Two Series of Microporous Lanthanide–Organic Frameworks with

Article Cite This: Inorg. Chem. 2019, 58, 339−348

pubs.acs.org/IC

Two Series of Microporous Lanthanide−Organic Frameworks with Different Secondary Building Units and Exposed Lewis Base Active Sites: Sensing, Dye Adsorption, and Magnetic Properties Jing Jin, Guoping Yang,* Yanchen Liu, Shan Cheng, Jiao Liu, Dan Wu, and Yao-Yu Wang 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 710127, Shaanxi, P. R. China

Downloaded via UNIV OF LOUISIANA AT LAFAYETTE on January 7, 2019 at 18:29:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Two series of new lanthanide complexes, {[Ln(L)1.5(H2O)]·DMA· 4H2O}n (1-Ln, Ln = Tb, Gd, and Dy) and {[La2(L)3]·4H2O}n (2-La), were prepared successfully by Ln3+ ions and a N-heterocyclic dicarboxylic (2-pyrimidin-5-yl)terephthalic acid (H2L) ligand. The four complexes are three-dimensional (3D) microporous frameworks with different secondary building units (SBUs) and exposed Lewis base active sites. Topology analyses reveal that 1-Ln are the binodal (3,8)-connected tfz-d (43)2(46· 618·84) nets and 2-La is a binodal (2,12)-connected (4)6(46·848·1212) net. The photoluminescence of 1-Tb, the dye adsorption of 1-Tb and 2-La, and the magnetism of 1-Dy have been well studied. The luminescent explorations indicate that 1-Tb is a highly efficient probe for sensing Fe3+ and Cr2O72−, respectively. Complexes 1-Tb and 2La display the unique selective adsorption to Congo red (CR) dyes. Magnetic measurements further indicate that 1-Dy has a slow magnetic relaxation performance.

■

INTRODUCTION The study of metal−organic frameworks (MOFs) has gained much more attention owing to their interesting structural features and excellent physical performances in the past decades.1,2 Chemists have often employed different polynuclear metal ions as secondary building units (SBUs) in the process of constructing functional MOFs.3 The SBUs may avoid the restriction of single-metal ion to combine with more ligands due to its limited coordination numbers;4 it will also result in distinctive luminescence and magnetism of MOFs.5 Particularly, lanthanide MOFs (Ln-MOFs) have recently attracted intense attention due to the flexible coordination geometries of lanthanide ions, high thermal stability, and unique properties,6,7 especially for the fluorescent probes8,9 and Dy-based single-molecule magnets (SMMs).10−13 Moreover, it is well known that the multidentate Nheterocyclic dicarboxylate ligands are the good precursors for preparing porous MOFs with excellent performances.14,15 Among them, the MOFs including pyrimidinyl−carboxylic acid ligands were still less studied previously, the related research is thus required urgently. Furthermore, ligands containing multiple various coordination sites can form different dimensions with metal ions through flexible coordination modes, such as monodentate, bidentate, or bridging chelated fashions. Beyond that, the pyrimidine rings can be considered as the antennas or sensitizers to enhance the light adsorption and transport energy to Ln3+ effectively. On the basis of the above discussions, a N-heterocyclic dicarboxylic (2-pyrimidin-5-yl)terephthalic acid (H2L, Scheme 1) ligand was employed to build new porous MOFs. Three © 2018 American Chemical Society

Scheme 1. Molecular Structure of (2-Pyrimidin-5yl)terephthalic Acid (H2L)

isostructural three-dimensional (3D) Ln-MOFs, {[Ln(L)1.5(H2O)]·DMA·4H2O}n (1-Ln, Ln = Tb, Gd, and Dy) and {[La2(L)3]·4H2O}n (2-La) were synthesized successfully in this work. Herein, the four complexes are 3D porous frameworks with active Lewis basic pyrimidine sites. Thereby, the luminescent experiments well indicated that 1-Tb is a highly efficient probe for sensing Fe 3+ and Cr2 O 72−, respectively. Also, complexes 1-Tb and 2-La display the unique selective adsorption to CR dyes, and 1-Dy has a slow magnetic relaxation performance. Received: August 28, 2018 Published: December 12, 2018 339

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry Table 1. Crystal Data and Structure Refinements for 1-Ln and 2-La complex

1-Tb

1-Gd

1-Dy

2-La

empirical formula formula mass crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ (mm−1) F (000) θ (deg) reflections collected goodness-of-fit on F2 final Ra indices [I > 2σ(I)]

C22H20N4O8Tb2 1254.70 triclinic P1̅ 9.7467(10) 11.4292(11) 12.6440(13) 88.1950(10) 83.530(2) 77.7360(10) 1367.6(2) 2 1.524 2.633 618 2.151−27.917 8004/5861 1.024 R1 = 0.0337 wR2 = 0.0846

C22H20N4O8Gd2 1251.34 triclinic P1̅ 9.7609(12) 11.4430(14) 12.6658(15) 87.971(2) 83.397(2) 77.771(2) 1373.3(3) 2 1.513 2.462 616 2.148−26.422 7521/5400 0.967 R1 = 0.0404 wR2 = 0.0812

C22H20N4O8Dy2 1261.84 triclinic P1̅ 9.6329(15) 11.4465(17) 12.4098(19) 91.065(2) 95.396(2) 100.658(2) 1337.9(4) 2 1.372 2.828 534 1.649−28.338 8334/6115 1.126 R1 = 0.0367 wR2 = 0.1063

C48H24N8O16La2 1246.58 cubic Ia3̅ 27.1289(18) 27.1289(18) 27.1289(18) 90 90 90 19966(4) 24 1.244 1.325 7319 1.839−26.961 54634/3634 1.058 R1 = 0.0326 wR2 = 0.0949

R1 = ∑∥Fo| − |Fc∥/∑|Fo|, wR2 = [∑w(Fo2 − Fc2)2/ ∑w(Fo2)2]1/2.

a

Figure 1. (a) Tb3+ coordination environment of 1-Tb (symmetry codes: #1 −x + 1, −y, −z + 1; #2 x, y − 1, z; #3 −x + 2, −y, −z + 1; #4 x, y + 1, z; #5 −x + 2, −y, −z; #6 −x + 1, −y, −z). (b) Two-dimensional (2D) layer. (c) Three-dimensional framework. (d) The binodal (3,8)-connected tfz-d topological net of 1-Tb.

■

Elemental analyses (C, H, and N) were tested on PerkinElmer 2400C elemental analyzer. The powder X-ray diffraction (PXRD) data were obtained on Bruker D8 ADVANCE X-ray powder diffractometer. Solid-state luminescent spectra were collected by Hitachi F-4500 fluorescence spectrophotometer. Magnetic data were carried out by Quantum Design MPMS-XL-7 SQUID magnetometer. The UV−vis spectra were measured on Hitachi U-3310 spectrometer. The X-ray photoelectron spectroscopy (XPS) measurement were performed on

EXPERIMENTAL SECTION

Materials and Physical Measurements. All the reagents were used from commercial sources without further purification. The H2L was obtained from Jinan Camolai Trading Company. Infrared (IR) spectra were collected on Bruker Equinox-55 FT-IR spectrometer (KBr disks) in 4000−400 cm−1. The thermogravimetric analyses (TGA) were performed on the NETZSCH STA 449C microanalyzer thermal analyzer (N2 stream) with the heating rate of 5 °C min−1. 340

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 2. Various coordination fashions of L2− in 1-Tb (a, b) and 2-La (c).

Figure 3. (a) La3+ coordination environment of 2-La. (b) The [La3(COO)12] SBU. (c) Three-dimensional framework of 2-La. (d) The (2,12)connected topological net of 2-La. 3.28, N 8.97. IR (KBr, cm−1): 3408(m), 3050(m), 2927(m), 1637(s), 1576(s), 1403(s), 1263(m), 1015(w), 842(s), 780(s), 639(m), 530(w), 472(m). {[La2(L)3]·4H2O}n (2-La). Yield 67% (based on the H2L). Anal calcd for C24H12LaN4O8 (%): C 46.21, H 1.93, N 8.98; found: C 46.26, H 1.97, N 8.93. IR (KBr, cm−1): 3402(s), 3144(m), 1964(w), 1626(s), 1570(s), 1527(s), 1404(s), 1371(s), 1280(m), 1028(s), 910(w), 836(s), 775(m), 719(m), 639(w), 546(w), 466(w). X-ray Crystal Structure Determination. The X-ray diffraction data were collected on Bruker SMART APEX II CCD diffractometer with graphite monochromated Mo Kα radiation (λ = 0.71073 Å) and ϕ/ω scan mode. The structures of four complexes were determined by direct method and refined anisotropically on F2 by a full-matrix least-squares refinement with SHELXTL program and OLEX2.16 The reflection data were corrected by SADABS program. Anisotropic thermal parameters were applied to nonhydrogen atoms and all hydrogen atoms of ligands were calculated and added at ideal positions. The squeeze command of the PLATON program was used in refinement process due to the disordered solvent molecules.17 The final formulae of 1-Ln (Ln = Tb, Gd, and Dy) were thus obtained by the elemental analyses, crystal structures, and TGA curves. The related crystallographic data are given in Table 1, and the selected bond lengths/angles are summarized in Table S1. The CCDC numbers are 1863473−1863476 for 1-Ln (Ln = Tb, Gd, and Dy) and 2-La, respectively.

AXIS Ultra spectrometer. And, the CO2 sorption isotherm was measured on Micrometrics ASAP 2020M. Synthesis of {[Ln(L)1.5(H2O)]·DMA·4H2O}n (1-Ln). A mixture of H2L (0.05 mmol, 12.2 mg), Ln(NO3)3·6H2O (0.1 mmol) (Ln = Dy, Tb, Gd, and La), dimethylacetamide (DMA, 2 mL), and H2O (4 mL) were mixed in a Teflon-lined stainless steel vessel (15 mL), kept 95 °C for 72 h, and then cooled to ambient temperature by 10 °C h−1. In general, the crystal structures made with Ln(NO3)3 salts are the same, but fortunately two completely different crystal forms are obtained, one is colorless strip crystals and the other is colorless square products. This phenomenon is rare. Finally, the colorless strip crystals of 1-Ln (Ln = Dy, Tb, and Gd) and square sample of 2-La were isolated by cleaning with DMA and dried in air. {[Ln(L)1.5(H2O)]·DMA·4H2O}n (1-Tb). Yield 85% (based on the H2L). Anal calcd for C22H20TbN4O8 (%): C 42.08, H 3.19, N 8.93; found: C 42.11, H 3.23, N 8.98. IR (KBr, cm−1; Figure S5): 3401(m), 3056(m), 2933(m), 1619(s), 1564(s), 1403(s), 1262(m), 1175(m), 1015(w), 848(s), 768(m), 641(m), 533(w), 479(m). 1-Dy. Yield 88% (based on the H 2 L). Anal calcd for C22H20DyN4O8 (%): C 41.84, H 3.17, N 8.88; found: C 41.87, H 3.14, N 8.92. IR (KBr, cm−1): 3408(m), 3057(m), 2931(m), 1619(s), 1562(s), 1403(s), 1379(s), 1268(m), 1021(w), 848(s), 775(m), 651(m), 516(w), 472(m). 1-Gd. Yield 76% (based on the H 2 L). Anal calcd for C22H20GdN4O8 (%): C 42.19, H 3.20, N 8.95; found: C 42.23, H 341

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 4. (a) Luminescent spectra of 1-Tb dispersed in water with different ions (λex = 351 nm). (b) The luminescent intensity at 545 nm of Mn+@ 1-Tb solutions. (c) Emission spectra. (d) The relative intensity of Tb3+@Fe3+@H2O with different concentrations of Fe3+.

■

RESULTS AND DISCUSSION Crystal Structure Description of {[Ln(L)1.5(H2O)]·DMA· 4H2O}n (1-Ln, Ln = Tb, Gd, and Dy). Single-crystal X-ray diffraction showed that the three complexes have the triclinic P1̅ space group and are isostructural 3D frameworks including dinuclear SBUs. Thereby, the representative 1-Tb is only displayed for clarity. The asymmetric building unit of 1-Tb contained one Tb3+ ion, one and a half fully L2− ligand, and one coordinated aqua molecule (Figure 1a). Each Tb3+ is ninecoordinated with seven O atoms of four L2− and one O atom of water, and one pyrimidinyl N atom, showing a distorted tetrakaidecahedron geometry (Figure S1). The L2− linkers of 1-Tb are fully deprotonated and take two different coordination fashions (Figure 2). The first ones can act as the 3-connected spacers to link Tb3+ ions to result in a 2D layer with the dinuclear [Tb2(COO)6N2] SBUs (Figures 1b and S2). Then, the other L2− ligands are regarded as the pillars and further combine these 2D layers to a 3D porous framework with the exposed Lewis pyrimidinyl bases sites (Figure 1c). However, due to the existence of the disordered pyrimidinyl rings of L2− ligands, the calculated potential void volume is only 17.3% of per unit cell volume of 1-Tb by the PLATON program. Topologically, each dinuclear SBU can be simplified as an 8-connected node; thus, 1-Tb is a binodal (3,8)-connected (43)2(46·618·84) tfz-d net gained by the TOPOS program (Figure 1d).18 Crystal Structure Description of {[La2(L)3]·4H2O}n (2La). Complex 2-La has the Ia3̅ cubic system, and its building unit includes two La3+ ion, three completely deprotonated L2− ligands, and four lattice water molecules (Figure 3a). Herein,

La1 takes coordination with 12 O atoms of 6 carboxylate groups, whereas La2 is ligated by 9 O atoms of 6 L2− ligands. The carboxylates of L2− ligand take two coordination fashions with La3+ ions in 2-La, i.e., the chelating bidentate (η2μ1χ2) and tridentate (η2μ2χ3); thus, the trinuclear [La3(COO)12] SBU is easily formed including one La1 and two La2 ions (Figure 3b). Like that of 1-Tb, these SBUs are also extended by the phenyl linkers to form a 3D framework with lots of exposed active Lewis sites (Figure 3c). Topologically, the SBUs can act as the 12-connected nodes and the ligands are 2connected linkages; so, the overall framework is a (2,12)connected (4)6(46·848·1212) net (Figure 3d). Powder X-ray Diffraction (PXRD), Thermogravimetric Analyses (TGA), and Gas Adsorption. The tested PXRD patterns of 1-Ln (Tb, Gd and Dy) and 2-La matched well with those obtained from the crystal data, demonstrating the great phase purity (Figure S3). The TGA curves of 1-Ln had the almost similar weight loss steps due to their isostructural frameworks. Thereby, the TGA of 1-Tb is only analyzed. The first loss of 9.42% in 1-Tb is the release of four lattice waters below 148 °C (calcd 9.15%). The second loss of 12.80% (calcd 13.39%) is attributed to dimethylacetamide and coordinated water at 148−376 °C. Then, the framework is destroyed after 508 °C. However, the TGA curve of 2-La has a 12.55% weight loss (calcd 12.62%) of all solvents molecules in ∼35−135 °C. The structure of 2-La keeps stable at ∼135−330 °C and collapses beyond 330 °C (Figure S4). Then, to further study the porous properties, the sample of 1-Tb was soaked in CH2Cl2 for 72 h and then heated at 120 °C in vacuum for 4 h to obtain the activated product of 1a-Tb. 342

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 5. (a) Luminescent spectra and (b) intensities at 545 nm of 1-Tb in different anion or pure solvent. Emission spectra (c) and relative intensity (d) of Tb3+@Cr2O72−@H2O in water with different concentrations of Cr2O72− by excitation at 351 nm.

suggests that 1-Tb may be a good luminescent probe for sensing ions. Due to the key role of ions in the environment and ecosystem, the synthesis of targeted probes has gained widespread attention for sensing different ions. Fe3+ is not only one of the most important ions but also a cation that is ubiquitous in biochemical processes.20 Excess or deficient amount of Fe3+ can cause different illnesses such as diabetes, anemia, mental decline, and so on.21 Moreover, a large amount of ions are released to pollute the environment due to the rapid development of industry.22 In light of the active sites of N atoms in pyrimidines exposed in the channels and the strong luminescence of 1-Tb, the luminescent sensing was further studied carefully for different ions. In the experiments, 3 mg sample of 1-Tb was immersed in 10−1 M aqueous solution with M(NO3)x (M = Cu2+, Zn2+, Na+, K+, Co2+, Cd2+, Ni2+, Mg2+, Ca2+, Al3+, and Fe3+) for 24 h at ambient temperature to form Mn+@1-Tb solutions and then the ultrasonic agitation was used for 15 min to get a uniform suspension before the test. Interestingly, the solutions of Mn+@ 1-Tb have different luminescent intensities (Figure 4a,b), that is, Ag+, Al3+, Ni+, Mg2+, Na+, and K+ ions slightly enhanced the luminescence of 1-Tb, whereas Cd2+, Co2+, Zn2+, and Cu2+ decreased the luminescence. The visible difference in the luminescence of Fe3+ means that 1-Tb may recognize and detect Fe3+. The PXRD of 1-Tb dispersed by M(NO3)n aqueous solutions proved that the skeleton of 1-Tb remained intact (Figure S12a), indicating that luminescent quenching was not affected by the collapse of the framework but by the Fe3+.

The TGA curve of 1a-Tb indicated the complete exclusion of guest solvents and coordinated waters (Figure S6), which let the active N atoms of pyrimidines expose in the pores. And at the same time, the skeletal robustness of 1a-Tb can be proved by the PXRD patterns (Figure S7). Thus, the adsorption of CO2 was carried out at 195 K, which displayed that 1a-Tb had the high uptake for CO2 (77.26 cm3 (STP) g−1 at 100 kPa), from which the Brunauer−Emmett−Teller and Langmuir surface areas are 177.14 and 496.64 m2 g−1, respectively. The pore size distribution is in 5.45−13.26 Å via the Horvath− Kawazoe model (Figure S8), in agreement with that of the crystal structure of 1-Tb. Luminescent Properties. The luminescent spectra of H2L and 1-Tb are tested at room temperature (Figures S9 and S10). The H2L has the strongest emission at 471 nm, ascribed to π → π* and n → π* electronic transitions excited at 240 nm. 1-Tb shows the typical Tb3+ luminescence under the excitation of 351 nm, with the four narrow bands at 491, 545, 584, and 620 nm corresponding to the typical transitions of 5 D4 → 7FJ (J = 6, 5, 4, and 3) (Figure S10). The strongest 5 D4−7F5 transition at 545 nm leads to the bright green luminescence. In the spectra of 1-Tb, the ligand-centered emission is almost quenched, indicating L2− tectons sensitize Tb3+ by the antenna effect, or, in more detail, because LnMOFs including N-heterocyclic ligands have great luminescence, where the function of N-ligand should act as a sensitizer.19 Moreover, 1-Tb displays the single-exponential luminescent decay with the lifetime of 0.99 ms (Figure S11). Sensing of Metal Ions. As the uncoordinated pyrimidine sites of 1-Tb can be explored as active functional groups, which 343

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 6. Color variations of the aqueous solutions with 1-Tb and 2-La and different dyes.

indicating the existence of a weak interplay between the active N atoms and Fe3+ (Figure S15b). Sensing of Anions. To study the probe of 1-Tb on anions, the samples (3 mg) were dispersed in Kx(A) (3 mL, A = Cl−, Br−, I−, NO3−, C2O42−, CO32−, SO42−, MnO4−, CrO42−, and Cr2O72−) solutions. As depicted in Figure 5a,b, the intensity was strengthened by the introduction of I− and Cl−, whereas the left anions had different quenching effects. More importantly, the luminescence of 1-Tb might be almost quenched by CrO42− and Cr2O72−. Take Cr2O72− for example, the titration experiments indicated that the luminescence of 1Tb was slowly quenched by increasing the concentration of Cr2O72−, and the luminescence was disappeared when the concentration of Cr2O72− reached 0.964 mM (Figure 5c). The luminescent intensity is similar to that of Fe3+ and meets the equation I0/I = 22.78 × exp([Cr2O72−]/3.55) − 10.74 (Figure 5d). The luminescent quenching could be explained as the interplay of Cr2O72− and framework, which might also result from the competitive adsorption of excitation wavelength energy of 1-Tb and Cr2O72−, because there was an overlap of UV−vis excitation spectra about 1-Tb and Cr2O72− in the aqueous solution (Figure S16b).26 Overall, 1-Tb may be highly efficient for probing Fe3+ and Cr2O72−. Particularly, 1-Tb maintained the integrity of its original framework (Figure S12b). Dye Adsorption. The organic dyes have been used commonly in lots of fields.27 Therefore, chemists have attempted different approaches to extract dyes from liquid phase.28,29 Recently, it is very popular to adsorb and separate dye molecules by employing porous MOFs. Due to the larger channel size of the complexes 1-Tb and 2La, the dye adsorption properties were tested carefully. The main factors affecting the dye adsorption performance are size selection, electrostatic attraction, and ion exchange. As shown in Figure 6, different size and electrical organic dye molecules, such as cresol red (o-CR), methyl green, malachite green, methylene blue, alizarin red, Congo red (CR), rhodamine B, and methyl orange, were chosen to observe. In view of the previous experimental exploration and sample preparation, 3 mg of 1-Tb and 2-La was dispersed in the aqueous solution of various dyes with the concentration of 30 ppm, respectively. After a period of time, the dye Congo red solution changed from red to pale pink, whereas the color of other solutions did not change significantly. Because the two synthetic Ln-MOFs are electrically neutral, the adsorption procedure may be

Furthermore, the crystalline sample of 1-Tb was randomly dispersed in four kinds of water solutions including mixed ions (Cu2+/Al3+/Cd2+, Zn2+/Ni2+, K+/Mg2+/Na+, and Ca2+/Co2+) with the concentration of 10−1 M to explore the selectivity for Fe3+ (Figure S13a). It is remarkable that the luminescent intensity of 1-Tb did not change obviously, whereas the luminescent intensity weakened sharply by the addition of Fe3+ into these solvent systems. The results indicate that 1-Tb has great selectivity and recognition of Fe3+ in aqueous solution. Then, the titration experiments were also explored by changing the concentration of Fe3+ (Figure 4c), displaying that the luminescent intensity reduces with increasing concentration of Fe3+ by degrees, and the luminescence is quenched completely at the concentration of 5.882 mM, indicating the smart quenching effect of Fe3+. Employing the traditional Stern− Volmer equation, I0/I = 1 + Ksv[M], where I0 and I are the luminescent intensities before and after ion incorporation; Ksv and [M] are the quenching constant and concentration, respectively. The correlation between the intensity and the concentration of Fe3+ may be described by a nonlinear curve. The exponential equation is close to equation I0/I = 2.562 3+

e6.048[Fe ] − 0.162, suggesting that the simultaneous involvement of static and dynamic quenching processes (Figure 4d).23 And, a good linear relationship is given for the plot of (I0/I) − 1 vs the concentration of Fe3+ in 0−7.13 × 10−5 M (Figure S14a). It is well known that the luminescence of Ln-MOFs is highly dependent on the energy transfer from ligand to Ln3+.24 The mechanism of luminescent quenching by Fe3+ may be attributed to the electron transfer process from donor to acceptor. Ligand may act as an electron donor, whereas Fe3+ retains the available orbitals and is an electron acceptor. On the basis of the above discussions, the luminescent quenching may be speculated as Fe3+ diffused into the one-dimensional channels of 1-Tb and contacted with the uncoordinated pyrimidine moiety, the electrons of L2− ligand are transferred from the donor to the acceptor, thus the antenna effect of the ligand was suppressed to result in luminescent quenching.25 To further verify these results, the XPS experiments were carried out to study 1-Tb and Fe3+@1-Tb, respectively. In the XPS experiment of Fe3+@1-Tb, the full spectrum showed the typical energy of Fe (713.6 and 718.9 for Fe3+@1-Tb), demonstrating the interaction between Fe3+ and 1-Tb (Figure S15a). The N 1s peak of pyrimidine at 400.1 eV in 1-Tb is transferred to 398.3 eV after the introduction of Fe3+, 344

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 7. UV−vis spectra of 1-Tb (a) and 2-La (b) in aqueous solutions of Congo red.

Figure 8. Time-resolved adsorption capacity of CR on the complexes 1-Tb (a) and 2-La (b).

quickly and reaches the minimum value of 10.78 cm3 K mol−1 at 1.8 K. The observed decrease in χMT may be explained by a collaboration of weak antiferromagnetic interlock and/or thermal depopulation of low-lying crystal-field states.30 Such a feature may be often ascribed to one or combination of the below phenomena: (i) the progressive depopulation of the excited stark sublevels of Dy3+31 and (ii) weak antiferromagnetic interplay of Ln3+ in the complexes.32 The isothermal magnetization (M) vs field (H) plots at 2, 3, and 5 K of 1-Dy are shown in Figure 9b; the curves displayed the rapid increases in the magnetization at low magnetic fields and then slow increase in higher fields to achieve a saturation value of 5 Nβ.33 The incomplete overlap of the three curves at different temperatures further proves that there may be magnetic anisotropy and/or low-lying excited state in 1Dy.34 In magnetic studies, Dy3+ has large magnetic moments and good magnetic anisotropy, so it has long been considered a candidate for obtaining SMM.35 Chemists are interested in SMM due to its various applications. For example, the freezing of magnetization is lower than the so-called blocking temperature, the quantum tunneling effect of magnetization (QTM).36,37 The ac susceptibility at an optimized dc field of 1200 Oe was further tested to study the inhibition of QTM (Figure 9c). The tested frequencies were 1, 100, 300, 500, 600, 800, and 1000 Hz for 1-Dy. The results prove that the in-phase (χ′) and out-of-phase (χ″) susceptibilities do not decline in the lower temperature, and the relaxation probability remains

largely governed by their size. The size of 1-Tb is 20.2 Å × 11.4 Å × 12.6 Å and 2-La is 13.5 Å × 13.5 Å × 13.5 Å, whereas the molecular size of the Congo red dye is (∼20.2 Å × 10.1 Å × 10.2 Å). The dye molecules can be captured when the size of dyes well matches the porosities of the sophisticated framework in any two directions. The concentration of the complexes 1-Tb and 2-La soaked in the CR is lowered after 180 min (Figure 7). The quantity of adsorbed dye could be calculated at equilibrium by the formula: Qeq = (C0 − Ceq)V/m, where C0 and Ceq represent the initial and the equilibrium concentrations of the dye (mg L−1), respectively, and m and V stand for the mass of adsorbent (g) and solution volume (L), respectively. By calculation, the values of Qeq for CR are 322 and 326 mg g−1 for 1-Tb and 2-La, respectively. A higher value of Qeq means a better capability to catch the dye. It is observed that the adsorption rate of 1-Tb is much quicker than that of 2La (Figure 8), but the adsorption amount of 2-La increases with time, proving that both 1-Tb and 2-La can adsorb CR effectively. Magnetic Properties. Considering the binuclear [Dy2(COO)6N2] SBU in 1-Dy, the variable temperature magnetism (χM) of 1-Dy was studied in the 1.8−300 K under 1000 Oe. The χMT value for one Dy3+ is 14.02 cm3 K mol−1 at 300 K (Figure 9a), which meets the theoretical value of 14.17 cm3 K mol−1 (6H15/2, S = 5/2, L = 5, g = 4/3). χMT values decrease gradually from 300 to 50 K. Then, the curve degrades 345

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

Figure 9. (a) χMT versus T plot of 1-Dy and (b) magnetization (M) vs field (H) plots at 2.0, 3.0, and 5.0 K of 1-Dy. Temperature dependence of the out-of-phase (c) and in-phase (d) alternating current (ac) susceptibility of 1-Dy under 1000 Oe direct current (dc) field.

■

through the quantum pathway. The frequency-dependent peaks in the out-of-phase susceptibility are not very clear; thus, the energy barrier can not be gained by the Arrhenius expression. Assuming there is only one typical relaxation step, the barrier may be yielded from the Debye model, ln(χ″/χ′) = ln(vτ0) + Ea/KBT,38 where v is the frequency, τ0 is the preexponential factor, and Ea is the energy barrier, giving Ea = 8.7 K and τ0 = 7.9 × 10−6 s (Figure S17). All of the above states prove that 1-Dy has a slow magnetic relaxation performance.39

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02435. Table S1 for selected bonds and distances of four LnMOFs, the PXRD patterns, the IR spectra, the TGA curves, luminescent and UV−vis adsorption spectrum, etc. (PDF) Accession Codes

CONCLUSIONS

CCDC 1863473−1863476 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Two series of Ln-MOFs have been obtained by an unsymmetrical N-heterocyclic dicarboxylic H2L ligand. All the complexes show 3D porous frameworks decorated by exposed Lewis basic pyrimidine sites. The luminescent studies indicate that 1-Tb is a highly efficient probe for sensing Fe3+ and Cr2O72−. The complexes 1-Tb and 2-La display a unique selective adsorption to CR dyes, and the adsorption amount increased rapidly with prolonging contact time. The adsorption equilibrium can almost be reached within 180 min, proving that both 1-Tb and 2-La can adsorb CR effectively. 1-Dy exhibits a slow magnetic relaxation performance. In short, this work may provide more options for building new versatile functional MOF materials.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Guoping Yang: 0000-0002-0230-6834 Yao-Yu Wang: 0000-0002-0800-7093 Notes

The authors declare no competing financial interest. 346

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry

■

highly selective CO2 adsorption and separation of organic dyes. J. Mater. Chem. A 2016, 4, 13844−13851. (14) (a) Li, H.; Li, H.; Li, L.; Xu, L.; Hou, K.; Zang, S. Q.; Mak, T. C. W. Syntheses, Structures, and Photoluminescent Properties of Lanthanide Coordination Polymers Based on a Zwitterionic Aromatic Polycarboxylate Ligand. Cryst. Growth Des. 2015, 15, 4331−4340. (b) Kanimozhi, A. J.; Alexander, V. Synthesis and photophysical and magnetic studies of ternary lanthanide(III) complexes of naphthyl chromophore functionalized imidazo[4,5-f]-[1,10]phenanthroline and dibenzoylmethane. Dalton Trans. 2017, 46, 8562−8571. (15) Wade, C. R.; Corrales-Sanchez, T.; Narayan, T. C.; Dinca, M. Postsynthetic tuning of hydrophilicity in pyrazolate MOFs to modulate water adsorption properties. Energy Environ. Sci. 2013, 6, 2172−2177. (16) Sheldrick, G. M. SHELXL-2014, Program for Refinement of Crystal Structures; University of Göttingen: Germany, 2014. (17) Spek, A. L. Single-crystal structure validation with the program PLATON. J. Appl. Crystallogr. 2003, 36, 7−13. (18) Blatov, V. A. March 5, 2018. http://topospro.com/. (19) Wang, Y.; Du, N.; Zhang, X.; Wang, Y.; Xing, Y. H.; Bai, F. Y.; Sun, L. X.; Shi, Z. Functional Sensing Materials Based on Lanthanide N-Heterocyclic Polycarboxylate Crystal Frameworks for Detecting Thiamines. Cryst. Growth Des. 2018, 18, 2259−2269. (20) Yan, W.; Zhang, C. L.; Chen, S. G.; Han, L. G.; Zheng, H. G. Two Lanthanide Metal−Organic Frameworks as Remarkably Selective and Sensitive Bifunctional Luminescence Sensor for Metal Ions and Small Organic Molecules. ACS Appl. Mater. Interfaces 2017, 9, 1629−1634. (21) Hyman, L.; Franz, K. Probing Oxidative Stress: Small Molecule Fluorescent Sensors of Metal Ions, Reactive Oxygen Species, and Thiols. Coord. Chem. Rev. 2012, 256, 2333−2356. (22) Liu, T. F.; Feng, D. W.; Chen, Y. P.; Zou, L. F.; Bosch, M.; Yuan, S.; Wei, Z. W.; Fordham, S.; Wang, K. C.; Zhou, H. C. Topology-Guided Design and Syntheses of Highly Stable Mesoporous Porphyrinic Zirconium Metal-Organic Frameworks with High Surface Area. J. Am. Chem. Soc. 2015, 137, 413−419. (23) Xu, H.; Hu, H. C.; Cao, C. S.; Zhao, B. Lanthanide Organic Framework as a Regenerable Luminescent Probe for Fe3+. Inorg. Chem. 2015, 54, 4585−4587. (24) Arnaud, N.; Vaquer, E.; Georges, J. Comparative study of the luminescent properties of europium and terbium coordinated with thenoyltrifluoroacetone or pyridine-2,6-dicarboxylic acid in aqueous solutions. Analyst 1998, 123, 261−265. (25) Yang, C. X.; Ren, H. B.; Yan, X. P. Fluorescent Metal−Organic Framework MIL-53(Al) for Highly Selective and Sensitive Detection of Fe3+ in Aqueous Solution. Anal. Chem. 2013, 85, 7441−7446. (26) Dang, S.; Ma, E.; Sun, Z.-M.; Zhang, H. A layer-structured EuMOF as a highly selective fluorescent probe for Fe3+ detection through a cation-exchange approach. J. Mater. Chem. 2012, 22, 16920−16926. (27) Adhikari, B.; Palui, G.; Banerjee, A. Self-assembling tripeptide based hydrogels and their use in removal of dyes from waste-water. Soft Matter 2009, 5, 3452−3460. (28) (a) Shi, B.; Li, G. H.; Wang, D. S.; Feng, C. H.; Tang, H. X. Removal of direct dyes by coagulation: The performance of preformed polymeric aluminum species. J. Hazard. Mater. 2007, 143, 567−574. (b) Mahanta, D.; Madras, G.; Radhakrishnan, S.; Patil, S. Adsorption of Sulfonated Dyes by Polyaniline Emeraldine Salt and Its Kinetics. J. Phys. Chem. B 2008, 112, 10153−10157. (29) Zhu, H. Y.; Jiang, R.; Xiao, L. Adsorption of an anionic azo dye by chitosan/kaolin/γ-Fe2O3 composites. Appl. Clay Sci. 2010, 48, 522−526. (30) Du, L. Y.; Wang, H.; Liu, G.; Xie, D.; Guo, F. S.; Hou, L.; Wang, Y. Y. Structural diversity of five new bitriazole-based complexes: luminescence, sorption, and magnetic properties. Dalton Trans. 2015, 44, 1110−1119. (31) (a) Ke, H. S.; Zhang, S.; Li, X.; Wei, Q.; Xie, G.; Wang, W. Y.; Chen, S. P. A Dy2 Single Molecule Magnet with Benzoate Anions and Phenol-O− Bridging Groups. Dalton Trans. 2015, 44, 21025−21031.

ACKNOWLEDGMENTS We are grateful for the financial support by the NSFC (21531007), the NSF of Shaanxi Province (2017KJXX-59), the China Postdoctoral Science Foundation (2016M600807 and 2017T100765), the Technology Foundation for Selected Overseas Scholars of Shaanxi Province (2018041), the Key Laboratory Projects of Shaanxi Provincial Educational Department (17JS132), and the National Demonstration Center for Experimental Chemistry Education (Northwest University).

■

REFERENCES

(1) (a) Li, B. Y.; Chrzanowski, M.; Zhang, Y. M.; Ma, S. Q. Applications of metal-organic frameworks featuring multi-functional sites. Coord. Chem. Rev. 2016, 307, 106−129. (b) Burgess, S. A.; Kassie, A.; Baranowski, S. A.; Fritzsching, K. J.; Schmidt-Rohr, K.; Brown, C. M.; Wade, C. R. Improved Catalytic Activity and Stability of a Palladium Pincer Complex by Incorporation into a Metal− Organic Framework. J. Am. Chem. Soc. 2016, 138, 1780−1783. (2) (a) Wu, Y.; Yang, G. P.; Zhao, Y.; Wu, W. P.; Liu, B.; Wang, Y. Y. Three new solvent-directed Cd(II)-based MOFs with unique luminescent properties and highly selective sensors for Cu2+ cations and nitrobenzene. Dalton Trans. 2015, 44, 3271−3277. (b) Li, C. P.; Zhou, H.; Wang, S.; Chen, J.; Wang, Z. L.; Du, M. Highly efficient Cr2O72− removal of a 3D metal-organic framework fabricated by tandem single-crystal to single-crystal transformations from a 1D coordination array. Chem. Commun. 2017, 53, 9206−9209. (3) Wen, L.; Zheng, X.; Lv, K.; Wang, C.; Xu, X. Two AminoDecorated Metal−Organic Frameworks for Highly Selective and Quantitatively Sensing of HgII and CrVI in Aqueous Solution. Inorg. Chem. 2015, 54, 7133−7135. (4) Asha, K. S.; Bhattacharjee, R.; Mandal, S. Complete Transmetalation in a Metal-Organic Framework by Metal Ion Metathesis in a Single Crystal for Selective Sensing of Phosphate Ions in Aqueous Media. Angew. Chem., Int. Ed. 2016, 55, 11528−11532. (5) Janiak, C. Engineering coordination polymers towards applications. Dalton Trans. 2003, 2781−2804. (6) Wu, Y. P.; Xu, G. W.; Dong, W. W.; Zhao, J.; Li, D. S.; Zhang, J.; Bu, X. Anionic Lanthanide MOFs as a Platform for Iron-Selective Sensing, Systematic Color Tuning, and Efficient Nanoparticle Catalysis. Inorg. Chem. 2017, 56, 1402−1411. (7) Kim, J. E.; Bogart, J. A.; Carroll, P. J.; Schelter, E. J. Rare earth metal complexes of bidentate nitroxide ligands: synthesis and electrochemistry. Inorg. Chem. 2016, 55, 775−784. (8) Zhao, J.; Wang, Y. N.; Dong, W. W.; Wu, Y. P.; Li, D. S.; Zhang, Q. A Robust luminescent Tb(III)-MOF with Lewis basic pyridyl Sites for the Highly Sensitive Detection of Metal Ions and Small Molecules. Inorg. Chem. 2016, 55, 3265−3271. (9) Bi, Y.; Chen, C.; Zhao, Y. F.; Zhang, Y. Q.; Jiang, S. D.; Wang, B. W.; Han, J. B.; Sun, J. L.; Bian, Z. Q.; Wang, Z. M.; Gao, S. Thermostability and photoluminescence of Dy(III) single-molecule magnets under a magnetic field. Chem. Sci. 2016, 7, 5020−5031. (10) Chen, C. H.; Krylov, D. S.; Avdoshenko, S. M.; Liu, F.; Spree, L.; Westerström, R.; Bulbucan, C.; Studniarek, M.; Dreiser, J.; Wolter, A. U. B.; Büchner, B.; Popov, A. A. Magnetic hysteresis in selfassembled monolayers of Dy-fullerene single molecule magnets on gold. Nanoscale 2018, 10, 11287−11292. (11) Zhang, S.; Ke, H. S.; Liu, X. Y.; Wei, Q.; Xie, G.; Chen, S. P. A Nine-coordinated Dysprosium(III) Compound with an Oxalatebridged Dysprosium(III) Layer Exhibiting Two Slow Magnetic Relaxation Processes. Chem. Commun. 2015, 51, 15188−15191. (12) Yin, D. D.; Chen, Q.; Meng, Y. S.; Sun, H. L.; Zhang, Y. Q.; Gao, S. Slow Magnetic Relaxation in a Novel Carboxylate/oxalate/ hydroxyl Bridged Dysprosium Layer. Chem. Sci. 2015, 6, 3095−3101. (13) Liu, X. P.; Xiao, Z. Y.; Xu, J.; Xu, W. B.; Sang, P. P.; Zhao, L. M.; Zhu, H. Y.; Sun, D. F.; Guo, W. Y. A NbO-type copper metal− organic framework decorated with carboxylate groups exhibiting 347

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348

Article

Inorganic Chemistry (b) Joarder, B.; Chaudhari, A. K.; Rogez, G.; Ghosh, S. K. A Carboxylate-based Dinuclear Dysprosium(III) Cluster Exhibiting Slow Magnetic Relaxation Behaviour. Dalton Trans. 2012, 41, 7695−7699. (32) Akhtar, M. N.; Chen, Y. C.; AlDamenb, M. A.; Tong, M. L. 3D oxalato-bridged lanthanide(III) MOFs with magnetocaloric, magnetic and photoluminescence properties. Dalton Trans. 2017, 46, 116−124. (33) Zhou, Q.; Yang, F.; Liu, D.; Peng, Y.; Li, G.-H.; Shi, Z.; Feng, S. H. Synthesis, Structures, and Magnetic Properties of Three FluorideBridged Lanthanide Compounds: Effect of Bridging Fluoride Ions on Magnetic Behaviors. Inorg. Chem. 2012, 51, 7529−7536. (34) Liang, L.; Peng, G.; Li, G. Z.; Lan, Y. H.; Powell, A. K.; Deng, H. In Situ Hydrothermal Synthesis of Dysprosium(III) SingleMolecule Magnet with Lanthanide Salt as Catalyst. Dalton Trans. 2012, 41, 5816−5823. (35) Guo, Y. N.; Xu, G. F.; Gamez, P.; Zhao, L.; Lin, S. Y.; Deng, R.; Tang, J.; Zhang, H. J. Two-Step Relaxation in a Linear Tetranuclear Dysprosium(III) Aggregate Showing Single Molecule Magnet Behavior. J. Am. Chem. Soc. 2010, 132, 8538−8539. (36) (a) Saitoh, E.; Miyajima, H.; Yamaoka, T.; Tatara, G. Currentinduced resonance and mass determination of a single magnetic domain wall. Nature 2004, 432, 203−206. (b) Sessoli, R.; Boulon, M. E.; Caneschi, A.; Mannini, M.; Poggini, L.; Wilhelm, F.; Rogalev, A. Strong Magneto-chiral Dichroism in a Paramagnetic Molecular Helix Observed by Hard X-rays. Nat. Phys. 2015, 11, 69−74. (37) Costes, J. P.; Titos-Padilla, S.; Oyarzabal, I.; Gupta, T.; Duhayon, C.; Rajaraman, G.; Colacio, E. Effect of Ligand Substitution around the DyIII on the SMM Properties of Dual-Luminescent Zn-Dy and Zn-Dy-Zn Complexes with Large Anisotropy Energy Barriers: A Combined Theoretical and Experimental Magnetostructural Study. Inorg. Chem. 2016, 55, 4428−4440. (38) Bartolomé, J.; Filoti, G.; Kuncser, V.; Schinteie, G.; Mereacre, V.; Anson, C. E.; Powell, A. K.; Prodius, D.; Turta, C. Magnetostructural correlations in the tetranuclear series of {Fe3LnO2} butterfly core clusters: Magnetic and Mö ssbauer spectroscopic study. Phys. Rev. B 2009, 80, No. 014430. (39) Liu, K.; Shi, W.; Cheng, P. Toward Heterometallic SingleMolecule Magnets: Synthetic Strategy, Structures and Properties of 3d-4f Discrete Complexes. Coord. Chem. Rev. 2015, 289−290, 74− 122.

348

DOI: 10.1021/acs.inorgchem.8b02435 Inorg. Chem. 2019, 58, 339−348