Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Chiral Silver−Lanthanide Metal−Organic Frameworks Comprised of One-Dimensional Triple Right-Handed Helical Chains Based on [Ln7(μ3‑OH)8]13+ Clusters Yan Guo,† Lijuan Zhang,*,† Nadeem Muhammad,† Yan Xu,‡ Yunshan Zhou,*,† Fang Tang,† and Shaowei Yang† †
State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology, Beijing 100029, P. R. China ‡ State Key Laboratory of Materials-oriented Chemical Engineering, College of Chemical Engineering, Nanjing Hightech University, Nanjing 211800, P. R. China S Supporting Information *
ABSTRACT: Three new isostructural chiral silver−lanthanide heterometal−organic frameworks [Ag3Ln7(μ3OH)8(bpdc)6(NO3)3(H2O)6](NO3)·2H2O [Ln = Eu (1), Tb (2, Sm (3); H2bpdc = 2,2′-bipyridine-3,3′-dicarboxylic acid] based on heptanuclear lanthanide clusters [Ln7(μ3-OH)8]13+ comprised of one-dimensional triple right-handed helical chains were hydrothermally synthesized. Various means such as UV−vis spectroscopy, IR spectroscopy, elemental analysis, powder X-ray diffraction, and thermogravimetric/differential thermal analysis were used to characterize the compounds, wherein compound 3 was crystallographically characterized. In the structure of compound 3, eight μ3OH− groups link seven Sm3+ ions, forming a heptanuclear cluster, [Sm7(μ3-OH)8]13+, and the adjacent [Sm7(μ3-OH)8]13+ clusters are linked by the carboxylic groups of bpdc2− ligands, leading to the formation of a one-dimensional triple right-handed helical chain. The adjacent triple right-handed helical chains are further joined together by coordinating the pyridyl N atoms of the bpdc2− ligands with Ag+, resulting in a chiral three-dimensional silver(I)−lanthanide(III) heterometal−organic framework with onedimensional channels wherein NO3− anions and crystal lattice H2O molecules are trapped. The compounds were studied systematically with respect to their photoluminescence properties and energy-transfer mechanism, and it was found that H2bpdc (the energy level for the triplet states of the ligand H2bpdc is 21505 cm−1) can sensitize Eu3+ luminescence more effectively than Tb3+ and Sm3+ luminescence because of effective energy transfer from bpdc2− to Eu3+ under excitation in compound 1.
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INTRODUCTION Polynuclear lanthanide (Ln) cluster complexes owing to their structural variety have shown great potential in the fields of magnetism,1 catalysis,2 adsorption,3 and photoluminescence.4 The reported work about polynuclear Ln clusters varied from Ln3 to Ln104,5−24 but the majority of them possessed discrete structures in view of crystallography.5−18 Among the reported extended frameworks constructed from Ln-based clusters,11,19−24 multidentate organic carboxylates like pyridine2,5-dicarboxylate,19 3,3′-dicarboxylate-2,2′-bipyridine,20 1,4naphthalenedicarboxyate,21 4-pyridin-4-ylbenzoic acid,22 and isonicotinic acid11,23 were employed to construct the Ln-based cluster organic frameworks. The aforementioned ligands were chosen because these are beneficial in producing open frameworks by bridging polynuclear Ln clusters and effectively assist hydrolysis of Ln cations into polynuclear Ln-based clusters. Therefore, multidentate organic carboxylates are suitable candidates for the construction of Ln-based cluster organic frameworks. On the other hand, the transition-metal− © XXXX American Chemical Society
Ln organic frameworks (MOFs) are important because of not only intriguing unique structures from one-dimensional chains to three-dimensional networks or topologies but also a strong effect in enhancing the capability of Ln clusters in the fields of magnetism, catalysis, adsorption, and photoluminescence.25−31 However, transition-metal−Ln heterometal MOFs composed of Ln clusters have rarely been reported until now.32 Therefore, the design and preparation of transition-metal−Ln MOFs based on Ln clusters is a challenging and promising work. The self-assembly method is proven to be a successful synthetic strategy for transition-metal−Ln MOFs with appropriate bridging ligands as linkers.33−35 As previously mentioned, multidentate organic carboxylates can assist in the hydrolysis of Ln cations into Ln clusters, and transition-metal cations easily bond to soft donors like N atoms,36 so polycarboxylates with N-atom donors are beneficial to the construction of transitionReceived: September 8, 2017
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DOI: 10.1021/acs.inorgchem.7b02324 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
g), Eu(NO3)3·6H2O (0.35 mmol, 0.112 g), and H2O (10 mL) were placed in a 25 mL Teflon-lined stainless steel vessel. The mixture was controlled at pH 6.3 and then kept under autogenous pressure at 170 °C for 3 days. Afterward, the reactors were slowly cooled to room temperature with a cooling rate of 10 °C/h. Colorless blocklike single crystals were acquired with a yield of 68.1% based on Ag. Anal. Calcd for C72H56Ag3Eu7N16O50 (1′, dehydrated compound after two crystal lattice H2O molecules are lost): C, 25.94; H, 1.69; N, 6.72; Ag, 9.71; Eu, 31.91. Found: C, 25.65; H, 1.60l; N, 6.74; Ag, 9.54; Eu, 31.45. IR (KBr disk, cm−1): 3545 (s), 3095 (v), 1603 (s), 1591 (s), 1444 (s), 1387 (s), 1156 (m), 1087 (v), 865 (v), 777 (s), 693 (m). Synthesis of [Ag3Tb7(μ3-OH)8(bpdc)6(NO3)3(H2O)6](NO3)· 2H2O (2). The same procedure as that for 1 was used except that Tb(NO3)3·6H2O (0.35 mmol, 0.114 g) was used to replace Eu(NO3)3· 6H2O. Colorless block crystals were harvested (yield: 67.4% based on Ag). Anal. Calcd for C72H56Ag3Tb7N16O50 (2′, dehydrated compound after two crystal lattice H2O molecules are lost): C, 25.57; H, 1.67; N, 6.62; Ag, 9.57; Tb, 32.90. Found: C, 25.55; H, 1.54; N, 6.46; Ag, 9.40; Tb, 31.5. IR (KBr disk, cm−1): 3547 (s), 3091 (v), 1607 (s), 1599 (s), 1448 (s), 1375 (s), 1156 (m), 1103 (v), 874 (v), 77 0 (s), 697 (m). Synthesis of [Ag3Sm7(μ3-OH)8(bpdc)6(NO3)3(H2O)6](NO3)· 2H2O (3). The same procedure as that for 1 was used except that Sm(NO3)3·6H2O (0.35 mmol, 0.112 g) was used to replace Eu(NO3)3·6H2O. Colorless block crystals were harvested with a yield of 62.5% based on Ag. Anal. Calcd for C72H56Ag3Sm7N16O50 (3′, dehydrated compound after two crystal lattice H2O molecules are lost): C, 26.03; H, 1.69; N, 6.74; Ag, 9.74; Sm, 31.69. Found: C, 25.76; H, 1.61; N, 6.55; Ag, 9.50; Sm, 31.85. IR (KBr disk, cm−1): 3540 (s), 3091 (v), 1606 (s), 1598 (s), 1448 (s), 1368 (s), 1153 (m), 1078 (v), 869 (v), 775 (s), 697 (m). X-ray Crystallographic Data Collection and Refinement of the Structure. A Bruker APEX2 X-ray diffractometer was used to collect X-ray diffraction data of the single crystals using Mo Kα radiation with λ = 0.71073 Å in a ω-scan fashion. Direct methods were adopted to solve the structure, and full-matrix least-squares methods were adopted for anisotropic refinement with the SHELX-97 program package.51 Successive difference Fourier synthesis was performed to locate the non-H atoms. Full-matrix least-squares methods were used for the final refinement, and anisotropic thermal parameters for non-H atoms were calculated based on F2. Table 1 summarizes the
metal−Ln MOFs based on polynuclear Ln-based clusters.21,22,37 Making all of the above-mentioned conclusions, we are very interested in choosing versatile carboxylic acids as ligands that consist of N and O atoms to synthesize highdimensional silver−lanthanide mixed-metal MOFs. In this scenario, 2,2′-bipyridine-3,3′-dicarboxylic acid (H2bpdc), whose bipyridyl moiety has strong chelating ability and the neighboring carboxyl groups have strong coordinating ability, can be chosen as a typical multidentate N- and O-atom donor ligand.38−45 From the reported literature data, it was found that bpdc2− can also act as a supporting ligand to the hydrolysis of Ln ions to form polynuclear Ln clusters.46,47 In addition, this ligand with a twisted geometrical conformation that exhibits an atropisomer-chirality bridging mode is certified to be effective for the generation of chirality and has been adopted to construct chiral coordination polymers.48 Therefore, it is expected to construct chiral transition-metal−Ln cluster MOFs using bpdc2− as the versatile ligand. Taking the above analysis into account, 2,2′-bipyridine-3,3′dicarboxylate (bpdc2−) of versatility, luminescent Ln3+ ions (Ln = Eu, Tb, Sm), and transition-metal ion Ag+ were selected to react under hydrothermal conditions, leading to three novel isostructural chiral three-dimensional silver(I)−lanthanide(III) heterometal−organic frameworks [Ag3Ln7(μ3OH)8(bpdc)6(NO3)3(H2O)6](NO3)·2H2O [Ln = Eu (1), Tb (2), Sm (3); H2bpdc = 2,2′-bipyridine-3,3′-dicarboxylic acid] comprised of triple right-handed chiral chains constructed from [Ln7(μ3-OH)8]13+ clusters. The optimal synthetic parameters, luminescence, and energy-transfer mechanism of the compounds were investigated in detail in this work. To our knowledge, the compounds reported in this work represent the first examples of chiral heterometal−organic frameworks containing triple right-handed chiral chains constructed from heptanuclear [Ln7(μ3-OH)8]13+ clusters.
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EXPERIMENTAL DETAILS
Materials and Measurements. H2bpdc49 and [Gd2(bpdc)3(phen)2(H2O)2]·6H2O (4)50 were prepared according to a previously reported method and characterized by UV−vis, IR, and elemental analysis. All of the solvents and other reagents were of reagent grade, were bought commercially, and were used directly. Elemental analysis for C, H, and N of the compounds was conducted using a CHN-O-Rapid elemental analyzer. Analyses for the rare-earth metals Ln and Ag of the samples were conducted on a ICPS-7500 model inductively coupled plasma emission spectrometer. A Nicolet FTIR-170SX spectrometer was used to record IR spectra of the samples (KBr pellets) in the 4000−400 cm−1 range. A Shimadzu UV2550 spectrophotometer in the range of 200−800 nm was used to obtain UV−vis spectra. A Shimadazu XRD-600 diffractometer at a 10°/min scanning rate in the 2θ range of 3−50° with graphitemonochromatized Cu Kα radiation (λ = 0.15405 nm) was used to obtain powder X-ray diffraction (PXRD) patterns of the samples. A Netzsch STA 449C unit at a heating rate of 10 °C/min was used for thermogravimetric measurement. A Hitachi F-7000 FL fluorescence spectrophotometer (both excitation and emission slits were set to 5 nm) with a xenon arc lamp (150 W) used as the light source was adopted to obtain excitation and emission spectra of the samples in the solid state. The scan speed was set to 1200 nm/min, and photomultiplier tube (PMT) voltage was set to 400 V. The phosphorescence spectra for compound 4 at low temperature in the solid state were recorded on a Hitachi F-7000 FL fluorescence spectrophotometer with 5 nm emission slits, 240 nm/min scan speed, and 700 V PMT voltage. The light source used was a xenon arc lamp (150 W). Synthesis of [Ag3Eu7(μ3-OH)8(bpdc)6(NO3)3(H2O)6](NO3)· 2H2O (1). H2bpdc (0.3 mmol, 0.073 g), AgNO3 (0.1 mmol, 0.017
Table 1. Detailed Crystal Parameters for Compound 3 empirical formula fw T (K) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume (Å3) Z Dcalc (Mg/m3) abs coeff (mm−1) F(000) cryst size (mm3) θ (deg) range index ranges GOF on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff peak and hole CCDC B
C72H60Ag3N16O52Sm7 3357.42 100.2 monoclinic P21 13.6538(3) 23.9977(5) 14.5873(4) 90.00 108.176(3) 90.00 4541.1(17) 2 2.455 5.195 3190 0.08 × 0.04 × 0.01 2.99−26.00 −16 ≤ h ≤ 15, −29 ≤ k ≤ 29, −17 ≤ l ≤ 17 0.983 R1 = 0.0468, wR2 = 0.1028 R1 = 0.0620, wR2 = 0.1072 3.269 and −1.503 1568608 DOI: 10.1021/acs.inorgchem.7b02324 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Table 2. Selected Metal−Oxygen Bond Distances (Å) and Bond Angles (deg) around the Metal Centers for Compound 3a moiety
bond distance (Å)
moiety
bond distance (Å)
moiety
bond angle (deg)
moiety
bond angle (deg)
Sm1−O5 Sm1−O8 Sm1−O10 Sm1−O18 Sm2−O1 Sm2−O9 Sm2−O11 Sm2−O12 Sm3−O2#1 Sm3−O14#1 Sm3−O17 Sm3−O21
2.406(17) 2.382(17) 2.618(18) 2.736(16) 2.419(17) 2.464(17) 2.599(17) 2.551(17) 2.464(18) 2.476(16) 2.586(16) 2.524(19)
Sm4−O51 Sm4−O4 Sm5−O3#1 Sm5−O6#1 Sm6−O7#1 Sm6−O24 Sm7−O18 Sm7−O19 Sm7−O24 Ag1−N7 Ag2−N6 Ag3−N2
2.687(19) 2.439(17) 2.359(19) 2.490(16) 2.345(17) 2.465(16) 2.547(16) 2.553(17) 2.356(15) 2.20(2) 2.19(2) 2.19(2)
O8−Sm1−O34 O35−Sm1−O34 O34−Sm1−O5 O8−Sm1−O40 O37−Sm2−O12 O35−Sm2−O12 O1−Sm2−O12 O1−Sm2−N15 O33−Sm2−N15 O22−Sm3−O21 O23−Sm3−O21 O25−Sm3−O20
147.6(6) 70.3(6) 90.7(6) 89.9(6) 130.6(6) 133.0(6) 76.8(6) 114.2(6) 141.0(6) 143.4(6) 134.4(6) 125.8(6)
O4−Sm4−O51 O33−Sm4−O51 O34−Sm4−O51 O49−Sm5−O50 O29−Sm5−O50 O24−Sm5−N16 O23−Sm6−O24 O25−Sm6−O24 O37−Sm7−O18 N7−Ag1−N3#2 N7−Ag1−N4#2 N2−Ag3−N12#3
74.8(6) 121.6(6) 68.3(6) 50.4(6) 105.3(6) 97.4(6) 67.5(6) 75.4(6) 70.0(5) 165.0(8) 123.0(8) 117.2(8)
Symmetry codes: (#1) x − 1, y, z; (#2) x − 1, y, z − 1; (#3) −x + 2, y − 1/2, −z − 5; (#4) x + 1, y, z; (#5) x + 1, y, z + 1; (#6) −x + 2, y + 1/2, −z − 5. a
of the reactants, type of Ln3+, and pH values of the selected starting materials are the most important reaction conditions rather than the reaction time and latter cooling rate for the preparation of compounds 1−3. PXRD Spectra of the Title Compounds. The PXRD patterns of compounds 1−3 essentially match that calculated based on the single-crystal X-ray diffraction data of compound 3, which not only indicates that the final products are highly pure and homogeneous (Figure S1) but also shows that compounds 1−3 are isostructural. Specific Structural Details of Compound 3. Because the three silver−lanthanide heterometallic compounds, namely, [Ag3Ln7(μ3−OH)8(bpdc)6(NO3)3(H2O)6](NO3)·2H2O [Ln = Eu (1), Tb (2), Sm (3)], are isostructural and have the same structure type, the structure of 3 is chosen as a representative to discuss all of the structural parameters. Compound 3 crystallized in the chiral space group P21 with a monoclinic crystal system. The asymmetric unit of compound 3 (Figure 1a) contains seven Sm3+ ions, three Ag+ ions, eight OH− ions, three coordination NO3− ions, one free NO3− ion, six bpdc2− ligands, and six coordination H2O and two lattice H2O molecules, which are crystallographically independent. The seven Sm3+ ions have different coordination spheres (Figures 1b and 2). Sm1 coordinates with nine O atoms, wherein O5, O8, O10, and O18 from carboxylate groups of three different bpdc2− ligands, O34, O35, and O37 from OH− groups as μ3-bridge-linking Sm3+ ions, and O40 and O41 from one NO3− group are used. The coordination environment of Sm2 is completed by nine O atoms in which O1, O9, O11, and O12 are from carboxylate groups of three different bpdc2− ligands, O36 and O38 from one NO3−, and O33, O35, and O37 are from OH− groups as μ3-bridge-linking Sm3+ ions are used. The coordination number of Sm3 is 9, comprised of four O atoms (O2, O14, O16, and O17) from carboxylate groups of three different bpdc2− ligands, three O atoms (O22, O23, and O25) from OH− groups as μ3-bridge-linking Sm3+ ions, and two O atoms (O20 and O21) belonging to two H2O ligands. Sm4, which is nine-coordinated, is described as O4, O13, O51, and O52 from carboxylate groups of three different bpdc2− ligands, O33, O34, and O35 from OH− groups as μ3-bridgelinking Sm3+ ions, and O31 and O32 from two H2O molecules. Sm5 is nine-coordinated and composed of all O atoms, in which O3, O6, O49, and O50 are from carboxylate groups of three different bpdc2− ligands, O28 and O29 are from one
crystallographic data and parameters for the structural determination of compound 3, and Table 2 shows the selected bond lengths along with the bond angles of compound 3.
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RESULTS AND DISCUSSION Hydrothermal Synthesis of Compounds 1−3. Optimization of the reaction conditions to obtain good-quality crystals with better yield was performed. The experimental results showed that a large amount of blocklike single crystals were obtained for compounds 1−3 when the molar ratio of the reactants H 2 bpdc/Ln(NO 3 ) 3 ·6H 2 O/AgNO 3 was set to 0.3:0.35:0.10 in the deionized H2O mixture with a pH value of 6.3, the temperature was in the range of 160−170 °C, the reaction time was 3−6 days, and the cooling rate was 1−15 °C/ h. The pH value was as important as the molar ratio of the reactants. Tubular crystals with the formula AgLn(bpdc)2 reported by our previous work50 could be formed when the pH value was
