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Porous tetrahedral Zn(II)-tetrazolate framework with highly adsorption selectivity of CO2 over N2
Journal of Molecular Structure 1125 (2016) 777e780
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Porous tetrahedral Zn(II)-tetrazolate framework with highly adsorption selectivity of CO2 over N2 Wu-wu Li a, b, c, Ying Guo b, Zun-ting Zhang a, b, * a
Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, Shaanxi Normal University, Xi’an 710062, China b National Engineering Laboratory for Resource Development of Endangered Crude Drugs in Northwest of China and School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, China c College of Chemistry & Chemical Engineering, Xianyang Normal University, Xianyang, 712000, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 May 2016 Received in revised form 13 July 2016 Accepted 13 July 2016 Available online 15 July 2016
Presented here is a new porous tetrahedral Zn(II)-tetrazolate framework, namely [Zn2(mtz)3 (OH)]n$n(DMF) (1, Hmtz ¼ 5-methyl-1H-tetrazole, DMF ¼ N,N’-dimethylformamide), has been successfully synthesized under solvothermal conditions. Single crystal X-ray structural analysis reveals that compound 1 features a three-dimensional (3D) porous framework with 4-connected dia-type topology. The 1D channels along the crystallograhical c axis are occupied by the lattice DMF molecules. The desolvated samples show highly adsorption selectivity of CO2 over N2. © 2016 Elsevier B.V. All rights reserved.
Keywords: Zn(II) compound Porous framework Topology Gas adsorption
1. Introduction Metal-organic frameworks (MOFs) as a new class of functional materials have great potential applications in the areas of luminescence, gas storage, catalysis, magnetism and so on [1e5]. Typically, MOFs are constructed by the self-assembly of metal ions with multidentate organic ligands via metal coordination bonds under approximate solvothermal conditions [6e8]. Up to now, it is still a great challenge in crystal engineering to obtain the predictable structures with potential properties. Therefore, selection of an approximate organic ligand can help us to direct the synthesis of the desired structures. Among various organic ligands, N-heterocyclic imidazole, triazole, tetrazole, and their derivatives have been investigated and proven to be a rational choice to synthesize MOFs with intriguing structural varieties and potential applications [9e13]. 5-methyl-1H-tetrazole (Hmtz) has four potential coordination sites, and can bridge metal ions on a plane. Among the reported tetrazole-based MOFs, tetrazole ligand often adopts a m2-
* Corresponding author. Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, Shaanxi Normal University, Xi’an 710062, China. E-mail address: [email protected] (Z.-t. Zhang). http://dx.doi.org/10.1016/j.molstruc.2016.07.051 0022-2860/© 2016 Elsevier B.V. All rights reserved.
bridging mode, and the uncoordinated N-donor sites can effectively improve the MOFs' gas sorption and separation properties [14e16]. In viewing of that, in this work, we select 5-methyl-1H-tetrazole as the organic ligand to react with tetrahedral Zn(II) ions under solvothermal conditions. Successfully, we obtained a new porous tetrahedral Zn(II)-tetrazolate framework, namely [Zn2(mtz)3 (OH)]n$n(DMF) (1 Hmtz ¼ 5-methyl-1H-tetrazole, DMF ¼ N,N’dimethylformamide). Single crystal X-ray diffraction analyses indicate that compound 1 displays a 3D porous framework with 4connected dia-type topology.
2. Experimental 2.1. Materials and instrumentation All reagents and solvents employed in this work were commercially available and used without further purification. Elemental analyses (C, H and N) were determined with an elemental Vario EL III analyzer. Infrared spectrum using the KBr pellet was measured on a Nicolet Magna 750 FT-IR spectrometer in the range of 400e4000 cm1. Powder X-ray diffraction (PXRD) analyses were recorded on a PANalytical X'Pert Pro powder diffractometer with Cu/Ka radiation (l ¼ 1.54056 Å) with a step size
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of 0.05 . Thermal analyses were carried out on a NETSCHZ STAe449C thermoanalyzer with a heating rate of 10 C/min under a nitrogen atmosphere. Gas adsorption measurement was performed in the ASAP (Accelerated Surface Area and Porosimetry) 2020 System. 2.2. Synthesis of [Zn2(mtz)3(OH)]n·n(DMF)(1) A mixture of Zn(NO3)2$6H2O (0.058 g, 0.2 mmol), Hmtz (0.034 g, 0.4 mmol), DMF (3 mL) and H2O (1 mL) was placed in a small vial at 110 C for 72 h and then cooled to room temperature slowly. Colorless prism crystals were obtained in 42% yield based on Zn(NO3)2$6H2O. Anal. calcd. for C9H16N13O2Zn2 (469.13): C, 23.02; H, 3.41; N, 33.25%. Found: C, 23.06; H, 3.45; N, 33.19%. IR (KBr pellet cm1): 3421(w), 1617 (s), 1584 (m), 1527 (s), 1371 (vs), 1315 (m), 1068 (s), 967 (w), 782 (m), 665(w). 2.3. X-ray crystallography Suitable single crystal of 1 was carefully selected under an optical microscope and glued to thin glass fibers. Structural measurement was performed with a computerecontrolled Oxford Xcalibur E diffractometer with graphiteemonochromated MoeKa radiation (l ¼ 0.71073 Å) at T ¼ 293(2) K. Absorption corrections were made using the SADABS program [17]. The structure was solved by direct methods and refined by fullematrix leastesquare methods on F2 by using the SHELXLe97 program package [18]. All nonehydrogen atoms were refined anisotropically. The H atoms attached to their parent atoms of organic ligands were geometrically placed and refined using a riding model. Crystal data, as well as details of data collection and refinements of 1 are summarized in Table 1, selected bond lengths and angles are given in Table 2.
Compound 1 Zn(1)eO(1) Zn(1)eN(8)a Zn(2)eO(1) Zn(2)eN(12)c O(1)eZn(1)eN(5) N(5)eZn(1)eN(8)a N(5)eZn(1)eN(1) O(1)eZn(2)eN(4)b N(4)beZn(2)eN(12)c N(4)beZn(2)eN(9)
1.909(3) 2.010(4) 1.902(3) 1.998(4) 109.67(14) 111.86(15) 107.70(15) 113.02(14) 116.73(15) 104.62(15)
Zn(1)eN(5) Zn(1)eN(1) Zn(2)eN(4)b Zn(2)eN(9) O(1)eZn(1)eN(8)a O(1)eZn(1)eN(1) N(8)aeZn(1)eN(1) O(1)eZn(2)eN(12)c O(1)eZn(2)eN(9) N(12)ceZn(2)eN(9)
1.990(4) 2.014(4) 1.990(4) 2.037(4) 109.01(15) 106.90(14) 111.57(16) 110.35(14) 101.25(14) 109.49(16)
Symmetry codes: compound 1 (a) 1 e x, 0.5 þ y, 0.5 e z; (b) x, 1.5 e y, 0.5 þ z; (c) ex, 0.5 þ y, 0.5 e z.
coordinated by three N atoms from three different m2-mtz- ligands and one O atom (O1) from one m2-OH- ligand. The Zn-N distances are in the range of 1.990(4)-2.037(4) Å, and the Zn-O distance is 1.909(3) Å. As shown in Fig. 2b, fourteen Zn(II) are bridged by twelve m2-mtz- ligands and six m2-OH- ligands, generating a diatype cage. Finally, these dia-type cages are further connected together by the connections of m2-mtz- and m2-OH ligands, affording a 3D framework (Fig. 1c). Viewing along crystallographical c axis, there exist large 1D channels which were occupied by the lattice DMF molecules. The solventeaccessible volume in this framework is approximate 624.9 Å3 per unit cell volume, and the pore volume ratio is to be 34% calculated by the PLATON program. If the Zn(II) ions were reduced into 4-connected nodes, and the m2mtz- and m2-OH- ligands were reduced into linear connectors, the whole framework of 1 can be simplified into a 4-connected diatype topological network with the point symbol of {66} (Fig. 1d). 3.2. Powder X-ray diffraction patterns (PXRD) and thermal analysis of compound 1
3. Results and discussions 3.1. Crystal structure of compound 1 Single crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic P21/c space group and features a 3D framework with 4-connected dia-type topology. The asymmetric unit of 1 contains two crystallographically independent Zn(II) ions, three m2-mtz- ligands, one m2-OH- ligand and one free DMF molecule. As shown in Fig. 1a, both Zn1 and Zn2 are tetrahedrally
Table 1 Crystal data and structure refinements for compound 1. 1 Formula Fw (g/mol) Crystal system Space group a (Å) b (Å) c (Å) a( ) b( ) g( ) Volume (Å3) Z Density (cm3/g) Abs. coeff. (mm1) Total reflections Unique reflections Goodness of fit on F2 Final R indices [I > 2sigma(I2)] R (all data)
Table 2 Selected bond lengths (Å) and angles ( ) for compound 1.
C9H16N13O2Zn2 469.13 Monoclinic P21/c 12.0236(8) 9.9851(6) 15.8600(9) 90.00 105.201(6) 90.00 1837.48(19) 4 1.696 2.646 6665 3240 (Rint ¼ 0.0237) 0.979 R ¼ 0.0436, wR2 ¼ 0.1117 R ¼ 0.0553, wR2 ¼ 0.1216
The phase purity of compound 1 has been identified by the powder X-ray diffraction analysis. As shown in Fig. 2a, the experimental pattern of compound 1 matches well with the simulated one based on the single crystal diffraction data, demonstrating the bulk samples of compound 1 are in pure phase. In addition, the thermal stability of compound 1 was also investigated by thermogravimetric analysis (TGA) under N2 atmosphere in the temperature range of 30e800 C (Fig. 2b). From the TGA curve of compound 1, we found that the first weight loss of 15.78% occurs from 30 to 235 C, corresponding to the departure of one lattice DMF molecule per unit cell (calcd: 15.56%). Then the desolvated samples can be stable up to 340 C, and after 340 C, the framework started to collapse owing to the decomposition of the organic ligands. Finally, the residues may be powder ZnO (obsd: 34.23%, calcd: 34.53%). 3.3. Gas adsorption properties The permanent porosity of the desolvated 1 was established by reversible gas adsorption experiments using N2 at 77 K. Before gas adsorption, compound 1 was activated under vacuum at 320 C for 24 h to obtain the desolvated 1. As shown in Fig. 3a, the N2 sorption isotherm of the desolvated samples at 77 K shows a type-I behavior with the maximum N2 uptake of 174.8 cm3/g at 1 bar, giving the BET and Langmuir surface areas of 596.2 and 734.6 m2/g, respectively. A single data point at a relative pressure of 0.99 bar gives a pore volume of 0.283 cm3/g by the Horvath-Kawazoe equation. To demonstrate the potential of this rigid framework material in CO2/ N2 gas separation, we performed the sorption behaviors for CO2
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Fig. 1. (a) View of the coordination environments of Zn(II) ions in 1. All hydrogen atoms were omitted for clarity. (Symmetry codes: (a) 1x, e0.5 þ y, 0.5ez; (b) x, 1.5ey, 0.5 þ z; (c) ex, 0.5 þ y, 0.5ez). (b) The dia-type cage in 1. (c) The 3D framework of 1. (d) Schematic representation of the 4-connected dia topological network for 1.
Fig. 2. (a) The PXRD patterns for compound 1. (b)The TGA curve for compound 1.
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Fig. 3. (a) The N2 sorption isotherms of the desolvated 1 at 77 K. (b) The CO2 and N2 adsorption isotherms for the desolvated 1 recorded at 273 K and 298 K, respectively.
and N2 at 273 K and 298 K. As illustrated in Fig. 3b, the CO2 uptakes are 71.3 cm3/g (140 mg/g) at 273 K and 1 bar, and 37.5 cm3/g (73.6 mg/g) at 298 K and 1 bar, respectively, which are higher than previously reported MOFs, such as PCN-16, CuBTTri and MOF-5 [19e21]. Notably, the N2 was hardly adsorbed at 298 K and 1 bar. In addition, the adsorption selectivity of CO2 and N2 at 298 K and 1 atm was also calculated using the ideal solution adsorbed theory (IAST). As shown in Fig. S1, it is observed that the selectivity value of CO2 over N2 is about 92.5 at 298 K under 1 atm, which is higher than previously reported [In3O(bpdc)3(HCOO)(H2O)3/2]$x(DMF) (H2bpdc ¼ 4,4’-biphenyldicarboxylic acid) [22]. This mainly due to the strong interactions between the CO2 and the microporous framework with exposed uncoordinated N-donor sites [23,24]. Therefore, the desolvated 1 can be served as an excellent candidate for the separation of CO2 and N2. 4. Conclusion In summary, a new porous tetrahedral Zn(II)-tetrazolate framework has been successfully obtained under solvothermal conditions. Compound 1 feature 3D 4-connected dia-type framework. It exhibits high CO2 adsorption capacity and high adsorption selective of CO2 over N2. We anticipate that it can open up a new method for the design and synthesis of porous MOFs for separation of CO2 and N2. Acknowledgements This research was supported by Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 14JK1801), Natural Science Basic Research Plan Funded by Shaanxi Province of China (No.2016JM5024 & 2014JM2049) and Scientific Research Project Funded by Xianyang Normal University (No. 10XSYK311).
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2016.07.051.
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Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Porous tetrahedral Zn(II)-tetrazolate framework with highly adsorption selectivity of CO2 over N2 Wu-wu Li a, b, c, Ying Guo b, Zun-ting Zhang a, b, * a
Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, Shaanxi Normal University, Xi’an 710062, China b National Engineering Laboratory for Resource Development of Endangered Crude Drugs in Northwest of China and School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, China c College of Chemistry & Chemical Engineering, Xianyang Normal University, Xianyang, 712000, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 May 2016 Received in revised form 13 July 2016 Accepted 13 July 2016 Available online 15 July 2016
Presented here is a new porous tetrahedral Zn(II)-tetrazolate framework, namely [Zn2(mtz)3 (OH)]n$n(DMF) (1, Hmtz ¼ 5-methyl-1H-tetrazole, DMF ¼ N,N’-dimethylformamide), has been successfully synthesized under solvothermal conditions. Single crystal X-ray structural analysis reveals that compound 1 features a three-dimensional (3D) porous framework with 4-connected dia-type topology. The 1D channels along the crystallograhical c axis are occupied by the lattice DMF molecules. The desolvated samples show highly adsorption selectivity of CO2 over N2. © 2016 Elsevier B.V. All rights reserved.
Keywords: Zn(II) compound Porous framework Topology Gas adsorption
1. Introduction Metal-organic frameworks (MOFs) as a new class of functional materials have great potential applications in the areas of luminescence, gas storage, catalysis, magnetism and so on [1e5]. Typically, MOFs are constructed by the self-assembly of metal ions with multidentate organic ligands via metal coordination bonds under approximate solvothermal conditions [6e8]. Up to now, it is still a great challenge in crystal engineering to obtain the predictable structures with potential properties. Therefore, selection of an approximate organic ligand can help us to direct the synthesis of the desired structures. Among various organic ligands, N-heterocyclic imidazole, triazole, tetrazole, and their derivatives have been investigated and proven to be a rational choice to synthesize MOFs with intriguing structural varieties and potential applications [9e13]. 5-methyl-1H-tetrazole (Hmtz) has four potential coordination sites, and can bridge metal ions on a plane. Among the reported tetrazole-based MOFs, tetrazole ligand often adopts a m2-
* Corresponding author. Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, Shaanxi Normal University, Xi’an 710062, China. E-mail address: [email protected] (Z.-t. Zhang). http://dx.doi.org/10.1016/j.molstruc.2016.07.051 0022-2860/© 2016 Elsevier B.V. All rights reserved.
bridging mode, and the uncoordinated N-donor sites can effectively improve the MOFs' gas sorption and separation properties [14e16]. In viewing of that, in this work, we select 5-methyl-1H-tetrazole as the organic ligand to react with tetrahedral Zn(II) ions under solvothermal conditions. Successfully, we obtained a new porous tetrahedral Zn(II)-tetrazolate framework, namely [Zn2(mtz)3 (OH)]n$n(DMF) (1 Hmtz ¼ 5-methyl-1H-tetrazole, DMF ¼ N,N’dimethylformamide). Single crystal X-ray diffraction analyses indicate that compound 1 displays a 3D porous framework with 4connected dia-type topology.
2. Experimental 2.1. Materials and instrumentation All reagents and solvents employed in this work were commercially available and used without further purification. Elemental analyses (C, H and N) were determined with an elemental Vario EL III analyzer. Infrared spectrum using the KBr pellet was measured on a Nicolet Magna 750 FT-IR spectrometer in the range of 400e4000 cm1. Powder X-ray diffraction (PXRD) analyses were recorded on a PANalytical X'Pert Pro powder diffractometer with Cu/Ka radiation (l ¼ 1.54056 Å) with a step size
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of 0.05 . Thermal analyses were carried out on a NETSCHZ STAe449C thermoanalyzer with a heating rate of 10 C/min under a nitrogen atmosphere. Gas adsorption measurement was performed in the ASAP (Accelerated Surface Area and Porosimetry) 2020 System. 2.2. Synthesis of [Zn2(mtz)3(OH)]n·n(DMF)(1) A mixture of Zn(NO3)2$6H2O (0.058 g, 0.2 mmol), Hmtz (0.034 g, 0.4 mmol), DMF (3 mL) and H2O (1 mL) was placed in a small vial at 110 C for 72 h and then cooled to room temperature slowly. Colorless prism crystals were obtained in 42% yield based on Zn(NO3)2$6H2O. Anal. calcd. for C9H16N13O2Zn2 (469.13): C, 23.02; H, 3.41; N, 33.25%. Found: C, 23.06; H, 3.45; N, 33.19%. IR (KBr pellet cm1): 3421(w), 1617 (s), 1584 (m), 1527 (s), 1371 (vs), 1315 (m), 1068 (s), 967 (w), 782 (m), 665(w). 2.3. X-ray crystallography Suitable single crystal of 1 was carefully selected under an optical microscope and glued to thin glass fibers. Structural measurement was performed with a computerecontrolled Oxford Xcalibur E diffractometer with graphiteemonochromated MoeKa radiation (l ¼ 0.71073 Å) at T ¼ 293(2) K. Absorption corrections were made using the SADABS program [17]. The structure was solved by direct methods and refined by fullematrix leastesquare methods on F2 by using the SHELXLe97 program package [18]. All nonehydrogen atoms were refined anisotropically. The H atoms attached to their parent atoms of organic ligands were geometrically placed and refined using a riding model. Crystal data, as well as details of data collection and refinements of 1 are summarized in Table 1, selected bond lengths and angles are given in Table 2.
Compound 1 Zn(1)eO(1) Zn(1)eN(8)a Zn(2)eO(1) Zn(2)eN(12)c O(1)eZn(1)eN(5) N(5)eZn(1)eN(8)a N(5)eZn(1)eN(1) O(1)eZn(2)eN(4)b N(4)beZn(2)eN(12)c N(4)beZn(2)eN(9)
1.909(3) 2.010(4) 1.902(3) 1.998(4) 109.67(14) 111.86(15) 107.70(15) 113.02(14) 116.73(15) 104.62(15)
Zn(1)eN(5) Zn(1)eN(1) Zn(2)eN(4)b Zn(2)eN(9) O(1)eZn(1)eN(8)a O(1)eZn(1)eN(1) N(8)aeZn(1)eN(1) O(1)eZn(2)eN(12)c O(1)eZn(2)eN(9) N(12)ceZn(2)eN(9)
1.990(4) 2.014(4) 1.990(4) 2.037(4) 109.01(15) 106.90(14) 111.57(16) 110.35(14) 101.25(14) 109.49(16)
Symmetry codes: compound 1 (a) 1 e x, 0.5 þ y, 0.5 e z; (b) x, 1.5 e y, 0.5 þ z; (c) ex, 0.5 þ y, 0.5 e z.
coordinated by three N atoms from three different m2-mtz- ligands and one O atom (O1) from one m2-OH- ligand. The Zn-N distances are in the range of 1.990(4)-2.037(4) Å, and the Zn-O distance is 1.909(3) Å. As shown in Fig. 2b, fourteen Zn(II) are bridged by twelve m2-mtz- ligands and six m2-OH- ligands, generating a diatype cage. Finally, these dia-type cages are further connected together by the connections of m2-mtz- and m2-OH ligands, affording a 3D framework (Fig. 1c). Viewing along crystallographical c axis, there exist large 1D channels which were occupied by the lattice DMF molecules. The solventeaccessible volume in this framework is approximate 624.9 Å3 per unit cell volume, and the pore volume ratio is to be 34% calculated by the PLATON program. If the Zn(II) ions were reduced into 4-connected nodes, and the m2mtz- and m2-OH- ligands were reduced into linear connectors, the whole framework of 1 can be simplified into a 4-connected diatype topological network with the point symbol of {66} (Fig. 1d). 3.2. Powder X-ray diffraction patterns (PXRD) and thermal analysis of compound 1
3. Results and discussions 3.1. Crystal structure of compound 1 Single crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic P21/c space group and features a 3D framework with 4-connected dia-type topology. The asymmetric unit of 1 contains two crystallographically independent Zn(II) ions, three m2-mtz- ligands, one m2-OH- ligand and one free DMF molecule. As shown in Fig. 1a, both Zn1 and Zn2 are tetrahedrally
Table 1 Crystal data and structure refinements for compound 1. 1 Formula Fw (g/mol) Crystal system Space group a (Å) b (Å) c (Å) a( ) b( ) g( ) Volume (Å3) Z Density (cm3/g) Abs. coeff. (mm1) Total reflections Unique reflections Goodness of fit on F2 Final R indices [I > 2sigma(I2)] R (all data)
Table 2 Selected bond lengths (Å) and angles ( ) for compound 1.
C9H16N13O2Zn2 469.13 Monoclinic P21/c 12.0236(8) 9.9851(6) 15.8600(9) 90.00 105.201(6) 90.00 1837.48(19) 4 1.696 2.646 6665 3240 (Rint ¼ 0.0237) 0.979 R ¼ 0.0436, wR2 ¼ 0.1117 R ¼ 0.0553, wR2 ¼ 0.1216
The phase purity of compound 1 has been identified by the powder X-ray diffraction analysis. As shown in Fig. 2a, the experimental pattern of compound 1 matches well with the simulated one based on the single crystal diffraction data, demonstrating the bulk samples of compound 1 are in pure phase. In addition, the thermal stability of compound 1 was also investigated by thermogravimetric analysis (TGA) under N2 atmosphere in the temperature range of 30e800 C (Fig. 2b). From the TGA curve of compound 1, we found that the first weight loss of 15.78% occurs from 30 to 235 C, corresponding to the departure of one lattice DMF molecule per unit cell (calcd: 15.56%). Then the desolvated samples can be stable up to 340 C, and after 340 C, the framework started to collapse owing to the decomposition of the organic ligands. Finally, the residues may be powder ZnO (obsd: 34.23%, calcd: 34.53%). 3.3. Gas adsorption properties The permanent porosity of the desolvated 1 was established by reversible gas adsorption experiments using N2 at 77 K. Before gas adsorption, compound 1 was activated under vacuum at 320 C for 24 h to obtain the desolvated 1. As shown in Fig. 3a, the N2 sorption isotherm of the desolvated samples at 77 K shows a type-I behavior with the maximum N2 uptake of 174.8 cm3/g at 1 bar, giving the BET and Langmuir surface areas of 596.2 and 734.6 m2/g, respectively. A single data point at a relative pressure of 0.99 bar gives a pore volume of 0.283 cm3/g by the Horvath-Kawazoe equation. To demonstrate the potential of this rigid framework material in CO2/ N2 gas separation, we performed the sorption behaviors for CO2
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Fig. 1. (a) View of the coordination environments of Zn(II) ions in 1. All hydrogen atoms were omitted for clarity. (Symmetry codes: (a) 1x, e0.5 þ y, 0.5ez; (b) x, 1.5ey, 0.5 þ z; (c) ex, 0.5 þ y, 0.5ez). (b) The dia-type cage in 1. (c) The 3D framework of 1. (d) Schematic representation of the 4-connected dia topological network for 1.
Fig. 2. (a) The PXRD patterns for compound 1. (b)The TGA curve for compound 1.
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Fig. 3. (a) The N2 sorption isotherms of the desolvated 1 at 77 K. (b) The CO2 and N2 adsorption isotherms for the desolvated 1 recorded at 273 K and 298 K, respectively.
and N2 at 273 K and 298 K. As illustrated in Fig. 3b, the CO2 uptakes are 71.3 cm3/g (140 mg/g) at 273 K and 1 bar, and 37.5 cm3/g (73.6 mg/g) at 298 K and 1 bar, respectively, which are higher than previously reported MOFs, such as PCN-16, CuBTTri and MOF-5 [19e21]. Notably, the N2 was hardly adsorbed at 298 K and 1 bar. In addition, the adsorption selectivity of CO2 and N2 at 298 K and 1 atm was also calculated using the ideal solution adsorbed theory (IAST). As shown in Fig. S1, it is observed that the selectivity value of CO2 over N2 is about 92.5 at 298 K under 1 atm, which is higher than previously reported [In3O(bpdc)3(HCOO)(H2O)3/2]$x(DMF) (H2bpdc ¼ 4,4’-biphenyldicarboxylic acid) [22]. This mainly due to the strong interactions between the CO2 and the microporous framework with exposed uncoordinated N-donor sites [23,24]. Therefore, the desolvated 1 can be served as an excellent candidate for the separation of CO2 and N2. 4. Conclusion In summary, a new porous tetrahedral Zn(II)-tetrazolate framework has been successfully obtained under solvothermal conditions. Compound 1 feature 3D 4-connected dia-type framework. It exhibits high CO2 adsorption capacity and high adsorption selective of CO2 over N2. We anticipate that it can open up a new method for the design and synthesis of porous MOFs for separation of CO2 and N2. Acknowledgements This research was supported by Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 14JK1801), Natural Science Basic Research Plan Funded by Shaanxi Province of China (No.2016JM5024 & 2014JM2049) and Scientific Research Project Funded by Xianyang Normal University (No. 10XSYK311).
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2016.07.051.
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