Lanthanide Anionic Metal–Organic Frameworks Containing Semirigid

Article pubs.acs.org/crystal

Lanthanide Anionic Metal−Organic Frameworks Containing Semirigid Tetracarboxylate Ligands: Structure, Photoluminescence, and Magnetism Shengqun Su,†,‡ Wan Chen,†,‡ Chao Qin,† Shuyan Song,† Zhiyong Guo,† Guanghua Li,§ Xuezhi Song,†,‡ Min Zhu,†,‡ Song Wang,†,‡ Zhaomin Hao,†,‡ and Hongjie Zhang*,† †

State Key Laboratory of Rare Earth Resource Utilizations, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China ‡ Graduate School of the Chinese Academy of Sciences, Beijing, 100039, P. R. China § State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China S Supporting Information *

ABSTRACT: A series of lanthanide anionic metal−organic frameworks, [NH2(CH3)2][Ln(MDIP)(H2O)] (Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7); H4MDIP = methylenediisophthalic acid) and [NH2(CH3)2][Ln(MDIP)(H2O)]·0.5NH(CH3)2 (Ln = Er (8), Tm (9), Yb (10)), have been synthesized and characterized. In compounds 1−7, the adjacent Ln3+ ions are intraconnected to form infinite metalcarboxylate oxygen chain-shaped building blocks along the [001] direction. In compounds 8−10, MDIP ligands bridge dinuclear lanthanide centers to form three-dimensional frameworks which can be rationalized as a (4,8)-connected topological net with the Schläfli symbol of (410.614.84)(45.6)2. Dimethylamine cations occupy the vacancy of all the compounds as counterions. The photophysical properties of trivalent Pr, Nd, Sm, Eu, Tb, Dy, Er, Yb compounds at room temperature were investigated and showed that MDIP is an efficient sensitizer of the luminescence of both the Tb3+ ion emitting visible light and the Yb3+ ion emitting in the near-IR. Antiferromagnetic interactions between Gd3+ ions were observed from magnetic susceptibility data.

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benzenetricarboxylate, and 4,4′-biphenyldicarboxylate,8,9 have been extensively studied. Nevertheless, far less research efforts have been devoted to semirigid V-shaped carboxylate ligands.10 Methylenediisophthalic acid (H4MDIP) is a V-shaped tetracarboxylate ligand which can impart a variety of connection modes to metal centers and abundant structural motifs. Meanwhile, this ligand with −CH2− spacer, as a typical flexible linker, is of particular interest because such a ligand can bend and rotate freely when it coordinates to metal centers, giving rise to structural peculiarity. In our previous work, we used the ligand to construct MOFs with metal ions (Mg2+, Mn2+, Co2+, Ni2+, Cu2+).11 It is revealed that the ligand is capable of producing a variable structural chemistry in those complexes. In continuation of the theme, we have now prepared a new series of lanthanide MOF compounds exhibiting two different structure types: [NH2(CH3)2][Ln(MDIP)(H2O)] (Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7)) for type

INTRODUCTION Lanthanide metal−organic frameworks (MOFs) are attracting increasing attention not only for their desirable structural features1,2 but also for their potential applications in catalysis,3 molecular recognition,4 optics and magnetics.5,6 A plethora of lanthanide MOFs have been synthesized, and most of them exhibit interesting photophysical and magnetic properties arising from 4f electrons. In contrast with the prolific production of MOFs based on d-block transition metal ions, however, the design and control of multidimensional lanthanide frameworks is currently a challenging task owing to the typically unspecific coordination properties of lanthanide ions. On the other hand, the high coordination number and flexible coordination geometry of lanthanide metal ions can provide unique opportunities for the discovery of unusual molecular architectures. As is well-known, lanthanide ions have high affinity for hard donor atoms and ligands containing oxygen or hybrid oxygen−nitrogen atoms, especially multicarboxylate ligands, which usually are employed in the architectures for lanthanide coordination polymers. Among them, aromatic multicarboxylic acids, such as benzenedicarboxylate,7 1,3,5© 2012 American Chemical Society

Received: September 27, 2011 Revised: February 7, 2012 Published: March 13, 2012 1808

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Table 1. Crystal Data and Structure Refinements for Complexes 1−10 formula formula weight crystal system space group T (K) a (Å) b (Å) c (Å) β (deg) V (Å3) Z Dcalcd (g cm−3) F(000) data collected unique data R(int) GOF on F2 R1a [I > 2σ(I)] ωR2b (all data) formula formula weight crystal system space group T (K) a (Å) b (Å) c (Å) β (deg) V (Å3) Z Dcalcd (g cm−3) F(000) data collected unique data R(int) GOF on F2 R1a [I > 2σ(I)] ωR2b (all data) a

1

2

3

4

5

C19H18PrNO9 545.25 monoclinic P21/n 185(2) 9.2770(6) 13.6193(9) 14.7288(11) 90.2740(10) 1860.90(2) 4 1.946 1080 10058 3678 0.0335 1.135 0.0400 0.0787 6

C19H18NdNO9 548.58 monoclinic P21/n 185(2) 9.2307(4) 13.6222(6) 14.7072(7) 90.3540(10) 1849.30(14) 4 1.970 1084 10048 3661 0.0253 1.103 0.0337 0.0727 7

C19H18SmNO9 554.69 monoclinic P21/n 185(2) 9.2161(6) 13.5618(9) 14.6623(9) 90.2090(10) 1832.6(2) 4 2.010 1092 9975 3609 0.0359 1.106 0.0405 0.0824 8

C19H18EuNO9 556.30 monoclinic P21/n 185(2) 9.2390(5) 13.5278(8) 14.6379(8) 90.3540(10) 1829.46(18) 4 2.020 1096 10018 3635 0.0412 1.026 0.0334 0.0735 9

C19H18GdNO9 561.59 monoclinic P21/n 185(2) 9.2275(5) 13.5056(8) 14.6122(8) 90.3280(10) 1820.99(18) 4 2.048 1100 9860 3601 0.0230 1.081 0.0273 0.0585 10

C19H18TbNO9 563.26 monoclinic P21/n 185(2) 9.2141(4) 13.4695(6) 14.5918(6) 90.2090(10) 1810.94(14) 4 2.066 1104 9859 3580 0.0207 1.059 0.0218 0.0481

C19H18DyNO9 566.84 monoclinic P21/n 185(2) 9.2006(4) 13.4378(6) 14.5636(6) 90.3560(10) 1800.55(13) 4 2.091 1108 9804 3563 0.0231 1.026 0.0251 0.0557

C20H21.5ErN1.5O9 594.14 orthorhombic Pbcn 185(2) 15.7340(5) 10.6914(4) 23.3260(8) 90 3923.9(2) 8 2.011 2336 20535 3891 0.0404 1.048 0.0232 0.0587

C20H21.5TmN1.5O9 595.82 orthorhombic Pbcn 185(2) 15.6958(5) 10.6984(4) 23.2644(7) 90 3906.6(2) 8 2.026 2344 20458 3875 0.0352 1.026 0.0207 0.0491

C20H21.5YbN1.5O9 599.92 orthorhombic Pbcn 185(2) 15.6733(4) 10.7028(5) 23.2631(3) 90 3902.3(2) 8 2.004 2352 20369 3868 0.0318 1.033 0.0192 0.0453

R1 = Σ∥Fo| − |Fc∥/Σ|Fo|. bωR2 = {Σ[ω(Fo2 − Fc2)2]/Σ[ω(Fo2)2]}1/2. Elmer TG-7 analyzer heated from 40 to 700 °C under nitrogen. Powder X-ray diffraction data were collected on a Bruker D8ADVANCE diffractometer equipped with Cu Kα at a scan speed of 5° min−1. The excitation and emission spectra of the complexes were measured with an Edinburgh Analytical Instruments FLS920 equipped with a stablespec-xenon lamp (450 w) as the light source. Temperature-dependent magnetic measurements were carried out on a Quantum Design SQUID MPMS-7 magnetometer with an applied field of 1000 Oe. The diamagnetic corrections for the compounds were estimated using Pascal’s constants, and magnetic data were corrected for diamagnetic contributions of the sample holder.13 Synthesis of Lanthanide Complexes. Compounds 1−10 were obtained in a typical procedure, a mixture of Ln(NO3)3·6H2O (0.15 mmol) (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm and Yb), H4MDIP (0.10 mmol), DMF (2 mL), and H2O (3 mL) was placed in a Teflon reactor (20 mL) and heated at 140 °C for four days. The mixture was gradually cooled to room temperature at a rate of 10 °C·h−1 to obtain crystals suitable for single crystal X-ray structure determination.

I, and [NH2(CH3)2][Ln(MDIP)(H2O)]·0.5NH(CH3)2 (Ln = Er (8), Tm (9), Yb (10)) for type II. The luminescence of these compounds have been well characterized containing excitation spectra, radiative and nonradiative lifetimes, and intensity parameters, although the reported research on lanthanide MOFs so far has been essentially devoted to their visible emission features rather than the NIR emission spectra.

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EXPERIMENTAL SECTION

Materials and Characterization. The Ln(NO3)3·6H2O (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb) compounds were prepared by dissolving the corresponding rare earth oxides in an aqueous solution of HNO3 (6.0 M) while adding a bit of H2O2 for Tb4O7 and then were evaporated at 100 °C. Methylenediisophthalic acid (H4MDIP) was synthesized as reported in the literature,12 and the other reagents were purchased from commercial sources and used as received. IR spectra were obtained from KBr pellets on a Perkin-Elmer 580B IR spectrometer in the 400−4000 cm−1 region (SI). Elemental analyses (C, H, N) were performed with a VarioEL analyzer. Thermogravimetric analysis (TGA) was performed on a Perkin1809

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[NH2(CH3)2][Pr(MDIP)(H2O)] (1). The yield was 35% based on Pr(III). Anal. Calcd for C19H18PrNO9 (Mr = 545.25): C, 41.85; H, 3.33; N, 2.57. Found: C, 40.68; H, 3.48; N, 2.52. [NH2(CH3)2][Nd(MDIP)(H2O)] (2). The yield was 34% based on Nd(III). Anal. Calcd for C19H18NdNO9 (Mr = 548.58): C, 41.60; H, 3.31; N, 2.55. Found: C, 41.56; H, 3.28; N, 2.59. [NH2(CH3)2][Sm(MDIP)(H2O)] (3). The yield was 37% based on Sm(III). Anal. Calcd for C19H18SmNO9 (Mr = 554.69): C, 41.14; H, 3.27; N, 2.52. Found: C, 41.38; H, 3.34; N, 2.65. [NH2(CH3)2][Eu(MDIP)(H2O)] (4). The yield was 28% based on Eu(III). Anal. Calcd for C19H18EuNO9 (Mr = 556.30): C, 41.02; H, 3.26; N, 2.52. Found: C, 41.22; H, 3.17; N, 2.41. [NH2(CH3)2][Gd(MDIP)(H2O)] (5). The yield was 32% based on Gd(III). Anal. Calcd for C19H18GdNO9 (Mr = 561.59): C, 40.63; H, 3.23; N, 2.49. Found: C, 40.55; H, 3.32; N, 2.55. [NH2(CH3)2][Tb(MDIP)(H2O)] (6). The yield was 35% based on Tb(III). Anal. Calcd for C19H18TbNO9 (Mr = 563.26): C, 40.51; H, 3.22; N, 2.49. Found: C, 40.43; H, 3.14; N, 2.47. [NH2(CH3)2][Dy(MDIP)(H2O)] (7). The yield was 31% based on Dy(III). Anal. Calcd for C19H18DyNO9 (Mr = 566.84): C, 40.26; H, 3.20; N, 2.47. Found: C, 40.17; H, 3.24; N, 2.51. [NH2(CH3)2][Er(MDIP)(H2O)]·0.5NH(CH3)2 (8). The yield was 23% based on Er(III). Anal. Calcd for C20H21.5ErN1.5O9 (Mr = 594.14): C, 40.43; H, 3.65; N, 3.54. Found: C, 40.58; H, 3.75; N, 3.59. [NH2(CH3)2][Tm(MDIP)(H2O)]·0.5NH(CH3)2 (9). The yield was 21% based on Tm(III). Anal. Calcd for C20H21.5TmN1.5O9 (Mr = 595.82): C, 40.31; H, 3.64; N, 3.53. Found: C, 40.43; H, 3.62; N, 3.57. [NH2(CH3)2][Yb(MDIP)(H2O)]·0.5NH(CH3)2 (10). The yield was 28% based on Yb(III). Anal. Calcd for C20H21.5YbN1.5O9 (Mr = 599.92): C, 40.04; H, 3.61; N, 3.50. Found: C, 39.97; H, 3.78; N, 3.56. X-ray Crystallography. The X-ray intensity data for the 10 compounds were collected on a Bruker SMART APEX CCD diffractometer with graphitemonochromatized Mo Kα radiation (λ = 0.71073 Å). The crystal structure was solved by means of Direct Methods and refined employing full-matrix least-squares on F2 (SHELXTL-97).14 Anisotropic thermal parameters were used to refine all non-hydrogen atoms except for some C and N atoms of compounds 1−10 (C20 for 8; N2 for 10). The disordered C atoms in compound 8 (C18, C18′) were refined using C atoms split over two sites, with a total occupancy of 1 and identical anisotropic displacement parameters. For compounds 8−10, the hydrogen atoms of the disordered dimethylamine molecules were not included in the model. The refinements converged with crystallographic agreement factors are summarized in Table 1. Selected bond lengths and Ln···Ln distances, and hydrogen-bond geometries of the 10 compounds are listed in Tables S1 and S2 (Supporting Information), respectively. Crystal Structures of [NH2(CH3)2][Ln(MDIP)(H2O)] (Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7). Since compounds 1−7 are isostructural, the structure of 4 is described representatively. A single-crystal X-ray diffraction study performed on compound 4 reveals that it is a three-dimensional (3D) framework, crystallizing in monoclinic space group P21/n. In the asymmetric unit of [NH2(CH3)2][Eu(MDIP)(H2O)], there are one nine-coordinated europium ion, one MDIP ligand, one aqua ligand, and one protonated dimethylamine cation. As shown in Figure 1. Eu1 is nine-coordinated with a tricapped trigonal prismatic geometry, coordinated by nine oxygen atoms from two chelating carboxyl group (O1, O2, O7E, and O8E), four dimonodentate carboxyl groups (O3A, O4C, O5D, and O6B), and one terminal H 2 O molecule (O9). The Eu−O (carboxylate) bond distances range from 2.326(4) to 2.624(3) Å,15 which are comparable to those reported for other Eu−O donor compounds. As seen in Figure 2, two crystallographically equivalent Eu atoms are bridged by two MDIP groups in a dimonodentate fashion to give a binuclear building block. The binuclear building blocks connect each other through two carboxyl groups (O5−C16−O6) along the [001] direction to lead to a one-dimensional (1D) infinite chain, ---Eu−O−C−O-Eu---, as reported in other lanthanide MOFs (the adjacent Eu···Eu separation is 5.353 Å). Then the Eu atoms of the adjacent 1D chains are connected by the chelating carboxylate groups

Figure 1. View of the environment of the nine-coordinated Eu(III) ion with a tricapped trigonal prism (EuO9). Symmetry codes: A, −x − 1/ 2, y + 1/2, −z + 1/2; B, x + 1/2, −y − 1/2, z − 1/2; C, −x + 1/2, y − 1/2, −z + 1/2; D, x + 1/2, −y + 1/2, z − 1/2; E, x + 1, y, z. (O1−C14−O2 and O7−C17−O8) to be two-dimensional (2D) grids. Along the [010] direction, the residual carboxylate groups (O3−C15−

Figure 2. (a) A view showing a metal chain running along the [001] direction. (b) Connectivity between the chains forming the twodimensional layer arrangement. (c) Connectivity between the layers via MDIP ligands. (d) The framework of the compound 4 is viewed along the [010] direction. 1810

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O4) coordinate with the Eu atoms of the adjacent layers to generate an anionic open 3D framework. The anionic framework is balanced by dimethylammonium counterions, which are formed in situ upon heating of DMF through the well-established decarbonylation reaction. There are strong hydrogen bonds between the carboxylate groups and dimethylamine cations [N1−H1B···O5, 2.765 Å and N1−H1A···O1 (x + 1/2, −y + 3/2, z + 1/2) 2.738 Å], which may be a paramount factor to stabilize the anionic framework. Crystal Structures of [NH2(CH3)2][Ln(MDIP)(H2O)]·0.5NH(CH3)2 (Ln = Er (8), Tm (9), Yb (10)). Atom numbering schemes for the isostructural 8−10 are represented by that of 10 shown in Figure 3a. The asymmetrical unit contains one ytterbium ion, one MDIP ligand, one aqua ligand, and one dimethylammonium cation. The ytterbium atom adopts an eight-coordinated mode, coordinated by eight oxygen atoms from one chelating carboxyl group (O1 and O2), four dimonodentate carboxyl groups (O5C, O6E, O7A, and O8D), one monodentate carboxyl groups (O3B), and one terminal H2O molecule (O9), with Yb−O ranging from 2.263(4) to 2.417(4) Å, to complete a dodecahedron environment (Figure 3a). The above Yb−O distances fall within the usual range for Yb compounds with carboxylate ligands.8b Two crystallographically equivalent Yb atoms are spanned by four independent syn-syn carboxylate bridges to furnish a paddle-wheel shaped building block with a Yb···Yb distance of 4.2543(5) Å. The neighboring paddle-wheel building blocks are linked through the isorphathalic carboxylates, the isorphathalic carboxylates and the carboxylates at the antiposition of MDIP ligand along the [001] and [110] direction, respectively (Figure 3b). Each paddlewheel building block is tethered to neighboring moieties through eight MDIP ligands to afford an anionic 3D open framework with elliptical channels viewed along the [001] direction (Figure 3c). The anionic framework is balanced by dimethylammonium counterions which are formed in situ. Moreover, the hydrogen bonds between the carboxylate groups and dimethylamine cations [N1−H1A···O4, 2.807 Å and N1−H1B···O6 (−x + 5/2, −y + 1/2, z + 1/2) 2.976 Å], are crucial for stabilizing the anionic framework. Interestingly, the binuclear [Ln2(COO)8]2− paddle-wheel building block with four bridging, two chelating, and two monodentate carboxylate groups is obviously different from the earlier reported binuclear [Ln2(COO)6] motif, which has been recognized in a few discrete complex molecules with monocarboxylate ligands and 3D lanthanide MOFs.16 As illustrated in Figure 4, the binuclear motif can be considered as an eight-connecting node since it is connected with eight neighboring identical motifs through eight MDIP, whereas the MDIP ligand can be regarded as the four-connecting nodes because each MDIP links four binuclear motifs. The resulting (4,8)-connected topological net with the Schläfli symbol of (410.614.84)(45.6)2 differs from the known flu and scu.17 To the best of our knowledge, such a 3D lanthanide anionic framework with a (4,8)-connected topological net has never been observed prior to this work. Although compounds 1−10 were obtained from the same starting materials and experimental method, it is interesting to observe that they exhibit two distinct structural motifs, which provides profound insights into the vital influence of lanthanide contraction. As the ionic radii of the Ln ions contract, the Ln−O bond lengths and coordination numbers present the tendency of decreasing (from nine for compounds 1−7, to eight for compounds 8−10) (Figure 5). In addition, it is worth noting that the coordination modes of the semirigid carboxylate ligand MDIP for compounds 1−7 and compounds 8−10 are varying (Figure 6). The bis-chelating and bismono coordination fashions exist in compounds 1−7 while in compounds 8−10, the carboxylate groups of MDIP adopt three kinds of coordination arrangements: mono, bis-mono, and bischelating coordination modes. The bis-mono coordination motif in all compounds leads to the infinite chain [---Ln−O−C−O−Ln---] in compounds 1−7 and the paddle-wheel building block in compounds 8−10. In the light of the diversities of the final products, it can be concluded that the central metal ions with different radii and the coordination modes of organic ligands have some influence on the structures of the resultant compounds.

Figure 3. (a) View of the environment of the eight-coordinated Yb(III) ion with a dodecahedron (YbO8). Symmetry codes: A, −x + 2, −y + 1, −z; B, −x + 2, y, −z + 1/2; C, −x + 5/2, y − 1/2, z; D, x, y − 1, z; E, x − 1/2, −y + 1/2, −z. (b) Connectivity between adjacent 1811

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Figure 3. continued paddle-wheel building blocks. (c) The framework of the compound 10 is viewed along the [001] direction.

Figure 6. The coordination modes of MDIP ligands in complexes 4 and 10. water molecule (calculated 3.86%). The decomposition of the compound started above 350 °C. For compounds 10, the weight loss of 6.30% corresponding to the release of the half dimethylamine molecule and one coordinated water molecule was observed from 140 to 420 °C (calculated 6.75%). Then, the backbone started to collapse. The experimental powder XRD patterns for compounds 1−10 and the corresponding simulated ones are almost identical (Figure S3, Supporting Information). Photoluminescence Properties. The solid-state excitation and emission spectrum of the Eu3+ complex at room temperature is shown

Figure 4. Schematic illustration of the (410·614·84)(45·6)2 topology of the 3D network of 10 (pink and green balls represent four-connected MDIP ligands and eight-connected paddle-wheel building blocks, respectively).

Figure 5. Variation of the average Ln−O bond length with the lanthanide ions. Figure 7. Room-temperature excitation and emission spectra for the Eu3+ complex in the solid state.

IR Spectra. The compounds display similar IR spectra (Figure S1, Supporting Information). For compound 4, the characteristic bands of carboxylate groups are shown in the range 1567−1655 cm−1 for asymmetric stretching and 1386−1444 cm−1 for symmetric stretching. The band at 3075, 783, and 711 cm−1 are attributed to the aromatic skeleton vibration of the benzene ring. Absorptions observed at 3260− 3530 cm−1 correspond to the O−H stretching vibrations of water molecules, in which the characteristic bands of dimethylamine cations are incorporated owing to the wide range. Thermal Analysis and Powder X-ray Diffraction. The isomorphous frameworks lead to a similar thermal decomposition process, so we took compounds 4 and 10 as representative examples for thermogravimetric analyses to study the stability of the two types of complexes. Their thermal behaviors were investigated under a nitrogen atmosphere with a heating rate of 10 °C/min (Figure S2, Supporting Information). The TG curve of 4 showed a weight loss of 3.24% from 100 to 280 °C corresponding to the loss of one terminal

in Figure 7. Obviously, the ligand makes insignificant contributions to the excitation spectrum of the Eu3+ complex exhibiting a series of sharp lines characteristic of the Eu3+ energy-level structure, which can be assigned to transitions between the 7F0 and the 5L6 and 5D2 levels. This indicates that luminescence sensitization of the Eu3+ complex via excitation of the ligand is not efficient.18 The ambient-temperature emission spectrum of the Eu3+ complex was measured in the 520−800 nm range (λex = 300 nm) and showed four major peaks assigned to the 5 D0 → 7FJ (J = 1−4) transitions, namely, 5D0 → 7F0 (579 nm), 5D0 → 7 F1 (589 nm), 5D0 → 7F2 (615 nm), and 5D0 → 7F4 (693 nm). The relative intensity of the 5D0 → 7F2 transition and the 5D0 → 7F1 transition is widely used as a measure of the coordination state and the site symmetry of the europium ion, while the intensity of the 5D0 → 7 F1 transition (magnetic dipole transition) is insensitive to the 1812

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coordination environment, the 5D0 → 7F2 transition is electric-dipole allowed, and its intensity increases as the site symmetry is lowered. In the spectrum of the Eu3+ complex, the intensity ratio 5D0 → 7F2/5D0 → 7F1 is much higher than a typical value for a centrosymmetric Eu3+ center, which signifies that the Eu3+ ion is not located at the inversion center and the symmetry of the Eu3+ ion site is low.19 Furthermore, the presence of the weak symmetry forbidden 5D0 → 7F0 emission suggests that the Eu3+ ions occupy low-symmetry coordination sites with no inversion centers, consistent with the result of X-ray structural analysis. The luminescence lifetime value for the 5D0 level of the Eu3+ complex was determined to be 0.42 ms from the luminescence decay profile at room temperature by fitting with a monoexponential curve, indicative of the presence of one distinct emitting species. For the Tb3+ complex (Figure 8), the excitation spectrum exhibits a broad band between 230 and 325 nm, and it is overlapped by the

second one being more intense. The lifetime of 4F9/2 excited state amounts to 3.19 μs. We have also observed emission in the near-IR from the Sm3+ and Dy3+ ions, which is a rarely described phenomenon.22 The three transitions 4G5/2 → 4F5/2 (943 nm), 4G5/2 → 4F7/2 (1023 nm), and 4G5/2 → 4F9/2 (1164 nm) are observed for the Sm3+ complex, and emission bands with maxima at 940 (4F9/2 → 6 F7/2), 994 (4F9/2 → 6F5/2), and 1171 nm (4F9/2 → 6F3/2) are observed for the Dy3+ complex. Notably, the emission of Dy3+ complex is not a single sharp transition with the presence of well-split NIR emission peaks, which may be ascribed to the crystal-field splitting.23 The NIR emission spectra of Pr3+ complex consist of two bands at 872 and 1024 nm, which can be attributable to 1D2 → 3F2 and 1D2 → 3 F4 transitions, respectively. The luminescent spectra of Pr3+ ion are more complicated compared with other lanthanide ions since the Pr3+ ion can show emissions from three different levels (3P0, 1D2 and 1G4) when the complexes are excited. The emitting peaks at 1024 nm arise from the 1D2, not 1G4 level, because the lack of the NIR emission at about 1320 nm corresponding to 1G4 → 3H5 indicates that the nonradiative process with phonon assistance dominates the relaxation of 1G4 manifold energy levels.24 Excited with UV light, the Nd3+ complex exhibited three bands: 898 nm (4F3/2 → 4I9/2), 1067 nm (4F3/2 → 4I11/2), and 1336 nm (4F3/2 → 4I13/2), respectively. For the Er3+ complex, the emission maxima located at 1534 nm which is attributed to the transition from the first excited state (4I13/2) to the ground state (4I15/2) of Er3+ ions. The emission bands cover large spectral ranges extending from 1445 to 1640 nm.25 For the emission spectra of Yb3+ complexes, the 2F5/2 → 2F7/2 transitions of the Yb3+ ions were split into two bands (982 and 1012 nm), which may be due to the crystal-field or stark splitting.26 The absence of typical Yb3+ ion excitation bands in the excitation spectra and the ligand-centered luminescence in the emission spectra indicate that the ligand-to-metal energy transfer takes place efficiently. The luminescence lifetimes of Ln3+ complexes (Ln = Nd, Er, and Yb) were measured using an excitation wavelength of 290 nm and monitored around the strongest emission line of the corresponding Ln3+ ions (Figure S4, Supporting Information). The luminescence lifetimes of Ln3+ complexes are all fitted well by a single-exponential function and yield the lifetimes of 0.014, 0.11, and 0.80 μs for the corresponding Nd3+, Er3+, and Yb3+ complexes, which reflects that the Ln3+ ions occupy the same average local environment. Magnetic Properties. Magnetic susceptibility measurement of compound 5 was performed with polycrystalline sample in a directcurrent field of 0.1 T in the 2−300 K range (Figure 10). χMT is almost a constant from 7.94 cm3 mol−1 K at 300K to 7.76 cm3 mol−1 K at 9 K, which is close to the spin-only (g = 2) value of 7.875 cm3 mol−1 K for a single Gd(III) ion. Upon further cooling, the decrease is abrupt but very small, with χMT reaching a value of 7.34 cm3 mol−1 K at 2.5 K. This feature is suggestive of the presence of very weak antiferromagnetic coupling between the Gd(III) ions. The magnetic susceptibility obeys the Curie−Weiss law with the Weiss constant, θ = −0.43 K, and Curie constant, C = 8.05 cm3 mol−1 K. The negative weiss constants bear evidence of weak antiferromagnetic interactions between the Gd(III) centers. The crystal structure of the compound has shown that the Gd(III) ions are bridged by carboxylate groups to form an infinite chain, and then the ligands connect the chains at a long distance. So, the magnetic interactions are negligible except for the coupling between the Gd(III) ions within the chain, which can be estimated by mean-field correction with zJ′ as the exchange coupling between Gd(III) ions as follows:18c

Figure 8. Room-temperature excitation and emission spectra for the Tb3+ complex in the solid state. absorption spectrum of the ligand employed in the corresponding complex, which reveals that energy transfer from the ligand to the metal ion is operative.20 Three sharp lines assigned to transitions between the 7F6 and the 6L9 and 5DJ (J = 2, 3) levels are also observed in the excitation spectrum. These transitions are weaker than the broad excitation band, which manifests that luminescence sensitization via excitation of the ligand is much more efficient than the direct excitation of the Tb3+ ion absorption level. The room-temperature emission spectrum of the Tb3+ complex exhibits the peculiar emission bands of the Tb3+ cation (λex = 300 nm) centered at 488, 544, 582, and 620 nm, which result from deactivation of the 5D4 excited state to the corresponding 7FJ ground state of the Tb3+ cation (J = 6, 5, 4, 3). The most intense emission corresponds to the hypersensitive transition 5D4 → 7F5 (544 nm).21 Lifetime measurements at room temperature provide the decay of the 5D4 luminescence at 544 nm (excited at 290 nm). The decay curve is well fitted with a monoexponential function and yields a lifetime of 0.85 ms. Comparing the emission spectra of the Eu3+ and Tb3+ complexes, it is easy to find that the transition intensity follows the trend Tb3+ ≫ Eu3+ which means that the energy transfer from the organic ligands to Tb3+ is more effective than to Eu3+. The lifetimes (0.42 ms) of Eu3+ complex is also relatively short, showing the luminescence of Eu3+ is only poorly sensitized, whereas the Tb3+ luminescence (0.85 ms) is preferably sensitized. Excitation and emission spectra of the other lanthanide complexes (Ln = Sm, Dy, Nd, Pr, Er, Yb) are reported in Figure 9. The Sm3+ complex emits orange light originating from the transitions 4G5/2 → 6 H5/2 (563 nm), 4G5/2 → 6H7/2 (595 nm), 4G5/2 → 6H9/2 (645 nm), and 4G5/2 → 6H11/2 (711 nm). A lifetime of 5.12 μs was found for the 4 G5/2 level. For the Dy3+ complex, two typical narrow bands can be seen in the emission spectrum, which are attributed to transitions of 4 F9/2 → 6H15/2 (480 nm) and 4F9/2 → 6H13/2 (570 nm) with the

χ=

Ng 2β2 S(S + 1) 3kT

χm =

χ 1 − χ2zJ ′/Ng 2β2

An excellent fit with the experimental data was obtained for g = 2.02 and zJ′ = −0.018 cm−1. The small negative zJ′ value suggests that there is very weak antiferromagnetic coupling between Gd(III) ions. 1813

dx.doi.org/10.1021/cg201283a | Cryst. Growth Des. 2012, 12, 1808−1815

Crystal Growth & Design

Article

Figure 9. The excitation and emission spectra of Ln3+ complexes (Ln = Dy, Yb, Sm, Pr, Nd, Er).

of both the Tb3+ and Yb3+ ions emitting. All the reported compounds display good performance in luminescent properties, which have potential applications in optical devices. Magnetic susceptibility data show that Gd(III) complex has weak antiferromagnetic behavior. Further studies along this line are underway to synthesize novel lanthanide complexes with amazing structural motifs and properties.

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ASSOCIATED CONTENT

S Supporting Information *

Selected bond lengths and Ln···Ln distances for compounds 1− 10; hydrogen-bond geometries for compounds 1−10; IR spectra of 4; TGA curves of 4 and 10; X-ray powder diffraction patterns for compounds 1−10; luminescent decay curves of Ln3+ complexes. This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 10. Temperature dependence of the χMT and χM−1 curve for Gd3+ complex. The red line represents the best fit to the fitted equation in the text. The blue line shows the Curie−Weiss fitting.

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AUTHOR INFORMATION

Corresponding Author

CONCLUSIONS Ten lanthanide anionic frameworks have been successfully constructed from lanthanide ions and H4MDIP under mild conditions. Compounds 1−7 exhibit an infinite metalcarboxylate oxygen chain structure, while compounds 8−10 are assembled from paddle-wheel building blocks forming (4,8)-connected topological networks. The two new coordination modes adopted by MDIP anion further reveal the versatility of MDIP anions as bridging ligands. The structural diversity principally stems from the flexibility of coordination fashions of the ligand employed and lanthanide contraction effect. Luminescence studies demonstrated that the semirigid carboxylate ligand is an efficient sensitizer of the luminescence

*Tel.: +86 431 85262127; fax: +86 431 85698041; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the financial aid from the National Natural Science Foundation of China Major Project (Grant No. 91122030), ‘863'-National High Technology Research and Development Program of China (Grant No. 2011AA03A407) and National Natural Science Foundation for Creative Research Group (Grant No. 20921002). 1814

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Article

(9) (a) Guo, X.; Zhu, G.; Fang, Q.; Xue, M.; Tian, G.; Sun, J.; Li, X.; Qiu, S. Inorg. Chem. 2005, 44, 3850. (b) Han, Y. F.; Zhou, X. H.; Zheng, Y. X.; Shen, Z.; Song, Y.; You, X. Y. CrystEngComm 2008, 10, 1237. (10) (a) Harbuzaru, B. V.; Corma, A.; Rey, F.; Atienzar, P.; Jordá, J. L.; García, H.; Ananias, D.; Carlos, L. D.; Rocha, J. Angew. Chem., Int. Ed. 2008, 47, 1080. (b) Lin, Y. W.; Jian, B. R.; Huang, S. C.; Huang, C. R.; Hsu, K. F. Inorg. Chem. 2010, 49, 2316. (c) Lama, P.; Aijaz, A.; Neogi, S.; Barbour, L. J.; Bharadwaj, P. K. Cryst. Growth Des. 2010, 10, 3410. (11) (a) Duan, X. Y.; Li, Y. Z.; Su, Y.; Zang, S. Q.; Zhu, C. J.; Meng, Q. J. CrystEngComm. 2007, 9, 758. (b) Duan, X. Y.; Lin, J. G.; Li, Y. Z.; Zhu, C. J.; Meng, Q. J. CrystEngComm. 2008, 10, 207. (c) Duan, X. Y.; Cheng, X.; Lin, J. G.; Zang, S. Q.; Li, Y. Z.; Zhu, C. J.; Meng, Q. J. CrystEngComm. 2008, 10, 706. (d) Su, S. Q.; Guo, Z. Y.; Li, G. H.; Song, S. Y.; Deng, R. P.; Qin, C.; Pan, C. L.; Guo, H. D.; Cao, F.; Wang, S.; Zhang, H. J. Dalton Trans. 2010, 39, 9123. (e) Su, S.; Qin, C.; Song, S.; Guo, Z.; Deng, R.; Chen, W.; Song, X.; Wang, S.; Li, G.; Zhang, H. CrystEngComm. 2011, 13, 6057−6064. (12) Blanc, J. R. L.; Sharp, D. B. J. Org. Chem. 1961, 26, 4631. (13) Theory and Applications of Molecular Paramagnetism; Boudreaux, E. A.; Mulay, L. N., Eds.; John Wiley & Sons: New York, 1976. (14) Sheldrick, G. M. SHELXL-97, Program for Refinement of Crystal Structures; University of Göttingen, Germany, 1997. (15) Wang, C. G.; Xing, Y. H.; Li, Z. P.; Li, J.; Zeng, X. Q.; Ge, M. F.; Niu, S. Y. Cryst. Growth Des. 2009, 9, 1525. (16) (a) Feng, X.; Wang, L. Y.; Wang, J. G.; Xie, C. Z.; Zhao, J. S.; Sun, Q. CrystEngComm. 2010, 12, 3476. (b) Ramya, A. R.; Reddy, M. L. P.; Cowley, A. H.; Vasudevan, K. V. Inorg. Chem. 2010, 49, 2407. (c) Xu, J.; Sun, L.; Xing, H.; Liang, Z.; Yu, J.; Xu, R. Inorg. Chem. Commun. 2011, 14, 978. (17) (a) Li, S. L.; Lan, Y. Q.; Qin, J. S.; Ma, J. F.; Su, Z. M. Cryst. Growth Des. 2008, 8, 2055. (b) Ma, L.; Mihalcik, D. J.; Lin, W. J. Am. Chem. Soc. 2009, 131, 4610. (18) (a) Biju, S.; Raj, D. B. A.; Reddy, M. L. P.; Kariuki, B. M. Inorg. Chem. 2006, 45, 10651. (b) Shyni, R.; Biju, S.; Reddy, M. L. P.; Cowley, A. H.; Findlater, M. Inorg. Chem. 2007, 46, 11025. (c) Zhang, A. J.; Wang, Y. W.; Dou, W.; Dong, M.; Zhang, Y. L.; Tang, Y.; Liu, W. S.; Peng, Y. Dalton Trans. 2011, 40, 2844. (19) Klink, S. I.; Grave, L.; Reinhoudt, D. N.; van Veggel, F. C. J. M.; Werts, M. H, V.; Geurts, F. A. J.; Hofstraat, J. W. J. Phys. Chem. A 2000, 104, 5457. (20) Guo, Y.; Dou, W.; Zhou, X.; Liu, W.; Qin, W.; Zang, Z.; Zhang, H.; Wang, D. Inorg. Chem. 2009, 48, 3581. (21) (a) Shyni, R.; Biju, S.; Reddy, M. L. P.; Cowley, A. H.; Findlater, M. Inorg. Chem. 2007, 46, 11025. (b) Wang, Y. W.; Zhang, Y. L.; Dou, W.; Zhang, A. J.; Qin, W. W.; Liu, W. S. Dalton Trans. 2010, 39, 9013. (22) (a) Driesen, K.; Van Deun, R.; Görller-Walrand, C.; Binnemans, K. Chem. Mater. 2004, 16, 1531. (b) Lunstroot, K.; Nockemann, P.; Van Hecke, K.; Van Meervelt, L.; Görller-Walrand, C.; Binnemans, K.; Driesen, K. Inorg. Chem. 2009, 48, 3018. (23) (a) Feng, J.; Zhang, H. J.; Song, S. Y.; Li, Z. F.; Sun, L. N.; Xing, Y.; Guo, X. M. J. Lumin. 2008, 128, 1957. (b) Stouwdam, J. W.; van Veggel, F. C. J. M. Nano Lett. 2002, 2, 733. (24) (a) Dang, S.; Sun, L. N.; Song, S. Y.; Zhang, H. J.; Zheng, G. L.; Bi, Y. F.; Guo, H. D.; Guo, Z. Y.; Feng, J. Inorg. Chem. Commun. 2008, 11, 531. (b) Voloshin, A. I.; Shavaleev, N. M.; Kazakov, V. P. J. Lumin. 2001, 93, 199. (25) Sun, L. N.; Yu, J. B.; Zhang, H. J.; Meng, Q. G.; Ma, E.; Peng, C. Y.; Yang, K. Y. Microporous Mesoporous Mater. 2007, 98, 156. (26) (a) Feng, J.; Yu, J. B.; Song, S. Y.; Sun, L. N.; Fan, W. Q.; Guo, X. M.; Dang, S.; Zhang, H. J. Dalton Trans. 2009, 2406. (b) Wolbers, P. O.; Van Veggel, F. C. J. M.; Snellink-Rüel, B. H. M.; Hofstraat, J.; Geurts, F. A. J.; Reinhoudt, D. N. J. Chem. Soc., Perkin Trans. 1998, 2, 2141. (c) Kang, T. S.; Harrison, B. S.; Bouguettaya, M.; Foley, T. J.; Boncella, J. M.; Schanze, K. S.; Reynolds, J. R. Adv. Funct. Mater. 2003, 13, 205. (d) Yan, P. F.; Chen, S.; Chen, P.; Zhang, J. W.; Li, G. M. CrystEngComm 2011, 13, 36.

REFERENCES

(1) (a) Dimos, A.; Tsaousis, D.; Michaelides, A.; Skoulika, S.; Golhen, S.; Ouahab, L.; Didierjean, C.; Aubry, A. Chem. Mater. 2002, 14, 2616. (b) Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X.; Zheng, C.; Hattori, Y.; Kaneko, K. J. Am. Chem. Soc. 2003, 125, 3062. (c) Devic, T.; Serre, C.; Audebrand, N.; Marrot, J.; Férey, G. J. Am. Chem. Soc. 2005, 127, 12788. (d) Hoffart, D. J.; Leob, S. J. Angew. Chem., Int. Ed. 2005, 44, 901. (e) Jeong, K. S.; Kim, Y. S.; Kim, Y. J.; Lee, E.; Yoon, J. H.; Park, W. H.; Park, Y. W.; Jeon, S. J.; Kim, Z. H.; Kim, J.; Jeong, N. Angew. Chem., Int. Ed. 2006, 45, 8134. (f) Zhang, J.; Yao, Y. G.; Bu, X. H. Chem. Mater. 2007, 19, 5083. (g) Deng, Z. P.; Kang, W.; Huo, L. H.; Zhao, H.; Gao, S. Dalton Trans. 2010, 39, 6276. (2) (a) Long, D. L.; Blake, A. J.; Champness, N. R.; Wilson, C.; Schröder, M. Angew. Chem., Int. Ed. 2001, 40, 2444. (b) Sun, Y. Q.; Zhang, J.; Chen, Y. M.; Yang, G. Y. Angew. Chem., Int. Ed. 2005, 44, 5814. (c) Maji, T. K.; Mostafa, G.; Chang, H. C.; Kitagawa, S. Chem. Commun. 2005, 2436. (d) Farha, O. K.; Spokoyny, A. M.; Mulfort, K. L.; Hawthorne, M. F.; Mirkin, C. A.; Hupp, J. T. J. Am. Chem. Soc. 2007, 129, 12680. (e) Luo, J.; Xu, H.; Liu, Y.; Zhao, Y.; Daemen, L. L.; Brown, C.; Timofeeva, T. V.; Ma, S.; Zhou, H. C. J. Am. Chem. Soc. 2008, 130, 9626. (f) Novitchi, G.; Wernsdorfer, W.; Chibotaru, L. F.; Costes, J. P.; Anson, C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2009, 48, 1614. (3) (a) Gándara, F.; García-Cortés, A.; Cascales, C.; Gómez-Lor, B.; Gutiérrez-Puebla, E.; Iglesias, M.; Monge, A.; Snejko, N. Inorg. Chem. 2007, 46, 3475. (b) Cunha-Silva, L.; Lima, S.; Ananias, D.; Silva, P.; Mafra, L.; Carlos, L. D.; Pillinger, M.; Valente, A. A.; Paz, F. A. A.; Rocha, J. J. Mater. Chem. 2009, 19, 2618. (c) Vitorino, M. J.; Devic, T.; Tromp, M.; Férey, G.; Visseaux, M. Macromol. Chem. Phys. 2009, 210, 1923. (d) Amghouz, Z.; Roces, L.; García-Granda, S.; Garcia, J. R.; Souhail, B.; Mafra, L.; Shi, F. N.; Rocha, J. Inorg. Chem. 2010, 49, 7917. (e) Choi, J. R.; Tachikawa, T.; Fujitsuka, M.; Majima, T. Langmuir 2010, 26, 10437. (f) Gustafsson, M.; Bartoszewicz, A.; Martín-Matute, B.; Sun, J.; Grins, J.; Zhao, T.; Li, Z.; Zhu, G.; Zhou, X. Chem. Mater. 2010, 22, 3316. (g) Rocha, J.; Carlos, L. D.; Paz, F. A. A.; Ananias, D. Chem. Soc. Rev. 2011, 40, 926. (4) (a) Guo, Z. Y.; Xu, H.; Su, S. Q.; Cai, J. F.; Dang, S.; Xiang, S. C.; Qian, G. D.; Zhang, H. J.; O’Keeffe, M.; Chen, B. L. Chem. Commun. 2011, 47, 5551. (b) Chen, B. L.; Wang, L. B.; Zapata, F.; Qian, G. D.; Lobkovsky, E. B. J. Am. Chem. Soc. 2008, 130, 6718. (5) (a) Mahata, P.; Natarajan, S. Inorg. Chem. 2007, 46, 1250. (b) Fratini, A.; Richards, G.; Larder, E.; Swavey, S. Inorg. Chem. 2008, 47, 1030. (c) Zucchi, G.; Maury, O.; Thuéry, P.; Gumy, F.; Bünzli, J. C. G.; Ephritikhine, M. Chem.Eur. J. 2009, 15, 9686. (d) Yan, L.; Yue, Q.; Jia, Q. X.; Lemercier, G.; Gao, E. Q. Cryst. Growth Des. 2009, 9, 2984. (6) (a) Han, Y. F.; Li, X. Y.; Li, L. Q.; Ma, C. L.; Shen, Z.; Song, Y.; You, X. Z. Inorg. Chem. 2010, 49, 10781. (b) Li, X.; Sun, H. L.; Wu, X. S.; Qiu, X.; Du, M. Inorg. Chem. 2010, 49, 1865. (c) Zhang, H. J.; Wang, X. Z.; Zhu, D. R.; Song, Y.; Xu, Y.; Xu, H.; Shen, X.; Gao, T.; Huang, M. X. CrystEngComm. 2011, 13, 2586. (d) Xu, N.; Wang, C.; Shi, W.; Yan, S. P.; Cheng, P.; Liao, D. Z. Eur. J. Inorg. Chem. 2011, 2387. (7) (a) Reineke, T. M.; Eddaoudi, M.; Fehr, M.; Kelley, M.; Yaghi, O. M. J. Am. Chem. Soc. 1999, 121, 1651. (b) Reineke, T. M.; Eddaoudi, M.; Keeffe, M. O.; Yaghi, O. M. Angew. Chem., Int. Ed. 1999, 38, 2590. (c) Pan, L.; Zheng, M.; Wu, Y.; Han, S.; Yang, R.; Huang, X.; Li, J. Inorg. Chem. 2001, 40, 828. (d) Guo, X.; Zhu, G.; Sun, F.; Li, Z.; Zhao, X.; Li, X.; Wang, H.; Qiu, S. Inorg. Chem. 2006, 45, 2581. (e) Daiguebonne, C.; Kerbellec, N.; Bernot, K.; Gérault, Y.; Deluzet, A.; Guillou, O. Inorg. Chem. 2006, 45, 5399. (f) Yang, X. P.; Jones, R. A.; Rivers, J. H.; Lai, R. P. Dalton Trans. 2007, 3936. (g) Black, C. A.; Costa, J. S.; Fu, W. T.; Massera, C.; Roubeau, O.; Teat, S. J.; Aromí, G.; Gamez, P; Reedijk, J. Inorg. Chem. 2009, 48, 1062. (8) (a) Yang, J.; Yue, Q.; Li, G.; Cao, J.; Li, G.; Chen, J. Inorg. Chem. 2006, 45, 2857. (b) Guo, X.; Zhu, G.; Li, Z.; Chen, Y.; Li, X.; Qiu, S. Inorg. Chem. 2006, 45, 4065. (c) Guo, X.; Zhu, G.; Li, Z.; Sun, F.; Yang, Z.; Qiu, S. Chem. Commun. 2006, 3172. (d) Jiang, H. L.; Tsumori, N.; Xu, Q. Inorg. Chem. 2010, 49, 10001. 1815

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