Assembly of Two MetalâOrganic Frameworks Based on Distinct Cobalt

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Assembly of Two Metal−Organic Frameworks Based on Distinct Cobalt Dimeric Building Blocks Induced by Ligand Modification: Gas Adsorption and Magnetic Properties Hui-Yan Liu,* Jie Liu, Gui-Mei Gao, and Hai-Ying Wang* School of Chemistry & Materials Science, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 221116, PR China

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF SUSSEX on 08/10/18. For personal use only.

S Supporting Information *

ABSTRACT: Solvothermal reaction of 3,5-di(pyridin-4-yl) benzoic acid (HDPB) with Co(II) leads to a novel metal− organic framework, [Co2O(DPB)2(DMF)2]·xS (1), which represents a rare reo-type net with trigonal prismatic cobalt dimer, [Co2O(CO2)2N4], as building blocks to construct a 3D framework containing three different types of nanoscale M12L12 and M24L12 polyhedron cages. More interestingly, under the same condition, the assembly of 4-methyl-3,5di(pyridin-4-yl) benzoic acid (HMDPB) with Co(II) facilitates the formation of a cationic framework, [Co2(MDPB)3(DMF)](NO3)·xS (2), with cobalt dimer, [Co2(CO2)3N4], as building blocks. Complex 2 represents the first example of a zeolite-like network with 48-nuclear SOD cage. The significant effect of subtle modification of ligand on the overall MOFs is discussed. Moreover, the gas adsorption studies reveal that 1 exhibits permanent porosity and selective CO2 uptake. Variable-temperature magnetic susceptibility measurements show that both 1 and 2 exhibit antiferromagnetic behavior.

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tetrahedral nodes and ditopic linkers.6 Recently, in order to break the dependence on ditopic linkers and make full use of diverse organic ligands, Bu and co-workers propose a strategy (denoted the 4 + 2 + 1 method) to assemble ZMOFs with polyfunctional ligands by delegating different roles to available functional groups.7 They construct several series of zeolite-like MOFs, CPM-5, -16, -17, and -26 with four-connected In(III) metal node and a tritopic ligand, 1,3,5-benzenetricarboxylic acid (H3BTC). Although this method is currently in its nascent stage with few known examples, it holds great promise for the creation of a new generation of zeolite-like materials. Nevertheless, it is an ongoing challenge to further demonstrate the general feasibility of this strategy by exploring more different and diverse polyfunctional ligands and metal nodes. We have been devoted to constructing MOFs based on the polyfunctional carboxylate and pyridine-carboxylate ligands for gas sorption.8 As a continuation of our work, herein, we report two novel cobalt-frameworks, [Co2O(DPB)2(DMF)2]·xS (1) and [Co2(MDPB)3(DMF)](NO3)·xS (2), constructed from 3,5-di(pyridin-4-yl) benzoic acid (HDPB) and methyl-functionalized derivative 4-methyl-3,5-di(pyridin-4-yl) benzoic acid (HMDPB). It is notable that the subtle modification of ligand has a significant effect on the overall MOFs. Careful structural analyses reveal that the introduction of the methyl group in HMDPB ligand can push away two pyridine rings and cause

INTRODUCTION Metal−organic frameworks (MOFs) assembled from metal ions or metal-based cluster and organic linkers are attracting considerable attention due to their potential applications in gas storage and separation, magnetism, and molecular sensing.1 The modular nature of MOFs stemming from the tenability of linker and metal-based cluster imparts unprecedented diversity in terms of composition and structure. Over the past couple of decades, various design approaches have been developed to target particular MOFs through exploitation of the modular nature of MOFs. Specially, the molecular building block approach offers a potential in the construction of novel porous materials.2 Conventional building blocks, such as square paddlewheels [Cu2(CO2)4],3 octahedral [Zn4O(CO2)6],4 and trigonal prismatic [M3(μ3-O)(CO2)6] (M = Cr, Fe, In)5 cluster with varied connectivity and specific geometry have been employed to access a huge number of porous MOFs. In this context, the trigonal prismatic cluster represents an ideal building block to sustain stable, extra-large surface area nets with excellent gas sorption performance, as exemplified by famous MIL-1005a and MIL-101.5b To the best of our knowledge, however, trigonal prismatic structure is only limited to the trimeric [M3(μ3-O)(CO2)6] (M = Cr, Fe, In) cluster and remains less exploited for other polynuclear clusters.5h In contrast, zeolite-like MOFs (ZMOFs) have fascinated generations of scientists due to its intrinsic structure and potential applications, and shaped one of the most fruitful materials design strategies (called the 4 + 2 method) with © XXXX American Chemical Society

Received: June 10, 2018

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DOI: 10.1021/acs.inorgchem.8b01615 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

and structure refinements for 1 and 2 are summarized in Table 1, and selected bond lengths and angles are given in Tables S1 and S2.

them to be significantly twisted out of the central phenyl ring. Therefore, assembly of HDPB and HMDPB with Co(II) under the same condition leads to two distinct cobalt dimeric building blocks, which further construct two distinctly different frameworks containing nanocages, one having a cubic structure with reo topology9 and the other exhibiting zeolite-like sod topology.6 Moreover, the gas adsorption studies reveal that 1 exhibits permanent porosity and selective CO2 uptake. Variable temperature magnetic susceptibility measurements are also investigated.

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Table 1. Crystallographic Data for 1 and 2 empirical formula formula wt cryst syst space group a (Å) b (Å) c (Å) γ (deg) V (Å3) Z ρcalcd (g cm−3) μ (mm−1) F (000)

EXPERIMENTAL SECTION

General Information. All reagents were commercially available and used as received. HDPB ligand was synthesized with the procedure reported by us previously.8a Elemental analyses (C, H, and N) were obtained on a PerkinElmer 240 analyzer. 1H NMR data of HDPB were performed on a Bruker DRX-500 spectrometer. Thermogravimetric analyses (TGA) were carried out under N2 atmosphere using a 2960 SDT thermogravimetric analyzer. The IR spectra were measured on a Bruker Tensor 27 spectrometer with KBr pellets in the range of 4000− 400 cm−1. A Bruker D8 ADVANCE diffractometer using Cu Kα radiation (λ = 1.5418 Å) was used to record powder X-ray diffraction (PXRD) at room temperature, and variable-temperature PXRD measurements with a Philip X’ Pert Pro system were recorded. Magnetic susceptibility measurements were obtained on a Quantum Design MPMS-XL7 SQUID magnetometer under an applied field of 2 kOe over the temperature range of 1.8−300 K. Diamagnetic corrections were calculated using Pascal’s constants,10 and an experimental correction for the diamagnetic sample holder was applied. Synthesis of HMDPB Ligand. A mixture of methyl 3,5-dibromo-4methylbenzoate (2.0 g, 6.4 mmol), pyridin-4-ylboronic acid (2.4 g, 19.2 mmol), K3PO4 (14.2 g, 53.2 mmol), and Pd(PPh3)4 (0.5 g, 0.4 mmol) in 1,4-dioxane (120 mL) was stirred at 80 °C for 3 days under N2 atmosphere. The resultant product was evaporated to dryness and then extracted with CH2Cl2 and later dried with MgSO4. After removal of the CH2Cl2 solvent, the residue was washed briefly with ethanol (20 mL). The crude product was hydrolyzed within 2 M aqueous NaOH, followed by acidification with 37% HCl to afford HMDPB. Yield = 1.45 g (78%). 1H NMR (500 MHz, DMSO-d6, δ ppm): 13.19 (s, COOH), 8.72 (d, 4H, J = 4.0 Hz, ArH), 7.93 (s, 2H, ArH), 7.52 (d, 4H, J = 4.5 Hz, ArH), 2.16 (s, 3H, CH3). Anal. Calcd (Found) for C18H14N2O2: C, 74.47 (74.42); H, 4.86 (4.66); N, 9.65 (9.45) %. Selected IR data (KBr, cm−1): 3396, 3066, 1705, 1633, 1604, 1545, 1505, 1407, 1335, 1266, 1065, 1016, 822, 775, 634, 623. Synthesis of 1. A mixture of HDPB (10.0 mg, 0.04 mmol), Co(NO3)2·3H2O (20 mg, 0.08 mmol), and 4 drops of pyridine in 2 mL of DMF was placed in a 23 mL glass vial and heated at 80 °C for 72 h. The purple octahedron crystals were obtained and washed with DMF (yield: 40% based on ligand). Selected IR data (KBr, cm−1): 3367, 2929, 1661, 1632, 1612, 1592, 1503, 1440, 1387, 1316, 1095, 833, 787, 658, 629. Synthesis of 2. The procedure for 2 was similar to that for 1 except that HMDPB was used in place of HDPB. The purple rhombic crystals were obtained (yield: 33% based on ligand). Selected IR data (KBr, cm−1): 3218, 1655, 1613, 1568, 1503, 1442, 1392, 1314, 1222, 1069, 827, 788, 657, 629. X-ray Crystallography. The X-ray diffraction data of 1 and 2 were recorded on a Bruker Apex II CCD diffractometer at 291 K using graphite monochromated Mo Kα radiation (λ = 0.71073 Å), and the Bruker SAINT program was applied to data reduction.11a The structure was solved by direct methods and refined with full-matrix least-squares technique using the SHELXTL package.11b Displacement parameters were refined anisotropically, and the positions of the hydrogen atoms were generated geometrically assigned isotropic thermal parameters. The diffused electron densities resulting from highly disordered solvent molecules were removed from the data set using the SQUEEZE routine of PLATON and refined further using the data generated. Crystal data

index ranges Rint Tmax, Tmin data/restraints/parameters goodness of fit R1a, wR2b (I > 2σ(I))a R1, wR2 (all data) (Δρ)max, (Δρ)min (e A−3) a

1

2

C40H36Co2N6O7 830.61 cubic Im3̅ 34.630(2) 34.630(2) 34.630(2) 90 41530(7) 24 0.797 0.511 10272 −44 ≤ h ≤ 44 −44 ≤ k ≤ 28 −44 ≤ l ≤ 44 0.0544 0.8871, 0.8871 7952/0/261 1.086 0.0525, 0.1526 0.0627, 0.1536 0.602, −0.529

C57H46Co2N8O10 1120.88 trigonal R3̅ 46.2728(16) 46.2728(16) 20.4602(15) 120 37940(3) 18 0.883 0.436 10404 −59 ≤ h ≤ 61 −61 ≤ k ≤ 39 −27 ≤ l ≤ 26 0.0621 0.8951, 0.9102 20360/0/699 1.067 0.0592, 0.1660 0.0699, 0.1684 0.384, −0.392

R1a = Σ||F0| − |Fc||/ΣF0|, wR2b = [Σw(F02 − Fc2)2/Σw(F02)2]1/2.

Gas Sorption Measurements. As-synthesized 1 was treated under dynamic vacuum condition at 60 °C for 20 h to obtain activated samples. Low-pressure gases (H2, N2, CH4, and CO2) sorption isotherms were obtained with a Quantachrome Autosorb-iQ volumetric gas adsorption analyzer. Calculation of Isosteric Heats of Adsorption. The isosteric heats of adsorption for H2 (at 77 and 87 K), CO2, and CH4 (at 273 and 298 K) on 1 were calculate with a virial-type expression.12 The data were fitted using m

ln P = ln N + 1/T ∑ aiN i + i=0

n

∑ bjN j j=0

(1)

where P is the pressure expressed in Torr, N is the amount adsorbed in mmol g−1, T is the temperature in K, ai and bj are virial coefficients, and m and n are the number of coefficients required to adequately describe the isotherms. Then, the coverage-dependent isosteric heats of adsorption (Qst) were estimated using the values of the virial coefficients a0 through am with the following expression, where R is the universal gas constant. m

Q st = − R ∑ aiN i

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i=0

(2)

RESULTS AND DISCUSSION Crystal Structure and Framework Stability. Solvothermal reaction between HDPB, HMDPB and Co(II) in DMF with pyridine afforded purple crystals of 1 and 2, respectively (Scheme S1 and Figure S1). Both structures are based on two distinct cobalt dimeric building blocks (Figure 1) and thus present distinctly different frameworks. Single-crystal structure analysis reveals that 1 is crystallized in the cubic space group Im3̅ with cell parameters a = b = c = 34.630(2) Å and V = 41530(7) Å3 (Table 1). The structure of 1 B


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Inorganic Chemistry

Figure 1. Two different cobalt dimeric molecular building blocks in 1 (a) and 2 (b) (color code: Co, green; N, blue; O, red; C, gray).

is built from a cobalt dimer with each DPB− ligand serving as a tritopic linker by its two pyridyl groups and one carboxylate group of bis-mondentate fashion (Figure S2). The dimer contains two cobalt-centered octahedral that share one μ-oxo anion, forming the trigonal prismatic building unit (Figure 1a). The well-known trigonal prismatic building block is trimeric [M3(μ3-O)(CO2)6] (M = Cr, Fe, In), which has been employed effectively to construct plenty of highly porous materials, as exemplified by MIL-1005a and MIL-101.5b However, to the best of our knowledge, trigonal prismatic building block of cobalt dimeric cluster is uncommon.2d Each dimer unit is connected to six separate tritopic linkers to build up a novel 3D structure, featuring three different types of polyhedron cages (cages A−C) (Figure 2). Cage A is an octahedron of M12L12 composition, with 6 dimer units at the vertices and 12 DPB− ligands spanning all 12 edges. It has 8 triangle-shaped windows with a Co−Co distance of about 10.2 Å along the edges and an internal diameter of about 0.95 nm (yellow sphere in Figure 2a). Furthermore, eight such octahedra enclose two distinct nanoscale cages of M24L12 composition (cage B and C). Generally, the composition of 8 planar tripodal ligands and 12 bidentate components may form a cuboctahedron with 8 triangular faces and 6 square faces.13 Several cuboctahedral cages, both as singular units14 and contained within a network of cages, have been reported.13,15 In the present case, however, cage B may be appropriately described as a icosahedron in which the 6 squares of the cage deviate significantly from the planar square required for the formation of a cuboctahedron.16 The dihedral angle between the two triangles that form the square is about 40.3° (Figure S3). Thus, the 6 squares occupied by 12 ligands may be better regarded as 12 equilateral triangles. In this way, the resulting icosahedron with a free internal diameter of about 1.62 nm (aqua sphere in Figure 2b) can be described as consisting of 20 triangles, 12 being occupied by 12 ligands and 8 being open. The cage C with a free internal diameter of about 1.2 nm (orange sphere in Figure 2c) has the same composition with that of cage B, but it is slightly different from cage B. In cage C, the 12 dimer units occupy 12 vertices, but unlike cage B, only 2 of 6 squares deviate significantly from the planar square. The other four squares of the cage present a small deformation with the dihedral angle between the two triangles that form the square are only 3.6° (Figure S3). Thus, cage C can be considered to consist of 12 triangles and 4 squares, in which 12 ligands occupied 4 triangles and 4 squares. Then, the novel 3D final framework is generated through the above cage-to-cage connections (Figures 2d and S4).

Figure 2. Structure in 1. (a−c) Three different cage. (left) Ball and stick representation. (right) Schematic drawing highlighting the cage topology and the ligand-decorated triangular planes. Green (b) and yellow (c) triangles represent the positions of the DPB− ligands. (d) Tiling representation of three interconnecting cages (left) and the reo net (right) (color code: Co, green; N, blue; O, red; C, gray).

C


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Inorganic Chemistry

Figure 3. Representation of two different nanocages, cage B (a) and cage C (b) in 1. (c) Linking mode of two cages. Blue trigonal prisms represent the dimeric cobalt units. Green and red triangles represent DPB− ligands located on squares with significantly large and small deformation, respectively.

Figure 4. Schematic showing the assembly of 2 by combining trifunctional ligand with 4-connected cobalt dimeric nodes, resulting in the sod topology (tiling representation).

As shown in Figure 3, there exist two types of DPB− ligand with different dihedral angle between the central benzene and pyridyl rings, one of about 28.2° and the other approximately of

37.5°. Such different ligand conformation plays a critical role in the formation of two nanoscale cages. Topologically, 1 can be described as a new (3,3,6)-connected 3-nodal net of (4·62)2(42· D


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Inorganic Chemistry

Figure 5. Structure of 2: (a) two types of hexagonal windows, (b) square windows, (c) view of the SOD cage along c axis with 12 uncoordinated pyridyl groups (space-filling mode) dangling in the pore. The yellow sphere shows an inner diameter of about 1.3 nm of cage (not considering dangling pyridyl groups).

67·86) with cobalt dimer units serving as a 6-connected trigonal prismatic nodes and the bridging ligands acting as 3-connected nodes (Figure S5a). Alternatively, each cobalt dimers can be simplified as an 8-connected node and the ligand as a linker is connected with the nodes, leading to an 8-connected network with a rare reo topology (Figure S5b).9 Reaction conditions similar to those for 1 with HMDPB as the organic linker gives purple rhombic crystals of 2. Single-crystal structure analysis reveals that 2 is crystallized in the trigonal space group R3̅ with cell parameters a = b = 46.2728(16) Å, c = 20.4602(15) Å and V = 37940(3) Å3 (Table 1). The cationic framework of 2 is entirely different from that of 1. Instead of the 6-connected trigonal prismatic building block observed in 1, a dimeric [Co2(CO2)3N4] unit is formed in 2, which is linked to seven separate organic linkers. In addition to 3-connected mode found in 1, MDPB− ligands in 2 present another two different 2connected modes (Figure S6). On the basis of the employment of three or two function groups, the ligands can be served as tritopic or ditropic linkers. Topologically, 2 is a new (3,7)connected net of (3·42) (32·46·57·64·72) with cobalt dimer units and the ligands serving as 7-connected nodes and 3-connected nodes, respectively (Figure S7). Alternatively, if only by considering the link between the cobalt dimer units, then the overall network of 2 adopts a distorted zeolitic sod topology (Figure 4), featuring truncated octahedral cages with eight hexagonal faces and six square faces shared with neighboring cages. As shown in Figure 5, six of eight hexagonal faces are occupied by both tritopic and ditropic linkers, while the other two are only occupied by six ditropic linkers. Two such types of hexagons are

significantly distorted and assume a chair conformation, distinctly different from planar hexagons observed in largely known zeolite-like frameworks.6 It is worth noting that tritopic linkers on the hexagonal faces do not devote any to the extension of cages because three functional groups of the 3-connected ligand are used up. Instead, cage-to-cage connection is achieved by linking cobalt dimeric nodes with the 2-connected ligands. Such 2-connected ligands only use one chelating −COO group and one pyridyl group to connect the cages, with another pyridyl group left. In other words, among seven separate organic ligands linked to a cobalt dimer, three ligands behave as tritopic linkers, while four ones are ditropic linkers. Therefore, cobalt dimer essentially behaved as 4-connected nodes required for zeolite formation, which makes 2 the first example of zeolite-like framework with 48-nuclear cobalt SOD cages (Figure 5c). Such a dimer 4-connected node is unique but significantly deviated from the perfect tetrahedron geometry required for zeolite formation.6a−c Thus, both the distorted 4-connected nodes and the unsymmetrical character of two functional groups of MDPB− ligand (one pyridyl and one −COO group) used for framework construction may be contributed to significantly deviated SOD architecture of 2 (Figure S8). While in CPM-5 and CPM-15 reported by Bu’s group,7 the choice of single In(III) metal with preferred tetrahedral geometry, in combination with symmetrical BTC ligands ensure the formation of perfect SOD cage, together with high hydrothermal and thermal stability. Notably, as shown in Figure 5c, along c axis, there are 12 pyridyl groups dangling within each SOD cage, which do not serve as hooks to capture single metal ions or clusters at the centers of the channels as observed in CPM-57a and CPM-15.7c E


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adsorption isotherm using density functional theory (DFT) (Figure 6). This revealed three types of pores with estimated diameters of 0.75, 1.1, and 1.4 nm, which were consistent with that of three different cages as observed in the crystal structure of 1. The permanent porosity of 1 encouraged us to further investigate the H2, CH4, CO2, and N2 adsorption isotherms at low pressure (0−1 bar). At 1 bar and 77 K, the H2 uptake of 1 is 190.7 cm3 g−1 (1.7 wt %) (Figure S17a), which is compared moderately with the best capacity MOFs (2.5−3 wt %).18 This value is larger than that of NJU-Bai18 (1.5 wt %)8b and those of MOFs with the reo topology, such as JLU-Liu2 (1.54 wt %)9b and PCN-105 (1.51 wt %).9c On the basis of the H2 adsorption isotherms at 77 and 87 K, the zero coverage isosteric heats (Qst) of H2 for 1 calculated by the virial method is 6.3 kJ mol−1 (Figure S17b), which is comparable to that of Cu-BTTri (6.1 kJ mol−1)19a and PCN-121 (6.6 kJ mol−1)19b and higher than that of NOTT-101 (5.3 kJ mol−1).19c As shown in Figure 7, 1 can adsorb a considerable amount of CO2 (67.8 and 35.3 cm3 g−1) under 1 bar at 273 and 298 K,

Not considering the dangling pyridyl groups, the SOD cage has an inner diameter of about 1.3 nm (Figure 5c). It is evident that the generation of the reo and sod networks of 1 and 2, respectively, is related to two distinctly different ligand configurations originated from the substitutes in the 4-position of HDPB ligand as shown in Figure S9. The 4-methyl groups may have key effects on the orientations of adjacent metal coordination polyhedra, which lead to different configurations in the interconnection of these metal ions and thus different 3D MOFs. These results demonstrated that a subtle modification of ligand can lead to drastically distinct frameworks. The total potential solvent-accessible volumes for 1 and 2 were 53.6 and 47.0%, respectively, as estimated by PLATON software (the coordinated DMF were not omitted).17 Thermogravimetric analysis (TGA) revealed that the framework of 1 and 2 can be thermally stable up to about 250 °C (Figure S10). The bulk identity of 1 and 2 were verified by powder X-ray diffraction (PXRD) measurements (Figures S11 and S12). The PXRD patterns for as-synthesized samples match well with the simulated patterns from crystal data, demonstrating that the crystal is representative of the pure bulk sample. The temperature dependent PXRD study for 1 shows that the crystallinity and overall framework is stable up to about 125 °C (Figure S13). The as-synthesized 1 was treated under dynamic vacuum condition at 60 °C for 20 h to obtain activated 1, which can retain crystallinity as confirmed by minor changes of the PXRD patterns (Figure S11). Unfortunately, numerous attempts to activate samples of 2 for gas sorption analysis resulted in loss of crystallinity. Clearly, the unique but significantly distorted architecture of 2 described above may mainly contribute to the lack of structure integrity after removing guest solvent molecules. Porosity and Gas Adsorption of 1. The permanent porosity of activated 1 was confirmed by N2 and Ar sorption experiments at 77 and 87 K, respectively. As shown in Figure 6,

Figure 7. CO2, CH4, and N2 adsorption isotherms of 1 at 273 and 298 K.

respectively, which are comparable to that of Tripp-1-Co (76.7 cm3 g−1 at 273 K and 49.2 cm3 g−1 at 293 K),20a JLU-Liu2 (79.1 cm3 g−1 at 273 K and 41.7 cm3 g−1 at 298 K),9b JUC-132 (60.9 cm3 g−1 at 273 K and 38.3 cm3 g−1 at 298 K),20b and {(H 2 N(CH 3 ) 2 )[Co 8 (μ 2 -OH) 4 (μ 3 -OH) 4 (μ 4 -OH)(Ina) 8 ](H2O)15(DMA)9}n (86.8 cm3 g−1 at 273 K and 39.1 cm3 g−1 at 298 K).20c In comparison, 1 can only exhibit limited amounts of CH4 (20.8 and 10.9 cm3 g−1) and N2 (5.4 and 2.8 cm3 g−1) under 1 bar at 273 and 298 K, respectively. The high CO2 uptake in 1 may be related with the significant quadruple moment of CO2 molecules (−1.34 × 10−39 cm2) arising from the strong dipolar CO bonds, which facilitates efficient interaction between CO2 molecules and frameworks, and further improves the CO2 uptake.20 Then, we performed a common method to calculate gas adsorption selectivity by using initial slop ratios estimated from Henry’s law constants for single-component gas adsorption isotherms. The calculated CO2/CH4 and CO2/N2 selectivities were found to be 4.9 and 19.4 at 273 K (Figure S18), respectively. This value is comparable to that of MOF-177 (4.4 for CO2/CH4 and 17.5 for CO2/N2).21 Moreover, the zero coverage isosteric heats (Qst) of CO2 and CH4 for 1 were estimated using the virial method (Figure S20).

Figure 6. N2 (at 77 K) and Ar (at 87 K) adsorption isotherm for 1 (inset: the pore size distributions for 1 derived from the Ar isotherms by using DFT method).

the N2 sorption isotherm reveals that 1 exhibits an uptake of about 411.5 cm3 g−1, featuring a characteristic type I behavior for microporous materials. A total pore volume is 0.63 cm3 g−1. The calculated Langmuir and Brunauer−Emmett−Teller (BET) surface area were 1668.2 and 1475.7 m2 g−1, respectively (Figure S16). 1 shows a high Ar uptake of about 458.2 cm3 g−1, and the pore size distribution (PSD) was determined by analyzing the Ar F


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The Qst value for CO2 (26.2 kJ·mol−1) is comparable to that of Tripp-1-Co (25.6 kJ mol−1)20a and JLU-Liu2 (26 kJ mol−1),9b demonstrating moderate interaction between CO2 and framework. As shown in Figure S20a, with the CO2 loading, Qst for CO2 adsorption first slowly decreases and then increases gradually. This indicates that at high-concentration CO2 loadings, the sorbate−sorbate interaction in addition to the sorbate-framework interaction becomes dominant as discovered in other MOFs.3h,5b As for CH4, 1 exhibits a lower Qst value (21.9 kJ mol−1) at zero coverage (Figure S20b). Magnetic Properties. The temperature-dependent magnetic susceptibility measurements of 1 and 2 were investigated on the polycrystalline sample in the ranges of 1.8−300 K under a field of 2 kOe. As shown in Figures S21 and S22, the observed values of χMT are 3.50 cm3 K mol−1 for 1 and 3.27 cm3 K mol−1 for 2 at 300 K, which are close to the expected value of 3.75 cm3 K mol−1 for uncoupled two high-spin Co(II) centers (S = 3/2). Upon cooling, the χMT value decreases gradually, and then rapidly reaches the lowest values of 1.16 and 0.55 cm3 K mol−1 for 1 and 2, respectively, at 1.8 K. This behavior may be caused by antiferromagnetic coupling between the Co(II) ions. The magnetic susceptibilities conform well to Curie−Weiss law [χM = C/(T − θ)] above 150 K, with Curie constant C values of 3.68 and 3.75 cm3 K mol−1, and Weiss constant θ values of −14.19 and −42.01 K for 1 and 2, respectively. The negative θ values also confirm the antiferromagnetic coupling between the metal sites.1d,22a As X-ray diffraction analysis revealed, 1 and 2 are two distinctly different 3D frameworks based on two different dinuclear cobalt clusters. In 1, the two central Co(II) ions are linked by one μ-oxo anion and two carboxylate groups in a bridging bidentate fashion, while in 2, three carboylate groups are combined with two Co(II) ions in a bridging bidentate mode as well as a chelating-bridging tridentate mode. Owing to the different bridging modes, the bridging angles, and the Co−Co distance within dinuclear cobalt clusters in 1 are different from that in 2, which may be responsible for slightly different magnetical behavior of 1 and 2.1d,22b

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01615. Additional characterization data (PDF) Accession Codes

CCDC 1823587 and 1823588 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.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Hui-Yan Liu: 0000-0002-2262-0775 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of Jiangsu Normal University, China (No. 17XLR044), the Key Basic Research Project of the Natural Science Foundation of the Jiangsu Higher Education Institutions, China (No. 13KJA430002), and PAPD of Jiangsu Higher Education Institution.

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REFERENCES

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CONCLUSIONS

On the basis of a trifunctional pyridine-carboxylate ligand and its methyl functionalized derivative, two metal−organic frameworks with the rare reo and sod topology have been achieved. The subtle modification of ligand exert a significant influence on the observed cluster nodes and hence the overall topology of the framework. Complex 1 represents a distinct example of porous MOF with uncommon cobalt dimeric clusters as trigonal prismatic building blocks to construct a novel framework consisting of nanoscale cages. Specifically, 2 represents the first example of zeolite-like MOF with 48-nuclear cobalt SOD cages. Although 2 fails to retain its structural integrity after removing guest solvent molecules, the successful synthesis of 2 demonstrates a potentially general and versatile method for the construction of zeolite-like MOFs with polyfunctional ligands. In addition, these two attractive examples presented here highlight the complexity and challenge of the ligand modification related to diverse net topologies. Work is in progress to employ the other functional group (such as methoxy group) to further explore the ligand function effect on topology diversities. G


Article

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