Structure, Near-Infrared Luminescence and Magnetic - American

Article pubs.acs.org/crystal

Five sra Topological Ln(III)-MOFs Based on Novel Metal-Carboxylate/ Cl Chain: Structure, Near-Infrared Luminescence and Magnetic Properties Li-Na Jia, Lei Hou,* Lei Wei, Xiao-Jing Jing, Bo Liu, Yao-Yu Wang,* and Qi-Zhen Shi Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China S Supporting Information *

ABSTRACT: Five isostructural three-dimensional (3D) lanthanide (Ln) frameworks [LnCl(bpdc)(DMF)] (Ln = La (1), Ce (2), Pr (3), Nd (4), and Sm (5), H2bpdc = 4,4′-biphenyl-dicarboxylic acid, DMF = N,Ndimethylformamide) have been solvothermally synthesized and characterized by TGA, IR, and X-ray single crystal diffraction. The frameworks contain unusual Ln-carboxylate/Cl chains, and which are extended by bpdc2‑ linkers to form 4-connected sra networks with 1D rhombic channels. The effect of lanthanide contraction induces the decreases of average Ln−O and Ln−Cl distances from La to Sm. 4 exhibits strong characteristic luminescence of Nd3+ ions in the near-infrared (NIR) region, resulting from the sensitization of bpdc2−. 3 displays weak NIR emission due to the inefficient sensitization of Pr3+ ions. The depopulation of the Stark levels and possible antiferromagnetic interactions within the Lncarboxylate/Cl chains lead to the continuous decreases of χMT for 2−4 along the decreasing temperatures.

■

INTRODUCTION Lanthanide metal−organic frameworks (Ln-MOFs) are considered as one of the promising materials for unique applications in optical, magnetic, sorption and catalytic fields.1 Especially, Ln-MOFs that emit in the near-infrared (NIR) region, such as Yb3+-, Nd3+-, Pr3+-, and Er3+-containing MOFs have attracted ever-increasing interest because of their important uses in the fields of luminescent materials, laser systems, and time-resolved imaging of biological tissues.2,3 However, because of the weak absorption coefficient for the forbidden f−f transitions of Ln3+ ions, the luminescence of LnMOFs is commonly sensitized through energy transfer from πconjugated organic chromophores to Ln3+ centers.4 With regard to the construction of functionalized Ln-MOFs, the aromatic multicarboxylate is the most important organic ligand because of its strong binding tendency toward Ln3+ ions, as well as serving potentially as a sensitizer to enhance the Ln3+ luminescence.5 So far a number of Ln-MOFs have been fabricated through using aromatic multicarboxylate as linkers, such as 1,4-benzene-dicarboxylate,6 4,4′-biphenyl-dicarboxylate, 7 1,3,5-benzene-tricarboxylate, 8 and benzophenon3,3′,4,4′-tetracarboxylate.9 Among these multicarboxylic acids, 4,4′-biphenyl-dicarboxylic acid (H2bpdc) is one of the simplest connectors, which can be partially or completely deprotonated to form Hbpdc− or bpdc2− ligand to bridge metal ions. More importantly, H2bpdc is a potential large π-conjugated system when its two benzene rings are coplanar, which can sensitize the luminescence of Ln3+ centers in MOFs.10 © 2013 American Chemical Society

While large numbers of Ln-MOFs have been documented, the high-dimensional Ln-MOFs are not well developed because of the high coordination numbers and flexible coordination geometries of Ln3+ ions.11 The rod-shaped Ln-carboxylate chain secondary building units (SBUs) are very favorable to generate high-dimensional frameworks, as a result, versatile Lncarboxylate chains SBUs have been utilized to build 3D frameworks.12 By contrast, the modified Ln-carboxylate chains with other small-sized anion, such as a soft Lewis base Cl−, are less investigated for the construction of MOFs. As we all know, Ln3+ ions feature the hard Lewis acid nature and oxyphilic coordination, so it is challenging to prepare carboxylate/Clcontaining Ln-complexes. Thanks to the different acid intensity for different Ln3+ ions, Cl− has been successfully incorporated into some Ln-carboxylate systems as bridging ligands.13 However, according to the latest CCDC research (version 5.33), only 59 carboxylate/Cl−Ln complexes can be found. In them, only four complexes involved Ln−carboxylate/Cl chains,14 which are much less than MOFs containing Ln− carboxylate chains.12 Huang and his co-workers15 have lately synthesized twelve isostructural rod-shaped Ln−carboxylate/Cl chain-based frameworks, [Hmim][Ln2Cl(1,4-ndc)3] (Hmim = 1-hexyl-3-methylimidazolium, 1,4-ndc = 1,4-naphthalenedicarboxylate), by employing LnCl3 and ion liquid [Hmim]Cl as Cl− resource. To explore the structural varieties and unique Received: December 10, 2012 Revised: March 4, 2013 Published: March 14, 2013 1570

dx.doi.org/10.1021/cg301810y | Cryst. Growth Des. 2013, 13, 1570−1576

Crystal Growth & Design

Article

Table 1. Crystallographic Data of 1−5 empirical formula formula weight crystal system space group T (K) a (Ǻ ) b (Ǻ ) c (Ǻ ) V (Ǻ 3) Z Dc (g·cm−3) μ (mm−1) reflns collected reflns unique Rint GOF R1,a R2b [I > 2σ(I)] R1, R2 (all data) a

1

2

3

4

5

C17H15ClLaNO5 487.66 orthorhombic Pnma 296(2) 7.464(2) 25.721(7) 9.446(3) 1813.5(8) 4 1.786 2.529 9715 1999 0.0372 1.098 0.0349, 0.0855 0.0426, 0.0894

C17H15CeClNO5 488.87 orthorhombic Pnma 296(2) 7.4355(12) 25.881(4) 9.5099(15) 1830.1(5) 4 1.774 2.659 8976 1828 0.0216 1.121 0.0319, 0.0734 0.0337, 0.0744

C17H15ClNO5Pr 489.66 orthorhombic Pnma 296(2) 7.3702(9) 25.843(3) 9.4821(12) 1806.1(4) 4 1.801 2.871 8925 1800 0.0466 1.073 0.0314, 0.0699 0.0395, 0.0729

C17H15ClNNdO5 492.99 orthorhombic Pnma 296(2) 7.3481(8) 25.927(3) 9.5122(10) 1812.2(3) 4 1.807 3.038 8933 1815 0.0323 1.138 0.0302, 0.0690 0.0337, 0.0704

C17H15ClNO5Sm 499.10 orthorhombic Pnma 296(2) 7.2822(14) 25.977(5) 9.5234(19) 1801.5(6) 4 1.840 3.434 8335 1799 0.0442 1.104 0.0508, 0.1208 0.0660, 0.1321

R1 = Σ∥Fo|−|Fc|)/Σ|Fo|. bR2 = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2. N, 2.83%. IR (KBr, cm−1): 2925(w), 1655(s), 1576(m), 1518(s), 1378(s), 1248(w), 1109(w), 1003(w), 852(m), 768(m), 671(m). [NdCl(bpdc)(DMF)] (4). Yield: ∼21 mg (42.6%). Anal. Calcd for C17H15ClNNdO5: C, 41.42; H, 3.07; N, 2.84. Found: C, 41.36; H, 3.04; N, 2.79%. IR (KBr, cm−1): 2925(w), 1669(vs), 1574(w), 1378(s), 1248(w), 1117(s), 1023(w), 856(m), 768(m), 659(m). [SmCl(bpdc)(DMF)] (5). Yield: ∼8 mg (16.0%). Anal. Calcd for C17H15ClNO5Sm: C, 40.91; H, 3.02; N, 2.81. Found: C, 41.97; H, 3.09; N, 2.75%. IR (KBr, cm−1): 2927(w), 1657(s), 1581(s), 1529(s), 1398(vs), 1111(m), 1007(w), 854(m), 769(m), 673(m). Besides prism crystals of complex 5, the sheet crystals (about 1:1, naked-eye observation under microscope) were also obtained, which are the reported complex [Sm2(bpdc)3(HCOO)2]n10 through X-ray diffraction verification. X-ray Crystallographic Measurements. Diffraction data were collected with a Mo Kα radiation (λ = 0.71073 Å) at 296(2) K on a Bruker-AXS SMART CCD area detector diffractometer. Absorption corrections were carried out utilizing SADABS routine. The structures were solved by the direct methods and refined by full-matrix leastsquares refinements based on F2.16 The DMF molecules in complexes 1−5 are 2-fold disordered with the O atoms locating at the mirror plane. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were added to their geometrically ideal positions. Relevant crystallographic data were given in Table 1.

properties of Ln-MOFs with rod-shaped SBUs, we are interested in constructing Ln-carboxylate/Cl chain-based MOFs. Herein, the solvothermal reaction of H2bpdc with LnCl3 gave five isostructural 3D Ln-MOF [LnCl(bpdc)(DMF)] (Ln = La, 1; Ce, 2; Pr, 3; Nd, 4; Sm, 5) based on unusual Ln-carboxylate/Cl chain. The effect of lanthanide contraction imposes an important effect on the Ln−O and Ln− Cl distances from 1 to 5. Compound 4 exhibits strong NIR luminescence from the Nd 3+ centers because of the sensitization of bpdc2− ligand, whereas 3 shows weak NIR emission. The temperature-dependent magnetic properties of 2−4 were investigated as well.

■

EXPERIMENTAL SECTION

Materials and General Methods. All solvents and starting materials for synthesis were purchased commercially and were used as received. Infrared spectra (IR) were obtained in KBr discs on a Nicolet Avatar 360 FTIR spectrometer in the 400−4000 cm−1 region. Elemental analyses of C, H and N were determined with a PerkinElmer 2400C Elemental Analyzer. UV−vis absorption spectra were collected on a U-3310 spectrophotometer. Photoluminescence analyses were performed on an Edinburgh FLS55 luminescence spectrometer. Thermalgravimetric analyses (TGA) were carried out in N2 stream using a Netzsch TG209F3 equipment at a heating rate of 5 °C/min. Powder X-ray diffraction (PXRD) data were recorded on a Bruker D8 ADVANCE X-ray powder diffractometer (Cu Kα, 1.5418 Å). Synthesis of Complexes 1−5. Complexes 1−5 were synthesized in a typical procedure. A mixture of LnCl3·6H2O (0.10 mmol) and H2bpdc (0.10 mmol) in DMF (5 mL) and CH3CN (5 mL) was placed in a Teflon-lined stainless steel vessel (15 mL), which was heated at 120 °C for 72 h, and then cooled to room temperature at a rate of 5 °C/h to give prism crystals of 1-5, respectively. [LaCl(bpdc)(DMF)] (1). Yield: ∼24 mg (49.2%). Anal. Calcd for C17H15ClLaNO5: C, 41.87; H, 3.10; N, 2.87. Found: C, 41.85; H, 3.14; N, 2.91%. IR (KBr, cm−1): 2926(w), 1653(s), 1574(s), 1525(s), 1383(vs), 1142(w), 1011(w), 854(m), 769(m), 6595(m). [CeCl(bpdc)(DMF)] (2). Yield: ∼22 mg (45.0%). Anal. Calcd for C17H15CeClNO5: C, 41.77; H, 3.09; N, 2.87. Found: C, 41.73; H, 3.12; N, 2.90%. IR (KBr, cm−1): 2927(m), 1651(vs), 1581(s), 1533(s), 1389(vs), 1109(w), 1007(w), 850(m), 768(m), 675(m). [PrCl(bpdc)(DMF)] (3). Yield: ∼22 mg (44.9%). Anal. Calcd for C17H15ClNO5Pr: C, 41.70; H, 3.09; N, 2.86. Found: C, 41.75; H, 3.04;

■

RESULTS AND DISCUSSION Coordination Trends of Cl− toward Ln3+. Complexes 1− 5 can be repeatedly prepared with a moderate yield by the solvothermal reaction of LnCl3 with H2bpdc in DMF-CH3CN solvents, indicating a significant affinity of La3+, Ce3+, Pr3+, Nd3+, and Sm3+ ions toward Cl− anion. It was failed to obtain the isostructural or Cl-containing frameworks through employing other Ln3+ ions, which should be ascribed to the effect of lanthanide contraction. It is known that the Lewis acidity of Ln3+ ion strengthens gradually with the increase of its chargeto-radius ratio.17 Accordingly, the light Ln3+ ion has softer acidity than the heavy one due to the radii contraction of Ln3+ ions. In terms of the hard−soft acids−bases (HSAB) principle, La3+, Ce3+, Pr3+, Nd3+, and Sm3+ ions are more facile to coordinate with soft base Cl− ion than other Ln3+ ions. Therefore, during crystallization of 5, a Cl-free framework [Sm2(bpdc)3(HCOO)2]n10 was formed as well, whereas 1571



Article

bridges leads to that the intrachain Nd···Nd separations (3.9166(5) Å) are shorter than the usually observed values in pure Ln−carboxylate units (∼4.0−4.6 Å, Supporting Information Table S2). In 4, the chains are further extended by bpdc2− to form a 3D framework (Figure 3). To the best of our

employing GdCl3 as a reactant, only the Cl-free framework [Gd2(bpdc)3(HCOO)2]n10 was obtained. Description of the Crystal Structure. Since complexes 1−5 are isostructural, the structure of 4 is discussed as an example. The X-ray diffraction analysis reveals that 4 is a noninterpenetrated 3D coordination polymer based on infinite metal-carboxylate/Cl chain SBUs. The asymmetric unit consists of one Nd3+ cation, one-half of fully deprotonated bpdc2− ligand, one coordinated DMF molecule, and one μ2-Cl atom. The Nd3+ cation and the Cl atom are located at the mirror plane with 50% occupancy. As shown in Figure 1, the Nd3+ ion

Figure 3. Projection view of the framework 4 along the a axis with the coordinated DMF in one channel highlighted.

knowledge, the Ln−carboxylate/Cl chain SBUs are only reported in five different types of coordination polymers, including three types of 3D MOFs14a,b,15 and two 1D complexes.14c,d However, different from the case in 4, all of those reported 3D MOFs were constructed through the ion liquids as templates, and then exhibited anionic frameworks. 4 is the first neutral Ln-carboxylate/Cl chain-based 3D MOFs. Along the a axis, 4 generates a narrow 1D rhombic channel with the window sizes of ∼18.1 × 3.4 Å2 (excluding van der Walls radii of the atoms). The channels possess 32.7% solvent accessible voids,18 which are occupied by DMF ligands. Topologically, the carboxylate C atoms in the metalcarboxylate chain are often treated as nodes.19 Thus each chain in 4 can be simplified as a rod-shaped SBU (Figure 2), and the whole framework forms a uninodal 4-connected sra net with the point symbol 42638 and vertex symbol 4.6.4.6.6.82 (Figure 4).20 The 4-connected sra, irl, and ukv nets have been

Figure 1. Coordination environment of Nd atom in 4. Symmetry codes: #1 x + 1/2, y, −z + 3/2; #2 x + 1/2, −y + 3/2, −z + 3/2; #3 x, −y + 3/2, z (azure C, red O, green Cl, blue N, purple Nd). Nd(1)− O(1) = 2.552(3) Å, Nd(1)−O(1)#1 = 2.475(3) Å, Nd(1)−O(2) = 2.532(4) Å, Nd(1)−O(3) = 2.430(6) Å, Nd(1)−Cl(1) = 2.8101(17) Å, Nd(1)−Cl(1)#1 = 2.9258(19) Å.

is nine-coordinated by six carboxylate O atoms from four carboxylate groups of four different bpdc2‑ [Nd−O = 2.532(4), 2.552(3), and 2.475(3) Å], two Cl atoms, and one O atom from a DMF ligand, forming a distorted monocapped squareantiprism geometry (Supporting Information Figure S1). Each bpdc2− bridges four Nd3+ ions through two carboxylate groups with the same μ2-η2:η1 mode. In 4, the interlinkage between Nd3+ ions and carboxylate groups of bpdc2− generates an infinite Nd−carboxylate chain along the a axis. The chain is strengthened by μ2-Cl atoms bridging adjacent Nd3+ centers, giving rise to an unusual Nd− carboxylate/Cl chain (Figure 2). The incorporation of Cl

Figure 4. 4-Connected sra topological net of 4.

documented in MOFs,19,21 interestingly, they have the same point symbols but different vertex symbols (irl = 4.6.4.6.6.1012, ukv = 4.6.4.6.6.1026).22 The sra net is usually reported in MOFs,23 whereas rarely observed in MOFs based on rodshaped SBUs.19,24 The Ln3+ ions have variable coordination geometries, and show no preference for any particular coordination geometry due to the buried valence orbits, which make it difficult to construct Ln-MOFs with certain topology. The results in 1−5 suggest that using rod-shaped SBUs may overcome this potential difficulty.

Figure 2. 1D Nd-carboxylate/Cl chain along the a axis and its simplified rod-shaped SBU in 4. 1572



Article

Figure 5. Variations of the average Ln−O and Ln−Cl distances, and the Ln···Ln, Cl···O, and O···O separations in 1−5.

Structural Effect of Lanthanide Contraction. Complexes 1−5 are isomorphous. The average Ln−O and Ln−Cl bond lengths and Ln···Ln separations decrease from La3+ to Sm3+ (Figure 5), consistent with the decreasing sequence of ionic radii due to the effect of lanthanide contraction. Generally, as the sizes of the Ln3+ ions decrease, the repulsions among the coordination atoms around one metal center increase, until the crystal structure becomes unstable and then forms a new structure.25 Around the nine-coordinated Ln3+ centers from 1 to 5, the closest intercarboxylate O···O separations decrease significantly from 2.811 to 2.743 Å (Figure 5), which is also imitated by Cl···O separations from 3.198 to 3.138 Å. The decreases induce the increasing repulsions among the coordinated atoms from 1 to 5. Especially during the formation of 5, a Cl-free framework [Sm2(bpdc)3(HCOO)2]n10 was concomitant, however, using GdCl3 as a reactant, even only the Cl-free framework [Gd2(bpdc)3(HCOOH)2]n10 was obtained. These two frameworks possess the eight-coordinated Ln3+ centers, presumedly to minimize the repulsions among the coordinated atoms. Following this trend, the isostructural frameworks of 1−5 could not be built employing other Ln3+ ions. The light Ln3+ ions forming high coordinated numbers and the heavier ions generating low coordinated geometries were also observed in other Ln-MOFs.11c TGA, PXRD, and IR. In line with the isostructural structures of 1−5, their TGA curves display the similar two-step weight losses (Suppporting Information Figure S2). TGA of 4 is herein discussed. It shows that 4 releases the coordinated DMF in the 100−310 °C temperature region with the weight loss of 17.8% (calcd14.8%). A stable plateau is following until ending at 540 °C. This thermal stable temperature is very high, and surpasses greatly the reported values for most MOFs (below 450 °C). Comparing with the decomposition temperature 320 °C of H2bpdc (Supporting Information Figure S2), the high thermostability of 4 is ascribed to the strong and multiple Nd−O bonds of bpdc2− involved, as well as the generation of Ndcarboxylate/Cl chain, which tighten the backbone of bpdc2− to increase the resistance to pyrolysis. The further heating on 4 leads to the framework decomposition due to the loss of bpdc2− from 540 to 660 °C. The experimental PXRD patterns of 1−5 are consistent with the simulated ones from the corresponding single crystal

structures (Figure 6 and Supporting Information Figure S3), demonstrating the phase purity. Upon heating the sample of 4

Figure 6. PXRD patterns of 4 obtained from different conditions: black, simulated from the single crystal data; red, as-synthesized; green, desolvated at 180 °C for 5 h under vacuum; blue, desolvated at 220 °C for 5 h under vacuum.

at 180 °C under vacuum to remove the coordinated DMF, the IR spectrum indicates the incomplete elimination of DMF because its characteristic CO stretching peak still exists at 1662 cm−1 (Figure 7). Raising the temperature to 220 °C, DMF in 4 can be completely excluded, which was verified by the disappearance of CO stretching peak from DMF in the IR spectrum of the desolvated sample. Noteworthily, some peaks in the PXRD of the desolvated 4 show low-angle shifting (Figure 6), especially hkl (020) peak (d(020) = 13.973 Å), which corresponds to the b/2 cell axis, and moves to 6.32° from 6.85° in the simulated one. This phenomenon indicates the significant b cell axis lengthening from the original 25.927(3)−27.946 Å after desolvation. Meanwhile, the new peaks at 2θ of 11.52° and 12.56° in the PXRD pattern of the desolvated 4 also imply obvious framework distortion. Because of the formation of rigid metal−carboxylate/Cl chain, the lengthening of the b-axis will cause the c axis to shorten. As a result, the channel in 4 is compressed to become narrower after DMF removal. This phenomenon is rarely documented, and similar with the cases in rod-shaped SUB-based frameworks MIL-53(Fe)26 and SUMOF-6-Sm.12b PXRD pattern of 4 can 1573



Article

Figure 8. Solid-state absorption and excitation spectra of 4, and the absorption spectrum of H2bpdc at room temperature.

Figure 7. IR spectra of 4 obtained from different conditions: black, assynthesized; red, desolvated at 180 °C for 5 h under vacuum; green, desolvated at 220 °C for 5 h under vacuum.

not be recruited from the desolvated sample which was reimmersed in DMF, methanol or acetonitrile solvent, indicating that its narrow channel windows prevent the solvent molecules from entering the pore to restore the framework (Supporting Information Figure S4). However, different from the significant structural change of 4 after desolvation, the diffraction peaks in the PXRD of desolvated 1−3 do not exhibit obvious shift (Supporting Information Figure S3), indicating no structural change after desolvation. These different observations are related with the change of the central metal ions in 1−4. According to the aforementioned results, the repulsions among the coordinated atoms around Ln3+ centers are increasing from 1 to 4 because of the effect of lanthanide contraction. Consequently, their stabilities decrease by turn. This trend can also be reflected by some gradually weakened and even disappeared diffraction peaks in the PXRD of the desolvated samples from 1 to 4. Therefore, upon desolvation, the framework of 4 is easily changed. Photoluminescence Properties. Although there are much known about Ln-MOFs with visible light-emitting, NIR emissive Ln-MOFs are rather rare. Nd-based systems have been considered as the most promising NIR luminescent materials in the fields of laser systems and optical telecommunication.3 Considering this view, the luminescent properties of the Nd-complex 4 were investigated detailedly. The solid state UV−vis absorption, emission, and excitation spectra were measured for H2bpdc and 4 to determine how the structure impacts the luminescent properties of the system. As shown in Figure 8, the absorption spectrum of H2bpdc displays the maximum peak centered at 310 nm and a weak shoulder at 219 nm, attributing to the π → π* and n → π* electron transitions, respectively. The absorption spectrum of 4 matches well with that of H2bpdc, implying the main H2bpdc-based absorption for 4. The excitation spectrum of 4 exhibits a broad band centered at 327 nm but no obvious line bands between 350 and 450 nm because of the f−f transitions of Nd3+ ion.27 This broad band is overlapped significantly with the absorption spectrum of H2bpdc, indicating that bpdc2− sensitizes Nd3+ ions via the antenna effect.28 Upon excitation at 310−350 nm region, 4 displays three strong emission bands in the NIR region, deriving from the typical f−f transitions of Nd3+ ion at 893 (4F3/2 → 4I9/2), 1060 (4F3/2 → 4I11/2), and 1336 nm (4F3/2 → 4I13/2) (Figure 9),29 respectively. The peak at 1060 and 1336 nm are very useful in laser system2b and telecommunction

Figure 9. Solid-state emission spectra of 3 (λex = 350 nm) and 4 (λex = 327 nm) at room temperature.

application,2e respectively. Notably, despite of the strong emission at 420 nm of the free H2bpdc (Supporting Information Figure S5), no remnant H2bpdc-based emission is observed in the emission range 400−750 nm of 4 (Supporting Information Figure S6), which verifies the energy transfer from bpdc2− to Nd3+ centers. To further evaluate the sensitization effect, the solid state emission of NdCl3 was also measured (Supporting Information Figure S7), which displays the very weak emission, indicating that the efficient energy is highly efficient in 4. For bpdc2− ligand in 4, its two benzene planes are coplanar, and the dihedral angles between benzene rings and carboxylate groups are small (17.7°). Therefore, bpdc2− forms a large π-conjugated system, and then functionalize as an organic chromophore to transfer energy to Nd3+ centers.4a,30 The NIR luminescent properties of Pr-complex 3 were also studied. Distinct from that of 4, 3 displays two bands (200−250 and 330−440 nm) in the excitation spectrum (Supporting Information Figure S8), which slightly overlap with the absorption spectrum of H2bpdc, indicating the incomplete energy transfer from bpdc2− to Pr3+ centers. This result is probably due to the mismatch of the energy levels between the triplet state of bpdc2− and the excited state of the Pr3+ ions. Because of the inefficient sensitization of Pr3+ ions, upon excitation at 350 nm, 3 shows very weak NIR emission at 889, 1013, and 1260 nm, as well as a shoulder peak at 1110 nm (Figure 9). These emission bands are assigned to the 1D2−3F2, 1 D2−3F3, 1G4−3H5, and 1D2−3F3 transitions of Pr3+ ion, respectively.2b,31 1574



Article

Magnetic Properties. Variable-temperature magnetic susceptibilities of 2−4 were measured at an imposed field of 1.0 kOe in the temperature range 1.8−300 K. For 2−4, the observed paramagnetism results uniquely from the 4f Ln3+ ions. As shown in Figure 10, at 300 K, the χmT products of 2, 3, and

architectures, photoluminescent characteristics, and magnetic properties will be created.

■

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic information file (CIF), additional crystallographic figures, TGA, PXRD, excitation and emission spectra, magnetic plots, and bond length/angle and hydrogen bond tables. This information is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (L. H.), [email protected] (Y.-Y. W.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful for financial support from the NSF of China (Grants 20771090, 21001088, 20931005 and 91022004), the Doctoral Program of Higher Education of China (Grant 20096101110005), China Postdoctoral Scientific Foundation (Grant 20100471627), and NSF of Shaanxi, China (Grants 2009JZ001 and 2010JK872).

Figure 10. Variable-temperature magnetic susceptibilities of 2−4 at 1.0 kOe.

4 are 0.64, 1.42, and 1.53 cm3 K mol−1, respectively, which are comparable to the expected values of 0.80, 1.60, and 1.64 cm3 K mol−1 for the noninteracting Ce3+, Pr3+, and Nd3+ ions in their respective ground states (Ce3+:2F5/2, g = 6/7; Pr3+:3H4, g = 4/5; Nd3+:4I9/2, g = 8/11). Generally, the spin−orbital coupling induces the 4fn configuration of Ln3+ ions to split into 2S+1LJ states, which are further splits into Stark components because of the crystal-field perturbation.32 As a result, the variabletemperature magnetic behavior of a free Ln3+ ion often exhibits the significant deviation from the Curie law, and χmT decreases along the cooling temperature because of the depopulation of Stark levels. When the temperature is decreased, the χMT products of 2, 3, and 4 decline monotously and slowly within the entire temperature range, and reach 0.43, 0.35, and 0.55 cm3 K mol−1 at 1.8 K, respectively. These magnetic behaviors arise mainly from the thermal depopulation of the crystal-field energy levels of the multiplet,33 as well as possible combination from the antiferromagnetic interactions34 between the intrachain Ln3+ ions owing to short Ln···Ln separations (2, 3.9657(6) Å; 3, 3.9290(5) Å; 4, 3.9166(5) Å).

■

REFERENCES

(1) (a) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330. (b) Cui, Y. J.; Yue, Y. F.; Qian, G. D.; Chen, B. L. Chem. Rev. 2012, 112, 1126. (c) Corma, A.; García, H.; Llabrés i Xamena, F. X. Chem. Rev. 2010, 110, 4606. (d) Jiang, H. L.; Xu, Q. Chem. Commun. 2011, 47, 3351. (2) (a) Auzel, F. Chem. Rev. 2004, 104, 139. (b) Bünzli, J. C. G.; Pigue, C. Chem. Soc. Rev. 2005, 34, 1048. (c) Lazarides, T.; Alamiry, M. A. H.; Adams, H.; Pope, S. J. A.; Faulkner, S.; Weinstein, J. A.; Ward, M. D. Dalton Trans. 2007, 1484. (d) Luo, F.; Batten, S. R. Dalton Trans. 2010, 39, 4485. (e) Jaque, D.; Enguita, O.; García Solé, J.; Jiang, A. D.; Luo, Z. D. Appl. Phys. Lett. 2000, 76, 2176. (3) (a) Wong, W. K.; Yang, X. P.; Jones, R. A.; Rivers, J. H.; Lynch, V.; Lo, W. K.; Xiao, D.; Oye, M. M.; Holmes, A. L. Inorg. Chem. 2006, 45, 4340. (b) Guo, X. M.; Guo, H. D.; Fu, L. S.; Carlos, L. D.; Ferreira, R. A. S.; Sun, L. N.; Deng, R. P.; Zhang, H. J. J. Phys. Chem. C 2009, 113, 12538. (c) Long, J.; Chelebaeva, E.; Larionova, J.; Guari, Y.; Ferreira, R. A. S.; Carlos, L. D.; Paz, F. A. A.; Trifonov, A.; Guérin, C. Inorg. Chem. 2011, 50, 9924. (4) (a) Dong, Y. B.; Wang, P.; Ma, J. P.; Zhao, X. X.; Wang, H. Y.; Tang, B.; Huang, R. Q. J. Am. Chem. Soc. 2007, 129, 4872. (b) Liu, T. F.; Zhang, W. J.; Sun, W. H.; Cao, R. Inorg. Chem. 2011, 50, 5242. (c) Chandler, B. D.; Cramb, D. T.; Shimizu, G. K. H. J. Am. Chem. Soc. 2006, 128, 10403. (d) Borkowski, L. A.; Cahill, L. Cryst. Growth Des. 2006, 6, 2248. (5) (a) Ji, B. M.; Deng, D. S.; He, X.; Liu, B.; Miao, S. B.; Ma, N.; Wang, W. Z.; Ji, L. G.; Liu, P.; Li, X. F. Inorg. Chem. 2012, 51, 2170. (b) Bünzli, J. C. G. Chem. Rev. 2010, 110, 2729. (c) Thuéry, P. Cryst. Growth Des. 2011, 11, 347. (d) Lattuada, L.; Barge, A.; Cravotto, G.; Giovenzana, G. B.; Tei, L. Chem. Soc. Rev. 2011, 40, 3019. (e) Shi, W. J.; Hou, L.; Zhao, W.; Wu, L. Y.; Wang, Y. Y.; Shi, Q. Z. Inorg. Chem. Commun. 2011, 14, 1915. (f) Thuéry, P.; Masci, B. CrystEngComm 2012, 14, 131. (6) (a) Wang, Z.; Xing, Y. H.; Wang, C. G.; Sun, L. X.; Zhang, J.; Ge, M. F.; Niu, S. Y. CrystEngComm 2010, 12, 762. (b) Wang, Y. L.; Jiang, Y. L.; Xiahou, Z. J.; Fu, J. H.; Liu, Q. Y. Dalton Trans. 2012, 41, 11428. (7) (a) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 2011, 111, 6810. (b) Guo, X. D.; Zhu, G. S.; Fang, Q. R.; Xue, M.; Tian, G.; Sun, J. Y.; Li, X. T.; Qiu, S. L. Inorg. Chem. 2005, 44, 3850.

■

CONCLUSION In summary, five isostructural 3D Ln-MOFs have been successfully constructed by linking the novel Ln−carboxylate/ Cl chains with dicarboxylate bpdc2− ligands. The framework shows a 4-connected sra net and contains 1D rhombic channel. The effect of lanthanide contraction leads to the decreases of average Ln−O and Ln−Cl distances from 1 to 5. Compound 4 displays strong near-infrared luminescence resulting from the sensitization of bpdc2− ligand through an efficient energy transfer from bpdc2− to Nd3+ centers. And this complex may be a potential near-infrared luminescent material. The variabletemperature magnetic investigations for 2−4 indicate that the magnetic interactions between Ln3+ ions are mainly ascribed to the depopulation of the Stark levels and possible antiferromagnetic couplings. On the basis of this work, it can be speculated that the similar Ln−carboxylate/Cl chain can be mimicked by employing other aromatic carboxylate linkers. Accordingly, the high-dimensional Ln-MOFs with different 1575



Article

(8) (a) Davies, K.; Bourne, S. A.; Oliver, C. L. Cryst. Growth Des. 2012, 12, 1999. (b) Jiang, H. L.; Tsumori, N.; Xu, Q. Inorg. Chem. 2010, 49, 10001. (9) (a) Thuéry, P.; Masci, B. CrystEngComm 2010, 12, 2982. (b) Zhao, J.; Long, L. S.; Huang, R. B.; Zheng, L. S. Dalton Trans. 2008, 4714. (10) Han, Y. F.; Zhou, X. H.; Zheng, Y. X.; Shen, Z.; Song, Y.; You, X. Z. CrystEngComm 2008, 10, 1237. (11) (a) Wang, Q. X.; Ye, J. W.; Tian, G.; Chen, Y.; Lu, X. Y.; Gong, W. T.; Ning, G. L. Inorg. Chem. Commun. 2011, 14, 889. (b) Wang, C. C.; Wang, Z. H.; Gu, F. B.; Guo, G. S. J. Mol. Struct. 2011, 1004, 39. (c) Su, S.; Chen, W.; Qin, C.; Song, S.; Guo, Z.; Li, G.; Song, X.; Zhu, M.; Wang, S.; Hao, Z.; Zhang, H. Cryst. Growth Des. 2012, 12, 1808. (12) (a) Qin, C.; Wang, X. L.; Wang, E. B.; Su, Z. M. Inorg. Chem. 2005, 44, 7122. (b) Gustafsson, M.; Su, J.; Yue, H. J.; Yao, Q. X.; Zou, X. D. Cryst. Growth Des. 2012, 12, 3243. (c) Poulsen, R. D.; Overgarrd, J.; Chevallier, M. A.; Clausen, H. F.; Lversen, B. B. Acta Crystallogr. 2005, E61, No. m2308. (d) Thirumurugan, A.; Natarajan, S. Eur. J. Inorg. Chem. 2004, 762. (e) Reineke, T. M.; Eddaoudi, M.; O’Keefe, M.; Yaghi, O. M. Angew. Chem., Int. Ed. 1999, 38, 2590. (f) Zhang, H. J.; Fan, R. Q.; Zhou, G. P.; Wang, P.; Yang, Y. L. Inorg. Chem. Commun. 2012, 16, 100. (13) (a) Wang, R.; Selby, H. D.; Liu, H.; Carducci, M. D.; Jin, T.; Zheng, Z.; Anthis, J. W.; Staples, R. J. Inorg. Chem. 2002, 41, 278. (b) Evans, W. J.; Greci, M. A.; Ansari, M. A.; Ziller, J. W. J. Chem. Soc., Dalton Trans. 1997, 4503. (c) Evans, W. J.; Rego, D. B.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Organometallics 2007, 26, 4737. (d) Yang, X.; Hahn, B. P.; Jones, R. A.; Wong, W. K.; Stevenson, K. J. Inorg. Chem. 2007, 46, 7050. (14) (a) Chen, W. X.; Ren, Y. P.; Long, L. S.; Huang, R. B.; Zheng, L. S. CrystEngComm 2009, 11, 1522. (b) Wang, M. X.; Long, L. S.; Huang, R. B.; Zheng, L. S. Chem. Commun. 2011, 9834. (c) Zhu, W. Q.; Wang, J. P.; Yuan, Y. K.; Li, Z. Acta Crystallogr. Sect. 2012, E68, No. m896. (d) Bertke, J. A.; Oliver, A. G.; Henderson, K. W. Acta Crystallogr. Sect. 2012, E68, No. m690. (15) Tan, B.; Xie, Z. L.; Feng, M. L.; Hu, B.; Wu, Z. F.; Huang, X. Y. Dalton Trans. 2012, 41, 10576. (16) Sheldrick, G. M. SHELXL-97, Program for the Refinement of the Crystal Structures; University of Göttingen: Göttingen, Germany, 1997. (17) Waller, F. J.; Barrett, A. G. M.; Braddock, D. C.; McKinnell, R. M.; Ramprasad, D. J. Chem. Soc., Perkin Trans. 1999, 1, 867. (18) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (19) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keefe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504. (20) Blatov, V. A. Topos, 2007. http://www.topos.ssu.samara.ru. (21) Hou, L.; Shi, W. J.; Wang, Y. Y.; Guo, Y.; Jin, C.; Shi, Q. Z. Chem. Commun. 2011, 47, 5464. (22) Please see the Web site of the O’Keeffe group at Arizona State University, http://rcsr.anu.edu.au. (23) (a) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEngComm 2004, 6, 378. (b) Sun, Y. Q.; Gao, D. Z.; Xu, Y. Y.; Zhang, G. Y.; Fan, L. L.; Li, C. P.; Hu, T. L.; Liao, D. Z.; Zhang, C. X. Dalton Trans. 2011, 40, 5528. (24) (a) Chen, S. C.; Zhang, Z. H.; Chen, Q.; Gao, H. B.; Liu, Q.; He, M. Y.; Du, M. Inorg. Chem. Commun. 2009, 12, 835. (b) Zhang, X. M.; Hao, Z. M.; Zhang, W. X.; Chen, X. M. Angew. Chem., Int. Ed. 2007, 46, 3456. (25) (a) Persson, I. Pure Appl. Chem. 2010, 82, 1901. (b) Zhuang, G.L.; Kong, X.-J.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. CrystEngComm 2010, 12, 2691. (26) Llewellyn, P. L.; Horcajada, P.; Maurin, G.; Devic, T.; Rosenbach, N.; Bourrelly, S.; Serre, C.; Vincent, D.; Loera-Serna, S.; Filinchuk, Y.; Férey, G. J. Am. Chem. Soc. 2009, 131, 13002. (27) Seidel, C.; Lorbeer, C.; Cybińska, J.; Mudring, A. V.; Ruschewitz, U. Inorg. Chem. 2012, 51, 4679. (28) (a) Mancino, G.; Ferguson, A. J.; Beeby, A.; Long, N. J.; Jones, T. S. J. Am. Chem. Soc. 2005, 127, 524. (b) Shavaleev, N. M.; Scopelliti, R.; Gumy, F.; Bunzli, J. C. G. Inorg. Chem. 2009, 48, 2908. (c) White, K. A.; Chengelis, D. A.; Zeller, M.; Geib, S. J.; Szakos, J.; Petoud, S.;

Rosi, N. L. Chem. Commun. 2009, 4506. (d) Yang, X.; Hahn, B. P.; Jones, R. A.; Stevenson, K. J.; Swinnea, J. S.; Wu, Q. Chem. Commun. 2006, 3827. (e) Lin, Z.-J.; Yang, Z.; Liu, T.-F.; Huang, Y.-B.; Cao, R. Inorg. Chem. 2012, 51, 1813. (f) Lin, Z.-J.; Han, L.-W.; Wu, D.-S.; Huang, Y.-B.; Cao, R. Cryst. Growth Des. 2013, 13, 255. (29) Li, C. J.; Peng, M. X.; Leng, J. D.; Yang, M. M.; Lin, Z. J.; Tong, M. L. CrystEngComm 2008, 10, 1645. (30) (a) Yue, Q.; Yang, J.; Li, G. H.; Li, G. D.; Chen, J. S. Inorg. Chem. 2006, 45, 4431. (b) Lu, W. G.; Jiang, L.; Lu, T. B. Cryst. Growth Des. 2010, 10, 4310. (31) Hong, Z.; Liang, C.; Li, R.; Zang, F.; Fan, D.; Li, W. Appl. Phys. Lett. 2011, 79, 1942. (32) (a) Zhang, Z.-H.; Song, Y.; Okamura, T.-a.; Hasegawa, Y.; Sun, W.-Y.; Ueyama, N. Inorg. Chem. 2006, 45, 2897. (b) Costes, J.-P.; Nicodème, F. Chem.Eur. J. 2002, 8, 3442. (c) He, Z.; Gao, E.-Q.; Wang, Z.-M.; Yan, C.-H.; Kurmoo, M. Inorg. Chem. 2005, 44, 862. (33) (a) Kahn, O. Molecular Magnetism; VCH: Weinheim, Germany, 1993. (b) Fisher, M. E. Am. J. Phys. 1964, 32, 343. (c) CañadillasDelgado, L.; Pasández-Molina, J.; Fabelo, O.; Hernádez-Molina, M.; Lloret, F.; Julve, M.; Ruiz-Pérez, C. Inorg. Chem. 2006, 45, 10585. (d) Xu, N.; Shi, W.; Liao, D. Z.; Yan, S. P.; Cheng, P. Inorg. Chem. 2008, 47, 8748. (e) Wang, S. N.; Sun, R.; Wang, X. S.; Li, Y. Z.; Pan, Y.; Bai, J.; Scheer, M.; You, X. Z. CrystEngComm 2007, 9, 1051. (34) (a) Liu, Q. Y.; Wang, W. F.; Wang, Y. L.; Shan, Z. M.; Wang, M. S.; Tang, J. Inorg. Chem. 2012, 51, 2381. (b) Li, F.; Xu, L.; Bi, B.; Liu, X.; Fan, L. CrystEngComm 2008, 10, 693. (c) Feng, X.; Wang, J.; Liu, B.; Wang, L. Y.; Zhao, J. S.; Ng, S.; Zhang, G.; Wang, J. G.; Shi, X. G.; Liu, Y. Y. Cryst. Growth Des. 2012, 12, 927.

1576


Structure, Near-Infrared Luminescence and Magnetic - American

Recommend Documents