above 289 °C, compound 2 decomposes gradually. Compound 3 is stable up to 77 °C, and the first weight loss occurs at 77−98 °C, which corresponds to the loss of the two NO3− counterions (observed: 4.6%, calculated: 4.9%). Eight aqua ligands are eliminated in the second step at 239−299 °C (observed: 5.3%, calculated: 5.7%). Above 289 °C, compound 3 decomposes gradually. Figure 17 shows TGA curves for Ag−Ln coordination polymers (4−6). Compound 4 is stable up to 69 °C, and the first weight loss at 69−119 °C corresponds to the elimination of four lattice water molecules (observed: 10.2%, calculated: 8.9%). Above 261 °C, compound 4 decomposes abruptly. Compound 5 is stable up to 73 °C, and the first weight loss occurs at 73−122 °C, which can be assigned to the loss of four lattice water molecules (observed: 10.0%, calculated: 8.8%). Its framework breaks down abruptly above 267 °C. In the TGA of compound 6, the first weight loss can also be ascribed to the elimination of four lattice water molecules (observed: 7.8%, calculated: 9.0%). Above 261 °C, it decomposes rather 3054



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ACKNOWLEDGMENTS

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REFERENCES

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This work was supported by Midcareer Researcher Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (No. 2009-0079916).

(1) Medina, M. E.; Platero-Prats, A. E.; Snejko, N.; Rojas, A.; Monge, A.; Gándara, F.; Gutiérrez-Puebla, E.; Camblor, M. A. Adv. Mater. 2011, 23, 5283−5292. (2) Jiang, H.-L.; Xu, Q. Chem. Commun. 2011, 47, 3351−3370. (3) Farha, O. K.; Hupp, J. T. Acc. Chem. Res. 2010, 43, 1166−1175. (4) Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250, 2127− 2157. (5) Ockwig, N. W.; Friedrichs, O. D.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2005, 38, 176−182. (6) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330−1352. (7) Cahill, C. L.; de Lill, D. T.; Frisch, M. CrystEngComm 2007, 9, 15−26. (8) Hemmilä, I.; Laitala, V. J. Fluoresc. 2005, 15, 529−542. (9) Patrícia, S.; Anabela, A. V.; João, R.; Filipe, A. A. P. Cryst. Growth Des. 2010, 10, 2025−2028. (10) Huh, H. S.; Lee, S. W. Bull. Korean Chem. Soc. 2006, 27, 1839− 1843. (11) Min, D.; Lee, S. W. Inorg. Chem. Commun. 2002, 5, 978−983. (12) Wang, N.; Yue, S.; Wu, H.; Li, Z.; Li, X.; Liu, Y. Inorg. Chim. Acta 2010, 363, 1008−1012. (13) Tang, Y.-Z.; Wen, H.-R.; Cao, Z.; Wang, X.-W.; Huang, S.; Yu, C.-Y. Inorg. Chem. Commun. 2010, 13, 924−928. (14) Yao, J.; Guo, J.; Wang, J.; Wang, Y.; Zhang, L.; Fan, C. Inorg. Chem. Commun. 2010, 13, 1178−1183. (15) Liu, Z.-H.; Qiu, Y.-C.; Li, Y.-H.; Deng, H.; Zeller, M. Polyhedron 2008, 27, 3493−3499. (16) Gu, X.; Xue, D. CrystEngComm 2007, 9, 471−477. (17) Gu, X.; Xue, D. Inorg. Chem. 2006, 45, 9257−9261. (18) Sun, Y.-Q.; Zhanga, J.; Yang, G.-Y. Chem. Commun. 2006, 4700−4702. (19) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.; Lemenovskii, D. A.; Majouga, A. G.; Zyk, N. V.; Schröder, M. Coord. Chem. Rev. 2001, 222, 155−192. (20) Martin, D. P.; Springsteen, C. H.; LaDuca, R. L. Inorg. Chim. Acta 2007, 360, 599−606. (21) Wang, Y.-H.; Suen, M.-C.; Lee, H.-T.; Wang, J.-C. Polyhedron 2006, 25, 2944−2952. (22) Jang, Y. O.; Lee, S. W. Acta Crystallogr. 2010, E66, m293. (23) Stéphane, D.; Shuhei, F.; Yohei, T.; Takaaki, T.; Susumu, K. Chem. Mater. 2010, 22, 4531−4538. (24) Schlesinger, M.; Schulze, S.; Hietschold, M.; Mehring, M. Microporous Mesoporous Mat. 2010, 132, 121−127. (25) El-Shall, M. S.; Abdelsayed, V.; Rahman, A. E.; Khder, S.; Hassan, H. M. A.; El-Kaderi, H. M.; Reich, T. E. J. Mater. Chem. 2009, 19, 7625−7631. (26) Zhuang, G.-L.; Sun, X.-J.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. Dalton Trans. 2009, 4640−4642. (27) Liu, H.-K.; Tsao, T.-H.; Zhang, Y.-T.; Lin, C.-H. CrystEngComm 2009, 11, 1462−1468. (28) Phetmung, H.; Wongsawat, S.; Pakawatchai, C.; Harding, D. J. Inorg. Chim. Acta 2009, 362, 2435−2439. (29) Liu, W.; Ye, L.; Liu, X.; Yuan, L.; Lu, X.; Jiang, J. Inorg. Chem. Commun. 2008, 11, 1250−1252. (30) Köberl, M.; Cokoja, M.; Herrmann, W. A.; Kühn, F. E. Dalton Trans. 2011, 40, 6834−6859. (31) Perry, J. J., IV; Perman, J, A.; Zaworotko, M. J. Chem. Soc. Rev. 2009, 38, 1400−1417. (32) Tranchemontagne, D. J.; Mendoza-Cortés, J. L.; O’Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1257−1283.

Figure 17. TGA curves of compounds 4−6.

gradually. In overall, compounds 1−3, molecular species, appear to be thermally somewhat more stable than compounds 4−6, coordination polymers. This observation may be attributed to the presence of lattice water molecules in compounds 4−6.

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CONCLUSIONS In summary, three 4d−4f coordination polymers were prepared by using 4f complexes as SBUs. The lanthanide (4f) complexes, [Ln2L6(H2O)4]·{[Ln2L4(H2O)8](NO3)2} (1−3), were prepared from HL, Ln(NO3)3·nH2O, and NaOH in water under microwave-heating (700 W) conditions. Compounds 1−3 were subsequently treated with AgNO3 by layer diffusion methods to prod uce the 3-D 4d−4f coordination p olymers, [AgLnL2(H2O)3](NO3)2(H2O)4 (4−6). Whereas compounds 1−3 are discrete molecular species, compounds 4−6 are 3-D coordination polymers. Each of compounds 1−3 consists of two dimers: a neural species and an ionic species. In compounds 1−3, the pyridyl N atoms of ligands are not coordinated to Ln3+ ions. By contrast, in compounds 4−6, the pyridyl N atoms are bonded to Ag+ ions, and the carboxylate oxygen atoms are bonded to the Ln3+ ions. In compounds 4−6, the Ag+ ion is 3-coordinate with the Ag−Ag bond, and the Ln3+ ion is 9-coordinate. Compounds 1 and 4 exhibit practically the same red luminescence in the solid state at room temperature, and their emission spectra can be explained by the Eu3+-based emission. Likewise, compounds 2 and 5 exhibit practically the same green luminescence. Consequently, the ligand does not act as a sensitizer, and the Ag+ ion has negligible effects on the emission spectra of compounds 1, 2, 4, and 5.

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

CIF files of compounds 1−6. This information is available free of charge via the Internet at http://pubs.acs.org/. Corresponding Author

*Tel: +82-31-290-7066. Fax: +82-31-290-7075. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 3055



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(33) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319−330. (34) Breck, D. W. Zeolite Molecular Sieves; John Wilkey & Sons: New York, 1974; Chapter 2. (35) Bhatia, S. Zeolite Catalysts: Principles and Applications; CRC Press, Inc.: Boca Raton, 1990; Chapter 2. (36) Lobo, R. F. Introduction to the Structural Chemistry of Zeolites. In Handbook of Zeolite Science and Technology, Auerbach, S. M., Carrado, K. A., Dutta, P. K, Eds.; Marcel Dekker: New York, 2003; Chapter 3. (37) Sheldrick, G. M. SADABS Program for Absorption Correction; University of Göttingen: Göttingen, 1996. (38) SHELXTL, Structure Determination Software Programs; Bruker Analytical X-ray Instruments Inc.: Madison, Wisconsin, USA, 1997. (39) Mehrotra, R. C.; Bohra, R. Metal Carboxylates; Academic Press: New York, 1983. (40) Gordon, A. J.; Ford, R. A. The Chemist’s Companion: A Handbook of Practical Data, Techniques and References; Wiley: New York, 1972. (41) Kim, H. K.; Oh, J. B.; Baek, N. S.; Roh, S.-G.; Nah, M.-K.; Kim, Y. H. Bull. Korean Chem. Soc. 2005, 26, 201−214. (42) Biju, S.; Raj, D. B. A.; Reddy, M. L. P.; Kariuki, B. M. Inorg. Chem. 2006, 45, 10651−10660. (43) Shyni, R.; Biju, S.; Reddy, M. L. P.; Cowley, A. H.; Findlater, M. Inorg. Chem. 2007, 46, 11025−11030. (44) Wang, Q.; Tang, K.-Z.; Liu, W.-S.; Tang, Y.; Tan, M.-Y. Eur. J. Inorg. Chem. 2010, 5318−5325. (45) Liu, G.-X.; Xu, Y.-Y.; Ren, X.-M.; Nishihara, S.; Huang, R.-Y. Inorg. Chim. Acta 2010, 363, 3727−3732. (46) Choppin, G. R.; Peterman, D. R. Coord. Chem. Rev. 1998, 174, 283−299. (47) Zhao, B.; Chen, X. Y.; Cheng, P.; Liao, D. Z.; Yan, S. P.; Jiang, Z. H. J. Am. Chem. Soc. 2004, 126, 15394−15395. (48) Liu, Z.-H.; Qiu, Y.-C.; Li, Y.-H.; Deng, H.; Zeller, M. Polyhedron 2008, 27, 3493−3499. (49) Peng, G.; Ma, L.; Liu, B.; Cai, J.-B.; Deng, H. Inorg. Chem. Commun. 2010, 13, 599−602.

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4f-Block Metal Complexes as Secondary Building Units in Preparing

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