Highly Water Stable Lanthanide MetalâOrganic Frameworks

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Highly Water Stable Lanthanide Metal-Organic Frameworks Constructed from 2,2'-Disulfonyl-4,4'biphenyldicarboxylic Acid: Syntheses, Structures, and Properties Jing Zhao, Xin He, Yuchi Zhang, Jie Zhu, Xuan Shen, and Dunru Zhu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01061 • Publication Date (Web): 05 Sep 2017 Downloaded from http://pubs.acs.org on September 6, 2017

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Crystal Growth & Design

Highly Water Stable Lanthanide Metal-Organic Frameworks Constructed from 2,2'-Disulfonyl-4,4'-biphenyldicarboxylic Acid: Syntheses, Structures, and Properties Jing Zhao,a,† Xin He,a,† Yuchi Zhang,a Jie Zhu,b Xuan Shen,a and Dunru Zhu*,a,c a

College of Chemical Engineering, State Key Laboratory of Materials-oriented Chemical

Engineering, Nanjing Tech University, Nanjing 210009, P. R. China, bDepartment of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0212, USA, cState Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China

ABSTRACT: A series of three-dimensional (3D) lanthanide metal-organic frameworks (LnMOFs), (Me2NH2)[LnL(H2O)] (Ln = Eu (1), Gd (2), Tb (3), Dy (4); H4L = 2,2′-disulfonyl-4,4′-biphenyldicarboxylic acid), have been successfully synthesized from H4L and Ln(NO3)3·6H2O under solvothermal conditions. Single crystal X-ray diffraction (SCXRD) shows that all LnMOFs 1–4 are isomorphous and isostructural with a hepta-coordinated Ln(III) being connected through the carboxylate groups of the L4− ligands, resulting in the formation of an one-dimensional (1D) inorganic rod-like [Ln(-COO)2)]+n chain along the c axis. The infinite 1D chains are further linked by the sulfonate and biphenyl groups, leading to formation of a uninodal 5-connected 3D network with bnn topology. The present LnMOFs are the first example of anionic 3D bnn-net constructed on Ln-O-C rods with channels being filled with (Me2NH2)+ cations. The L4− ligand shows a penta-dentate coordination mode with two bound sulfonate groups. All the LnMOFs are insoluble in water and highly stable against moisture. 1

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Cation-exchange with Li+, Na+ and K+ ions can be easily performed at room temperature (RT). In addition, LnMOFs 1 and 3 display characteristic photoluminescence of Eu(III) and Tb(III) ions upon excitation at 394 and 353 nm, respectively. The investigation of magnetism demonstrates relatively weak antiferromagnetic interactions between Gd(III) ions (J = −0.0042(5) cm-1) in 2, and between Dy(III) ions (θ = −0.20(2) K) in 4. The proton conductivity of 1 is 4.14 × 10−8 S cm−1 at 95% relative humidity (RH) and 25°C.

Introduction Lanthanide(III) complexes can exhibit unique intrinsic magnetism and optical properties because of their intra-4f electronic transitions of the metal ions.1 The flexible coordination modes and high coordination number of the Ln(III) cations can also endow their complexes with aesthetically appealing structural topologies. Recently, much effort has been made in designing and synthesizing lanthanide metal-organic framework (LnMOFs) due to their attractive supramolecular structures as well as unique luminescent, magnetic, ion exchange, gas adsorption and proton conductive properties.2-5 All kinds of organic ligands like amino acids, Schiff-bases and pyridine carboxylic acids have been widely used for the construction of LnMOFs.6-9 Another type of particularly interested organic ligands are polycarboxylic acids, due to their versatile coordination modes as bridging linkers. With the high oxygen-affinity of Ln(III) ions, highly interesting LnMOFs can be prepared.10 For example, aromatic polycarboxylic acids like 1,4-benzenedicarboxylic acid (H2BDC),11 1,3,5-benzenetricarboxylic acid (H3BTC)12 and 4,4'-biphenyldicarboxylic acid (H2BPDC)13 are excellent linkers for the construction of 3D LnMOFs providing additional stability and structural diversity. BPDC-based ligands have robust biphenyl backbone that allows the construction of highly thermal stable MOFs or LnMOFs. By incorporation of substitutes into the biphenyl ring, the structures of the MOFs or LnMOFs can be finely tuned by utilizing the space-filling effect of the 2


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substitutes. We are particularly interested in building MOFs (or LnMOFs) by using the symmetrically substituted BPDC ligands because the functionalization of the ligands can provide control of the structure and properties of the resulting materials.14 For instance, the MOF constructed from 2,2'-dimethoxy-BPDC and Cd(II) ion exhibits an unusual 3D/3D hetero-interpenetrating network,14d,f while the LnMOFs derived from the same ligand and Eu(III), Gd(III), Dy(III) ions show an unprecedented (3,20)-connected binodal 3D framework based on a novel secondary building unit (SBU), [Ln4@Ln4] matryoshka tetrahedron.14i Notably, the LnMOF built from Sm(III) ions and 3,3'-disulfonyl-BPDC ligand exhibits humidity- and temperature-dependent proton conductivity with a value of 1.11 × 10−3 S cm−1 at 80°C and 98% RH.15 However, to our knowledge, LnMOFs derived directly from 2,2'-disulfonyl-BPDC acid (H4L, Scheme 1), an isomer of 3,3'-disulfonyl-BPDC, have not been reported so far. We expect that by changing the position of sulfonic group to the carboxylate group, the H4L ligand will provide additional coordination sites and subsequently the structures and properties of the resulting LnMOFs can be varied. We present herein the crystal structure of the H4L·4H2O ligand and the successful construction of a series of 3D LnMOFs, (Me2NH2)[LnL(H2O)] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)) using the H4L as linkers. All the four LnMOFs 1-4 are fully characterized using spectroscopic techniques and SCXRD analysis. They show a 3D hexagonal BN (Boron Nitride) network with bnn topology and high water stabilities. Additional, the cation-exchange behavior and proton conductivity of 1, the photoluminescence of 1 and 3, and magnetism of 2 and 4 are also reported.

Experimental Section Materials and Methods. All chemical reagents were commercial available and used as received. 2,2′-Disulfonyl-4,4′-biphenyldicarboxylic acid (H4L) was synthesized based on our improved method.16 C, H, N, S analyses were measured by a Perkin-Elmer 240 instrument. Cation exchange of 1 with Li+, Na+ and K+ ions were performed on a PE 7000DV inductively coupled plasma (ICP) spectrometer. FT-IR spectra were carried out on a Nicolet 380 FT-IR instrument 3



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(KBr pellets). 1H NMR spectra were determined on a Bruker AM 400 MHz spectrometer in D2O solution. Chemical shifts are recorded in ppm. Powder X-ray diffraction (PXRD) data were recorded on a Bruker D8 Advance diffractometer under Cu Kα radiation (λ = 1.5406 Å). Thermogravimetric analyses (TGA) were performed on a NETZSCH STA 449C thermal analyzer under a N2 with the warming rate of 10°C min-1. Fluorescence spectra of 1 and 3 were performed on a Perkin-Elmer LS-55 spectrophotometer. Variable-temperature magnetic susceptibilities of 2 and 4 were recorded on a Quantum Design MPMS-7 SQUID magnetometer. Pascal’s constants was used for the diamagnetic correction.1c Alternating current (AC) conductivities of 1 were recorded on a pellet sample (2.5 mmϕ with a thickness of 0.60 mm), made under a pressure of ~1.2 GPa. Two faces of the pellet were coated with gold paste and then the pellet was pressed between parallel circular titanium electrodes in specially designed porous quartz cells. In general, the impedance data were measured under multiple different environmental conditions by the ordinary quasi-four-probe method, making use of gold wires (50 µmϕ) and gold paste with a Solartron SI 1260 Impedance/Gain-Phase Analyzer and 1296 Dielectric Interface in the frequency range of 1 MHz–1 Hz. Data points were recorded after the samples attaining an equilibrated state, with no error within one hour; this took on the order of half day per point. Caution: Because of the increased explosion potential, extreme caution must be used when working with perchloric acid and inorganic perchlorates. Synthesis of 2,2′-Disulfonyl-BPDC (H4L). The H4L ligand was prepared using an improved reference method (Scheme S1).16 In contrast to the method provided by Lazarev,16 our improved synthetic route can provide H4L in pure crystalline form with a higher yield without the use of NaNO2. Furthermore, colorless single crystals of H4L·4H2O were also obtained. In order to obtain the H4L ligand without potassium, K2H2L (3.5000 g, 7.3 mmol) was dissolved in 10 mL water, and perchloric acid (72%, 2 mL) was added slowly with stirring. After the insoluble potassium perchlorate was filtrated off, the resulting clear solution was evaporated to small volume at a reduced pressure and cooled to RT to give colorless solids of H4L·4H2O 4


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(2.7000 g, 78%). Single crystals of H4L·4H2O suitable for SCXRD were achieved through slow evaporation of a saturated water solution at RT. IR (KBr, cm-1): 3480(s), 3120(w), 1710(s), 1600(s), 1400(vs), 1220(s), 1040(s), 852(m), 620(s). 1H NMR (D2O, 400 MHz): δ 8.40 (d, 2H, Ph-H3), 7.96 (m, 2H, Ph-H6), 7.32 (d, 2H, Ph-H5). Anal. Calcd for C14H18O14S2 (%): C, 35.44; H, 3.82; S, 13.52. Found: C, 35.22; H, 3.76; S, 13.85. Synthesis of (Me2NH2)[EuL(H2O)] (1). Eu(NO3)3·6H2O (44.6 mg, 0.1 mmol), H4L·4H2O (47.4 mg, 0.1 mmol), DMF (0.1 mL), and H2O (4.6 mL) were placed in a stainless-steel reactor (25 mL) lined with Teflon. The resulting solution was kept at 150°C for 48 hours and then cooled to RT. The formed colorless crystals of 1 were collected by filtration. Yield: 82.3% (50.6 mg) based on Eu(III). IR (cm-1): 3225(m), 1578(m), 1409(vs), 1250(m), 1031(s). Anal. calcd for C16H16EuNO11S2 (%): C, 31.28; H, 2.62; N, 2.28; S, 10.44. Found: C, 31.12; H, 2.81; N, 2.15; S, 10.31. Synthesis of (Me2NH2)[GdL(H2O)] (2). The procedure was the same as that for 1 except using Gd(NO3)3·6H2O (45.1 mg, 0.1 mmol) to displace Eu(NO3)3·6H2O. Yield of 2: 80.7% (50 mg) based on Gd(III). IR (cm-1): 3230(m), 1580(m), 1410(vs), 1250(m), 1030(s). Anal. calcd for C16H16GdNO11S2 (%): C, 31.01; H, 2.60; N, 2.26; S, 10.35. Found: C, 31.32; H, 2.35; N, 2.11; S, 10.21. Synthesis of (Me2NH2)[TbL(H2O)] (3). The procedure was the same as that for 1 except that Tb(NO3)3·6H2O (45.3 mg, 0.1 mmol) was used to replace Eu(NO3)3·6H2O. Yield of 3: 80.1% (49.8 mg) based on Tb(III). IR (cm-1): 3240(m), 1580(s), 1410(vs), 1250(m), 1031(s). A nal. calcd for C16H16TbNO11S2 (%): C, 30.93; H, 2.60; N, 2.25; S, 10.32. Found: C, 30.77; H, 2.78; N, 2.12; S, 10.46. Synthesis of (Me2NH2)[DyL(H2O)] (4). The procedure was the same as that for 1 only using Dy(NO3)3·6H2O (45.7 mg, 0.1 mmol) to replace Eu(NO3)3·6H2O. Yield of 4: 79.0% (49.4 mg) based on Dy(III). IR (cm-1): 3230(s), 1580(s), 1410(vs), 1250(s), 1030(s). Anal. calcd for C16H16DyNO11S2 (%): C, 30.75; H, 2.58; N, 2.24; S, 10.26. Found: C, 30.91; H, 2.22; N, 2.18; S, 10.52. 5



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X-ray Crystallography. SCXRD data for ligand H4L·4H2O and 1-4 were recorded on a Bruker Apex II CCD with a Mo-Kα X-ray source (λ = 0.71073 Å) at RT. These structures have been determined via direct methods with a SHELXTL-97 software package.17 The crystallographic data of H4L·4H2O and 1–4 are presented in Table 1. The main bond distances and angles are summarized in Table S1–3 (Supporting Information), respectively. CCDC 1503116-1503120 include the crystallographic data (H4L·4H2O and 1–4, respectively) for this paper. These data can be available from the Cambridge Crystallographic Date Center via www.ccdc.cam.ac.uk. Cation Exchange. Freshly prepared crystals of LnMOF 1 (20 mg) were immersed in 0.03 M solution (3 mL) of LiNO3, NaNO3 and KNO3, respectively, with stirring at RT. After 1, 6 and 12 h, the exchanged samples were filtered, washed with H2O (3 × 2 mL) and CH3OH (3 × 2 mL) and dried in air. The products were measured by ICP analyses (Table 2).

Results and Discussion Syntheses of H4L·4H2O and LnMOFs 1-4. The ligand H4L has been reported,16 but it was not fully characterized and the X-ray crystal structure has not been published. We used a modified synthetic route and obtained the ligand H4L·4H2O in pure crystalline form. The H4L·4H2O was fully characterized by elemental analyses, FT-IR, 1H NMR, and SCXRD analyses. Under solvothermal conditions, the ligand H4L·4H2O was allowed to react with Ln(NO3)3·6H2O (Ln = Eu, Gd, Tb, and Dy, respectively) in binary solvent DMF/H2O (0.1/4.6, V/V) resulting in formation of LnMOFs 1-4 in high yields. The LnMOFs 1-4 have been characterized by elemental analyses, FT-IR, TGA, powder and SCXRD studies. All the crystals of 1–4 are stable in air and do not dissolve in commonly used solvents, such as H2O, (CH3)2CO, CH3OH, C2H5OH, CH3CN, and DMF. The SCXRD studies show that all 1–4 exhibit same structural topology. Crystal Structure of H4L·4H2O. The SCXRD analysis shows that the ligand H4L·4H2O has a monoclinic C2/c space group. The asymmetric unit of H4L·4H2O is composed of a half of (H2L)2− ligand, one H2O molecule and a H3O+ ion (Figure S1). The phenyl ring and carboxyl 6


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group are almost co-planar with a dihedral angle of 8.25(1)°. Within the biphenyl group, the two phenyl rings are almost vertical with a dihedral angle of 79.57(1)° (Figure 1a). As expected, strong hydrogen bonding interactions are found between the O atoms from the sulfonate, carboxylate, and H atoms from H2O and H3O+ cation. These hydrogen bonds form an extended 3D supramolecular network (Figure 1b, Table S4). Crystal Structures of LnMOFs 1-4. The SCXRD analyses indicate that all the LnMOFs 1– 4 are isomorphous and belong to the monoclinic C2/c space group (Table 1). Because all the 1–4 are isostructural LnMOFs, here only the structure of 1 was chosen for a detailed discussion. The asymmetric unit of 1 is composed of 0.5 Eu(III) ion, 0.5 L4− ligand, 0.5 (Me2NH2)+ ion and 0.5 H2O molecule (Figure S2). The Eu(III) center is hepta-coordinated by two sulfonate O atoms from one L4− and four carboxylate O atoms from four different L4− ligands, and one H2O (Figure 2). It is noteworthy that although two sulfonate groups lie at meta-position to the carboxyl groups in H4L ligand, they can still take part in coordination to the same Eu(III) ion, together with the carboxylate groups to complete a EuO7 sphere. Although hepta-coordinated Ln(III) complexes have been extensively reported, the MOFs built from pure hepta-coordinated Ln(III) ion are still very rare.18 In 1, the Eu-O (COO-) distances (2.3169(17)-2.3400(16) Å), Eu-O (SO3-) distance (2.3952(17) Å), and the Eu-O (H2O) bond length (2.371(3) Å) are all similar to those found in reported Eu-MOFs.15 The EuO7 unit showing a decahedron geometry (Figure 2b) is jointly connected by carboxyl groups of L4- to generate an 1D rod-like inorganic [Eu(-COO)2]+n chain12b along the c axis and the distance of Eu···Euvi is 5.286(1) Å (Figure 3b). The 1D inorganic chains are linked by the biphenyl groups and sulfonate groups of L4- to produce a 3D framework supported by hydrogen bond interactions involving C-H···O, N-H···O and O-H···O (Table S5, Figure S6). Interestingly, there are 1D rhombus pores with the sizes of 5.0 × 3.6 Å2 (the atoms’ van der Walls radii are excluded) in 1 along the c axis (Figure 3a). The pores have 16.7% solvent accessible volume occupied by (Me2NH2)+ ion. In order to further examine the topology of 1, the SBUs for the construction of the 3D framework is simplified. Each Eu(III) ion is connected to five L4− ligand, and each L4− ligand is 7



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also linked to five Eu(III) ions. Thus, taking Eu(III) ion as a node of framework, each Eu(III) center can be described as a 5-connected node. Meanwhile, each L4− ligand is also a 5-connected node. On the basis of the simplified principle, the final structure of 1 is a uninodal 5-connected bnn hexagonal BN network with (46·64) topology (Figure 3). Although many bnn-net MOFs have been reported,19 the bnn-net LnMOF is still very unusual. To the best of our knowledge, 1-4 represent the first example of anionic Ln-carboxylate chain-based 3D bnn LnMOFs.20 Coordination Pattern of the L4- Ligand. Aromatic multicarboxylic acids have been commonly used for the preparation of LnMOFs mainly owing to their ready availability and versatile coordination patterns. In LnMOFs 1-4, both carboxyl groups of the H4L ligand are deprotonated, but only one syn–anti bis(bridging bidentate) pattern was found to coordinate the Ln(III) center. In addition, two sulfonic groups are also deprotonated and are bound to the same Ln(III) ion in a syn monodentate mode to form a nine-membered ring (Figure S7). Therefore, the deprotonated ligand in 1-4 acts as a L4- anion and exhibits a penta-dentate coordination mode. The dihedral angles of the -Ph group and the -COO– ion in L4- are in a narrow range of 14.89(1)-15.28(1)°, whereas those of the biphenyl rings are 85.43(1)-86.63(1)° (Table S6). Notably, the dihedral angles (-COO–/-Ph ring and biphenyl rings) of L4- in 1-4 are larger than those in the free H4L ligand due to coordination of the sulfonate groups, which is very rare in coordination chemistry.21 FTIR Spectra. As shown in Figures S9-S12, the asymmetric or symmetric stretching bands of -COO– groups in LnMOFs 1-4 are found around 1579 or 1410 cm-1, respectively. Disappearance of very strong vibration bands at ~1710 cm-1 demonstrates the entire deprotonation of the -CO2H of the H4L during the reaction. The typical asymmetric or symmetric stretching peaks of -SO3– ions are around 1250 or 1030 cm−1, respectively. The bands at 3225 (for 1), 3230 (for 2), 3240 (for 3) and 3230 (for 4) cm-1 are assigned to N-H stretching bands of (Me2NH2)+ ion, respectively. These characteristics are in consistence with the SCXRD results. PXRD and TGA. The experimental and simulated PXRD modes of LnMOFs 1–4 can be found in Figures S13-S16 (Supporting Information). Both peak locations are consistent with each 8


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other, showing the high phase purity of the experimental samples. The TGA experiments for LnMOFs 1–4 are carried out under nitrogen atmosphere. They reveal same thermal decomposing behaviors (Figures S17-S20). For 1, the first lost weight (9.9%) between 40 and 362°C is observed due to the loss of one H2O molecule and one Me2NH molecule (calcd: 10.3%). The network of 1 started to decompose above 350°C leaving the final residue of Eu2O3 at 748°C (the found loss of 28.2% and calcd. 28.6%). The lost weight analyses of 2-4 are listed in Table S7 and the results are similar to 1, a further evidence of the isostructural nature of all 1-4. Photoluminescence. With the excitation at 394 nm (Figure S21a), the characteristic photoluminescence of Eu(III) ions has been observed in 1 without the emission peak of the ligand (Figure 4a), which attributes to an LMET (ligand to metal energy transfer) process.2,12b The emission peaks of 1 are due to the electronic transitions of the Eu(III) ions from 5D0 to 7Fn (n = 0-4).14c,h The very weak 5D0 to 7F0 emission cannot be observed. The strongest emission peak at 613 nm is owing to the transition of 5D0 to 7F2 induced by electric dipole, which is highly sensitive to the coordinated geometries of the Eu(III) ion. An emission peak at 590 nm is attributed to the transition of 5D0 to 7F1 induced by magnetic dipole, which is quite insusceptible to the surroundings of the Eu(III) cation. The ratio of (5D0 to 7F2)/(5D0 to 7F1) emission intensity is 5.7, revealing that the Eu(III) cation is not fixed at the symmetry center, which is consistent with the SCXRD of 1. When excited at 353 nm (Figure S21b), 3 shows the characteristic photoluminescence of Tb(III) cations (Figure 4b), exhibiting that there is also an LMET process during luminescence. The emission peaks of 3 are owing to the electronic transitions of the Tb(III) cations from 5D4 to 7

Fn (n = 6-3). The most striking green luminescence at 543 nm is due to the 5D4 to 7F5 electronic

transition, while an emission band at 488 nm is assigned to 5D4 to 7F6 transition. Both 1 and 3 show high thermal stabilities and may find potential application as light-emitting materials. Water Stability and Cation-Exchange. The design and synthesis of water stable MOFs are very important for practical applications as functional materials because many carboxylate-based 9



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porous MOFs are prone to decomposition upon exposure to moisture.5c,14j Recently, Jiang et al. have developed an efficient strategy to improve the stability of moisture-sensitive MOFs and synthesized some highly water stable porous MOFs materials for real application.22 To explore the water stability of LnMOFs 1-4, the samples of 1 were immersed in water at RT for three months, then the dried powders were characterized by PXRD. The experimental pattern of the water-treated samples is good consistent with the simulated one, revealing that the LnMOF material has a high water stability. Moreover, the framework integrity of 1 can also be well retained in pH = 4–12 aqueous solutions (Figure 5). The high water stability and the fact that the 1D channels of 1 are filled with (Me2NH2)+ cations allowed us to further study its cation-exchange behavior in aqueous solution. Table 2 represents ICP results of the cation-exchange experiments at RT for 1 in LiNO3, NaNO3 and KNO3 solutions, in different time intervals. The results indicate that the (Me2NH2)+ ions in the pores can be displaced by the alkali metal (Li+, Na+, K+) cations. Moreover, the exchange ratio increases with a longer time of exchange. For example, only 9.1% of (Me2NH2)+ in 1 was replaced by Na+ ions within 1h, while 44.9% of the (Me2NH2)+ in 1 was exchanged when the time is extended to 12 h. The exchange rate is higher than those found in two related MOFs, (Me2NH2)2[Co3X2]·DMA

(2.18%/45°C/48

h,

=

acid),23a

tetrakis[4-(carboxyphenyl)oxamethyl]methane (Me2NH2)[Co2Y(H2O)]·3DMF·3H2O

H4X

(a

small

amount/RT/24

and h,

H5Y

=

5,5ʹ-(6-(4-carboxyphenylamino)-1,3,5-triazine-2,4-diyldiimino)diisophthalic acid).19i The order of the cation-exchange ratio is K+ > Na+ > Li+, probably due to the fact that radius of K+ (1.52 Å) is very close to that of (Me2NH2)+ (1.50 Å). Notably, the framework of 1 remains intact after cation exchange, as further confirmed by the PXRD patterns (Figure S22). Because of the high water stability, 1 could be a good precursor for post-synthesizing the other functional materials by cation-exchange.23b-d Proton Conduction. It is well-known that the organic polymers with sulfonate group, like Nafion, are important solid proton-conductive materials.24 The high water stability, along with 10


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the abundant hydrogen bond interactions consisting of the sulfonate groups and the coordinated water molecules, makes LnMOF 1 a potential candidate for solid proton-conductive material under humid conditions. Therefore, the proton conductivities (σ) of 1 were evaluated by the AC impedance method using a pellet sample. The Nyquist plot of the sample was obtained under different RH at RT (Figure S23). Unfortunately, the σ value of 1 is 4.14 × 10−8 S cm−1 at 95% RH and 25°C (Figure 6), which is significantly lower than that reported for a Sm-MOF with 3,3'-disulfonyl-BPDC ligand (4.69 × 10−5 S cm−1 at 30°C and 98% RH)15. Thus, the variable-temperature conductivities of 1 were not further recorded due to its low σ value at 25°C and 95% RH. The low proton conductivity of 1 may be due to an inefficient proton mobilizing pathway via the hydrogen-bonding networks within the small 1D channels of 1.5c,15 The exploration of improving the σ values of these LnMOFs is in progress. Magnetism. Varying-temperature magnetic susceptibilities for 2 and 4 were carried out in 1.8-300 K on polycrystalline samples under 1000 Oe of external field (Figure 7 and 8). The χMT value of 2 keeps constant from 7.93 cm3 K mol-1 at RT to 7.76 cm3 K mol-1 at 30 K, near to 7.875 cm3 K mol-1 of one spin-only Gd(III) ion (Figure 7b). When temperature descends further, χMT vs. T plot shows a quick decrease from 7.74 cm3 K mol-1 at 25 K to 7.18 cm3 K mol-1 at 2 K. According to the Curie−Weiss principle, χM-1 = (T − θ)/C, the values in 1.8−300 K reveal a well linear correlation between χM-1 and T with θ = −0.3(1) K and C = 7.92 cm3 mol−1 K (Figure 7a). The small −θ value exhibits that there is a very weak antiferromagnetic interaction involving Gd(III) ions. Based on the SCXRD result of 2, COO- groups bridging-link the Gd(III) cations to produce a uniform 1D chain, and the biphenyl rings further link the 1D chains in a big length giving a 3D bnn framework. Thus, the inter-chain magnetic interactions in 2 can be ignored, whereas the intra-chain coupling interactions between Gd(III) cations may be treated via the following equation (eqn 1)14g,25 for a uniform 1D chain of S = 7/2 under spin Hamiltonian H = –J∑SiSi+1:

χ chain =

Ng 2 β 2 S ( S + 1) 1 + u  JS ( S + 1)   kT  − and u = coth   3kT 1− u  kT   JS ( S + 1)  11


(1)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

where N, g, β, k, T and J possess the usual definition. The best fitting parameters were: g = 2.014(6), J = −0.0042(5) cm-1 and R = Σ[(χMT)calc – (χMT)obs]2/Σ(χMT)obs2 = 3.1 × 10−4. The low −J number reveals that a very small antiferromagnetic interaction exists between Gd(III) ions in 2.14g The χMT value of 14.82 cm3 K mol−1 for 4 at RT (Figure 8b) is slightly larger than 14.17 cm3 K mol−1 for a free Dy(III) ion contributed from the 4f orbital (4f9, S = 5/2, g = 4/3, L = 5, J = 15/2, 6H15/2). The χMT value gradually drops to 14.54 cm3 K mol−1 at 80 K as the temperature decreases, then abruptly decreases to a minimum value of 14.01 cm3 K mol−1 at 18 K, because of the gradual depopulation of the Stark sublevels.26 After that, the χMT number suddenly increases to 14.36 cm3 K cm−1 (a maximum value) at 1.8 K, suggesting the existence of ferromagnetic couplings involving the Dy(III) cations, which has been found in the related Dy(III) compounds.27 By using the Curie−Weiss equation to fit the data in 1.8−300 K, a result of θ = −0.20(2) K and C = 14.9(1) cm3 mol−1 K is produced (Figure 8a). The low −θ value shows that a very small antiferromagnetic coupling interaction of Dy(III) cations occurs in 4.

Conclusions In conclusion, a series of 3D LnMOFs with 2,2′-disulfonyl-4,4'-biphenyldicarboxylic acid (H4L), (Me2NH2)[LnL(H2O)] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)), have been successfully prepared by solvothermal reactions. The LnMOFs 1–4 display an anionic 3D framework with bnn topology constructed on Ln-O-C rods consisting of a unusual hepta-coordinated Ln(III) ion and two bound sulfonate groups. All the LnMOFs are highly water stable and cation-exchange can be easily performed. LnMOFs 1 and 3 show characteristic photoluminescence of Eu(III) and Tb(III) ion but LnMOFs 2 and 4 show relatively weak antiferromagnetic coupling interactions. This work is an excellent example in utilizing the positioning functional groups as coordination site that may provide new opportunities in design and preparation of highly water-stable LnMOFs materials with tunable properties.

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Acknowledgement We gratefully acknowledge financial supports from the National Natural Science Foundation of China (Nos. 21171093; 21476115). We also thank Prof. Song-Song Bao, Nanjing University, for the AC conductivity measurements. Supporting Information Available: Synthetic procedure for K2H2L compound, crystal structures, tables of bond diatances and angles, hydrogen bonding interactions, FTIR, figures for experimental and simulated P-XRD and TGA plots of 1-4, cation exchange and impedance analysis of 1. These materials can be obtained free of charge via the Internet at http://pubs.acs.org. Corresponding Author: [email protected] Author Contributions: †J.Z. and X.H. contributed equally to this work. Notes: The authors declare no competing financial interest. References (1) (a) Roy, S.; Chakraborty, A.; Maji, T. K. Coord. Chem. Rev. 2014, 273, 139. (b) Fordham, S.; Wang, X.; Bosch, M.; Zhou, H.-C. Struct. Bonding 2015, 163, 1. (c) Kahn, O. Molecular Magnetism; VCH: Weinheim, Germany, 1993. (2) (a) Zheng, M.; Tan, H.; Xie, Z.; Zhang, L; Jing, X.; Sun, Z. ACS Appl. Mater. Interfaces 2013, 5, 1078. (b) Li, H.-Y.; Xu, H.; Zang, S.-Q.; Mak, T. C. W. Chem. Commun. 2016, 52, 525. (c) Zhou, Y.; Yan, B. Chem. Commun. 2016, 52, 2265. (d) Colodrero, R. M. P.; Papathanasiou, K. E.; Stavgianoudaki, N.; Olivera-Pastor, P.; Losilla, E. R.; Aranda, M. A. G.; León-Reina, L.; Sanz, J.; Sobrados, I.; Choquesillo-Lazarte, D.; García-Ruiz, J. M.; Atienzar, P.; Rey, F.; Demadis, K. D.; Cabeza, A. Chem. Mater. 2012, 24, 3780. (e) Cui, Y.; Xu, H.; Yue, Y.; Guo, Z.; Yu, J.; Chen, Z.; Gao, J.; Yang, Y.; Qian, G.; Chen, B. J. Am. Chem. Soc. 2012, 134, 3979. (3) (a) Cui, P.-P.; Zhang, X.-D.; Zhao, Y.; Fu, A.-Y.; Sun, W.-Y. Dalton Trans. 2016, 45, 2591. (b) Lin, Z.-J.; Yang, Z.; Liu, T.-F.; Huang, Y.-B.; Cao, R. Inorg. Chem. 2012, 51, 1813. (c) He, Y.-P.; Tan, Y.-X.; Zhang, J. Inorg. Chem. 2013, 52, 12758. (d) Li, G.-P.; Liu, G.; Li, Y.-Z.; Hou, L.; Wang, Y.-Y.; Zhu, Z. Inorg. Chem. 2016, 55, 3952. (4) (a) Wang, S.; Cao, T.; Yan, H.; Li, Y.; Lu, J.; Ma, R.; Li, D.; Dou, J.; Bai, J. Inorg. Chem. 13



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Scheme 1. 2,2′-Disulfonyl-4,4′-biphenyldicarboxylic acid (H4L)

17



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Table 1. Crystallographic data for H4L·4H2O and LnMOFs 1-4 Compounds

H4L·4H2O

1

2

3

4

formula fw T (K) crystal system space group a (Å)

C14H18O14S2 474.40 293(2) monoclinic C2/c 13.668(7)

C16H16EuNO11S2 614.38 293(2) monoclinic C2/c 14.154(3)

C16H16GdNO11S2 619.67 293(2) monoclinic C2/c 14.151(4)

C16H16TbNO11S2 621.34 293(2) monoclinic C2/c 14.116(2)

C16H16DyNO11S2 624.92 293(2) monoclinic C2/c 14.101(4)

b (Å) c (Å) β (deg)

11.352(6) 12.374(7) 99.115(6)

13.408(3) 9.920(2) 98.367(3)

13.395(3) 9.911(3) 98.331(3)

13.381(2) 9.9030(16) 98.375(2)

13.366(4) 9.870(3) 98.431(3)

V (Å3) Z F(000) Dcalcd (g·cm-3) µ (mm-1) GOF on F2 R1/wR2 (I > 2σ(I)) R1/wR2 (all data)

1895.7(18) 4 984 1.662 0.357 1.061 0.0341/0.0917 0.0429/0.0962

1862.5(7) 4 1208 2.191 3.658 1.082 0.0139/0.0363 0.0142/0.0364

1858.7(8) 4 1212 2.214 3.860 1.072 0.0151/0.0378 0.0155/0.0380

1850.6(5) 4 1216 2.230 4.114 1.097 0.0165/0.0451 0.0171/0.0454

1840.1(10) 4 1220 2.256 4.355 1.068 0.0162/0.0407 0.0168/0.0409

18


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Table 2. Exchange ratio of (Me2NH2)+ in 1 in different time intervals Alkali metal +

Li Na+ K+

Exchange ratio (%) 1h

6h

12 h

7.7 9.1 9.7

19.1 20.1 20.7

38.4 44.9 46.4

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Captions for the illustrations

Figure 1. (a) Ball-and-stick structure view of H4L·4H2O. (b) The 3D hydrogen bonds network of H4L·4H2O. Figure 2. (a) Ball-and-stick structure view of LnMOF 1. (b) View of the environment of Eu(III) ion with the EuO7 decahedron.

Figure 3. (a) 1D rhombus channels in 1 along the c axis. (b) View of a 1D inorganic rod-shaped chain [Eu(-COO)2]n along the c axis. All hydrogen atoms are omitted for clarity. (c) Topological simplification of the 3D bnn network of 1 with a 5-connected node. Figure 4. The photoluminescence spectra of LnMOF 1 (λex = 394 nm) (a) and 3 (λex = 353 nm) (b) at RT. Figure 5. PXRD patterns for water-treated samples of LnMOF 1. Figure 6. Dependence of the conductivity of 1 on humidity at 25°C. Figure 7. Temperature dependence of the molar magnetic susceptibilities of 2. (a) The plots of χM and χM-1 vs. T. Solid blue lines were derived from the fitting by the Curie-Weiss law. (b) The plots of χM and χMT vs. T. Solid red line represents the best fitting curve with the model as described in the text. Figure 8. Temperature dependence of the molar magnetic susceptibilities of 4. (a) The plots of χM and χM-1 vs. T. Solid red lines were derived from the fitting by the Curie-Weiss law. (b) The plot of χMT vs. T.

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Figure 1. (a) Ball-and-stick structure view of H4L·4H2O. (b) The 3D hydrogen bonds network of H4L·4H2O.

Figure 2. (a) Ball-and-stick structure view of LnMOF 1. (b) View of the environment of Eu(III) ion with the EuO7 decahedron.

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Figure 3. (a) 1D rhombus channels in 1 along the c axis. (b) View of a 1D inorganic rod-shaped chain [Eu(-COO)2]n along the c axis. All hydrogen atoms are omitted for clarity. (c) Topological simplification of the 3D bnn network of 1 with a 5-connected node.

Figure 4. The photoluminescence spectra of LnMOF 1 (λex = 394 nm) (a) and 3 (λex = 353 nm) (b) at RT.

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Figure 5. PXRD patterns for water-treated samples of LnMOF 1.

Figure 6. Dependence of the conductivity of 1 on humidity at 25°C.

23



40

(a)

4

10

0

0

-1 3

2 6

-1

χ M / cm mol

-1 3

-3

1

7

3

χM / cm mol

3

-1

20

2

8

χMT / cm K mol

30 3

(b)

4

χM / cm mol

1 5 0 4

0

50

100

150

200

250

0

300

50

100

150

200

250

300

T/K

T/K

Figure 7. Temperature dependence of the molar magnetic susceptibilities of 2. (a) The plots of χM and χM-1 vs. T. Solid blue lines were derived from the fitting by the Curie-Weiss law. (b) The plots of χM and χMT vs. T. Solid red line represents the best fitting curve with the model as described in the text.

15.0

8

(a)

20 -1

4

10

χ MT / cm K mol

15

-1

6

-3

5

2

14.7

3

3

-1

χ M / cm mol

(b)

χM / cm mol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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14.4

14.1 0 0 0

50

100

150

200

250

0

300

50

100

150

200

250

300

T/K

T/K

Figure 8. Temperature dependence of the molar magnetic susceptibilities of 4. (a) The plots of χM and χM-1 vs. T. Solid red lines were derived from the fitting by the Curie-Weiss law. (b) The plot of χMT vs. T.

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For Table of Contents Use Only

Highly

Water

Stable

Lanthanide

Metal-Organic Frameworks Constructed from 2,2'-Disulfonyl-4,4'-biphenyldicarboxylic Acid: Syntheses, Structures, and Properties Jing Zhao, Xin He, Yuchi Zhang, Jie Zhu, Xuan Shen, Dunru Zhu The first example of anionic Ln-carboxylate chain-based 3D bnn-LnMOF built from a hepta-coordinated Ln(III) ion (Ln = Eu, Gd, Tb, Dy) was synthesized and structurally characterized.

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Figure 2 65x20mm (300 x 300 DPI)


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Figure 3 95x71mm (300 x 300 DPI)


Highly Water Stable Lanthanide MetalâOrganic Frameworks

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