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Porous pcu-type Zn(II) framework material with high adsorption selectivity for CO2 over N2
Journal of Molecular Structure 1107 (2016) 66e69
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Porous pcu-type Zn(II) framework material with high adsorption selectivity for CO2 over N2 Yiping Lu a, Yanli Dong b, *, Jing Qin c a
Hebei North University, Zhangjiakou 075000, PR China College of Sciences, Agricultural University of Hebei, Baoding 071001, PR China c Hebei University of Architecture, Zhangjiakou 075000, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 August 2015 Received in revised form 19 November 2015 Accepted 19 November 2015 Available online 23 November 2015
Reported here is a new Zn(II) compound, namely [Zn2(tdc)2(MA)]n (H2tdc ¼ 2,5-thiophenedicarboxylic acid, MA ¼ melamine), which has been constructed by the self-assembly reaction of Zn(NO3)2, H2tdc and MA under solvothermal conditions. Single crystal X-ray diffraction analysis reveals that this compound features a 3D porous framework with 6-connected pcu topology. Notably, this compound exhibits high CO2 sorption capacity and high sorption selectivity for CO2 over N2 at 298 K. © 2015 Elsevier B.V. All rights reserved.
Keywords: Zn(II) compound Solvothermal synthesis Melamine CO2 adsorption
1. Introduction The design and construction of porous metal-organic frameworks as adsorbents for CO2 capture is a vital technology to address the green house effect caused by the large emissions of CO2 from modern industry [1e4]. In order to enhance the CO2 sorption capacity in MOFs, many successfully strategies for tuning the MOFs' surface properties, such as polar functional groups, uncoordinated metal sites and extraframework cations and so on, have been well established [5e7]. Through these methods, the CO2 adsorption capacity in MOFs can be significantly improved owing to the strong interactions between the MOFs' active sites and CO2 molecules [8,9]. Thus, selection of appropriate organic ligands and metal ions is crucial to synthesize porous MOFs. As we all know that the amino groups of MOFs have great affinity for CO2 molecules. Melamine (MA), which has three amino groups, is a good multidentate organic ligand and can brigde metal ions in various coordination modes. Using MA as the organic ligand provides huge potential for building porous MOFs with high CO2 sorption capacity. 2, 5-thiophenedicarboxylic acid (H2tdc) has two carboxylate groups and can bridge metal ions in linear mode, which
* Corresponding author. E-mail address: [email protected] (Y. Dong). http://dx.doi.org/10.1016/j.molstruc.2015.11.045 0022-2860/© 2015 Elsevier B.V. All rights reserved.
may help us to construct porous MOFs with high thermal stabilities [10]. In previously reported literature, numerous porous MOFs are constructed from linear organic ligands [11e13]. Considering that, in this work, we select linear H2tdc and amino-containing MA as the organic ligands to assemble with Zn(II) ions, successfully obtaining a new porous pcu-type Zn(II) compound, namely [Zn2(tdc)2(MA)]n (H2tdc ¼ 2,5-thiophenedicarboxylic acid, MA ¼ melamine). This compound exhibits high CO2 sorption capacity and high sorption selectivity for CO2 over N2 at 298 K. 2. Experimental 2.1. Materials and methods All the starting materials and reagents used in this work were obtained commercially and used without further purification. Element analyses (C, H and N) were determined with an elemental Vairo 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. TGA analyses were carried out on a NETSCHZ STAe449C thermoanalyzer with a heating rate of 10 C/min under a nitrogen atmosphere. 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 of 0.05 . Gas adsorption measurement was performed in the ASAP (Accelerated
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
Surface Area and Porosimetry) 2020 System. Gas adsorption measurement was performed in the ASAP (Accelerated Surface Area and Porosimetry) 2020 System. Single crystal X-ray diffraction was carried out by an Oxford Xcalibur E diffractometer. 2.2. Synthesis of [Zn2(tdc)2(MA)]n A mixture of Zn(NO3)2$6H2O (0.1 mmol, 0.0297 g), H2tdc (0.1 mmol, 0.0172 g) and MA (0.1 mmol, 0.0126 g) and DMA (2 mL) was sealed in a small vial, which was kept at 100 C for 60 h and then cooled to the room temperature slowly. Colorless prism crystals yield in 43% based on Zn(NO3)2$6H2O. Anal. Calcd. (%) for C15H10N6O8S2Zn2 (597.19): C, 30.14; N, 14.07; H, 1.67. Found (%): C, 30.22; N, 14.02; H, 1.68. IR(cm1, KBr pellet): 3076 (w), 1702 (s), 1618(s), 1589(w), 1566(w), 1506(m), 1430(s), 1372(s), 1263(s), 1224(s), 1031(m), 963(m), 833(m).
67
Table 2 Selected bond lengths (Å) and angles ( ) for this Zn(II) compound. Zn(1)-O(2)
2.011(5)
Zn(1)-O(8)a
2.020(6)
Zn(1)-O(6) Zn(1)-O(4) Zn(2)-O(5) Zn(2)-O(1) O(2)-Zn(1)-O(8)a O(8)a-Zn(1)-O(6) O(8)a-Zn(1)-N(3)b O(2)-Zn(1)-O(4) O(6)-Zn(1)-O(4) O(3)-Zn(2)-O(5) O(5)-Zn(2)-O(7)a O(5)-Zn(2)-O(1) O(3)-Zn(2)-N(1) O(7)a-Zn(2)-N(1)
2.046(5) 2.058(5) 2.022(6) 2.052(5) 86.9(2) 157.9(2) 102.1(3) 153.1(2) 87.3(2) 86.6(3) 153.8(2) 90.7(3) 101.4(2) 103.4(3)
Zn(1)-N(3)b Zn(2)-O(3) Zn(2)-O(7)a Zn(2)-N(1) O(2)-Zn(1)-O(6) O(2)-Zn(1)-N(3)b O(6)-Zn(1)-N(3)b O(8)a-Zn(1)-O(4) N(3)b-Zn(1)-O(4) O(3)-Zn(2)-O(7)a O(3)-Zn(2)-O(1) O(7)a-Zn(2)-O(1) O(5)-Zn(2)-N(1) O(1)-Zn(2)-N(1)
2.053(6) 2.022(5) 2.051(6) 2.063(7) 87.8(2) 104.6(2) 100.0(3) 87.8(2) 102.4(2) 86.5(2) 157.9(2) 86.3(2) 102.7(3) 100.6(3)
a b
Symmetry codes: x þ 1/2, y, ez þ 1/2. ex þ 1/2, ey þ 1, z þ 1/2.
2.3. X-ray crystallography Single crystal Xeray structure analysis of this compound was performed on Oxford Xcalibur E diffractometer (Mo/Ka radiation, l ¼ 0.71073 Å, graphite monochromator) at 293(2) K. Empirical absorption corrections were applied to the data using the SADABS program [14]. The structure was solved by the direct method and refined by the full-matrix least-squares on F2 using the SHELXL-97 program [15]. All of the non-hydrogen atoms were refined anisotropically, and the hydrogen atoms attached to carbon atoms were located at their ideal positions. Experimental details for the structure determination are presented in Table 1. Selected bond lengths and angles for this compound are listed in Table 2. 3. Result and discussion 3.1. Structural description Single crystal structural analysis reveals that this compound crystallizes in the orthorhombic Pnma space group. The asymmetric unit consists of two Zn(II) ions, one and two halves tdc2 ligands and one MA ligand. As shown in Fig. 1, both Zn1 and Zn2 ions are five-coordinated by four carboxylate oxygen atoms and Table 1 Crystallographic data for this Zn(II) compound. Empirical formula
C15H10N6O8S2Zn2
Temperature(K) Crystal color Formula weight Crystal system Space group a (Å) b (Å) c (Å) a ( ) b ( ) g ( ) Volume(Å3) Z Density (calculated) Abs. coeff. (mm1) F(000) q for data collection ( ) Reflections collected Unique reflections Rint Goodness-of-fit on F2 R1, wR2 [I > 2sigma(I)] R1, wR2 (all data)
293 colorless 597.19 orthorhombic Pnma 20.1368(10) 20.2976(8) 17.4633(12) 90 90 90 7137.8(7) 8 1.112 1.495 2408 2.53 to 25.00 17376 6441 0.0273 1.152 0.0392, 0.0953 0.0686, 0.1093
Fig. 1. View of the coordination environments of Zn(II) ions in Zn(II) compound. All hydrogen atoms were omitted for clarity. Symmetry codes: (a) x þ 1/2, y, ez þ 1/2; (b)ex þ 1/2, ey þ 1, z þ 1/2.
one nitrogen atom, showing distorted square pyramidal geometries. The ZneO and ZneN distances are in the range of 2.011(5)e 2.058(5) Å, 2.053(6)e2.063(7) Å, respectively. Each tdc2 ligand links four Zn(II) ions with its two carboxylate groups in uniform bis-monodentate mode. Zn1 and Zn2 ions are bridged by four bismonodentate carboxylate groups into a paddle wheel shaped dinuclear [Zn2(COO)4] subunits with the Zn … Zn separation of 3.069 Å (Fig. 2a). These dinuclear [Zn2(COO)4] subunits are further bridged together by the tdc2 ligands, generating a 2D layer extending along ab plane (Fig. 2b). These adjacent 2D layers are further linked into a 3D porous framework via the connection of MA ligands, which adopt m2-N1, N2 mode (Fig. 2c). The solvent accessible volume of this compound is estimated to be about 52.3% of the total crystal volume calculated by the PLATON program. In this 3D pillar-layer framework, there exist abundant hydrogen bonds between the carboxylate oxygen atoms and nitrogen atoms from MA ligands, which further consolidate the
68
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
Fig. 2. (a) Paddle wheel shaped dinuclear [Zn2(COO)4] subunit. (b) 2D layer constructed from Zn(II) ions and tdc2 ligands. (c) 3D pillar-layer framework of Zn(II) compound. (d) Schematic representation of 6-connected pcu topological network for this compound.
whole framework of this compound (Fig. S1). The detailed hydrogen bond parameters are listed in Table S1. To further understand the structure, we define the dinuclear [Zn2(COO)4] subunits as 6-connected nodes, tdc2 and MA ligands as the bridge linkers. Such 3D framework can be described as a 6-connected pcu topological network with the point symbol of {412.63} (Fig. 2d). 3.2. PXRD and thermal analysis Powder X-ray diffraction (PXRD) has been used to check the phase purity of the bulk samples. The measured pattern closely matches with the simulated pattern based on the single crystal diffraction data, indicative of the pure product (Fig. S2). The thermogravimetric analysis (TGA) was performed to investigate the thermal behavior under N2 atmosphere. This Zn(II) compound exhibits good thermal stability indicated by the TGA curve (Fig. S3). The framework of this compound began to collapse accompanied by the decomposition of the organic ligands at 360 C and ended at 663 C, leading to the formation ZnO as the remnants (obsd: calcd: 27.13%) (Fig. S3). 3.3. Gas adsorption properties The N2 adsorption measurement was performed on a Micromeritics ASAP 2020 surface area and pore size analyzer to demonstrate the permanent porosity of this compound. As shown in Fig. 3, at 77 K, the N2 sorption isotherm of this Zn(II) compound exhibits a typical I behavior with a significant sorption hysteresis, which could be due to hindered diffusion through the narrow pore apertures. The N2 uptake capacity for this compound was
Fig. 3. N2 sorption isotherm for this Zn(II) compound at 77 k.
189.2 cm3/g at 1 bar. The Langmuir and BET surface areas were 986.5 m2/g and 765.0 m2/g, respectively. In addition, the CO2, CH4, C2H4 and N2 sorption isotherms were also measured at 298 K. As shown in Fig. 4, the uptake values of CO2, CH4, C2H4 and N2 were 188.7 cm3/g, 137.8 cm3/g, 98.7 cm3/g, 33.8 cm3/g, respectively, which are significantly higher than FIR-28-ht, TIF-Al and FIR-3c-ht [16e18]. Considering that this compound has many exposed eNH2 groups in the channels, so the adsorption selectivities of this compound for equimolar mixture of CO2 with respect to N2 are also
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
69
Acknowledgments This work was supported by the Grants from Agricultural University of Hebei Science and Technology Fund (LG201505).
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2015.11.045.
References
Fig. 4. Gas sorption isotherms for this Zn(II) compound at 298 K (a) for CO2, (b) for CH4, (c) for C2H4 and (d) for N2.
calculated using the ideal solution adsorbed theory (IAST). As shown in Fig. S4, this porous compound shows an excellent CO2/N2 adsorption selectivity of 109. The result indicates that this compound may be a potential candidate for separation of CO2 and N2. 4. Conclusions In summary, a new Zn(II) compound based on the mixed ligands of H2tdc and MA has been solvothermally synthesized. This compound features a 3D porous pcu-type topological framework. Gas adsorption investigations reveal that this compound displays high CO2 adsorption capacity and high sorption selectivity for CO2 over N2 at 298 K.
[1] M. Eddaoudi, D.B. Moler, H.L. Li, B.L. Chen, T.M. Reineke, M. O'Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. [2] J.R. Li, R.J. Kuppler, H.C. Zhou, Chem. Soc. Rev. 38 (2009) 1477. [3] J.J. Qian, F.L. Jiang, L.J. Zhang, K.Z. Su, J. Pan, Q.P. Li, D.Q. Yuan, M.C. Hong, Chem. Comm. 50 (2014) 1678. [4] S.D. Burd, S.Q. Ma, J.A. Perman, B.J. Sikora, R.Q. Snurr, P.K. Thallapally, J. Tian, L. Wojtas, M.J. Zawororko, J. Am. Chem. Soc. 134 (2012) 3663. [5] G. Xing, Q.F. Liu, Y. Zhang, S.F. Zhang, Y.L. Dong, Z. Anorg. Allg. Chem. 641 (2015) 1307. [6] J.G. Duan, Z. Yang, J.F. Bai, B.S. Zhang, Y.Z. Li, S.H. Li, Chem. Comm. 48 (2012) 3058. [7] R. Vaidhyanathan, S.S. Iremonger, G.K.H. Shimizu, P.G. Boyd, S. Alavi, T.K. Woo, Science 330 (2010) 650. [8] Z.H. Zhang, Z. Anorg, Allg. Chem. 640 (2014) 1737. [9] J.Y. An, S.J. Geib, N.L. Rosi, J. Am. Chem. Soc. 132 (2010) 38. [10] M.V. Rous, M. Temprado, P.J. Jimenez, C. Foces-Foces, R. Notario, S.P. Verevkin, J.F. Liebman, J. Phys. Chem. A 110 (2006) 12477. [11] F. Wang, Y.X. Tan, H. Yang, Y. Kang, J. Zhang, Chem. Comm. 48 (2012) 4842. [12] Y.X. Tan, F. Wang, Y. Kang, J. Zhang, Chem. Comm. 47 (2011) 770. [13] B. Liu, L. Hou, W.P. Wu, A.N. Dou, Y.Y. Wang, Dalton Trans. 44 (2015) 4423. €ttingen, Go €ttingen, Germany, 1996. [14] G.M. Sheldrick, SADABS, University of Go [15] G.M. Sheldrick, SHELXL-97: Program for Refining Crystal Structure Refine€ttingen, Germany, 1997. ment, University of Go [16] Y.P. He, Y.X. Tan, J. Zhang, Inorg. Chem. 54 (2015) 6653. [17] Y.P. He, Y.X. Tan, J. Zhang, Inorg. Chem. 51 (2012) 11232. [18] F. Wang, Y.X. Tan, H. Yang, H.X. Zhang, Y. Kang, J. Zhang, Chem. Comm. 47 (2011) 5828.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Porous pcu-type Zn(II) framework material with high adsorption selectivity for CO2 over N2 Yiping Lu a, Yanli Dong b, *, Jing Qin c a
Hebei North University, Zhangjiakou 075000, PR China College of Sciences, Agricultural University of Hebei, Baoding 071001, PR China c Hebei University of Architecture, Zhangjiakou 075000, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 August 2015 Received in revised form 19 November 2015 Accepted 19 November 2015 Available online 23 November 2015
Reported here is a new Zn(II) compound, namely [Zn2(tdc)2(MA)]n (H2tdc ¼ 2,5-thiophenedicarboxylic acid, MA ¼ melamine), which has been constructed by the self-assembly reaction of Zn(NO3)2, H2tdc and MA under solvothermal conditions. Single crystal X-ray diffraction analysis reveals that this compound features a 3D porous framework with 6-connected pcu topology. Notably, this compound exhibits high CO2 sorption capacity and high sorption selectivity for CO2 over N2 at 298 K. © 2015 Elsevier B.V. All rights reserved.
Keywords: Zn(II) compound Solvothermal synthesis Melamine CO2 adsorption
1. Introduction The design and construction of porous metal-organic frameworks as adsorbents for CO2 capture is a vital technology to address the green house effect caused by the large emissions of CO2 from modern industry [1e4]. In order to enhance the CO2 sorption capacity in MOFs, many successfully strategies for tuning the MOFs' surface properties, such as polar functional groups, uncoordinated metal sites and extraframework cations and so on, have been well established [5e7]. Through these methods, the CO2 adsorption capacity in MOFs can be significantly improved owing to the strong interactions between the MOFs' active sites and CO2 molecules [8,9]. Thus, selection of appropriate organic ligands and metal ions is crucial to synthesize porous MOFs. As we all know that the amino groups of MOFs have great affinity for CO2 molecules. Melamine (MA), which has three amino groups, is a good multidentate organic ligand and can brigde metal ions in various coordination modes. Using MA as the organic ligand provides huge potential for building porous MOFs with high CO2 sorption capacity. 2, 5-thiophenedicarboxylic acid (H2tdc) has two carboxylate groups and can bridge metal ions in linear mode, which
* Corresponding author. E-mail address: [email protected] (Y. Dong). http://dx.doi.org/10.1016/j.molstruc.2015.11.045 0022-2860/© 2015 Elsevier B.V. All rights reserved.
may help us to construct porous MOFs with high thermal stabilities [10]. In previously reported literature, numerous porous MOFs are constructed from linear organic ligands [11e13]. Considering that, in this work, we select linear H2tdc and amino-containing MA as the organic ligands to assemble with Zn(II) ions, successfully obtaining a new porous pcu-type Zn(II) compound, namely [Zn2(tdc)2(MA)]n (H2tdc ¼ 2,5-thiophenedicarboxylic acid, MA ¼ melamine). This compound exhibits high CO2 sorption capacity and high sorption selectivity for CO2 over N2 at 298 K. 2. Experimental 2.1. Materials and methods All the starting materials and reagents used in this work were obtained commercially and used without further purification. Element analyses (C, H and N) were determined with an elemental Vairo 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. TGA analyses were carried out on a NETSCHZ STAe449C thermoanalyzer with a heating rate of 10 C/min under a nitrogen atmosphere. 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 of 0.05 . Gas adsorption measurement was performed in the ASAP (Accelerated
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
Surface Area and Porosimetry) 2020 System. Gas adsorption measurement was performed in the ASAP (Accelerated Surface Area and Porosimetry) 2020 System. Single crystal X-ray diffraction was carried out by an Oxford Xcalibur E diffractometer. 2.2. Synthesis of [Zn2(tdc)2(MA)]n A mixture of Zn(NO3)2$6H2O (0.1 mmol, 0.0297 g), H2tdc (0.1 mmol, 0.0172 g) and MA (0.1 mmol, 0.0126 g) and DMA (2 mL) was sealed in a small vial, which was kept at 100 C for 60 h and then cooled to the room temperature slowly. Colorless prism crystals yield in 43% based on Zn(NO3)2$6H2O. Anal. Calcd. (%) for C15H10N6O8S2Zn2 (597.19): C, 30.14; N, 14.07; H, 1.67. Found (%): C, 30.22; N, 14.02; H, 1.68. IR(cm1, KBr pellet): 3076 (w), 1702 (s), 1618(s), 1589(w), 1566(w), 1506(m), 1430(s), 1372(s), 1263(s), 1224(s), 1031(m), 963(m), 833(m).
67
Table 2 Selected bond lengths (Å) and angles ( ) for this Zn(II) compound. Zn(1)-O(2)
2.011(5)
Zn(1)-O(8)a
2.020(6)
Zn(1)-O(6) Zn(1)-O(4) Zn(2)-O(5) Zn(2)-O(1) O(2)-Zn(1)-O(8)a O(8)a-Zn(1)-O(6) O(8)a-Zn(1)-N(3)b O(2)-Zn(1)-O(4) O(6)-Zn(1)-O(4) O(3)-Zn(2)-O(5) O(5)-Zn(2)-O(7)a O(5)-Zn(2)-O(1) O(3)-Zn(2)-N(1) O(7)a-Zn(2)-N(1)
2.046(5) 2.058(5) 2.022(6) 2.052(5) 86.9(2) 157.9(2) 102.1(3) 153.1(2) 87.3(2) 86.6(3) 153.8(2) 90.7(3) 101.4(2) 103.4(3)
Zn(1)-N(3)b Zn(2)-O(3) Zn(2)-O(7)a Zn(2)-N(1) O(2)-Zn(1)-O(6) O(2)-Zn(1)-N(3)b O(6)-Zn(1)-N(3)b O(8)a-Zn(1)-O(4) N(3)b-Zn(1)-O(4) O(3)-Zn(2)-O(7)a O(3)-Zn(2)-O(1) O(7)a-Zn(2)-O(1) O(5)-Zn(2)-N(1) O(1)-Zn(2)-N(1)
2.053(6) 2.022(5) 2.051(6) 2.063(7) 87.8(2) 104.6(2) 100.0(3) 87.8(2) 102.4(2) 86.5(2) 157.9(2) 86.3(2) 102.7(3) 100.6(3)
a b
Symmetry codes: x þ 1/2, y, ez þ 1/2. ex þ 1/2, ey þ 1, z þ 1/2.
2.3. X-ray crystallography Single crystal Xeray structure analysis of this compound was performed on Oxford Xcalibur E diffractometer (Mo/Ka radiation, l ¼ 0.71073 Å, graphite monochromator) at 293(2) K. Empirical absorption corrections were applied to the data using the SADABS program [14]. The structure was solved by the direct method and refined by the full-matrix least-squares on F2 using the SHELXL-97 program [15]. All of the non-hydrogen atoms were refined anisotropically, and the hydrogen atoms attached to carbon atoms were located at their ideal positions. Experimental details for the structure determination are presented in Table 1. Selected bond lengths and angles for this compound are listed in Table 2. 3. Result and discussion 3.1. Structural description Single crystal structural analysis reveals that this compound crystallizes in the orthorhombic Pnma space group. The asymmetric unit consists of two Zn(II) ions, one and two halves tdc2 ligands and one MA ligand. As shown in Fig. 1, both Zn1 and Zn2 ions are five-coordinated by four carboxylate oxygen atoms and Table 1 Crystallographic data for this Zn(II) compound. Empirical formula
C15H10N6O8S2Zn2
Temperature(K) Crystal color Formula weight Crystal system Space group a (Å) b (Å) c (Å) a ( ) b ( ) g ( ) Volume(Å3) Z Density (calculated) Abs. coeff. (mm1) F(000) q for data collection ( ) Reflections collected Unique reflections Rint Goodness-of-fit on F2 R1, wR2 [I > 2sigma(I)] R1, wR2 (all data)
293 colorless 597.19 orthorhombic Pnma 20.1368(10) 20.2976(8) 17.4633(12) 90 90 90 7137.8(7) 8 1.112 1.495 2408 2.53 to 25.00 17376 6441 0.0273 1.152 0.0392, 0.0953 0.0686, 0.1093
Fig. 1. View of the coordination environments of Zn(II) ions in Zn(II) compound. All hydrogen atoms were omitted for clarity. Symmetry codes: (a) x þ 1/2, y, ez þ 1/2; (b)ex þ 1/2, ey þ 1, z þ 1/2.
one nitrogen atom, showing distorted square pyramidal geometries. The ZneO and ZneN distances are in the range of 2.011(5)e 2.058(5) Å, 2.053(6)e2.063(7) Å, respectively. Each tdc2 ligand links four Zn(II) ions with its two carboxylate groups in uniform bis-monodentate mode. Zn1 and Zn2 ions are bridged by four bismonodentate carboxylate groups into a paddle wheel shaped dinuclear [Zn2(COO)4] subunits with the Zn … Zn separation of 3.069 Å (Fig. 2a). These dinuclear [Zn2(COO)4] subunits are further bridged together by the tdc2 ligands, generating a 2D layer extending along ab plane (Fig. 2b). These adjacent 2D layers are further linked into a 3D porous framework via the connection of MA ligands, which adopt m2-N1, N2 mode (Fig. 2c). The solvent accessible volume of this compound is estimated to be about 52.3% of the total crystal volume calculated by the PLATON program. In this 3D pillar-layer framework, there exist abundant hydrogen bonds between the carboxylate oxygen atoms and nitrogen atoms from MA ligands, which further consolidate the
68
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
Fig. 2. (a) Paddle wheel shaped dinuclear [Zn2(COO)4] subunit. (b) 2D layer constructed from Zn(II) ions and tdc2 ligands. (c) 3D pillar-layer framework of Zn(II) compound. (d) Schematic representation of 6-connected pcu topological network for this compound.
whole framework of this compound (Fig. S1). The detailed hydrogen bond parameters are listed in Table S1. To further understand the structure, we define the dinuclear [Zn2(COO)4] subunits as 6-connected nodes, tdc2 and MA ligands as the bridge linkers. Such 3D framework can be described as a 6-connected pcu topological network with the point symbol of {412.63} (Fig. 2d). 3.2. PXRD and thermal analysis Powder X-ray diffraction (PXRD) has been used to check the phase purity of the bulk samples. The measured pattern closely matches with the simulated pattern based on the single crystal diffraction data, indicative of the pure product (Fig. S2). The thermogravimetric analysis (TGA) was performed to investigate the thermal behavior under N2 atmosphere. This Zn(II) compound exhibits good thermal stability indicated by the TGA curve (Fig. S3). The framework of this compound began to collapse accompanied by the decomposition of the organic ligands at 360 C and ended at 663 C, leading to the formation ZnO as the remnants (obsd: calcd: 27.13%) (Fig. S3). 3.3. Gas adsorption properties The N2 adsorption measurement was performed on a Micromeritics ASAP 2020 surface area and pore size analyzer to demonstrate the permanent porosity of this compound. As shown in Fig. 3, at 77 K, the N2 sorption isotherm of this Zn(II) compound exhibits a typical I behavior with a significant sorption hysteresis, which could be due to hindered diffusion through the narrow pore apertures. The N2 uptake capacity for this compound was
Fig. 3. N2 sorption isotherm for this Zn(II) compound at 77 k.
189.2 cm3/g at 1 bar. The Langmuir and BET surface areas were 986.5 m2/g and 765.0 m2/g, respectively. In addition, the CO2, CH4, C2H4 and N2 sorption isotherms were also measured at 298 K. As shown in Fig. 4, the uptake values of CO2, CH4, C2H4 and N2 were 188.7 cm3/g, 137.8 cm3/g, 98.7 cm3/g, 33.8 cm3/g, respectively, which are significantly higher than FIR-28-ht, TIF-Al and FIR-3c-ht [16e18]. Considering that this compound has many exposed eNH2 groups in the channels, so the adsorption selectivities of this compound for equimolar mixture of CO2 with respect to N2 are also
Y. Lu et al. / Journal of Molecular Structure 1107 (2016) 66e69
69
Acknowledgments This work was supported by the Grants from Agricultural University of Hebei Science and Technology Fund (LG201505).
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2015.11.045.
References
Fig. 4. Gas sorption isotherms for this Zn(II) compound at 298 K (a) for CO2, (b) for CH4, (c) for C2H4 and (d) for N2.
calculated using the ideal solution adsorbed theory (IAST). As shown in Fig. S4, this porous compound shows an excellent CO2/N2 adsorption selectivity of 109. The result indicates that this compound may be a potential candidate for separation of CO2 and N2. 4. Conclusions In summary, a new Zn(II) compound based on the mixed ligands of H2tdc and MA has been solvothermally synthesized. This compound features a 3D porous pcu-type topological framework. Gas adsorption investigations reveal that this compound displays high CO2 adsorption capacity and high sorption selectivity for CO2 over N2 at 298 K.
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