End-End Connection Pattern of Trinuclear-Triangular Copper Cluster

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End-End Connection Pattern of Trinuclear-triangular Copper Cluster for Construction of Two Novel Metal-Organic Frameworks: Syntheses, Structures, Magnetic and Gas Adsorption Properties Mingli Deng, Pan Yang, Xiaofeng Liu, Bing Xia, Zhenxia Chen, Yun Ling, Lin-Hong Weng, Yaming Zhou, and Jinyu Sun Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00018 • Publication Date (Web): 02 Feb 2015 Downloaded from http://pubs.acs.org on February 9, 2015

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Crystal Growth & Design

End-End Connection Pattern of Trinuclear-triangular Copper Cluster for Construction of Two MetalOrganic Frameworks: Syntheses, Structures, Magnetic and Gas Adsorption Properties Mingli Deng,a Pan Yang,b Xiaofeng Liu,a Bing Xia,a Zhenxia Chen,a Yun Ling, a,* Linhong Weng, a

Yaming Zhou,a Jinyu Sun b

a

Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of

Chemistry, Fudan University, Shanghai, 200433, China. b

Department of Chemistry, Liaoning University, Shenyang, 110036, China.

ABSTRACT: Two metal-organic frameworks containing geometrically spin frustrated trinuclear-triangular copper cluster ([Cu3O]) have been successfully isolated, which are {[Cu4.5(µ3-OH)(dmtrz)3(mbdc)2.5(H2O)2(CH3OH)(DMF)]·DMF·5H2O}n

(MAC-8),

{[Cu5(µ3-

OH)(dmtrz)3(bdc)3(H2O)4]·3H2O}n (MAC-9, Hdmtrz = 3,5-dimethyl-1H,1,2,4-triazole, H2mbdc = 1,3-benzenedicarboxylic acid, H2bdc = 1,4-benzenedicarboxylic acid, DMF = N',Ndimethylformamide). Magnetic and gas adsorption studies revealed the successful combination of strong antiferromagnetic properties (Jav = −106.6 and −113.7 cm-1 for [Cu3O] in MAC-8 and

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MAC-9 respectively) and high surface areas (1058 m2/g for MAC-8 and 1242 m2/g for MAC-9) in both of the structures. Further structural studies revealed that the high surface areas could be ascribed to the unique two-dimensional hexagonal pattern of [Cu3(O)] cluster, in which the [Cu3(O)] cluster is connected to each other in an end-end fashion via mononuclear copper ions/paddle-wheel

units.


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INTRODUCTION Metal-organic frameworks (MOFs, also called Porous Coordination Polymers, PCPs) have shown unique advantages in both structures and functionalities,1-11 and have been actively explored as potential candidates for multifunctional materials,12-17 especially in designed crystal materials which could combine in the same structure a set of well-defined physical properties (such as optics, electrical conductivity, magnetism) together with porosity.18-24 Among the multifunctionalities, the combination of magnetism and porosity have received considerable interest due to their promising applications in chemical switches, memories, and magnetic sensors.25-30

However, the combination of porosity and magnetic properties into a single

crystalline material still remains great challenges since magnetic spin superexchange generally requires relatively short bridges, whereas porosity usually depends on the use of relatively long linkers.31-38 Up to now, general strategies have been proposed for the synthesis of magnetic MOFs: (i) using a stable organic radical ligand to link the adjacent metal centers to build porous skeleton;39 (ii) using secondary building units (SBUs) (possessing magnetic coupling) to topologically expend into porous structures by organic linkers.40-44 The latter is regarded to be an efficient way, not only because of the variety of SBUs, but also because of the relatively stable unit with desired directionality and specific geometric shape.45-46 Beside this, the characteristic of SBUs also play crucial roles in affecting the magnetic coupling. Taking the triangular-trinuclear copper SBU ([Cu3O]) (Scheme 1) for an example, three spins locate on the corners of a triangle with antiferromagnetic interactions between them.47 Once the first two spins align anti-parallel, the third one is frustrated because there is two possible orientations (up and down) that give the same energy. This kind of geometrically spin-frustrated system offers a magnetic exchange model for


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the investigation of interesting magnetic ground states.48-58

Owing to the possible spin

perturbation state, the magnetic MOFs could be prospected, in which the magnetic property might contribute to the porous structures to guarantee its response to the external stimulus. Therefore, great efforts have been paid to the construction of their porous structures.55,59-66 However, low dimensional or interpenetrated structures are commonly observed, structures with large pore volume and high surface areas are rarely known up to now.55,60,63 We have previously reported a serious of porous MOFs constructed from triazolate and dicarboxylate ligands,67-72 in which metal-triazolate units (such as dinuclear/trinuclear SBUs) are further bridged by long carboxylate ligands. Encouraged by our previous work and taking the above mentioned issues in consideration, in this paper, solvothermal reactions of copper(II) ions with 3,5-dimethyl-1H,1,2,4-triazole (Hdmtrz) and 1,3-Benzenedicarboxylic acid (H2mbdc)/1,4Benzenedicarboxylic acid (H2bdc) ligands were carried out, and two novel three-dimensional (3D)

magnetic

porous

MOFs

were

isolated,

which

are

{[Cu4.5(µ3-OH)(dmtrz)3(m-

bdc)2.5(H2O)2(CH3OH)(DMF)]·DMF·5H2O}n (MAC-8, DMF = N',N-dimethylformamide), {[Cu5(µ3-OH)(dmtrz)3(bdc)3(H2O)4]·3H2O}n (MAC-9). Single-crystal X-ray diffraction studies revealed the combination of porosity and [Cu3O] SBUs in both MAC-8 and MAC-9. The strong antiferromagnetic exchange coupling (Jav = −106.6 and −113.7 cm-1 for [Cu3O] in MAC-8 and MAC-9 respectively) was confirmed. The accessible porosity was identified by N2 sorption showing a high surface area of ca. 1058 and 1242 m2/g for MAC-8 and MAC-9 respectively. Furthermore, structural analyses revealed that the large pore volumes and high surface areas could be related to the unique end-end connection pattern of [Cu3O] domain compared with previously observed end-on connection pattern. EXPERIMENTAL SECTION


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Materials and General measurements. All of the reagents were obtained from commercial sources and used without further purification, except for the 3,5-dimethyl-1H,1,2,4-triazole (Hdmtrz), which was synthesized according to literature reports.73-76 The FT-IR spectra (KBr pellets) were recorded on a Nicolet 470 FT-IR spectrometer in the range of with KBr pellets. C, H, and N elemental analyses were determined on an Elementar Vario EL III elemental analyzer. Thermal stability studies were carried out on a Mettler Tolepo TGA/SDTA 851 thermoanalyzer under N2 flow in the range of 30-800 °C at a heating rate of 10 K·min-1. Powder X-ray diffraction data were recorded on a Bruker D8 Advance diffractometer 40 kV, 40mA with CuKα radiation (λ = 1.5406 Å) and a scan speed of 0.02 °·min-1. N2 sorption at 77 K was measured on an ASAP 2020 gas adsorption apparatus (Micromeritics). CO2 adsorption at 298 and 288 K was carried out on IGA-001 (Hiden). Before gas adsorption, the as-made sample (about 100 mg) was degassed at 50 °C for 8 h. Magnetic measurement was carried out on a MPMS (SQUID) VSM magnetometer. The variabletemperature magnetic susceptibility was measured with an external magnetic field. The magnetization isotherm was collected at 2 and 10 K between 0 and 5 T, respectively. Pascal’s constants were used to estimate the diamagnetic corrections, which were subtracted from the experimental susceptibilities to give the molar paramagnetic susceptibilities. Synthesis

of

{[Cu4.5(µ3-OH)(dmtrz)3(m-bdc)2.5(H2O)2(CH3OH)(DMF)]·DMF·5H2O}n

(MAC-8). Cu(NO3)2·3H2O (0.073 g, 0.3 mmol), H2mbdc (0.033 g, 0.2 mmol) and Hdmtrz (0.020 g, 0.2 mmol) was added to the mixed solvent of DMF, methanol and H2O in a volume ratio of 1:1:1 (9 mL). The mixture was stirred at room temperature for 10 minutes and then the clear blue solution was introduced into a Teflon-lined stainless steel vessel (15 mL), which was sealed and heated at 60 °C for 3 days. After cooling down to room temperature, blue block


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crystal solids of MAC-8 were isolated and obtained by filtration. The products were washed by the mixed solution of DMF, methanol and H2O (in a volume ratio of 1:1:1, 9 mL) for three times. Yields: 45% based on Cu(II). Anal. Calcd. for C39H61Cu4.5N11O21: C, 35.87; H, 4.71; N, 11.80. Found: C, 36.01; H, 4.68; N, 11.89. IR (KBr pellets, λ/cm-1): 3428 (m), 2964 (m), 1609 (s), 1561 (s), 1479 (w), 1383 (s), 1262 (s), 1098 (m), 1024 (m), 803 (m), 721 (w), 660 (w), 625 (w). Synthesis of {[Cu5(µ3-OH)(dmtrz)3(bdc)3(H2O)4]·3H2O}n (MAC-9). Cu(NO3)6·3H2O (0.3 mmol, 0.074g) was dissolved in 2 mL DMF and then was added to the mixture of Hdmtrz (0.2mmol, 0.021g) and H2bdc (0.2 mmol, 0.032 g) in 2 mL DMF. The solution was supersonic for 10 min, resulting a clear blue solution. The blue clear solution was then transferred into Teflon-lined stainless steel vessel (15 mL), which was sealed and heated at 50 °C for 2 days. After cooling down to temperature, clear blue solution was obtained by filtration. Then, blue crystals of MAC-9 were finally obtained by slow evaporation of the blue solution at room temperature. Yields: 32 % yield based on Cu(II). Anal. Calcd. for C36H45Cu5N9O20: C, 34.83; H, 3.65; N, 10.15. Found: C, 35.01; H, 3.59; N, 10.25. IR (KBr pellets, λ/cm-1): 3418 (m), 2964 (w), 1567 (s), 1531 (w), 1504 (w), 1384 (s), 1149 (w), 1104 (w), 1016 (w), 882 (w), 829 (w), 748 (m), 515 (w) X-ray Crystallography. The crystal data of MAC-8 and MAC-9 were collected on a Bruker Apex Duo diffractometer with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) at 173 K. Data reduction was performed with SAINT, and absorption corrections were applied by the SADABS program.77 The structures were solved by direct methods using the SHELXS program78 and refined with the SHELXL program79-80 and final refined by full-matrix leastsquares methods with anisotropic thermal parameters for all non-hydrogen atoms on F2. Heavy atoms and other non-hydrogen atoms were directly obtained from a difference Fourier map.


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Hydrogen atoms attached to carbon were placed in geometrically idealized positions and refined using a riding model. Hydrogen atoms of lattice water were not added in MAC-8 because of serious atomic disorder. In the case of MAC-9, they were directly located from the difference Fourier maps and then refined as rigid modes. Crystallographic data as well as details of structural refinements for MAC-8 and MAC-9 are summarized in Table 1, and selected bond lengths and angles are given in Table S1 and S2. RESULTS AND DISCUSSION Synthesis The coordination compounds containing [Cu3O] SBUs, which were connected by azolate ligands and centered with oxygen atom or hydroxyl group, were previously synthesized in water reaction systems by slow solvent diffusion, evaporation48,51,53,59,62,63 or hydrothermal method.52,57,65,66 To introduce the [Cu3O] SBUs into MOFs, we have tried those classic synthetic condition in the presence of H2bdc or H2mbdc. However, only light blue powder products showing unidentifiable solid phases were isolated. Then, solvothermal synthesis in the presence of N,N′-dimethylformamide (DMF) was adopted. Although the target crystal samples could be isolated as described in the experimental section, it is instructive to note that some red powder products could be obtained if the solvothermal temperature is higher than 120 °C, which might be ascribed to the products of the redox reaction of Cu2+ to Cu2O in the presence of DMF.81 In addition, for the synthesis of MAC-9, when the temperature is higher than 60 °C, some of light blue cubic crystals can be isolated, which is formula as [Cu(bdc)(Hdmtrz)]n (Figure S1), in which the paddle-wheel SBUs of [Cu2(COO)4] are linked by bdc ligands forming a (4,4)-layer structure, and then Hdmtrz ligands link the neighboring layers in the coordination model of imidazole through the sites of paddle-wheel SBUs, generating the pcu net with 1D channels. The


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structure is similar to that of pillar-layered [Cu(bdc-OH)(dabco)0.5]n.82 So, the filtration and slow evaporation of the filtrate at room temperature is an important procedure for the isolation of MAC-9. Structural Description {[Cu4.5(µ3-OH)(dmtrz)3(m-bdc)2.5(H2O)2(CH3OH)(DMF)]·DMF·5H2O}n (MAC-8). MAC8 (Figure 1) crystallizes in trigonal system, P3221 chiral space group. The asymmetric unit contains one trinuclear triangular [Cu3(µ3-OH)(dmtrz)3(H2O)2(CH3OH)2(DMF)2]2+ SBU ([Cu3(µ3-OH)(dmtrz)3], Figure 2a), one and a half Cu(II) ions (Cu4 and Cu5), two and a half mbdc ligands. In the SBU, Cu1, Cu2, Cu3 are all located in distorted five-coordinated square pyramidal geometries with the distortion parameter τ = 0.27, 0.28 and 0.311 respectively. In [Cu3(µ3-OH)(dmtrz)3], the Cu−N and Cu−O bond distances are in the normal range with the average dCu−N and dCu−O of ~1.98 and 2.08 Å respectively (Table S1 for detailed bond distances). These three copper ions form a [Cu3] triangle, and the Cu1···Cu2, Cu2···Cu3, Cu1···Cu3 distance is measured to be ~3.38, 3.27, 3.21 Å, respectively (Figure 2b). The centered O(1) is located above the [Cu3] plane in a distance of ca. 0.65 Å (Figure 2b), indicating that it is a hydroxyl group.65,67 The [Cu3(µ3-OH)(dmtrz)3] SBU is then connected to Cu4 and Cu5 via 4N site of dmtrz ligand, extending into a 2D honeycomb layer in which each hexagonal structure has a six-member of [Cu3(µ3-OH)(dmtrz)3] SBUs (Figure 2c). The diameter of this hexagonal structure is measured to be ~22.5 Å. Then, each honeycomb layer is further linked by m-bdc ligands in [ABCA] packing style, resulting into a 3D porous structure within intersection channels (Figure 2d, e, Figure S2). The open window size of the channel is measured to be ~14 Å and the narrow pore size is about 8 Å (taking van der Waals radii in to consideration), and the solvent-accessible volume is estimated to be ca. 60 % after theoretical removal of the guest


8

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molecules (Calculated by Connolly method with the probe atom radii settled to be 1.4 Å). Furthermore, topological analysis indicates that MAC-8 can be described as a novel (4,4,5) net with a short (Schläfli) vertex symbol of (44.62)·(42.52.6.7)·(44.55.62) after considering the mononuclear Cu4 and Cu5 as planar 4-connected node, respectively and [Cu3(µ3-OH)(dmtrz)3] SBU as a 5-connected node (Figure S3). {[Cu5(µ3-OH)(dmtrz)3(bdc)3(H2O)4]·3H2O}n (MAC-9). MAC-9 (Figure 3) crystallizes in monoclinic system, C2/m space group. The structural motif contains a trinuclear triangular [Cu3(µ3-OH)(dmtrz)3(H2O)4]2+ SBU ([Cu3(µ3-OH)(dmtrz)3], Figure 4a), a paddle-wheel unit, mononuclear Cu(II) ion (Cu4) and bdc ligands. Similar as that of MAC-8, the three copper ions (Cu1, Cu2, Cu2A) in the [Cu3(µ3-OH)(dmtrz)3] SBU are also located in distorted fivecoordinated square pyramidal geometries with distortion parameter τ = 0.182 and 0.164, respectively. The average dCu−N and dCu−O is calculated to be ~1.94 and 2.12 Å, respectively (Table S2 for detailed bond distances). The three copper ions form an isosceles triangle with the length of the bottom side ~3.34 Å (Cu1···Cu2), and the length of two equal sides 3.203 Å (Cu2···Cu2A). Similar to MAC-8, the centered O(1) is a hydroxyl group with a distance of ca. 0.65 Å (Figure 4b). The [Cu3(µ3-OH)(dmtrz)3] SBU is then connected to the mononuclear copper ion (Cu4) via 4N site of dmtrz ligand (N3), generating a zig-zag chain along b axis (Figure 4c). This 1D chain is further connected to each other via paddle-wheel SBUs, generating a 2D honeycomb layer in the plane of [1 0 1], in which the hexagonal structure has a 6-member of [Cu3(µ3-OH)(dmtrz)3] SBUs and 2-member of paddle-wheel SBUs. The diameter is measured to be ~26.8 × 18.6 Å. Then, bdc ligands connect the neighboring 2D honeycomb layers in [ABA] packing style (Figure 4d), resulting into a 3D porous structure within intersection channels (Figure 4e and Figure S4). The open windows size is measured to be ~5.2 × 13.6 Å and ~3.3 ×


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5.6 Å along c and b axis respectively (taking van der Waals radii in to consideration,), and the solvent-accessible volume is estimated to be ca. 65 % after theoretical removal of the guest molecules (Calculated by Connolly method with the settled probe atom radii of 1.4 Å). Considering the mononuclear Cu4, [Cu3(µ3-OH)(dmtrz)3] and paddle-wheel SBU as a 4connected, 5-connected and 6-connected node respectively (Figure S5), MAC-9 can be described as a novel (4,5,6)-connected framework with a short (Schläfli) vertex symbol of (44.62)·(46.64.85)·(45.65). Powder X-ray Diffraction (PXRD) and Thermogravimetric Analysis (TGA). The bulk pure crystal phases of MAC-8 and MAC-9 were evidenced by the experimental PXRD patterns, which match well with the simulated one from CIF file respectively (Figure S6). Notably, the slight differences in intensities for experimental and theoretical powder diffraction data were probably due to the crystallographically preferred orientation in lattice strain. Thermal stability analysis (Figure S7) reveal that there is about 19.8 % weight loss from room temperature to ca. 126 °C for the as-made MAC-8 sample, which could be ascribed to the release of guest molecules. Then, a weight plateau is observed until to ca. 265 °C, after that a huge weight loss is followed, indicating the decomposition of the entire framework. The thermal behavior of asmade MAC-9 is similar to that of MAC-8. A weight loss of 20.9 % from room temperature to ca. 145 °C is observed and then the framework remains weight stable till to ca. 280 °C. After that, a huge weight loss is observed, suggesting the decomposition of its framework. Magnetic Properties Previously studies on the magnetostructural correlation of [Cu3O] trimers suggest that bond lengths and angles are the relevant structural parameters in affecting the magnetic coupling51,56


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(Scheme 2, Table 2). When the bond distances of dCu-O and dCu-N are in the normal range, the angle of Cu−O−Cu plays the significant role.83 In general, when the angle is higher than 101.3°,51 the magnetic property will vary from ferromagnetic to antiferromagnetic coupling. As summarized by Ferrer et.al.,51 the magnetic exchange parameter Jav can be estimated by the empirical formula Jav = −13.65θav + 1385, where the θav is the average of Cu−O−Cu angles in [Cu3O]. Using the empirical formula, it gives the exchange parameter Jav of −106.6 and −113.7 cm−1 for the [Cu3(µ3-OH)(dmtrz)3] cluster in MAC-8 and MAC-9 respectively. It is necessary to note the Jav values here, which is slightly smaller than those observed in previous compounds, but higher than that of [Cu3(µ3-OH)3(L5)3(DMF)4] (Table 2). This could be explained by the parameter of dO-[Cu3O]. Given a [Cu3O] cluster, the longer of the distance of the centered O to the [Cu3] plane is, the longer of the Cu-O bond distances and the smaller of the Cu-O-Cu angles will be, where both of the dependent variables could significantly decrease the strength of antiferromagnetic coupling. Magnetic susceptibility data obtained for the as-synthesized MAC-8, 9 follows the typically behaviors previously predicted by antiferromagnetic coupling in the [Cu3O] trimer. The temperature dependent magnetic susceptibilities per molecule for MAC-8, 9 are shown in Figure 5. At room temperature, the values of χMT are of 1.11 and 1.12 cm3·mol−1·K, which are much lower than the expected for non-interacting S = 1/2 spins (∼1.69 and 1.88 cm3·mol−1·K) for MAC-8 and MAC-9, respectively. The χMT decreases continuously when samples are cooled, and reaches 0.18 cm3·mol−1·K at 2 K for MAC-8. While for MAC-9, the χMT reaches a minim data of 0.35 cm3·mol−1·K at 15 K, then increase to 0.45 cm3·mol−1·K at 5 K before further decreasing to 0.34 cm3·mol−1·K at 2 K. The temperature dependence of 1/χm is then fitted by Curie−Weiss function (Figure S8a, 9a), giving C = 1.3 cm3·mol−1·K, θ = − 56 K for MAC-8 in


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the temperature range of 300 – 50 K, while C = 1.7 cm3·mol−1·K and θ = − 168 K for MAC-9 in the temperature range of 300 – 90 K. The negative θ values indicates antiferromagnetic interactions between Cu(II) centers. Magnetization data over the field range of 0 – 5 T at 2 and 10 K along with the Brillouin function for the ST = 1/2 system with g = 2 are shown in Figure S10b and 11b. The discrepancy between the Brillouin curve and the data indicates the strong antiferromagnetic coupling might be mediated between Cu(II) centers. Due to the fact that there is lack of proper magnetostructural models, direct deduction of the exchange J parameters for MAC-8 and MAC-9 has failed. It should be mentioned that reasonable fits to the magnetic parameters of the [Cu3O] cluster are reported only in a limited number of simple trinuclear-triangular structures.48,51,52,56 This could be ascribed to the strong antisymmetric interaction (G), which is comparable to the isotropic exchange parameter J in the case of [Cu3O] core as well as its lability.52 Here, for MAC-8 and MAC-9, the [Cu3(µ3OH)(dmtrz)3] cluster is expected to govern the magnetic coupling in MAC-8, and together with paddle-wheel unit (antiferromagnetic coupling) in MAC-9 due to that the distance of Cu···Cu bridged by µ1,4-triazoalte is around 6.0 Å which is insufficient for the intercluster spin transfer. In addition, it is interesting to note the inflection of χmT versus T at low-temperature stage for MAC-9. We assume that the stoichiometry and connecting mode of the paramagnetic mono-, antiferromagnetic dimer and frustrated trinuclear motifs in the 2D lattice would lead to an uncompensated spin moment, which might cause a rise at low temperature. Gas Adsorption The porous structures of MAC-8 and MAC-9 were then assessed by the N2 sorption at 77 K (Figure 6). It shows a typical-I sorption isotherm on activated MAC-8 and MAC-9, and the Brunauer−Emmett−Teller (BET) surface area is ca. 1058 and 1242 m2/g respectively.


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Considering the density of these two materials, it gives the surface area of 1118.4 and 1395.5 m2/mL, which are greatly higher than the reported ones (Table 3). As shown in Figure 6 insert, the pore size distribution is around 15, 11 and 8.1 Å for MAC-8, and 8, 5.8 Å for MAC-9 (Horvath−Kawazoe analysis), which is very close to the theoretically measured one from its structure data (Figure S2, S4). The pore volume (using the t-Plot method) is calculated to be ∼0.42 and 0.46 cm3·g−1 for MAC-8 and MAC-9 respectively. The CO2 sorption studies show that MAC-8 and MAC-9 has the capacity of 35.8 and 37.9 mg/g at 298 K, 1000 mbar (Figure 6). The isosteric heat Qst is calculated to be ca. 25 and 23 kJ/mol for MAC-8 and MAC-9 respectively (Figure S10), which is slightly higher than the liquefaction enthalpy of CO2 (17 kJ/mol), but lower than those of most MOFs with exposed active sites,38,84-91 indicating the weak interaction of the surface to CO2. In order to better understand the porous properties, we compared the data with previously reported structures (Table 3). Since the pore volume data were not found in previous literatures, theoretically calculated data was adopted based the Connolly method with the probe radius settled to be of 1.4 Å (Table S3). It could be found that MAC-8 and MAC-9 has lower density and large pore volume as well as high BET surface areas compared with previous reported structures. In terms of structures, {[Cu3(µ3-O)(µ2-OH)(L1)2]3(µ3-Cl)2(µ3-L4)}·8.5H2O [Cu3(µ3-OH)(µ2-O)(dmtrz)2(HCOO)(µ2-H2O)(H2O)3]·H2O variant

[Cu3O]

units

(Scheme

OH)(L2)3(DMF)4]·5DMF·3MeOH,55 NH4[Cu3(µ3-OH)(L3)3]

63

1d).

67

92

and

are the two examples built of the

[Cu3(µ3-O)(L1)3]2(OH)2·15H2O,57,65,66

[Cu3(µ3-OH)(L3)3(H3O)]·2C2H5OH·4H2O,60

[Cu3(µ3and

are the iso-reticular framework built of the prototypical [Cu3O] SBUs

(Scheme 1b). From the viewpoint of connection patterns, these structures are formed by propagating the [Cu3O] SBU itself in a manner of end-on mode, resulting into a dendrimer-like


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pattern (Figure 8a,b). However, here in MAC-8 and MAC-9, the discrete [Cu3O] SBUs are linked together via mononuclear copper ions or paddle-wheel units in a manner of end-end mode (Figure 8c), forming a 2D hexagonal pattern with large open window size. When these neighboring 2D layers are loosely connected together by long pillars, it will leads to the formation of porous structures with large open pore sizes, pore volumes and high BET surface areas. CONCLUSION In this paper, we have successfully synthesized two MOFs (MAC-8 and MAC-9) containing geometrically spin frustrated trinuclear-triangular copper clusters ([Cu3(µ3-OH)(dmtrz)3]). The magneto-structural studies revealed that [Cu3(µ3-OH)(dmtrz)3] clusters are expected to govern the strong antiferromagnetic coupling in MAC-8 and together with paddle-wheel units in MAC-9. Structural analyses and gas adsorption revealed their lower density and large pore volumes, and high surface areas (BET) for MAC-8 and MAC-9. The large pore volume and high surface areas of MAC-8 and MAC-9 could be ascribed to the unique end-end connection fashion of [Cu3(µ3OH)(dmtrz)3] SBUs. It could be expected that the incorporation of specific SBUs (functional domains) into the tunable crystalline porous materials will lead to the discovery of novel MOFs with not only fascinating frameworks but also promising multifunctionalities. ASSOCIATED CONTENT Supporting Information. CIF file, tables and figures. These materials are available free of charge via the Internet at http://pubs.acs.org AUTHOR INFORMATION Corresponding Author


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* E-mail: [email protected] (Prof. Dr. Ling, Y.) Notes The authors declare no competing financial interests. Funding Sources We gratefully acknowledge the financial support from NSFC (Nos. 21201039, 21203032 and 21471035), the Shanghai Leading Academic Discipline Project (B108), and the Program for Changjiang Scholars and Innovative Research Team in University (IRT1117). REFERENCES (1)Stock, N.; Biswas, S. Chem. Rev. 2012, 112, 933-969; (2) O'Keeffe, M.; Yaghi, O. M. Chem. Rev. 2012, 112, 675-702; (3) Li, J.R.; Sculley, J.; Zhou, H.C. Chem. Rev. 2012, 112, 869-932; (4) Deng, H.; Doonan, C. J.; Furukawa, H.; Ferreira, R. B.; Towne, J.; Knobler, C. B.; Wang, B.; Yaghi, O. M. Science. 2010, 327, 846-850; (5) Chen, B. L.; Xiang, S. C.; Qian, G. D. Acc. Chem. Res. 2010, 43, 1115-1124; (6) Zhang, J. P.; Huang, X. C.; Chen, X. M. Chem. Soc. Rev. 2009, 38, 2385-2396; (7) Yaghi, O. M.; Li, Q. W. Mrs Bull. 2009, 34, 682-690; (8) Wang, Z. Q.; Cohen, S. M. Chem. Soc. Rev. 2009, 38, 1315-1329; (9) Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O'Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1257-1283; (10) Qiu, S. L.; Zhu, G. S. Coord. Chem. Rev. 2009, 253, 2891-2911; (11) Doonan, C. J.; Morris, W.; Furukawa, H.; Yaghi, O. M. J. Am. Chem. Soc. 2009, 131, 94929493. (12) Stavila, V.; Talin, A. A.; Allendorf, M. D. Chem. Soc. Rev. 2014, 43, 5994-6010; (13) Wang, C.; Liu, D.; Lin, W. J. Am. Chem.Soc.2013, 135, 13222-13234; (14) Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D. W. Chem. Rev. 2012, 112, 782-835;


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Tables and Figures Table 1. Crystal and structure refinement data for MAC-8 and MAC-9 MAC-8 MAC-9 Empirical formula C39H61Cu4.5N11O21 C36H45Cu5N9O20 Formula weight 1305.91 1241.51 Temperature (K) 173(2) 173(2) Wavelength (Å) 0.71073 0.71073 Crystal system Trigonal Monoclinic Space group P3221 C2/m a (Å) 22.741(2) 27.313(18) b (Å) 22.741(2) 22.017(14) c (Å) 30.380(3) 15.836(11) α (°) 90 90 β (°) 90 103.218(10) γ (°) 120 90 13606(2) 9271(11) V (Å3) Z 6 4 0.946 0.890 Dc (g cm-3) µ (mm-1) 1.089 1.172 F(000) 3939 2516 Total collected 85202 16373 Unique data, Rint 16284, 0.134 6942, 0.116 Observed data (I > 2σ(I)] 12583 2631 1.09 1.01 GOF on F2 R1a. wR2b 0.1025, 0.3073 0.0841, 0.2941 Flack parameter 0.488(9) Min./max. resd. dens. (e/Å3) -1.18, 1.23 -0.45, 1.01 CCDC 1041798 1041738 a b

= ∑ || | − | ||/ ∑ | |; w = [∑ ( − ) / ∑ ( ) ]/ .


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Table 2. A summary of some magnetostructural data together with exchange coupling J parameter based on the [Cu3O] given in Scheme 1. Structural Parameters b Compd.a

[Cu3O]

-J (cm-1)

dO-[Cu3O]

dCu-N

dCu-O

θav

(Å)

(Å)

(Å)

(°)

Ref.

Empiricalc

Fitted

1

Scheme 1b 0

1.99

1.98

120

112.5/395.5 255.0

65,66

2

Scheme 1c 0.4

1.94

1.99

114.2

177.3d

175.8

51

114.5

d

179.9

51

3

Scheme 1c 0.4

1.93

4

Scheme 1c 0.89

2.078 1.995 103.25 27.5

26.4

55

5

Scheme 1c 0.45

1.955 2.000 115.15 184.2d

188.8

52

6

Scheme 1d 0.53

2.051 1.94

113.09 140.8d

160.7

52

7

Scheme 1d 0.79

1.96

1.98

103.27 N.A.

26.63

67

MAC-8

Scheme 1c 0.65

1.98

2.018 109.13 N.A.

106.6

here

MAC-9

Scheme 1c 0.65

1.994 1.945 109.65 N.A.

113.7

here

a

2.02

178.0

1 = {[Cu3(µ3-O)(L1)3](OH)}n; 2 = [Cu3(µ3-OH)(L2)(L3)2(ClO4)2(H2O)3](ClO4)2·2H2O; 3 =

[Cu3(µ3-OH)(L4)3(H2O)3](ClO4)2·3H2O; OH)(H2O)3(L5)3(SO4)];

6

=

4

=

[Cu3(OH)3(L5)3(DMF)4];

[Cu3(µ3-OH)2(H2O)3(L6)2(SO4)];

7

=

5

=

[Cu3(µ3-

[Cu3(µ3-OH)(µ2-

O)(dmtrz)2(HCOO)(µ2-H2O)(H2O)3]·H2O (L1 = 1,2,4-triazolate; L2 = 3,5-diacetylamino-1,2,4triazolate; L3 = 3,5-diamino-1,2,4-triazole; L4= 3-acetylamino-5-amino-1,2,4-triazolate; L5 = 4pyridyltetrazolate; L5 = 2-hydroxy-3-Hpyridyltetrazolate; L6 = 3-pyridyltetrazolate); . b

the magnetostructural parameters from scheme 2.

c

the calculated Jav parameter by the magnetostructure empirical formula of Jav = − 13.65θav +

1383. d

the fitted J parameter is a mean value by J = (J12+J13+J23)/3.


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Table 3. A summary of 3D porous structures built of [Cu3O] unit.

Compd.

a

[Cu3O]

Pattern

Pore Structure

Size (Å)

Porosity b (%)

Pore Volume c (cm3/g)

Surface Area m2/g

m2/mL

Ref.

1

1b

end-on

Cage

12.0/3.5

37

0.19

160d

81.8

93

2

1c

end-on

Cage

18.0/9.5

68

0.40

1243

763.5

55

3

1c

end-on

Cage

13/3

47

0.45

121

86.9

60

4

1c

end-on

Cage

13/8/4.5

49

0.32

680

503.3

63

d

79.9

67

5

1d

end-on

Channel

6.9

46

0.38

105

6

1d

end-on

Channel

5.5

17

0.09

N.A.

N.A.

92

MAC-8

1c

endend

Channel

15/11/8.1

61

0.64

1058

1118.4

here

MAC-9

1c

endend

Channel

8/5.8

65

0.73

1242

1395.5

here

a

1 = {[Cu3(µ3-O)(L1)3]·(OH)}n; 2 = [Cu3(µ3-OH)3(L2)3(DMF)4]; 3 = [Cu3(OH)3(L3)3(H3O)]; 4 = NH4[Cu3(µ3-OH)(L3)3]; 5 = [Cu3(µ3-OH)(µ2-O)(dmtrz)2(HCOO)(µ2-H2O)(H2O)3]; 6= {[Cu3(µ3-OH)(µ2-O)(L1)2]3(µ3-Cl)2(µ3-L4)} (L1 = 1,2,4-triazolate; L2 = 4-pyridyltetrazolate; L3 = pyrazole-4-carboxylate; L4 = cyanuric acid). b

theoretically accessible pore volumes per unit cell.

c

theoretically calculated pore volume based on the crystal structure data by Connolly method with the probe atomic radius settled to be 1.4 Å (Table S3). d

the surface area is calculated based on the data of CO2 isotherm.


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Scheme 1. (a) the structural model of geometrically spin frustrated [Cu3O] model; (b)-(c) the prototype structure of trinuclear-triangle [Cu3O] cluster centered with µ3-O and µ3-OH respectively; (c) the variant trinuclear-triangle [Cu3O] cluster centered with µ3-OH but with one of vertexes replaced by oxygen atom in µ2-connection.


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Figure 1. the structure motif of MAC-8 showing in ball and stick model (the methyl groups of 3,5-dimethyl-1H,1,2,4-triazole and guest molecules and all hydrogen atoms are omitted for clarity, Symmetry codes used: A: y, -1+x, -z; B: 2-x, 1-x+y, -1/3-z; C: 1+y, x, -z; D: y, x, -z ; E: x-y, 1-y, 1/3-z; F: 1-y, x-y, -1/3+z; G: 1+x-y, 1-y, 1/3-z)


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Figure 2. (a) the trinuclear-triangular [Cu3(µ3-OH)(dmtrz)3(H2O)2(CH3OH)2(DMF)2]2+ SBU ([Cu3(µ3-OH)(dmtrz)3]); (b) the µ3-O located above [Cu3] plane with a distance of ~0.65Å; (c) the [Cu3(µ3-OH)(dmtrz)3] SBUs propagates itself infinitely via Cu4, Cu4A, Cu5 forming a 2D layer with hexagonal pattern (A: y, -1+x, -z); (d) the space filling model of MAC-8 showing the 1D channel along c axis (methyl groups and guest molecules are omitted for clarity); (e) [ABCA] packing style in MAC-8 of the 2D layer.


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Figure 3. the structure motif of MAC-9 showing in ball and stick model (the methyl groups of 3,5-dimethyl-1H,1,2,4-triazole and guest water molecules and all hydrogen atoms are omitted for clarity. Symmetry codes used: A: x, 1-y, z; B: 1.5-x, 0.5-y, 1-z; C: x, y, 1+z; D: 1.5-x, 0.5-y, 2-z; E: 2-x, y, 1-z; F: 2-x, 1-y, 1-z)


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Figure 4. (a) the trinuclear triangular [Cu3(µ3-OH)(dmtrz)3(H2O)4]2+ SBU ([Cu3(µ3OH)(dmtrz)3]) in MAC-9 (A: x, 1-y, z); (b) the µ3-O located above [Cu3] plane with a distance of 0.65 Å; (c) the [Cu3(µ3-OH)(dmtrz)3] SBUs propagates itself infinitely via Cu4, Cu4A and paddle-wheel unit forming a 2D layer with hexagonal pattern (A: x, 1-y, z; B:1.5-x, 0.5+y, 2-z ); (d) the [ABA] packing style of the 2D layer in MAC-9; (e) the space filling mode of MAC-9 showing 1D channel along c axis (methyl groups and guest molecules are omitted for clarity).


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Scheme 2. The simplified magnetic model of [Cu3O] showing the related magnetostructural parameters (d

Cu-N

and d

Cu-O:

the average bond distances of related bonds, and the θav =

(α+β+γ)/3; J12 ≠ J23 ≠ J13 and J12 = J23 ≠ J13 for the [Cu3O] in scalene (MAC-8) and isosceles (MAC-9) triangle respectively, and Jav = (J12 + J13 + J23)/3)


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Figure 5. Experimental χmT curve for MAC-8 (a) and MAC-9 (b) (χm being the magnetic susceptibility per formula. The inset displays thermal dependence of χmT at different applied fields in the low-temperature region)


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Figure 6. the N2 isotherms at 77 K for MAC-8 (a) and MAC-9 (b). The inset shows pore size distribution calculated by H-K method.


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Figure 7. The CO2 adsorption isotherms at 283 and 298 K on MAC-8 (a) and MAC-9 (b).


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Figure 8. A view of the classification of 3D structures built of variant [Cu3O] via end-on connection pattern (a), [Cu3O] SBUs via end-on connection pattern (b), and [Cu3O] via end-end connection pattern (c).


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For Table of Contents Use Only

End-End Connection Pattern of Trinuclear-triangular Copper Cluster for Construction of Two Metal-Organic Frameworks: Syntheses, Structures, Magnetic and Gas Adsorption Properties Mingli Deng,a Pan Yang,b Xiaofeng Liu,a Bing Xia,a Zhenxia Chen,a Yun Ling, a,* Linhong Weng, a

Yaming Zhou,a Jinyu Sun b

a

Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of

Chemistry, Fudan University, Shanghai, 200433, China. b

Department of Chemistry, Liaoning University, Shenyang, 110036, China.

Two porous metal-organic frameworks containing geometrically spin frustrated [Cu3O] units have been successfully synthesized, in which [Cu3(O)] unit connects each other via mononuclear copper and/or paddle-wheel unit, resulting into an unique end-end connection pattern of 2D hexagonal structure. The magnetic and gas adsorption properties have been studied.


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End-End Connection Pattern of Trinuclear-Triangular Copper Cluster

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