Cluster Organic Frameworks Constructed from Heterometallic

Mar 27, 2017 - The two novel cluster organic frameworks based on heterometallic supertetrahedral cluster secondary building units (SBUs) [Cd4Cu6(L)4(A...
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Cluster Organic Frameworks Constructed from Heterometallic Supertetrahedral Cluster Secondary Building Units Li-Dan Lin,† Xin-Xiong Li,*,†,‡ Yan-Jie Qi,† Xiang Ma,† and Shou-Tian Zheng*,†,‡ †

State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, People’s Republic of China ‡ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350108, People’s Republic of China S Supporting Information *

ABSTRACT: The two novel cluster organic frameworks based on heterometallic supertetrahedral cluster secondary building units (SBUs) [Cd4Cu6(L)4(Ac)7(H2O)4](Ac)·7H2O (1) and [Mn4Cu6(L)4(Ac)4.5(H2O)9]CuCN(Ac)3.5·H2O (2), where H3L = 2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol and Ac = CH3COO−, have been prepared under solvothermal conditions. 1 and 2 are the first cases of cluster organic frameworks containing Cd-Cu/Mn-Cu heterometallic supertetrahedral cluster SBUs. Furthermore, 1 and 2 show an integration of magnetic properties and adsorption properties from both the heterometallic cluster secondary building units and the framework in a porous material.

INTRODUCTION Cluster-organic frameworks, built from cluster secondary building units (SBUs) and organic ligand linkers, are of high current interest in account of their intriguing structures, interesting properties, and potential applications in areas including magnetism, sorption, molecular recognition, catalysis, and other areas.1 Usually, their performance and properties are largely determined by the compositions and structural characteristics of their inorganic SBUs. This is because the inorganic SBUs can not only produce robust frameworks but also transmit their unique physical and chemical properties to the final products.2 Transition metal (TM) clusters with different compositions usually exhibit different sizes, shapes, and coordination numbers as well as coordination modes, offering a variety of SBUs for creating original cluster-organic frameworks with more versatile, stable, and porous structures.3 For example, square paddlewheel dimer [Cu2(CO2)4] SBUs have been used extensively in designing a variety of porous materials for small gas molecule separation.4 Similarly, triangular In3O(CO2)3 SBUs have been widely employed in building a large family of cluster-organic frameworks for gas storage.5 In addition, octahedral tetramer [Zn4O(CO2)] SBUs have also been broadly applied in creating many intriguing architectures.6 Using dodecahedral hexamer [Zr6O4(CO2)12] SBUs, a great number of porous cluster-organic frameworks with high thermal and chemical stability can be obtained.7 More recently, a large number of cluster organic frameworks consisting of polyoxometalate (POM) cluster SBUs have also been made.8 © 2017 American Chemical Society

In comparison with the aforementioned TM cluster SBUs, the exploration of cluster organic frameworks from supertetrahedral cluster SBUs has been relatively less studied.9 During the past decade, the fabrication of supertetrahedral chalcogenide clusters into three-dimensional (3-D) architectures has been successfully achieved.10 Recently, further development has led to the 3-D assembly of inorganic TM (TM = Co, Cu, Mn, Pb) supertetrahedral clusters.11 Despite these prospective advantages, a limitation still exists before this work, as supertetrahedral cluster SBUs consisting of two different kinds of metal ions are rare.12 In particular, the exploration of extended frameworks based on supertetrahedral cluster SBUs that contain mixed TM ions has been little explored even though they have promising unique applications. Integration of different TM ions into supertetrahedral clusters offers a new opportunity not only for new archetectures but also for synergistic properties derived from different TM ions through uniform integration at the molecular level. We are particularly interested in using the bifunctional ligand 2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol (H3L) to induce the aggregation of TM clusters and further join them into cluster organic frameworks. This approach has successfully prepared a series of cluster organic frameworks containing uncommon {Mn12} cluster SBUs.13 In this work, we intend to discover a new kind of cluster organic framework based on heterometallic supertetrahedral cluster SBUs. We report here the synthesis, crystal structures, and properties of two Received: February 2, 2017 Published: March 27, 2017 4635

DOI: 10.1021/acs.inorgchem.7b00267 Inorg. Chem. 2017, 56, 4635−4642


Inorganic Chemistry

SQUEEZE function in PLATON. The final formulas of 1 and 2 were determined by a combination of single-crystal X-ray diffraction with the elemental analysis, thermogravimetric analysis, and charge balance. Crystallographic data and structure refinements for 1 and 2 are summarized in Table 1. CCDC 1523857 and 1527682 contain

unprecedented cluster-organic frameworks, [Cd4Cu6(L)4(Ac)7(H2O)4](Ac)·7H2O (1) and [Mn4Cu6(L)4(Ac)4.5(H2O)9]CuCN(Ac)3.5·H2O (2) (Ac = CH3COO−), built from heterometallic supertetrahedral cluster SBUs. As far as we are aware, 1 and 2 are the first cases of cluster-organic frameworks based on Cd-Cu/Mn-Cu heterometallic supertetrahedral cluster SBUs, although some discrete monometallic supertetrahedral TM clusters have been reported.14

Table 1. X-ray Crystallographic Data for 1 and 2 1 empirical formula formula wt cryst syst space group a (Å) b (Å) c (Å) V (Å3) Z F(000) ρcalcd (g cm−3) temp (K) μ (mm‑1) no. of rflns collected no. of indep rflns no. of params GOF on F2 final R indices (I = 2σ(I))a R indices (all data)a


Materials and General Methods. All chemicals were commercially purchased and used without further purification. The ligand H3L15 was synthesized according to a literature procedure. Elemental analyses of C, H, and N were carried out with a Vario EL III elemental analyzer. IR spectra were recorded on an Opus Vertex 70 FT-IR infrared spectrophotometer in the range of 450−4000 cm−1. Thermogravimetric analysis was performed on a Mettler Toledo TGA/SDTA 851e analyzer under an air-flow atmosphere with a heating rate of 10 °C/min in the temperature range 30−800 °C. Powder XRD patterns were obtained using a Philips X’Pert-MPD diffractometer with Cu Kα radiation (λ = 1.54056 Å). Variabletemperature susceptibility measurements were carried out in the temperature range 2−300 K at a magnetic field of 0.1 T on polycrystalline samples with a Quantum Design PPMS-9T magnetometer. The experimental susceptibilities were corrected with Pascal’s constants. Gas adsorption measurement was performed with the ASAP (accelerated surface area and porosimetry) 2020 System. Before measurement, 1 and 2 were activated by soaking the crystals in acetonitrile for 3 days to exchange DMA and H2O solvent molecules and then degassed at 353 K for 12 h under vacuum. Synthesis of [Cd4Cu6(L)4(Ac)7(H2O)4](Ac)·7H2O (1). Cd(Ac)2· 2H2O (0.039 g, 0.146 mmol), Cu(Ac)2·H2O (0.020 g, 0.191 mmol), H3L (0.035 g, 0.191 mmol), N,N′-dimethylacetamide (DMA, 3 mL), and acetonitrile (CH3CN, 0.5 mL) were placed respectively in a 20 mL vial, which was sealed and heated to 100 °C for 72 h and then cooled to room temperature. Large pure green blocklike crystals were obtained after cooling to room temperature. The yield was about 86% on the basis of Cu(Ac)2·H2O. Anal. Calcd for C52H86O39N4Cd4Cu6 (Mr = 2222.16): C, 28.12; H, 3.91; N, 2.52. Found: C, 27.80; H, 4.01; N, 2.58. IR (solid ATR, ν/cm−1): 3407 (m), 2923 (w), 1563 (vs), 1406 (vs), 1342 (w), 1229 (w), 1072 (s), 1015 (w), 935 (m), 818 (w), 669 (m), 617 (w), 561 (w), 521 (m). Synthesis of [Mn4Cu6(L)4(Ac)4.5(H2O)9]CuCN(Ac)3.5·H2O (2). Mn(Ac)2·2H2O (0.025 g, 0.10 mmol), Cu(Ac)2·H2O (0.060 g, 0.30 mmol), H3L (0.018 g, 0.10 mmol), N,N′-dimethylacetamide (DMA, 3 mL), and acetonitrile (CH3CN, 1 mL) were placed respectively in a 20 mL vial, which was sealed and heated to 100 °C for 72 h and then cooled to room temperature. Large pure green hexagonal crystals were obtained after cooling to room temperature. The yield was about 79% on the basis of Mn(Ac)2·2H2O. Anal. Calcd for C52H84O38N5Mn4Cu7 (Mr = 2063.82): C, 30.84; H, 4.10; N, 3.39. Found: C, 30.91; H, 4.20; N, 3.34. IR (solid ATR, ν/cm−1): 3379 (m), 2924 (w), 1559 (vs), 1409 (vs), 1337 (w), 1230 (w), 1073 (s), 1021 (w), 933 (m), 816 (w), 666 (m), 618 (w), 563 (w), 527 (m). Single-Crystal Structure Analysis. Single-crystal X-ray diffraction data for 1 and 2 were collected on a Bruker APEX II diffractometer at 150 K equipped with a fine-focus, 2.0 kW sealedtube X-ray source (Mo Kα radiation, λ = 0.71073 Å) operating at 50 kV and 30 mA. The program SADABS was used for the absorption correction. The structures were solved by direct methods and refined on F2 by full-matrix least-squares methods using the SHELX-2013 program package. All hydrogen atoms attached to carbon atoms were generated geometrically. Due to the highly porous nature of the structures, the charge compensation anions and guest solvent molecules could not be definitely mapped by single-crystal X-ray diffraction. The residual electron density that could not sensibly be modeled as solvents or anions was removed via application of the

C52H86O39N4Cd4Cu6 2222.16 orthorhombic Pbca 26.343(3) 27.158(4) 27.158(4) 19429(3) 8 8024.0 1.387 296(2) 3.301 49244 13787 829 1.024 R1 = 0.0651, wR2 = 0.1650 R1 = 0.1099, wR2 = 0.1588

2 C52H84O38N5Mn4Cu7 2063.82 hexagonal P63/mmc 17.1184(8) 17.1184(8) 42.734(2) 10845.1(12) 4 3606.0 1.108 296(2) 1.843 66641 3596 179 1.026 R1 = 0.0959, wR2 = 0.2921 R1 = 0.1005, wR2 = 0.2790

R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2; w = 1/[σ2(Fo2) + (xP)2 + yP], P = (Fo2 + 2Fc2)/3, where x = 0.1600 and y = 4.3344 for 1 and x = 0.0691 and y = 0.3314 for 2.


supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via

RESULTS AND DISCUSSION Structural Description of [Cd4Cu6(L)4(Ac)7(H2O)4](Ac)· 7H2O (1). Single-crystal X-ray structural analysis revealed that 1 crystallizes in the orthorhombic space group Pbca and displays a 3D framework structure based on decanuclear 3d−4d heterometallic cluster SBUs {Cd 4 Cu 6 L 7 (Ac) 7 (H 2 O) 4 } (Cd4Cu6, Figure 1a). The asymmetric unit of the Cd4Cu6 cluster is composed of four Cd2+ ions, six Cu2+ ions, four L ligands, seven acetyl groups, and four coordinated water ligands. In the Cd4Cu6 cluster, four crystallographically independent Cd2+ ions adopt two kinds of coordination geometries (Figure S1 in the Supporting Information). With the exception of Cd4, which is six-coordinated with a distortedoctahedral geometry, all of the Cd2+ ions are seven-coordinated. Cd4 is surrounded by six O atoms from three neighboring L ligands, one acetyl group, and two terminally coordinated water molecules. The coordination of each of the seven-coordinated Cd2+ ions (Cd1, Cd2, and Cd3) is completed by six O atoms from three L ligands, two acetyl groups, and one N atom derived from the 4-pyridyl group of one L ligand. The Cd−O bond distances fall in the range of 2.191(1)−2.499(3) Å, and the Cd−N bond lengths vary from 2.275(2) to 2.337(1) Å. All Cu2+ ions are five-coordinated with a tetragonal-pyramidal geometry. Each CuO5 tetragonal pyramid shares four corners of the tetragonal plane with four neighboring groups, generating a {Cu6O18} core (Figure S2 in the Supporting Information), 4636

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Inorganic Chemistry

evident in the following aspects. (1) {[Cu6Cd4(HL)4(piv)8(H2O)6]·4MeOH} is stabilized only by O-containing ligands, while the Cd4Cu6 cluster comprises not only O-containing ligands but also N-donor pyridyl ligands. (2) Tthe Cd2+ ions in the Cd4Cu6 cluster exhibit two different coordination modes; however, the Cd 2 + ions in {[Cu6Cd4(HL)4(piv)8(H2O)6]·4MeOH} have only one coordination mode. The most striking structural feature of 1 is that Cd4Cu6 clusters can further self-assemble into a 3D framework, which is rarely observed in heterometallic cluster organic frameworks. As shown in Figure S3 in the Supporting Information, each Cd4Cu6 cluster was connected to six neighboring ones through sharing six L ligands, leading to the formation of a cationic framework (Figure 1c). The framework exhibits 1D parallelogram channels with a size of 3.82 × 9.65 Å (measured between opposite polyhedra) along the c axis. The channels are filled with lattice water molecules and charge compensation anions Ac−. Interestingly, a side view of the 1D channel in 1 indicates that it can be viewed as face-sharing parallelepiped cages (Figure S4 in the Supporting Information), in which every huge parallelepiped cage is formed by eight Cd4Cu6 clusters at the eight vertex sites (Figure 2). The size of the parallelepiped cage

Figure 1. (a) Ball and stick representation of the coordination environment of Cd4Cu6 cluster in 1. (b) Formation scheme of the Cd4Cu6 cluster. (c) Polyhedra and stick structure of the 3D framework based on Cd4Cu6 clusters in 1.

Figure 2. (a) View of the parallelepiped cage based on self-aggregation of eight Cd4Cu6 clusters in 1. (b) Topology of the parallelepiped cage. The Cd4Cu6 clusters are simplified as green tetrahedra.

which is similar to Lindqvist-type POMs.16 The oxidation states of Cu atoms confirmed by bond valence sum (BVS) calculations17 are in the range of 2.043−2.128 (Table S1 in the Supporting Information). All four of the L ligands are fully deprotonated with two distinct coordination modes: one ofthe four acts as a terminal ligand to bind with the Cd4Cu6 cluster through its three hydroxyl groups, while the rest of the L ligands serve as bridging ligands to join two neighboring Cd4Cu6 clusters by hydroxyl groups and 4-pyridyl groups. It is noteworthy that each hydroxyl group in the four L ligands is deprotonated into a μ3-O bridge to bond with two Cu2+ ions and one Cd2+ ion. Peripheral ligation of the Cd4Cu6 cluster is further provided by seven acetyl groups and four terminal water ligands. Four of the seven acetyl groups show a syn−syn η1:η1:μ2 coordition mode to link one Cd2+ ion and one Cu2+ ion, and the other three adopt a common chelating mode to chelate with one Cd2+ ion. The structure of the Cd4Cu6 cluster can be viewed as one {CdO6} octahedron and three {CdO6N} polyhedra capped on four of eight triangular apertures of the Lindqvist-like {Cu6O18} core (Figure 1b). Notably, though the configuration of Cd4Cu6 cluster is similar to that of the reported discrete Cd−Cu heterometallic supertetrahedral cluster {[Cu6Cd4(HL)4(piv)8(H2O)6]·4MeOH} (H4L = pentaerythritol, Hpiv = pivalic acid),14b the difference between the Cd4Cu6 cluster and {[Cu6Cd4(HL)4(piv)8(H2O)6]·4MeOH} is

is about 23.28 × 23.82 × 24.47 Å3. In other words, the whole 3D framework can be described as the assembly of these nanosized parallelepiped cages by sharing six faces. Viewed from a topological standpoint, the overall 3D framework can be rationalized as a six-connected NaCl-like topology in which the nodes are Cd4Cu6 clusters (Figure S5 in the Supporting Information). Such a network is similar to that of TAF-1a on the basis of decanuclear {Co10} clusters.11a Structural Description of [Mn4Cu6L4(Ac)4.5(H2O)9]CuCN(Ac)3.5·H2O (2). Single-crystal X-ray structural analysis has revealed that 2 crystallizes in the hexagonal space group P63/mmc and displays a 2D bilayer structure based on the heterometallic supertetrahedral cluster {Mn 4 Cu 6 L 4 (Ac) 6 (H 2 O) 9 } (Mn 4 Cu 6 ; Figure 3a,b) and {CuL3(CN)} fragments (Figure 3c). The structure of the Mn4Cu6 cluster is slightly different from that of the Cd4Cu6 cluster in not only the simple substitution of four Cd2+ ions of the Cd4Cu6 skelton by four Mn2+ ions but also the peripheral coordination environment (Figure S6 in the Supporting Information). The Mn4Cu6 cluster is stabilized by four L ligands, six acetyl groups, and nine coordinated water molecules, while the numbers of the corresponding ligands in Cd4Cu6 cluster are seven, seven, and four, respectively. The coordination model of hydroxyl oxygen atoms in H3L is the same as that in compound 1. In addition, all of the six acetyl 4637

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Inorganic Chemistry

Figure 3. (a) Ball and stick representation of the coordination environment of the supertetrahedral Mn4Cu6 cluster in 2. (b) Ball and polyhedral representation of the supertetrahedral Mn4Cu6 cluster in 2. (c) Ball and stick representation of the coordination environment of the monovalent Cu+ ion in 2. (d) View of the linking style of the Mn4Cu6 cluster with three neighboring {CuL3(CN)} fragments. (e) View of the linking style of the {CuL3(CN)} fragment with its three neighboring Mn4Cu6 clusters. (f) View of the 2D layer based on Mn4Cu6 clusters and {CuL3(CN)} fragments. (g) View of the linking style of two Mn4Cu6 clusters from different 2D layers. (h) View of the linking style of two {CuL3(CN)} fragments from two different 2D layers. (i) Polyhedra and stick structure of the 2D bilayer structure in 2. (j) Topology of the bilayer in 2. The Mn4Cu6 clusters are simplified as purple tetrahedra, and {CuL3(CN)} fragments are simplified as cyan tetrahedra. In (a)−(i), all hydrogen atoms attached to carbon atoms are omitted for clarity. Color codes: CuO5/CuO4, cyan; MnO6, purple. In (j), the Mn4Cu6 clusters are simplified as purple tetrahedra.

Cu+ ions may be formed through in situ reduction of divalent Cu2+ ions by organic species.20 Worthy of mention is the further assembly of Mn4Cu6 clusters with {CuL3(CN)} fragments. As shown in Figure 3d,e, each Mn4Cu6 cluster is connected to three {CuL3(CN)} fragments through L ligands, while every {CuL3(CN)} fragment shares its three L ligands with three Mn4Cu6 clusters. The linking of Mn4Cu6 clusters and {CuL3(CN)} fragments gives rise to a 2D layer with hexagonal apertures of 17.118 Å (Figure 3f, measured between opposite atoms). The most striking structural characteristic of 2 is that these 2D layers can elaborately self-assemble into a 2D bilayer structure. First, two layers are stacked in parallel with mirror symmetry. Next, the two Mn4Cu6 clusters from different layers can self-interlink by sharing three acetyl groups (Figure 3g); similarly, the two {CuL3(CN)} fragments of different layers are also interconnected through sharing CN− groups (Figure 3h). In this way, two mirror-symmetrical layers aggregate into a 2D bilayer structure (Figure 3i,j). The layer shows a honeycomblike topology along the c axis, which can be regarded as a (6, 3) topology net. The Schläfli symbol of this network is (43.63). Although a good many coordination bilayer materials have been investigated,21 bilayer strucutures containing heterometallic supertetrahedral clusters have not been reported. The last structural characteristic of 2 is the stacking style of those bilayers. As shown in Figures S8−S10 in the Supporting Information, packing of the 2D bilayers in parallel along the c axis and rotating each bilayer by about 60° with respect to the previous layer led to the generation of a 3D supramolecular framework with hexagonal channels. The distance between the

groups in the Mn4Cu6 cluster employ only one kind of syn-syn η1:η1:μ2 coordination mode to link one Mn2+ ion and one Cu2+ ion or one Mn2+ ion and one symmetrically related Mn2+ ion of another Mn4Cu6 cluster, which is different from the two types of coordination modes in the Cd4Cu6 cluster. In Mn4Cu6, two crystallographically independent Mn2+ ions (Mn1, Mn2) adopt a slightly contorted octahedral geometry. Mn1 is surrounded by six O atoms of three different acetyl groups and three unique L ligands, while Mn2 is defined by three O atoms from three L ligands, two coordinated water molecules, and one O atom of an acetic group. The Mn−O bond distances fall in the range of 2.048(2)−2.300(1) Å, which are comparable with those in reported Mn-based cluster-organic frameworks.18 BVS calculations indicated that the Cu and Mn atoms in the Mn4Cu6 cluster are all in the +2 oxidation state (Table S1 in the Supporting Information), which is further supported by an XPS spectrum (Figure S7 in the Supporting Information). Until now, a great number of supertetrahedral TM clusters have been reported, such as {Co10},14a {Ni10},14b {Cu10},14c and {Rh4V6};14d however, such a Mn-Cu heterometallic supertetrahedral cluster has yet not been reported, to the best of our knowledge. The structure of the {CuL3(CN)} fragment can be considered as one tetrahedrally coordinated monovalent Cu+ ion defined by three L ligands and one CN− group created by in situ C−C bond cleavage of the CH3CN solvent.19 BVS (Table S1 in the Supporting Information) and the XPS spectrum (Figure S7 in the Supporting Information) also confirm the existence of Cu+ ions in 1. Althouth a divalent Cu2+ salt was used as the starting material, a monovalent Cu+ ion was observed in the final product, indicating that the monovalent 4638

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Inorganic Chemistry adjacent bilayers is about 4.616 Å (measured between opposite polyhedra). PXRD, TGA, and Gas Adsorption Properties. As shown in Figure S11 in the Supporting Information, the good consistency between the experimental PXRD pattern and the simulated peaks on the basis of single-crystal structural results testify to the phase purity of 1 and 2. Thermogravimetric analysis (Figure S12 in the Supporting Information) and variable-temperature PXRD measurements (Figure S11) indicate that 1 and 2 are thermally stable up to about 240 and 200 °C. PLATON calculations show that 1 and 2 have respectively 49.7% and 59.6% potential solvent-accessible void volumes. Considering the good stability and porous characteristics of the frameworks, we thus investigated the gas adsorption properties of 1 and 2 on a Micrometrics ASAP 2020 surfacearea and pore-size analyzer. As shown in Figure 4, the N2

which is not only better than that of TAF-1a (35 cm3 g−1)11a but is also comparable to that of the well-known porous material ZIF-69 (70 cm3 g−1, Langmuir surface area 1070 m2 g−1) under similar conditions.22 For 2, the CO2 uptake capacities reached 48.90 cm3 g−1 at 273 K and 760 mmHg, which is smaller than that of 1. The H2 uptake capacities of 1 and 2 reached 124.0 and 108.16 cm3 g−1, respectively, at 77 K and 760 mmHg. Powder X-ray diffraction further confirms that the frameworks still retain their crystallinity after gas adsorption measurements (Figure S11). Magnetic Properties. The magnetic susceptibilities of 1 and 2 were measured at 2−300 K under a constant magnetic field of 1 kOe. The experimental χmT values (χm is the molar magnetic susceptibility and T is the temperature) of 1 and 2 at 300 K are 1.35 and 15.62 cm3 K mol−l (Figure 5), respectively,

Figure 4. Gas-sorption isotherms of 1 (top) and 2 (bottom).

Figure 5. Temperature dependence of χmT and 1/χmT for 1 (top) and 2 (bottom).

adsorption studies revealed that both 1 and 2 exhibit reversible type I isotherms, which testify to the retention of microporosity with saturated uptakes of 217.88 and 211.23 cm3 g−1 at 77 K for 1 and 2, respectively. As typical microporous materials, the Brunauer−Emmett−Teller (BET) and Langmuir surface areas and micropore volumes are 860.4 and 951.2 m2 g−1 and 0.337 cm3 g−1 for 1 and 768.7 and 894.2 m2 g−1 and 0.327 cm3 g−1 for 2. Furthermore, a density functional theory (DFT) model analysis reveals that 2 exhibits a narrow pore distribution of the micropores with a diameter of about 7.33 Å (Figure S13 in the Supporting Information). The pore distribution analyzed by a density functional theory (DFT) model suggests a narrow distribution of the micorpores with a diameter of about 7.33 Å (Figure S13). The CO2 and H2 uptake capacities of 1 and 2 were further investigated. 1 exhibits a significant uptake capacity for CO2 of 75.36 cm3 g−1 at 273 K and 760 mmHg,

being smaller than the theoretical value (2.25 cm3 K mol−1 for 1 and 19.75 for 2 cm3 K mol−1) expected for six Cu2+ ions (g = 2, S = 1/2) in 1 and six Cu2+ ions (g = 2, S = 1/2) and four Mn2+ ions (g = 2, S = 5/2) in 2. As the temperature is decreased, the χmT value of 1 shows a sustained decline to the minimum value of 0.06 cm3 K mol−1 at 2 K. For 2, the χmT value drops smoothly to 12.56 cm3 K mol−1 at 52 K, then decreases sharply to reach 6.12 cm3 K mol−1 at 2 K. The above behaviors suggest the existence of dominant antiferromagnetic coupling within the cluster in 1 and 2. Additionally, the temperature dependence of the reciprocal susceptibility (1/χm) obeys the Curie−Weiss law above 50 K for 1 and 2 K for 2, respectively. The Weiss constants for 1 and 2 are −153.10 and −18.55 K, respectively, which further support the existence of antiferromagnetic coupling between the metal ions within the 4639

DOI: 10.1021/acs.inorgchem.7b00267 Inorg. Chem. 2017, 56, 4635−4642


Inorganic Chemistry cluster. The Curie constants C = 2.05 and 16.35 cm3 K mol−1 for 1 and 2, respectively, are also reasonable for six Cu2+ ions in 1 and six Cu2+ ions and four Mn2+ ions in 2 per formula unit.

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CONCLUSIONS In conclusion, two unprecedented cluster organic frameworks based on heterometallic supertetrahedral cluster SBUs, {Cd4Cu6} and {Mn4Cu6}, have been successfully constructed under solvothermal conditions. 1 and 2 show an integration of magnetic properties and adsorption properties from both the heterometallic cluster SBUs and the framework in a porous structure. In addition, the CO2 uptake capacity of 1 is superior to that of the analogous framework TFA-1a based on monometallic cluster SBUs, indicating that the search for heterometallic clusters as SBUs is a promising method in the exploration of functional materials with desired properties. Finally, this work also confirms the possibility of building a large class of functional materials by using a variety of heterometallic clusters such as 3d−4f clusters, 4d−4f clusters, and TM-substituted POM clusters8 as SBUs.


S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00267. Bond valence sum calculations for 1 and 2, additional structural figures, PXRD patterns, XPS spectrum, and TGA curves for complexes 1 and 2 (PDF) Crystallographic data (CIF) Crystallographic data (CIF)


Corresponding Authors

*E-mail for X.-X.L.: [email protected]. *E-mail for S.-T.Z.: [email protected]. ORCID

Xin-Xiong Li: 0000-0002-9903-2699 Shou-Tian Zheng: 0000-0002-3365-9747 Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundations of China (No. 21371033, 21671040, and 21401195), the Natural Science Foundation For Young Scholars of Fujian Province (No. 2015J05041), and Projects from State Key Laboratory of Structural Chemistry of China (Nos. 20150001 and 20160020).


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