A Multifunctional Lanthanide Carbonate Cluster ... - ACS Publications

Apr 14, 2018 - Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering,...
1 downloads 0 Views 2MB Size
Download PDF
Article Cite This: Inorg. Chem. 2018, 57, 9020−9027

pubs.acs.org/IC

A Multifunctional Lanthanide Carbonate Cluster Based Metal− Organic Framework Exhibits High Proton Transport and Magnetic Entropy Change Qun Tang,† Yan-Li Yang,† Ning Zhang,† Zheng Liu,† Shu-Hua Zhang,† Fu-Shun Tang,† Jia-Yi Hu,† Yan-Zhen Zheng,*,‡ and Fu-Pei Liang*,†

Downloaded via KAOHSIUNG MEDICAL UNIV on September 1, 2018 at 19:08:27 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin, Guangxi 541004, P. R. China ‡ Frontier Institute of Science and Technology (FIST), State Key Laboratory for Mechanical Behavior of Materials and MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710054, P. R. China S Supporting Information *

ABSTRACT: A novel multifunctional, three-dimensional (3D) lanthanide carbonate cluster based metal−organic framework (MOF) with the general formula {[Gd2(CO3)(ox)2(H2O)2]·3H2O}n (1) has been synthesized via self-assembly of gadolinium (Gd) carbonate and oxalate under hydrothermal conditions. Single-crystal X-ray diffraction reveals that the compound 1 consists of the Gd carbonate cluster with oxalic acid ligands, which form a 3D framework structure with an ordered onedimensional (1D) pore channel along the a-axis. The coordination water molecules of Gd3+ ions point to the interior of the pore and form a 1D hydrogen bond pathway with oxygen atoms in adjacent oxalic acid that is stable at high temperature (up to 150 °C). The compound 1 features multiple hydrogen-bonding walls and good thermal stabilities, and shows the highest proton conductivity of 1.98 × 10−3 S cm−1 at T = 150 °C and in room air without additional humidity. Magnetic investigations of compound 1 demonstrate that weak antiferromagnetic couplings between adjacent Gd3+ ions bring about large cryogenic magnetocaloric effects. Remarkably, the maximum entropy change (−ΔSm) of compound 1 reaches 58.5 J kg−1 K−1 at 2 K for a moderate field change (ΔH = 7 T). Moreover, the isomorphous MOFs: {[Ln2(CO3)(ox)2(H2O)2]·3H2O}n (Ln3+ = Ce3+(2), Pr3+(3), Nd3+(4), Tb3+(5)) also are structurally and functionally characterized, and compounds 2−5 exhibit proton conductivity above 10−3 S cm−1 in room air and without additional humidity.

■

(CO32−) ligand with high negative charge and multicoordination sites is a versatile bridging ligand.33,34 Moreover, the coordination topology of CO32− is in favor of constructing multinuclear Ln clusters. Accordingly, the carbonate ligands are used instead of the small carboxylate ligands, which show promise for inducing formation of the multinuclear Ln carbonate clusters. The extended Ln clusters with short bridging ligands are beneficial to construct a highly dense MOF. The highly dense MOFs are expected to break the deadlock of the application of the magnetic reagents, adopting magnetic entropy change (−ΔSm) or single-molecule magnet behavior (SMM).35−37 More importantly, skeletons of Ln cluster-based MOFs usually include high-density hydrophilic hydroxyl oxygen/carboxyl oxygen (OH−/O2−) groups, which can serve as either donors or acceptors for hydrogen bonding with other molecules to improve the conduction of protons.38−43 However, the syntheses of the Ln carbonate

INTRODUCTION Lanthanide-based metal−organic frameworks (Ln-MOFs) featuring lanthanide atoms or cluster units bridged by organic linking groups have received considerable attention because of their employment in gas adsorption and separation,1−3 luminescence,4−7 magnetism,8−10 catalysis,11−13 and proton conductor aspects in the past few decades.14−16 The rational design and construction of Ln-MOFs have attracted much interest, not only because of their versatile topological structures but also because of their multifunctional applications. The lanthanide ions with unique f electronic structures could be useful metal nodes as an oxophilic center.17−21 The wisely alternative of the organic linking groups is a predominant influence in the Ln-MOFs. To achieve this goal, a ligand with multicoordination sites and high negative charge is important for meeting the high coordination requirement and counterbalancing the positive charges of the lanthaninde ions. Usually, carboxylate ligands, especially small formates and acetates, are preferred for this purpose and further lead to a Ln cluster.22−32 The carbonate © 2018 American Chemical Society

Received: April 14, 2018 Published: July 13, 2018 9020

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry Table 1. Crystal Data and Structure Refinement for 1−5 compounds

1

2

3

4

5

formula fw T (K) wavelength (Å) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) μ (mm−1) reflns coll./unique Rint GOF on F2 R1 [I > 2σ(I)]a wR2 (all data)b CCDC

C5H10Gd2O16 640.62 293(2) 0.71073 triclinic P1̅ 6.2914(5) 8.6698(8) 12.9473(16) 105.482(9) 90.462(8) 105.181(8) 654.53(12) 2 3.210 10.138 4395/2292 0.0360 1.087 0.0477 0.1178 1564990

C5H10Ce2O16 606.35 293(2) 0.71073 triclinic P1̅ 6.3300(6) 8.7424(8) 12.9927(13) 105.570(9) 90.451(8) 105.192(8) 666.05(12) 2 2.993 6.840 4991/3035 0.0416 1.048 0.0541 0.1221 1567333

C5H10Pr2O16 607.94 293(2) 0.71073 triclinic P1̅ 6.2596(5) 8.6136(9) 12.9308(19) 105.430(11) 90.422(9) 105.069(8) 646.77(14) 2 2.823 7.508 5014/2966 0.0467 1.093 0.0549 0.1331 1567335

C5H10Nd2O16 614.61 293(2) 0.71073 triclinic P1̅ 6.2596(5) 8.6108(7) 12.9187(7) 105.366(6) 90.451(5) 105.115(6) 645.98(9) 2 3.041 8.033 4614/2943 0.0449 1.038 0.0534 0.1561 1567334

C5H10Tb2O16 643.97 293(2) 0.71073 triclinic P1̅ 6.2723(8) 8.6246(11) 12.9484(14) 105.348(10) 90.404(9) 105.058(11) 650.12(15) 2 3.274 10.890 4668/2929 0.0332 1.049 0.0514 0.1369 1567336

R1 = ∑| |Fo| − |Fc| |/∑|Fo|. bwR2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2.

a

solved using direct methods and refined through full matrix leastsquares technique using SHELXL-97.47,48 Anisotropic thermal parameters were refined for all non-hydrogen atoms. The crystallization water molecules were highly disordered and could not be modeled properly, and thus the crystallization water molecules were estimated by TGA and X-ray structure analysis. Crystal data and refinement parameters for compounds 1−5 are summarized in Table 1. The selected bond distances and bond angles of compound 1 are presented in Table S4. Proton Conductivity Measurements. The samples of compounds 1−5 were pressed into disk-shaped pellets with a diameter of 9.8 mm and thickness of 1.8 mm (±0.06%) by using a laboratory press. Impedance of the above pelletized samples was carried out on a frequency response analyzer/potentiostat (Princeton Applied Research PARSTAT 2273, EG&GPARC, Princeton, NJ) from 0.1 to 1 MHz with 30 mV applied ac voltage. The pelletized sample attached with Ag-pressed electrodes was placed in a quasi-four probe electrochemical cell and equilibrated for at least 5 h under test conditions. The measurements were respectively conducted at different temperature (25−160 °C) and 95% relative humidity (RH) or in indoor air without additional humidity conditions. The measured impedance data were fitted according to the literature procedure by using the ZSimpWin software.46 Magnetic Analyses. Magnetic measurements were carried out using a SQUID magnetometer (Quantum Design MPMS XL-7). The susceptibilities data were obtained after correcting for the sample holder and diamagnetic contribution. The isothermal magnetization was measured in applied field of 0−7 T and at temperatures between 2 to 10 K. At each temperature, the M−H curves were measured isothermally from 0 to 7.0 T with a step size of 0.25 T during 0−1.0 and 0.5 T during 1.0−7.0 T, and then the field was set to 0 T to begin another measurement. Synthesis of 1−5. All compounds were prepared by utilizing the same procedure, and thus the synthesis of 1 is presented here in detail as a representative. The crystals of 1 were synthesized in the hydrothermal reaction system of Gd2(CO3)3-H2(ox)·2H2O−H2O. Typically, a mixture of Gd2(CO3)3 (0.4 mmol), H2(ox)·2H2O (0.4 mmol), and deionized water (15 mL) was vigorous stirred at room temperature for 1 h. The resulting mixture gel was introduced into a 25 mL stainless-steel PTFE autoclave liner, heated at 140 °C for 4

cluster-based MOFs are challenging. The reports on highnuclearity Ln carbonate clusters used for multifunctional materials are still rare.34,44−46 Thus, further systematic investigation on the Ln carbonate cluster-based MOFs to discover their potentials multifunctional applications is very necessary. Our interest is in obtaining the multinuclear Ln carbonate cluster-based MOFs with multifunctional applications. In our previous work, a tetranuclear Eu cluster-based MOF was designed and synthesized.46 Herein, we provide a new family of the Ln carbonate cluster-based MOFs: {[Ln2(CO3)(ox)2(H2O)2]·3H2O}n (Ln3+ = Gd3+(1), Ce3+(2), Pr3+(3), Nd3+(4), Tb3+(5)) were structurally and functionally characterized. The Ln-MOFs 1−5 display high proton conductivity (above 10−3 S cm−1) achieved at 150 °C and in indoor air without any additional humidity. Moreover, compound 1 displays a large value of ΔSm = 58.5 J kg−1 K−1 in all reported Ln carbonate cluster-base MOFs.

■

EXPERIMENTAL SECTION

Materials and Methods. The reagents and solvents employed in the synthesis were commercially available and used as received without further purification. The Fourier transform infrared (FT-IR) spectra were measured with an Alpha Centaurt FT-IR spectrophotometer using the KBr method. The elemental analyses (C and H) were carried out using a PerkinElmer 2400 CHN elemental analyzer, and the microanalysis of Ln was performed on a PLASMA-SPEC(I) ICP atomic emission spectrometer. The morphology of the assynthesized compound 1 was observed by field emission scanning electron microscopy (SEM) (SU-5000, Hitachi, Japan). Thermogravimetric analyses (TGA) were performed on a PerkinElmer TGA7 instrument (under a nitrogen flow with the heating rate of 10 °C/ min). Powder X-ray diffraction (PXRD) patterns were collected from 3° to 60° by using a Rigaku D/MAX-3 instrument with Cu−Kα radiation. Structural Determination. Crystallographic data of compounds 1−5 were collected on a Bruker Smart Apex CCD diffractometer with Mo Kα monochromated radiation (λ = 0.71073 Å). The structure was 9021

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry days 12 h in an oven, and then cooled to room temperature. The obtained colorless, block-shaped crystals were washed with distilled water and then dried at room temperature overnight. The product was recovered with a yield about 71.2% based on Gd. Anal. Calcd for C5H10Gd2O16 (%): C, 9.37; H, 1.57; Gd, 49.09; found: C, 9.02; H, 1.71; Gd, 48.88. Anal. Calcd for C5H10Ce2O16 (%): C, 9.90; H, 1.66; Ce, 46.22; found: C, 9.80; H, 1.74; Ce, 46.56. Anal. Calcd for C5H10Pr2O16 (%): C, 9.87; H, 1.66; Pr, 46.36; found: C, 9.95; H, 1.61; Pr, 46.25. Anal. Calcd for C5H10Nd2O16 (%): C, 9.77; H, 1.64; Nd, 46.93; found: C, 9.66; H, 1.72; Nd, 46.89. Anal. Calcd for C5H10Tb2O16 (%): C, 9.33; H, 1.57; Tb, 49.36; found: C, 9.43; H, 1.69; Tb, 49.47. These were consistent with the elemental contents calculated from the molecular formula of [Ln2(CO3)(ox)2(H2O)2]· 3H2O}n (Ln3+ = Gd3+(1), Ce3+(2), Pr3+(3), Nd3+(4), Tb3+(5)). Anhydrous sample of 1 was obtained by baking the as-synthesized 1 at 250 °C in a vacuum oven for 24 h. Exposing the anhydrous sample in deionized water for 12 h reproduced the rehydration 1. Immersing assynthesized 1 in H2O, CH3OH, C2H5OH, CH3CN, (CH3)2CO, and DMF for 5 days produced respectively 1-H2O, 1-CH3OH, 1C2H5OH, 1-CH3CN, 1-(CH3)2CO, and 1-DMF. The crystal samples were obtained by centrifugation, dried in a desiccator at 50 °C for 10 h, and used for all characterization and physical measurement.

from oxalate, and two water O atoms. The bond distances of Gd(1)−O vary from 2.476(8) to 2.675(8) Å with the two coordinated water molecules (Gd(1)−O10 = 2.547(8) Å and Gd(1)−O13 = 2.542(8) Å), which are obviously longer than those with the oxalate groups (barring Gd(1)−O2 = 2.675(8) Å). Atom Gd(2), also nonacoordinate, is coordinated by four O atoms from three carbonato groups and five O atoms from three oxalate groups, yet with no water ligands (Figure S9). The bond distances of Gd−O range from 2.434 to 2.675 Å, the bond angles of Gd−O−Gd vary from 102.73 to 171.21°, and the distances of adjacent Gd···Gd are 4.077 and 5.078 Å respectively. The part bond length and angle data of 1 are listed in Table S4. Each carbonato ligand bridges one Gd(1) and three Gd(2) atoms, resulting in a four nuclear Ln carbonate cluster (Figure 1b). The CO32− groups are μ4-bridging with three μ-O atoms bound to adjacent Gd3+ ions. The bridging interactions are responsible for organization of the Gd carbonate clusters into a double-edge, sawtooth-like Gd carbonate belt structure (Figure S10). The Gd carbonate belts are connected by oxalate groups into 2D layers and further form an overall 3D framework structure along the a axis. The guest water molecules are filled in highly ordered hexagonal channels (diameter of about 6.8 Å) (Figure 2). Two coordinated water molecules of Gd(1)

■

RESULTS AND DISCUSSION Syntheses and Crystal Structures. Under solvothermal conditions, the Ln carbonates (Ln = Gd, Ce, Pr, Nd, and Tb, respectively) were allowed to provide CO32− group and react with H2(ox) in water resulting in the formation of 1−5 in high yields. Compounds 1−5 have been characterized by elemental analyses, FT-IR (Figure S1), TGA (Figure 4 and Figure S2), and powder and single-crystal XRD studies (Figure 1−3 and

Figure 1. (a) SEM image of compound 1, (b) representation of the Gd3+ coordination environments of compound 1; Gd, green; O, red; C, gray.

Figure 2. Crystal structure for 1 showing the 1D channels along the aaxis.

Figures S3−S11). All the crystals of 1−5 are stable in air and do not dissolve in commonly used solvents, such as H2O, CH3OH, C2H5OH, CH3CN, (CH3)2CO, and DMF. The single-crystal XRD studies show that all 1−5 exhibit the same structural topology. Figure 1a shows the morphology and particle size of compound 1 observed by SEM. In Gd-MOF 1, prepared for the studies of proton conductivity and magnetic properties, the largest block-like particles with dimensions of ∼12 μm can be observed, while smaller sized particles ≤5 μm are also be found. The Ln-MOFs 1−5 are isostructures and crystallizes in the triclinic space group P1̅ (Table 1 and Table S4). In view of their isostructural characteristics, the structure of Ln-MOF 1 is fully detailed and discussed as a representative. Each asymmetric unit of 1 consists of two independent Gd3+ ion centers, one CO32−, two ox2− ion, and two aqua ligands, besides three crystallization water molecules. Each Gd3+ ion is coordinated with nine O atoms in tetrakaidecahedron geometry as shown in Figure S9. The independent Gd(1) is coordinated with two O atoms from carbonato, five O atoms

directed into the channels of the framework and connected the adjacent ox groups to form a 1D hydrogen-bonding array along the a-axis (Figure 3). The hydrogen-bonding lengths of coordinated water molecules and adjacent ox groups fall into the range from 2.573(2) to 3.245(2) Å (Table S1).49 And the 1D hydrogen-bonding arrays occupy four sides of the hexagonal channel and offer multiple hydrogen-bonding walls for proton transfer (Figure S11). In addition, the 1D hydrogen

Figure 3. View showing the 1D hydrogen-bonding array between the coordinated water molecules and the adjacent ox groups. 9022

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry

compounds 1−5. The good thermal stability will greatly benefit the usage and storage of this material. Proton conductivity. To characterize the proton conductivity of 1−5, alternating current (AC) impedance analyses were performed on microcrystal samples from 25 to 160 °C in indoor air and without additional humidity (Figures S12−S16 and Tables S2−S3). At 25 °C, typical impedance plots for 1 can be seen in Figure S12, and the proton conductivity is 8.27 × 10−6 S cm−1. Because the sample of 1 is microcrystalline, the impedance plot can be mainly attributed to the bulk and grainboundary resistance besides electrode contributions. As the temperature is increased, the proton conductivity of 1 increases significantly. A jump in conductivity at around 100 °C can be observed; the conductivity dramatically increases by 2 orders of magnitude to 7.96 × 10−4 S cm−1 (Figure 5). The highest

bond arrays remain stable when the guest water molecules are removed. The coordinated water molecules are Lewis base and act as a proton donor due to the good Lewis acidity of the Gd3+ ion with a high charge density by a gradual filling of the 4f orbitals. On the basis of this, the highly hydrated nature of the channel, and the existence of the highly ordered hydrogen bond arrays, suggest the possibility of proton conductivity behavior for 1−5. FT-IR Spectra. In the FT-IR spectra of compounds 1−5, the presence of broad and strong characteristic stretches in the frequency region of 3050−3480 cm−1 are assigned to the characteristic OH vibration of water molecules. FT-IR spectra of 1−5 are shown in Figure S1. The weak absorption peaks on 790 cm−1 can separately refer to face and out-face deformation vibration absorption of CO32− anions, and strong peaks of 1442, 1490, and 1635 cm−1 can refer to asymmetric stretching vibration absorption of CO 3 2− and carboxyl groups, respectively. Thermogravimetric Analysis. Thermogravimetric analysis (TGA) indicates good thermal stability of 1−5 (Figure 4

Figure 5. Impedance plots of 1 at 100 and 150 °C and without additional humidity.

value in conductivity is observed at 150 °C and reaches 1.98 × 10−3 S cm−1. Remarkably, this value is one of the largest intrinsic hydrous proton conductivity values reported in hydrated MOF materials.14 Moreover, the conductivity value can remain almost unchanged, while the sample of 1 is maintained at 150 °C for 12 h (Figure S14). However, as temperature increased to 160 °C, the proton conductivity of 1 is rapidly reduced to just 2.56 × 10−7 S cm−1 (Figure S15). It is obviously because coordinated water molecules are unstable at above 150 °C, which is supported by the TGA analysis (Figure 4). At 25 °C and 95% RH, the conductivity is 1.18 × 10−5 S cm−1, with the value being essentially the same as that measured at 25 °C and in room air without additional humidity (Figure S16). So RH does not seem to be the key influencing factor of the proton conductivity for as-synthesized 1. The rehydration 1 shows similar trends of change to assynthesized 1 for the proton conductivities at 25−160 °C and in room air without additional humidity. There is a very small but still observable difference in the proton conductivity under the same temperature between the rehydration 1 and the assynthesized 1, and probably is justified by the loss of crystallization water molecules of rehydration 1. The ac impedance analyses of compounds 2−5 show similar trends of change to compound 1 for the proton conductivities at 25− 160 °C and in indoor air without additional humidity. Comparison of proton conductivity (Table S2) of 1−5 displays that the corresponding proton conductivity slightly

Figure 4. Thermogravimetric analysis of compound 1. Inset: the mass loss at 130−210 °C.

and Figure S2). The TGA curves of 1−5 are similar, and there are three steps of weight loss in the temperature region of 25− 650 °C. Take 1 as an example: the TGA of 1 shows an initial stage of weight loss of 8.37% (calculated at 8.44%) with a temperature up to 100 °C, which is ascribed to the loss of three crystallization water molecules per formula unit. Little weight loss was observed from 100 to 150 °C, suggesting that the coordinated water molecules are stable below 150 °C (Figure 4 inset). The second step of weight loss of 5.60% (calculated at 5.62%) between 150 and 380 °C is due to the loss of two coordinated water molecules. Further weight loss of 52.34% between 380 and 650 °C can be related to the thermal decomposition of the skeleton, accompanying the generation of Gd2O3 at 56.36% of the as-synthesized 1 gross weight (calculated at 56.58%). Then the variable-temperature PXRD measurements were conducted on the sample of as-synthesized 1 at 25−450 °C. As shown in Figure S3, the PXRD patterns of compound 1 at 25−350 °C are coincident with the simulated patterns from the crystal structures, whereas the PXRD pattern looks very different at 450 °C. The above results clearly reveal that the compound 1 possesses good thermal stability up to ∼350 °C. Additionally, the experimental PXRD patterns of assynthesized 1−5 are agree well with the simulated patterns (Figures S4−S8), confirming the bulk phase purity of the 9023

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry increases with the rising of atomic number of Ln, which is consistent with the lanthanide contraction effect. To understand the proton-conducting mechanism, the activation energy for 1 was obtained through fitting the conductivity data to the Arrhenius equation.50,51 The Arrhenius-type plot of conductivities of 1 displayed a change in slope, and thus two activation energy (Ea) values were determined (Figure 6), equal to 0.47 eV between 25 and 90

Figure 7. Temperature dependence of the χmT and the inverse molecular susceptibility plots at 2 kOe for 1; the red line represents the fitted result using a Curie−Weiss law.

for compound 1 at 300 K is 15.88 cm3 mol−1 K, close to that of 15.75 cm3 mol−1 K calculated for two noninteracting Gd3+ ions (S = 7/2, g = 2). With decreasing temperature, the χmT value for 1 remains almost constant and then drops gradually in the temperature range of 100−25 K. Upon further cooling, the χmT value of compound 1 drops abruptly and reaches 13.78 cm3 mol−1 K. The shape of the curve indicates a weak antiferromagnetic coupling in compound 1. Such a weak antiferromagnetic coupling in compound 1 not only arises from the Ln···Ln separation in the Gd3+ chains [Gd3+···Gd3+, 4.077−5.078 Å], but is also due to the μ4 bridging mode of the carbonato ligands. The molar magnetic susceptibility data of compound 1 were fitted according to the Curie−Weiss equation χm = C/(T − θ) (C = Curie constants, θ = Weiss constants) in the hole temperature, which acquired C = 15.87 cm3 mol−1 K and θ = −0.63 K. The small negative θ value further confirms weak antiferromagnetic coupling between adjacent Gd3+ ions in 1. The measurement of the field dependences magnetization (M) of as-synthesized 1 at low temperature (1.9−10 K) was also performed (Figure S18). The magnetization of 1 shows a gradual increase with the applied field increasing and reaches a saturation of 14.12 NμB at 7 T and 1.9 K, in good agreement with the calculated value for two Gd3+ ions. Magnetocaloric Effect. There is Gd3+···Gd3+ magnetic coupling in 1, united with the four nuclear Gd carbonate cluster structure and low MW/NGd ratio of 320.31 (MW = 640.62 g mol−1 is molecular mass and NGd = 2 is the number of Gd3+ present per mol of 1). This prompted us to assess the magnetocaloric effect (MCE) of 1. The magnetic entropy change ΔSm for 1 is calculated from the experimental magnetization data by using the Maxwell relation ΔSm(T) = ∫ [∂M(T,H)/∂T]H dH.54,55 The resulting ΔSm values at different magnetic fields and temperatures are shown in Figure 8. The −ΔSm vs T plots gradually increase from 9 to 2 K. The maximal entropy change value of 58.5 J kg−1 K−1 (193.1 mJ cm−3 K−1) is obtained at 2.0 K for H = 7 T. Indeed, it not only surpasses the recently reported values of [Ln7(DPA)5(NA)3(μ3-OH)8(H2O)3]·2.5H2O (−ΔSm,max = 34.15 J kg−1 K−1, H2DPA = diphenic acid; HNA = nicotinic acid)23 and [Gd 7 (CDA) 6 (HCOO) 3 (μ 3 -OH) 6 (H 2 O) 8 ] n (−ΔS m,max = 47.30 J kg−1 K−1, H2CDA = 1,1′-cyclopropane-dicarboxylic acid),27 but also exceeds the former reported records with a −ΔSm,max of 46.6 J kg−1 K−1 for {[Gd6(μ6-O)(μ3-OH)8(μ4-

Figure 6. Arrhenius-type plot of conductivities of 1 from 25 to 150 °C and without additional humidity, and the Arrhenius-type plot of the proton conductivity fitted with a dotted line.

°C, and 0.27 eV between 100 and 150 °C, respectively. The range of Ea of compounds 2−5 is similar to that of 1 (Table S3). Typically, the behavior of proton conduction can be explained by the Grotthuss mechanism or vehicle mechanism according to the value of Ea.15 It can be expected a Grotthus mechanism with the value of Ea between 0.1−0.4 eV, and vehicle mechanism with the value of Ea between 0.5−0.9 eV.52,53 Therefore, the above results suggest that two different proton conductive mechanisms should exist in the temperature range of 25−150 °C. The proton pathways and mechanisms of compounds 1−5 were further understood by analyzing the structure and Ea of these five compounds. In the temperature range of 100−150 °C, it can be concluded that the coordinated water molecules with the adjacent ox groups could construct hydrogen-bonded arrays in the ordered hexagonal channels for proton hopping, leading to a lower Ea and Grotthuss mechanism in proton conduction. The proton conduction in the temperature range of 25−90 °C is probably governed by translational motion or rotation of crystallization water molecules in the hexagonal channels, causing a high Ea and vehicular mechanism. The proton-hopping and proton-transporting pathways could be constructed by combining crystallization water molecules, coordinated water molecules with O atoms of the adjacent ox groups (Figure S17). Magnetic Properties. The Gd 3+ with unpaired f 7 electrons, characterizing a large spin ground state S, negligible magnetic anisotropy, and low-lying excited spin states, will be propitious to improve MCEs well.35 Owing to the presence of a lanthanide carbonate belt structure and Gd3+ with characteristic f electron structure, the Gd-MOF (compound 1) was preferentially selected for presentation of the magnetic properties studies. The variable temperature magnetic susceptibility measurement for the crystal sample of assynthesized 1 was performed from 1.8 to 300 K in the applied magnetic field of 2000 Oe. As shown in Figure 7, the χmT value 9024

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Inorganic Chemistry

■

Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail: fliangoffi[email protected] (F.-P.L.). *E-mail: [email protected] (Y.-Z.Z.). ORCID

Shu-Hua Zhang: 0000-0002-1097-1674 Yan-Zhen Zheng: 0000-0003-4056-097X Fu-Pei Liang: 0000-0001-7435-0140 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21501033, 51572050, and 21771043), the Natural Science Foundation of Guangxi Province of China (Grants 2015GXNSFBA139024, 2016GXNSFAA380062, and 2016GXNSFBA380162), and the Program of the Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi (No. GXYSXTZX2017-II-3).

Figure 8. Experimental ΔSm calculated by using the magnetization data of 1 at various fields and temperatures.

ClO 4 ) 4 (H 2 O) 6 ](OH) 4 } n and 46.1 J kg − 1 K − 1 for [Gd24(DMC)36(μ4-CO3)18 (μ3-H2O)2]·nH2O.17,18 Notably, MCE for Ln-MOF 1 can also reach a satisfying value of 34.4 J kg−1 K−1 (115.5 mJ cm−3 K−1) at ΔH = 2 T. This value is higher than that for GGG (ΔSm ≈ 14.6 J kg−1 K−1 (105 mJ cm−3 K−1), at ΔH = 2 T),56,57 indicating that 1 is a promising magnetic refrigeration material.

■

■

CONCLUSIONS In summary, a series of novel 3D Ln carbonate cluster-based MOFs: {[Ln2(CO3)(ox)2(H2O)2]·3H2O}n (Ln = Gd3+(1), Ce3+(2), Pr3+(3), Nd3+(4), Tb3+(5)), have been synthesized by solvothermal methods. By virtue of the 1D hydrogenbonding arrays on four sides of the hexagonal channel structure, the Ln carbonate cluster-based MOFs 1−5 exhibit high proton conduction (above 10−3 S cm−1 at 150 °C and in room air without additional humidity), which makes them a promising solid electrolyte for use in the fuel cell technology. Importantly, MCE studies of compound 1 reveal that Gd carbonate cluster-based MOF possesses the large value of ΔSm = 58.5 J kg−1 K−1 in all reported Ln carbonate cluster-based MOFs, which is a promising candidate in the molecular magnetic cryogenic material. The preparation of nanostructured materials of these crystalline Ln-MOFs and the fabrication of proton exchange membrane and magnetic refrigerant using these materials are in progress.

■

REFERENCES

(1) Adil, K.; Belmabkhout, Y.; Pillai, R. S.; Cadiau, A.; Bhatt, P. M.; Assen, A. H.; Maurin, G.; Eddaoudi, M. Gas/vapour separation using ultra-microporous metal-organic frameworks: insights into the structure/separation relationship. Chem. Soc. Rev. 2017, 46, 3402− 3430. (2) Li, J.-R.; Kuppler, R. J.; Zhou, H.-C. Selective gas adsorption and separation in metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1477−1504. (3) Yang, Q.; Liu, D.; Zhong, C.; Li, J.-R. Development of Computational Methodologies for Metal−Organic Frameworks and Their Application in Gas Separations. Chem. Rev. 2013, 113, 8261− 8323. (4) Lustig, W. P.; Mukherjee, S.; Rudd, N. D.; Desai, A. V.; Li, J.; Ghosh, S. K. Metal−organic frameworks: functional luminescent and photonic materials for sensing applications. Chem. Soc. Rev. 2017, 46, 3242−3285. (5) Hu, Z.; Deibert, B. J.; Li, J. Luminescent metal−organic frameworks for chemical sensing and explosive detection. Chem. Soc. Rev. 2014, 43, 5815−5840. (6) Rocha, J.; Carlos, L. D.; Paz, F. A.; Ananias, D. Luminescent multifunctional lanthanides−based metal−organic frameworks. Chem. Soc. Rev. 2011, 40, 926−940. (7) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Luminescent functional metal−organic frameworks. Chem. Rev. 2012, 112, 1126−1162. (8) Minguez Espallargas, G.; Coronado, E. Magnetic functionalities in MOFs: from the framework to the pore. Chem. Soc. Rev. 2018, 47, 533−557. (9) Liu, K.; Zhang, X.; Meng, X.; Shi, W.; Cheng, P.; Powell, A. K. Constraining the coordination geometries of lanthanide centers and magnetic building blocks in frameworks: a new strategy for molecular nanomagnets. Chem. Soc. Rev. 2016, 45, 2423−2439. (10) Kurmoo, M. Magnetic metal−organic frameworks. Chem. Soc. Rev. 2009, 38, 1353−1379. (11) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Metal−organic framework materials as catalysts. Chem. Soc. Rev. 2009, 38, 1450−1459. (12) Yang, Q.; Xu, Q.; Jiang, H. L. Metal−organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis. Chem. Soc. Rev. 2017, 46, 4774−4808. (13) Huang, Y. B.; Liang, J.; Wang, X. S.; Cao, R. Multifunctional metal−organic framework catalysts: synergistic catalysis and tandem reactions. Chem. Soc. Rev. 2017, 46, 126−157.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01023. IR, TGA, PXRD, impedance plots, and field dependent magnetization plots (PDF) Accession Codes

CCDC 1564990 and 1567333−1567336 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. 9025

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry

magnetic-cooling material Gd(OH)CO3. J. Mater. Chem. A 2014, 2, 9851−9858. (34) Chen, H.-M.; Wang, W.-M.; Li, X.-Q.; Chu, X.-Y.; Nie, Y.-Y.; Liu, Z.; Huang, S.-X.; Shen, H.-Y.; Cui, J.-Z.; Gao, H.-L. Luminescence and magnetocaloric effect of Ln4 clusters (Ln = Eu, Gd, Tb, Er) bridged by CO32‑ deriving from the spontaneous fixation of carbon dioxide in the atmosphere. Inorg. Chem. Front. 2018, 5, 394−402. (35) Zheng, Y.-Z.; Zhou, G.-J.; Zheng, Z.; Winpenny, R. E. P. Molecule-based magnetic coolers. Chem. Soc. Rev. 2014, 43, 1462− 1475. (36) Yang, Y.; Zhang, Q. C.; Pan, Y. Y.; Long, L. S.; Zheng, L. S. Magnetocaloric effect and thermal conductivity of Gd(OH)3 and Gd2O(OH)4(H2O)2. Chem. Commun. 2015, 51, 7317−7320. (37) Liu, J.-L.; Chen, Y.-C.; Tong, M.-L. Symmetry strategies for high performance lanthanide-based single-molecule magnets. Chem. Soc. Rev. 2018, 47, 2431−2453. (38) Vuilleumier, R.; Borgis, D. Proton conduction: Hopping along hydrogen bonds. Nat. Chem. 2012, 4, 432−433. (39) Qin, L.; Yu, Y.-Z.; Liao, P.-Q.; Xue, W.; Zheng, Z.; Chen, X.M.; Zheng, Y.-Z. A “Molecular Water Pipe”: A Giant Tubular Cluster {Dy72} Exhibits Fast Proton Transport and Slow Magnetic Relaxation. Adv. Mater. 2016, 28, 10772−10779. (40) Ramaswamy, P.; Wong, N. E.; Gelfand, B. S.; Shimizu, G. K. H. A Water Stable Magnesium MOF That Conducts Protons over 10−2 S cm−1. J. Am. Chem. Soc. 2015, 137, 7640−7643. (41) Zhang, K.; Xie, X.; Li, H.; Gao, J.; Nie, L.; Pan, Y.; Xie, J.; Tian, D.; Liu, W.; Fan, Q.; Su, H.; Huang, L.; Huang, W. Highly WaterStable Lanthanide-Oxalate MOFs with Remarkable Proton Conductivity and Tunable Luminescence. Adv. Mater. 2017, 29, 1701804. (42) Li, B.; Wen, H.-M.; Cui, Y.; Zhou, W.; Qian, G.; Chen, B. Emerging Multifunctional Metal−Organic Framework Materials. Adv. Mater. 2016, 28, 8819−8860. (43) Bao, S.-S.; Otsubo, K.; Taylor, J. M.; Jiang, Z.; Zheng, L.-M.; Kitagawa, H. Enhancing Proton Conduction in 2D Co−La Coordination Frameworks by Solid-State Phase Transition. J. Am. Chem. Soc. 2014, 136, 9292−9295. (44) Smolders, S.; Struyf, A.; Reinsch, H.; Bueken, B.; Rhauderwiek, T.; Mintrop, L.; Kurz, P.; Stock, N.; De Vos, D. E. A precursor method for the synthesis of new Ce(iv) MOFs with reactive tetracarboxylate linkers. Chem. Commun. 2018, 54, 876−879. (45) Biswas, S.; Mondal, A. K.; Konar, S. Densely Packed Lanthanide Cubane Based 3D Metal−Organic Frameworks for Efficient Magnetic Refrigeration and Slow Magnetic Relaxation. Inorg. Chem. 2016, 55, 2085−2090. (46) Tang, Q.; Liu, Y.; Liu, S.; He, D.; Miao, J.; Wang, X.; Yang, G.; Shi, Z.; Zheng, Z. High Proton Conduction at above 100 °C Mediated by Hydrogen Bonding in a Lanthanide Metal−Organic Framework. J. Am. Chem. Soc. 2014, 136, 12444−12449. (47) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (48) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341. (49) Okawa, H.; Sadakiyo, M.; Yamada, T.; Maesato, M.; Ohba, M.; Kitagawa, H. Proton-conductive magnetic metal−organic frameworks, {NR3(CH2COOH)}[M(a)(II)M(b)(III)(ox)3]: effect of carboxyl residue upon proton conduction. J. Am. Chem. Soc. 2013, 135, 2256−2262. (50) Hurd, J. A.; Vaidhyanathan, R.; Thangadurai, V.; Ratcliffe, C. I.; Moudrakovski, I. L.; Shimizu, G. K. H. Anhydrous proton conduction at 150 °C in a crystalline metal−organic framework. Nat. Chem. 2009, 1, 705−710. (51) Zhang, F.-M.; Dong, L.-Z.; Qin, J.-S.; Guan, W.; Liu, J.; Li, S.L.; Lu, M.; Lan, Y.-Q.; Su, Z.-M.; Zhou, H.-C. Effect of Imidazole Arrangements on Proton-Conductivity in Metal−Organic Frameworks. J. Am. Chem. Soc. 2017, 139, 6183−6189. (52) Sadakiyo, M.; Yamada, T.; Kitagawa, H. Proton Conductivity Control by Ion Substitution in a Highly Proton-Conductive Metal− Organic Framework. J. Am. Chem. Soc. 2014, 136, 13166−13169.

(14) Meng, X.; Wang, H.-N.; Song, S.-Y.; Zhang, H.-J. Protonconducting crystalline porous materials. Chem. Soc. Rev. 2017, 46, 464−480. (15) Ramaswamy, P.; Wong, N. E.; Shimizu, G. K. H. MOFs as proton conductors−challenges and opportunities. Chem. Soc. Rev. 2014, 43, 5913−5932. (16) Horike, S.; Umeyama, D.; Kitagawa, S. Ion Conductivity and Transport by Porous Coordination Polymers and Metal−Organic Frameworks. Acc. Chem. Res. 2013, 46, 2376−2384. (17) Hou, Y.-L.; Xiong, G.; Shi, P.-F.; Cheng, R.-R.; Cui, J.-Z.; Zhao, B. Unique (3,12)-connected coordination polymers displaying high stability, large magnetocaloric effect and slow magnetic relaxation. Chem. Commun. 2013, 49, 6066−6068. (18) Chang, L.-X.; Xiong, G.; Wang, L.; Cheng, P.; Zhao, B. A 24Gd nanocapsule with a large magnetocaloric effect. Chem. Commun. 2013, 49, 1055−1057. (19) Zhang, Y.; Wang, Y.; Liu, L.; Wei, N.; Gao, M. L.; Zhao, D.; Han, Z. B. Robust Bifunctional Lanthanide Cluster Based Metal− Organic Frameworks (MOFs) for Tandem Deacetalization-Knoevenagel Reaction. Inorg. Chem. 2018, 57, 2193−2198. (20) Dong, J.; Xu, H.; Hou, S.-L.; Wu, Z.-L.; Zhao, B. Metal− Organic Frameworks with Tb4 Clusters as Nodes: Luminescent Detection of Chromium(VI) and Chemical Fixation of CO2. Inorg. Chem. 2017, 56, 6244−6250. (21) Zhang, Z. M.; Zangana, K. H.; Kostopoulos, A. K.; Tong, M. L.; Winpenny, R. E. A pseudo-icosahedral cage {Gd12} based on aminomethylphosphonate. Dalton. Trans. 2016, 45, 9041−9044. (22) Zhang, J.-P.; Zhou, H.-L.; Zhou, D.-D.; Liao, P.-Q.; Chen, X.M. Controlling flexibility of metal−organic frameworks. Natl. Sci. Rev. 2017, DOI: 10.1093/nsr/nwx127. (23) Hu, F.-L.; Jiang, F.-L.; Zheng, J.; Wu, M.-Y.; Pang, J.-D.; Hong, M.-C. Magnetic Properties of 3D Heptanuclear Lanthanide Frameworks Supported by Mixed Ligands. Inorg. Chem. 2015, 54, 6081− 6083. (24) Zheng, X.-Y.; Peng, J.-B.; Kong, X.-J.; Long, L.-S.; Zheng, L.-S. Mixed-anion templated cage-like lanthanide clusters: Gd27 and Dy27. Inorg. Chem. Front. 2016, 3, 320−325. (25) Peng, J. B.; Zhang, Q. C.; Kong, X. J.; Ren, Y. P.; Long, L. S.; Huang, R. B.; Zheng, L. S.; Zheng, Z. P. A 48-Metal Cluster Exhibiting a Large Magnetocaloric Effect. Angew. Chem., Int. Ed. 2011, 50, 10649−10652. (26) Wang, K.; Chen, Z. L.; Zou, H. H.; Hu, K.; Li, H. Y.; Zhang, Z.; Sun, W. Y.; Liang, F. P. A single-stranded {Gd18} nanowheel with a symmetric polydentate diacylhydrazone ligand. Chem. Commun. 2016, 52, 8297−8300. (27) Song, T.-Q.; Dong, J.; Yang, A.-F.; Che, X.-J.; Gao, H.-L.; Cui, J.-Z.; Zhao, B. Wheel-like Ln18 Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO2. Inorg. Chem. 2018, 57, 3144−3150. (28) Tang, Q.; Li, P.-F.; Zou, Z.-M.; Liu, Z.; Liu, S.-X. A novel cryogenic magnetic refrigerant metal−organic framework based on 1D gadolinium(III) chain. J. Solid State Chem. 2017, 246, 329−333. (29) Zhang, Y.; Huang, L.; Miao, H.; Wan, H. X.; Mei, H.; Liu, Y.; Xu, Y. Hydrothermal Synthesis, Structure, and Optical Properties of Two Nanosized Ln26@CO3 (Ln= Dy and Tb) Cluster-Based Lanthanide-Transition-Metal-Organic Frameworks (Ln MOFs). Chem. - Eur. J. 2015, 21, 3234−3241. (30) Shi, P.-F.; Cao, C.-S.; Wang, C.-M.; Zhao, B. Several [Gd-M] Heterometal−Organic Frameworks with [Gdn] as Nodes: Tunable Structures and Magnetocaloric Effect. Inorg. Chem. 2017, 56, 9169− 9176. (31) Zhang, S.; Cheng, P. Coordination-Cluster-Based Molecular Magnetic Refrigerants. Chem. Rec. 2016, 16, 2077−2126. (32) Lu, D.-F.; Hong, Z.-F.; Xie, J.; Kong, X.-J.; Long, L.-S.; Zheng, L.-S. High-Nuclearity Lanthanide−Titanium Oxo Clusters as Luminescent Molecular Thermometers with High Quantum Yields. Inorg. Chem. 2017, 56, 12186−12192. (33) Chen, Y.-C.; Qin, L.; Meng, Z.-S.; Yang, D.-F.; Wu, C.; Fu, Z.; Zheng, Y.-Z.; Liu, J.-L.; Tarasenko, R.; Orendác,̌ M.; et al. Study of a 9026

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027

Article

Inorganic Chemistry (53) Ludueña, G. A.; Kühne, T. D.; Sebastiani, D. Mixed Grotthuss and Vehicle Transport Mechanism in Proton Conducting Polymers from Ab initio Molecular Dynamics Simulations. Chem. Mater. 2011, 23, 1424−1429. (54) Tegus, O.; Brück, E.; Buschow, K. H. J.; de Boer, F. R. Transition-metal-based magnetic refrigerants for room-temperature applications. Nature 2002, 415, 150−152. (55) Peng, J. B.; Zhang, Q. C.; Kong, X. J.; Zheng, Y. Z.; Ren, Y. P.; Long, L. S.; Huang, R. B.; Zheng, L. S.; Zheng, Z. High-nuclearity 3d4f clusters as enhanced magnetic coolers and molecular magnets. J. Am. Chem. Soc. 2012, 134, 3314−3317. (56) Slack, G. A.; Oliver, D. W. Thermal Conductivity of Garnets and Phonon Scattering by Rare-Earth Ions. Phys. Rev. B: Solid State 1971, 4, 592−609. (57) Daudin, B.; Lagnier, R.; Salce, B. Thermodynamic properties of the gadolinium gallium garnet, Gd3Ga5O12, between 0.05 and 25 K. J. Magn. Magn. Mater. 1982, 27, 315−322.

9027

DOI: 10.1021/acs.inorgchem.8b01023 Inorg. Chem. 2018, 57, 9020−9027