Three-Dimensional Pillared-Layer 3d-4f Heterometallic Coordination

May 23, 2012 - They are formulated as [Ln2Cu2(μ2-X)(hma)(ina)4(H2O)2]n·2nH2O [Ln .... 32.95; H, 2.22; N, 4.68. IR (KBr pellet, cm. −1. ): 3420 (br...
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Three-Dimensional Pillared-Layer 3d-4f Heterometallic Coordination Polymers With or Without Halides Xinfa Li,†,‡ Yuanbiao Huang,† and Rong Cao*,† †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China ‡ Department of Chemistry, Zunyi Normal College, Zunyi, 563002, P. R. China S Supporting Information *

ABSTRACT: Hydrothermal reactions of isonicotinic acid (Hina) and hemimellitic acid (H3hma) with lanthanide oxides and copper halides yielded 10 three-dimensional (3D) pillared-layer 3d-4f heterometallic coordination polymers (HCPs) with three structural types. They are formulated as [Ln2Cu2(μ2-X)(hma)(ina)4(H2O)2]n·2nH2O [Ln = La, X = Cl (I-A), Ln = La, X = Br (I-B), Ln = La, X = I (I-C), Ln = Nd, X = Cl (I-D), Ln = Nd, X = Br (I-E)], [Ln3Cu4.5I3.5(μ3-OH)(hma)(ina)6(H2O)]n·nH2O [Ln = Pr (II-A), Nd(II-B)], and [LnCu0.5(hma)(ina)(H2O)]n·nH2O [Ln = La (III-A), Ce (III-B), Pr (III-C)]. All the HCPs are characterized by single-crystal X-ray diffractions. In type I structures, Ln-organic layers are pillared by halide-bridged dinuclear [Cu2(μ2-Cl)(ina)4] units through Ln−O bonds. In type II structures, Ln-organic layers are pillared by two different kinds of monovalent Cu-based building units, namely, halide-free [Cu(ina)2] and halide-containing [Cu8(μ3-I)6(μ4-I)(ina)10]n. In type III structures, undulate heterometallic Cu(II)−Ln(III) layers are pillared by organic ina ligands via Ln−O and Cu−N bonds. The solid-state photoluminescent properties of I-D and II-B were also investigated at room temperature.

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INTRODUCTION The rational design and synthesis of lanthanide−transition metal (3d-4f) heterometallic coordination polymers (HCPs) are one of the most attractive areas of materials research. The intense interests in this area are driven by not only their aesthetically beautiful architectures and topologies but also their potential applications in magnetism, luminescence, adsorption, and chemical sensing.1−5 A feasible strategy for synthesizing 3d4f HCPs is using N/O mixed ligands based on the guidance of the hard−soft acid base theory.6 Isonicotinic acid (Hina) is one of the excellent N/O mixed ligands for construction of high dimensional 3d-4f HCPs due to its unique coordination behaviors. It can bond to d-block metal ion via its pyridyl N atom and simultaneously coordinate to lanthanide ions with the opposite side carboxylate group in bridging and/or chelating modes, acting as a rigid linear linker. Therefore, ina or inacontaining sub-building units always play the role of pillars in three-dimensional (3D) HCPs, and a lot of ina-based 3D pillared-layer 3d-4f HCPs have been reported in the past decade.5,7 Monovalent copper halides have been of great interest due to their rich electronic and optical properties.8 The ball-shaped halide ligands have high affinities to monovalent copper ions and exhibit variable coordination modes ranging from μ2-X to μ4-X. Furthermore, Cu(I) halide coordination motifs have large structural variation. Until now, various structural motifs of Cu(I) halides have been reported, for example, Cu2X,7b Cu2X2,9 Cu4X3,10 Cu4X4,11 Cu5X4,7e,12 Cu6X5,13 Cu6X6,14 Cu7X6,10 and Cu8X7.7c,15 Hina is an excellent linear bridge with both N and O © 2012 American Chemical Society

donors. Its carboxylate group can bond to lanthanide ions, while the N atom can easily coordinate to soft metal copper ion, making it feasible to incorporate copper halides into lanthanide building units and prone to generate pillared-layer structures. However, only ina ligand is not sufficient and the rational choice of an auxiliary ligand is necessary to obtain desired structural types. 1,2-Benzenedicarboxylic acid (1,2-bdc) has been employed as an auxiliary ligand, and some structurally beautiful 3d-4f HCPs have been reported.5b,7a,d As we referred to the Cambridge Crystallographic Data Centre (CCDC) updated to November 2011, no lanthanide hemimellitate has been reported except several lanthanide mellitates. H3hma has three neighboring carboxylate groups, which can bond to several lanthanide ions to form different two-dimensional (2D) networks. It is expected that H3hma will demonstrate different coordination modes from 1,2-benzenedicarboxylic acid. In this research, we select H3hma as an auxiliary ligand to construct 3d-4f HCPs. Hydrothermal reactions of Hina and H3hma ligands with different lanthanide oxides and copper halides produced 10 3D pillared-layer 3d-4f HCPs. Singlecrystal X-ray diffractions reveal that they belong to three structural types, namely, [Ln2Cu2(μ2-X)(hma)(ina)4(H2O)2]n·2nH2O [Ln = La, X = Cl (I-A), Ln = La, X = Br (I-B), Ln = La, X = I (I-C), Ln = Nd, X = Cl (I-D), Ln = Nd, X = Br (I-E)], [Ln 3 Cu 4 . 5 I 3 . 5 (μ 3 -OH)(hma)Received: March 19, 2012 Revised: May 12, 2012 Published: May 23, 2012 3549

dx.doi.org/10.1021/cg300362d | Cryst. Growth Des. 2012, 12, 3549−3556

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(ina)6(H2O)]n·nH2O [Ln = Pr (II-A), Nd(II-B)], and [LnCu0.5(hma)(ina)(H2O)]n·nH2O [Ln = La (III-A), Ce (III-B), Pr (III-C)]. Interestingly, hma ligands displayed three kinds of coordination modes in these structures and two types of structures incorporated copper halide building units as pillars. Herein, we report the syntheses, crystal structures, and photoluminesecent properties of them.

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31.38; H, 2.15; N, 4.44. Found (%): C, 31.56; H, 2.14; N, 4.41. IR (KBr pellet, cm−1): 3430 (br), 1595 (vs), 1549 (s), 1456 (w), 1379 (s). Syntheses of II-A and III-C. A mixture of Pr6O11 (1/6 mmol), CuI (0.50 mmol), Hina (2.0 mmol), H3hma (0.40 mmol), and HClO4 (0.50 mmol) in deionized water (10 mL) was placed in a 23 mL Teflon-lined stainless autoclave. The following procedure is similar to that of I-A. Orange crystals (II-A), red purple crystals (III-C), and unknown impurities were obtained. Most of the impurities were washed away with running water and the remaining crystals were separated manually with the help of a microscope. For II-A: lower than 3% yield based on CuI. Calcd for C90H64Cu9I7N12O42Pr6 (%): C, 25.19; H, 1.50; N, 3.92. Found (%): C, 25.27; H, 1.53; N, 3.88. IR (KBr pellet, cm−1): 3430 (br), 1612 (m), 1589 (vs), 1545 (s), 1410 (vs), 1382 (m), 1320 (w). For III-C: 10% yield based on CuI. Calcd for C30H22CuN2O20Pr2 (%): C, 33.49; H, 2.06; N, 2.60. Found (%): C, 33.52; H, 2.05; N, 2.59. IR (KBr pellet, cm−1): 3280 (br), 1592 (s), 1550 (s), 1453 (m), 1402 (s), 1371 (s), 1342 (m), 1240 (w), 1062 (w). Synthesis of II-B. A mixture of Nd2O3 (0.50 mmol), CuI (0.30 mmol), Hina (2.0 mmol), H3hma (0.57 mmol), and deionized water (10 mL) was placed in a 23 mL Teflon-lined stainless autoclave. The following procedure is similar to that of I-A. Orange crystals (II-B) and unknown impurities were separated manually with the help of a microscope. Yield 45% (based on CuI). Calcd for C90H64Cu9I7N12Nd6O42 (%): C, 25.07; H, 1.50; N, 3.90. Found (%): C, 25.31; H, 1.59; N, 3.87. IR (KBr pellet, cm−1): 3435 (br), 1613 (m), 1589 (vs), 1546 (s), 1411 (vs), 1384 (m), 1322 (w). Synthesis of III-B. A mixture of CeO2 (1.0 mmol), CuCl2·2H2O (0.30 mmol), Hina (2.0 mmol), H3hma (0.57 mmol), and deionized water (10 mL) was placed in a 23 mL Teflon-lined stainless autoclave. The following procedure is similar to that of I-A. Red purple crystals (III-B) were manually separated from unknown impurities with the help of a microscope. Yield: ca. 8% (based on CuCl2·2H2O). C30H22Ce2CuN2O20 (%): C, 33.54; H, 2.06; N, 2.61. Found (%): C, 33.46; H, 2.02; N, 2.58. IR (KBr pellet, cm−1): 3276 (br), 1589 (s), 1548 (s), 1451 (m), 1400 (s), 1371 (s), 1340 (m), 1238 (w), 1061 (w). All of the crystals are insoluble in water and common organic solvents. The phase purity of I-D, II-B, and III-A is confirmed by powder X-ray diffraction (XRD) (see Figures S1−S3 in Supporting Information). Because of the low yield and separation difficulty, the powder XRD and photoluminescent properties of the other HCPs are not done here. In order to know what the above-mentioned impurities are, we selected some impurities to do XRD analyses. However, it was fruitless. X-ray Crystallographic Studies. Crystal structure determinations of HCPs I-A to III-C (except I-E) were performed on Oxford Xcalibur E CCD-based diffractometers equipped with graphite-monochromated Mo−Kα radiation (λ = 0.71073 Å) at room temperature. The intensity data sets were collected with the ω-scan technique. The CrysAlisPro (Version 1.171.34.49) software was used for data reduction and empirical absorption correction. Crystal structure determination of I-E was performed on Rigaku SCXmini CCD-based diffractometers equipped with graphite-monochromated Mo−Kα radiation (λ = 0.71073 Å) at room temperature. The CrystalClear software was used for data reduction and empirical absorption correction. All the structures were solved by direct methods and successive Fourier difference syntheses, and refined by full-matrix least-squares on F2 (SHELXTL Version 5.1).16 All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms attached to C atoms were generated geometrically and refined by a riding-mode with isotropic thermal parameters fixed at 1.2-times that of the mother atoms. Hydrogen atoms bonding to water molecules were placed on calculated positions and refined with isotropic thermal parameters fixed at 1.5 times that of the O atoms, while for disordered lattice water molecules in type I structure, hydrogen atoms were not added. Elemental analysis confirms that there are two lattice water molecules in type I crystals. Detailed crystallographic data and structure refinement parameters of HCPs I-A to III-C are summarized in

EXPERIMENTAL SECTION

Materials and General Methods. All chemicals were obtained from commercial sources and used as received. Elemental analyses of C, H, and N were measured on a Vario MICRO E III elemental analyzer. Infrared (IR) spectra were recorded on PerkinElmer Spectrum One instrument as KBr pellets in the range of 4000−400 cm−1. Thermogravimetric analyses were performed on an SDT Q600 instrument at a heating rate of 10 °C/min under nitrogen atmosphere. Powder X-ray diffraction (XRD) patterns were collected on a Rigaku Mini Flex II diffractometer using Cu Kα Radiation (λ = 1.54056 Å) under ambient conditions. Solid-state photoluminescent spectra were measured at room temperature with an Edinburgh FLS920 fluorescence spectrometer. The instrument is equipped with a Xe900 xenon arc lamp as the exciting light source. Syntheses of I-A and III-A. A mixture of La2O3 (0.50 mmol), CuCl (0.30 mmol), Hina (2.0 mmol), H3hma (0.40 mmol), and HClO4 (0.50 mmol) in deionized water (10 mL) was placed in a 23 mL Teflon-lined stainless autoclave. After 20 min of stirring, it was sealed and heated at 175 °C for 130 h and then slowly cooled down to room temperature at a rate of 3 °C·h−1. Yellowish green crystals (I-A), red purple crystals (III-A), and unknown impurities were obtained. Most of the impurities were washed away with running water, and the remaining crystals were separated manually with the help of a microscope. For I-A: lower than 3% yield based on CuCl. Calcd for C33H27ClCu2La2N4O18 (%): C, 32.81; H, 2.25; N, 4.64. Found (%): C, 32.95; H, 2.22; N, 4.68. IR (KBr pellet, cm−1): 3420 (br), 1598 (vs), 1545 (s), 1455 (w), 1380 (s). For III-A: 21% yield based on CuCl. Calcd for C30H22CuLa2N2O20 (%): C, 33.62; H, 2.07; N, 2.61. Found (%): C, 33.45; H, 2.11; N, 2.70. IR (KBr pellet, cm−1): 3272 (br), 1590 (s), 1549 (s), 1452 (m), 1400 (s), 1370 (s), 1341 (m), 1239 (w), 1060 (w). Synthesis of I-B. Similar to the procedure of I-A, CuCl was replaced by CuBr. Very small yellowish green crystals of I-B were obtained with a large amount of unknown impurities. The yield of yellowish green crystals is very low and difficult to be separated. Only one crystal was selected for single-crystal X-ray diffraction. Red purple crystals (III-A) were not observed in this product. Synthesis of I-C. Similar to the procedure of I-A, CuCl was replaced by CuI. Yellowish green crystals (I-C), red purple crystals (III-A), and unknown impurities were obtained. Impurities were washed away with running water and the remaining crystals were separated manually with the help of a microscope. For I-C: ca. 5% yield based on CuI. Calcd for C33H27Cu2ILa2N4O18 (%): C, 30.50; H, 2.09; N, 4.31. Found (%): C, 30.33; H, 2.08; N, 4.26. IR (KBr pellet, cm−1): 3424 (br), 1599 (vs), 1546 (s), 1457 (w), 1381 (s). Red purple crystals (III-A) were also obtained with ca. 20% yield based on CuI. Synthesis of I-D. Similar to the procedure of I-A, a mixture of Nd2O3 (0.50 mmol), CuCl2·2H2O (0.30 mmol), Hina (2.0 mmol), H3hma (0.57 mmol), and deionized water (10 mL) was used as the reactant. Yellowish green crystals (I-D) and unknown impurities were obtained. Yellowish green crystals were separated manually with the help of a microscope. Yield 33% (based on CuCl2·2H2O). Calcd for C33H27ClCu2N4Nd2O18 (%): C, 32.53; H, 2.23; N, 4.60. Found (%): C, 32.50; H, 2.29; N, 4.69. IR (KBr pellet, cm−1): 3436 (br), 1593 (vs), 1548 (s), 1454 (w), 1377 (s). Red purple crystals were not observed in this product. Synthesis of I-E. Similar to the procedure of I-D, CuCl2·2H2O was replaced by CuBr. Small yellowish green crystals of I-E were obtained with a large amount of unknown impurities. Yellowish green crystals were separated manually with the help of a microscope. Lower than 3% yield based on CuBr. Calcd for C33H27BrCu2N4Nd2O18 (%): C, 3550

dx.doi.org/10.1021/cg300362d | Cryst. Growth Des. 2012, 12, 3549−3556

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Table 1. Crystallographic Data for HCPs I-A to III−C HCP

I-A

I-B

I-C

I-D

I-E

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) β/° V (Å) Z Dc/g cm−3 μ/mm−1 R(int) GOF on F2 R1, wR2 (I > 2σ(I))a Δρmin/max [e/Å3] HCP

C33H27ClCu2 La2N4O18 1207.94 monoclinic C2/c 15.2594(5) 31.5686(7) 16.8770(5) 107.906(3) 7736.2(4) 8 2.074 3.402 0.0311 1.056 0.0366, 0.0997 1.937/−1.846 II-A

C33H27BrCu2 La2N4O18 1252.40 monoclinic C2/c 15.2400(7) 31.4564(11) 16.8503(8) 107.784(5) 7691.9(6) 8 2.163 4.391 0.0414 1.014 0.0379, 0.0803 1.438/−1.025 II-B

C33H27Cu2I La2N4O18 1299.39 monoclinic C2/c 15.2485(5) 31.4732(10) 16.8546(5) 107.647(4) 7708.2(4) 8 2.239 4.146 0.0283 1.020 0.0334, 0.0940 1.088/−1.138 III-A

C33H27ClCu2 N4Nd2O18 1218.60 monoclinic C2/c 15.1392(3) 31.4410(6) 16.7589(4) 108.327(2) 7572.5(3) 8 2.138 3.961 0.0232 1.047 0.0310, 0.0948 1.696/−1.207 III-B

C33H27BrCu2 N4Nd2O18 1263.06 monoclinic C2/c 15.149(4) 31.394(8) 16.763(5) 108.193(4) 7574(3) 8 2.215 4.945 0.0468 1.012 0.0453, 0.1139 1.043/−2.113 III-C

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å) Z Dc/g cm−3 μ/mm−1 R(int) GOF on F2 R1, wR2 (I > 2σ(I))a Δρmin/max [e/Å3] a

C90H64Cu9I7 N12O42Pr6 4291.15 triclinic P1̅ 11.4105(7) 15.4575(12) 18.0044(9) 69.975(6) 80.507(5) 68.549(6) 2774.1(3) 1 2.569 6.301 0.0289 1.017 0.0324, 0.0796 1.546/−2.812

C90H64Cu9I7 N12Nd6O42 4311.13 triclinic P1̅ 11.3895(3) 15.3887(6) 17.9731(6) 70.025(3) 80.612(2) 68.612(3) 2754.07(16) 1 2.599 6.521 0.0309 1.016 0.0350, 0.0814 1.510/−2.693

C30H22CuLa2 N2O20 1071.86 orthorhombic Pbca 8.0191(2) 17.3050(5) 23.3034(5) 90 90 90 3233.82(14) 4 2.202 3.343 0.0233 1.010 0.0227, 0.0514 0.760/−1.000

C30H22Ce2Cu N2O20 1074.28 orthorhombic Pbca 7.9905(3) 17.2450(5) 23.2987(7) 90 90 90 3210.47(18) 4 2.223 3.542 0.0275 1.021 0.0267, 0.0695 0.594/−1.209

C30H22CuN2 O20Pr2 1075.86 orthorhombic Pbca 7.9529(2) 17.2466(7) 23.2702(7) 90 90 90 3191.75(18) 4 2.239 3.763 0.0298 1.018 0.0261, 0.0644 0.653/−0.731

R = ∑||F0| − |Fc||)/∑|F0|, wR = [∑w(F02 − Fc2)2/∑w(F02)2]1/2.

Table 1. Selected bond lengths and angles are listed in Tables S1−S2 (Supporting Information).

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RESULTS AND DISCUSSION Crystal Structure of Type I HCPs. [Ln2Cu2(μ2-X)(hma)(ina)4(H2O)2]n·2nH2O [Ln = La, X = Cl (I-A), Ln = La, X = Br (I-B), Ln = La, X = I (I-C), Ln = Nd, X = Cl (I-D), Ln = Nd, X = Br (I-E)]. As revealed by single-crystal X-ray diffractions, HCPs I-A to I-E are isostructural. So I-D is selected to depict type I structure as a representative. I-D crystallized in the C2/c space group. It is a 3D pillared-layer heterometallic organic framework, where Ln-organic layers are pillared by [Cu2(μ2Cl)(ina)4] units along the crystallographic b-axis. As shown in Figure 1, the asymmetric unit contains two crystallographically independent Nd (III) ions, two Cu (I) ions, two half-occupied hma, four ina, one Cl, and two aqua ligands. Both of the hma ligands locate the on C2 axis (Scheme 1a), while all the other atoms lie on general positions. Both Nd(1) and Nd(2) are nine-coordinated by four O atoms deriving from carboxylate groups of two hma, four O atoms from carboxylate groups of four ina ligands, and one H2O molecule. The [NdO9] coordination polyhedra can be described as slightly distorted monocapped square antiprism. The Nd−O bond lengths vary

Figure 1. ORTEP drawing of the asymmetric unit of I-D with 30% probability of thermal ellipsoids. Hydrogen atoms and disordered lattice H2O are omitted.

from 2.368(3) to 2.613(3) Å, with an average value of about 2.499 Å (Table S1). Two Cu(I) ions adopt distorted “T-shape” coordination geometry [CuN2Cl], which is commonly 3551

dx.doi.org/10.1021/cg300362d | Cryst. Growth Des. 2012, 12, 3549−3556

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Scheme 1. Coordination Modes of hma and ina Ligands Exhibited in I-A to III-C

Figure 3. View of the Ln-organic layer in I-D.

encountered for monovalent Cu. The bar positions of the “T” are occupied by two pyridyl N atoms from ina ligands, while the bottom site is taken up by an μ2-Cl, generating a dinuclear unit [Cu2(μ2-Cl)(ina)4] (Figure S4). The Cu(1)−N(1), Cu(1)− N(4A), Cu(2)−N(2), Cu(2)−N(3A), Cu(1)−Cl(1A), and Cu(2)−Cl(1) bond lengths are 1.923(4), 1.928(4), 1.937(4), 1.948(5), 2.589(2), and 2.393(2) Å, respectively (Table S1). The N(1)−Cu(1)−N(4A), N(1)−Cu(1)−Cl(1A), N(4A)− Cu(1)−Cl(1A), N(2)−Cu(2)−N(3A), N(2)−Cu(2)−Cl(1), and N(3A)−Cu(2)−Cl(1) bond angles are 155.3(2), 104.18(17), 100.57(15), 143.8(2), 110.60(17), and 105.37(16)°, respectively (Table S2), indicating the “T” is distorted. The μ2-Cl bridges two Cu(I) in a “V-shape” mode with Cu−Cl−Cu bond angle of about 74.06(6)°. It is different from a reported [Gd2CuII2CuI5(ina)10(μ2-Cl)(μ2-OH2)2(μ3− OH)2]n·2n(ClO4) coordination polymer, in which the Cu−Cl− Cu bond angle of the [Cu2(μ2-Cl)(ina)4] pillar is 180°.17 Interestingly, the Cu−X bond lengths increase but the Cu−X− Cu angles decrease ongoing from Cl to I (Tables S1−S2). All of the four ina ligands coordinate tridentately to one Cu (I) and two Nd(III) ions via their pyridyl and carboxylate groups, respectively (Scheme 1d). Both of the hma ligands chelate octadentately to four Nd(III) ions by their carboxylate groups (Scheme 1a). As displayed in Figure 2, the connection between

Figure 4. View of the 3D pillared-layer structure of I-D along the caxis.

Crystal Structure of Type II HCPs. [Ln3Cu4.5I3.5(μ3OH)(hma)(ina)6(H2O)]n·nH2O [Ln = Pr (II-A), Nd(II-B)]. HCPs II-A and II-B are isostructural. So II-B is selected as an example to describe the type II structures. II-B belongs to the P1̅ space group, in which 2D layers of lanthanide clusters are pillared by two different kinds of monovalent Cu-containing building units, namely, [Cu(ina)2] and [Cu8(μ3-I)6(μ4-I)(ina)10]n. As displayed in Figure 5, the asymmetric unit of IIB consists of three crystallographically unique Nd(III) ions, four and a half Cu(I) ions, one hma, six ina, three and a half I, an μ3-OH and an aqua ligand. Cu(5) and I(3) locate on inversion centers, so they are half-occupied in the asymmetric unit. All the other atoms lie on general positions. Cu(5) adopts an unusually perfect linear coordination geometry, where the ligand sphere is taken up by two crystallographically identical pyridyl N atoms. The thus formed [Cu(ina)2] unit is one kind of pillar. A similar linear pillar has also been observed in a reported [Ln2(1,2-bdc)2(H2O)2Cu(ina)2]n·n(ClO4) HCP.7a Cu(1), Cu(2), Cu(3), and Cu(4) are bridged by I(1), I(2), I(3), and I(4) to give rise to a [Cu4I3.5] cluster. I(1), I(2), and I(4) are μ3-I. The half-occupied I(3) is μ4-I, which coordinates to two Cu(2) and two Cu(3) to form a parallelogram. The

Figure 2. View of the Ln-organic “zigzag” chain linked by hma in I-D.

Nd(III) ions and hma ligands leads to a Ln-organic “zigzag” chain extending along the crystallographic a-axis. Neighboring “zigzag” chains are further interlinked by 2 equiv of ina carboxylate groups to give rise to a Ln-organic layer on the crystallographic ac-plane (Figure 3). Adjacent Ln-organic layers are pillared by [Cu2(μ2-Cl)(ina)4] units along the b-axis via Ln−O bonds between Ln (III) and ina ligands (Figure 4). The structure is the strictly alternating arrangement of Ln-organic layers and dinuclear copper-halide pillars. The shortest distance between adjacent Ln-organic layers is 14.9 Å, about a half length of the b-axis. 3552

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Figure 5. ORTEP drawing of the asymmetric unit of II-B with 30% probability of thermal ellipsoids. For the sake of seeing, the [Cu4I3.5] cluster is drawn on another picture. Hydrogen atoms and lattice water molecules are omitted.

The coordination sites of Nd(1) are occupied by one μ3-OH and seven O atoms from carboxylate groups of hma and ina ligands, while those of Nd(2) are taken up by six carboxylate O atoms and two identical μ3-OH. The Nd−O bond lengths vary from 2.357(4) to 2.638(5) Å, with an average value of about 2.461 Å, shorter than those of nine-coordinated Nd(III) ions. One ina coordinates tetradentately to one Cu(I) and three Nd(III) ions through its pyridyl and carboxylate groups, respectively (Scheme 1e), and the other five ina ligands exhibit the same coordination mode as that in type I structure (Scheme 1d). The hma ligand chelates octadentately to four Nd(III) ions by five of its carboxylate O atoms (Scheme 1b), different from that in type I structure. As displayed in Figure 7,

Cu−I bond lengths range from 2.5849(12) to 3.1240(16) Å. Cu(1), Cu(2), and Cu(4) are four-coordinated in tetrahedral geometry with [CuI3N] coordination environment, where the apical site is occupied by a pyridyl N atom and the three bottom positions are taken up by three iodine ligands. Cu(3) is also four-coordinated but with a [I2N2] donor set, resulting in a distorted tetrahedron. An unusual feature of this cluster is its short Cu−Cu distance. The distance of Cu(1)−Cu(2) within the [Cu4I3.5] cluster is 2.659 Å, shorter than the van der Waals’ radius of two monovalent Cu ions (1.4 × 2 Å), indicative of a strong Cu−Cu interaction. As shown in Figure 6, two adjacent

Figure 6. View of the ladder-like centrosymmetric [Cu8I7] chain in IIB. The inversion center is drawn as a brown ball.

[Cu4I3.5] clusters are symmetry-related by an inversion center, generating a centrosymmetric [Cu8I7] dimer. It is distinct from the documented Cu 8 X 7 clusters due to the different coordination mode of halide ligands,7c,15 presenting another example of the large structural variation of Cu(I) halide motifs. The linkage of [Cu8I7] dimers by μ4-I (3) leads to a laddershaped copper iodinate infinite chain extending along the baxis. The remaining ligand sphere of Cu(I) in the chain are completed by pyridyl N atoms from ina ligands, giving rise to the other pillar [Cu8(μ3-I)6(μ4-I)(ina)10]n. Nd(3) is nine-coordinated by four O atoms from two hma, four O atoms from three ina and one H2O molecule. The [NdO9] coordination polyhedron can be depicted as a slightly distorted monocapped square antiprism. The Nd(3)−O bond lengths range from 2.407(4) to 2.583(4) Å, with an average value of about 2.489 Å, close to those of nine-coordinated Nd (III) ions in type I structure. Both Nd(1) and Nd(2) are eightcoordinated in [O8] donor sets, and the coordination polyhedra of Nd(III) ions adopt double-capped trigonal prism geometry.

Figure 7. The centrosymmetric hexanuclear [Nd6(hma)2] unit in II-B. The inversion center is drawn as a brown ball.

two Nd(1), two Nd(2), and two Nd(3) ions are joined together by two identical hma ligands to form a centrosymmetric hexanuclear cluster [Nd6(hma)2], comparable to one of our previously published [Gd6] oxalatophosphonate cluster.18 The further linkage between μ3-OH and [Nd6(hma)2] clusters generates a Ln-organic chain running along the b-axis (Figure S5). Neighboring chains are interconnected by ina carboxylate groups to give rise to a Ln-organic layer on the crystallographic ab-plane (Figure 8). Interestingly, adjacent Ln-organic layers are pillared simultaneously by the discrete [Cu(ina)2] and infinite [Cu8(μ3-I)6(μ4-I)(ina)10]n building units along the caxis through Ln−O bonds between Ln(III) and ina ligands (Figure 9). The distance between two adjacent layers is about 17.5 Å, close to the length of the c-axis. 3553

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Figure 10. ORTEP drawing of the asymmetric unit of III-A with 30% probability of thermal ellipsoids. Hydrogen atoms and lattice H2O are omitted. Figure 8. View of the Ln-organic layer in II-B.

antiprism. La−O bond lengths range from 2.400(2) to 2.679(2) Å, with an average value of about 2.563 Å. Ina ligand shows similar coordination mode to those in type I structure (Scheme 1d). However, hma exhibits a completely different coordination mode from those in type I and II structures: chelates hexadentately to three identical La(1) by its carboxylate groups and simultaneously coordinates to a Cu(1) via one of its carboxylate O atom (Scheme 1c). As displayed in Figure 11,

Figure 11. View of the Ln-organic “zigzag” chain bridged by hma in III-A.

La(III) ions are connected by hma and ina ligands to form a Ln-organic “zigzag” chain running along the a-axis. Each “zigzag” chain is linked to two neighboring chains via Cu−O bonds between Cu(II) and hma, generating an undulate heterometallic Cu-Ln layer on the ac-plane. Adjacent heterometallic layers are further pillared by ina ligands along the b-axis via Cu−N and Ln−O bonds, giving rise to the type III 3D pillared-layer structure (Figure 12). The shortest separation between two adjacent layers is 8.8 Å, about a half length of the b-axis. Thermogravimetric Analysis. The thermal stabilities of HCPs I-D, II-B, and III-A were examined by thermogravimetric analysis (TGA) in nitrogen atmosphere from 40 to 900 °C (Figure S6 in Supporting Information). These HCPs show similar thermal behavior and undergo two stages of weight losses. The lattice and coordinated water molecules were gradually lost in the temperature range 40−240 °C for I-D (theoretical/found: 5.9%/6.2%), 40−250 °C for II-B (theoretical/found: 1.7%/1.9%), 40−260 °C for III-A (theoretical/ found: 6.7%/6.8%), respectively. Upon further heating, the weight losses are due to the decomposition of organic ligands and backbone collapse of the coordination polymer. Photoluminescent Properties. Nd(III)-containing complexes show emissions in the near-infrared region (800−1400 nm), and the advantages of signal transmittance of near-infrared radiation make them show widespread applications in areas

Figure 9. View of the 3D pillared-layer structure of II-B along the baxis. [NdO9] and [NdO8] are drawn as golden polyhedra.

Crystal Structure of Type III HCPs. [LnCu0.5(hma)(ina)(H2O)]n·nH2O [Ln = La (III-A), Ce (III-B), Pr (III-C)]. Single-crystal X-ray diffraction reveals that HCPs III-A and IIIC are isostructural, and the unit cell volumes and Ln−O bond lengths decrease on going from La(III) to Pr(III) because of the lanthanide contraction effect. The structure of III-A is described here as a representative. III-A crystallizes in the orthorhombic crystal system, Pbca space group. As exhibited in Figure 10, the asymmetric unit of III-A is comprised of one unique La(III) ion, a half-occupied Cu(II) ion, one hma, one ina, and an aqua ligand. Cu(1) lies on an inversion center, the ligand sphere of which is occupied by two identical pyridyl N atoms and two identical carboxylate O atoms from hma. It adopts a parallelogram-shaped coordination geometry, implying that the Cu ion is divalent. The Cu(1)−N(1) and Cu(1)− O(6A) bond lengths are 2.005(3) and 1.910(2) Å, respectively. The O(6B)−Cu(1)−N(1) and O(6A)−Cu(1)−N(1) bond angles are 86.66(11) and 93.34(11)°, respectively. La(1) is nine-coordinated by six O atoms from hma, two O atoms from ina and one H2O molecule. The [LaO9] coordination polyhedron can be depicted as a distorted monocapped square 3554

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of the excited 4F3/2 states of Nd(III) ions are 0.16 μs for I-D and 0.13 μs for II-B.

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CONCLUSIONS Three structural types of 3D pillared-layer HCPs with or without halides were synthesized by the synergistic coordination of isonicotinate and hemimellitate ligands with Ln(III) and Cu(I)/(II) ions under hydrothermal conditions. Halides were successfully incorporated into the pillars of type I and II structures, where halides bridged monovalent Cu ions from μ2X to μ4-X. Interestingly, halide-free and halide-containing pillars coexisted in type II structures. Type III structures is halide-free, and pure organic isonicotinate ligands act as pillars. This work provides new perspectives on construction of structurally diversified pillared-layer 3d-4f HCPs.

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Figure 12. View of the 3D pillared-layer structure of III-A along the aaxis.

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic file for HCPs I-A to III-C in CIF format; powder XRD patterns (Figures S1−S3) and TGA curves for ID, II-B, and III-A (Figure S6); Figures S4 and S5; selected bond lengths and angles (Tables S1−S2). This material is available free of charge via the Internet at http://pubs.acs.org.

such as laser systems, medical diagnosis and telecommunications.19 Bearing this in mind, we measured the solid-state photoluminescent (PL) spectra of I-D and II-B at room temperature. As shown in Figure 13, they display characteristic

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by 973 Program (2011CB932504, 2012CB821705), 863 Program (2011AA03A407), NSFC (91022007, 21003128), Fujian Key Laboratory of Nanomaterials (2006L2005), and Key Projects from CAS. We greatly thank Prof. Huang Xiaoying for his help on crystal structure refinement.

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REFERENCES

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Figure 13. Solid-state emission spectra for I-D (a) and II-B (b) at room temperature (excitation at 397 nm).

emission spectra of Nd (III) ions upon 397 nm radiation excitation. The emission bands at 870 (m), 1057 (s), and 1331 nm (w) for I-D and 895 (m), 1057 (s), and 1333 nm (w) for II-B are attributed to the 4F3/2 → 4IJ (J = 9/2, 11/2, 13/2, respectively) transitions of Nd (III) ions. Their decay curves are recorded by monitoring the strongest 4F3/2 → 4I11/2 transition. The decay curves are well fitted with a monoexponential function. The room temperature lifetimes 3555

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