Article pubs.acs.org/crystal
Molecular Tectonics of Four-Connected Network Topologies by Regulating the Ratios of Tetrahedral and Square-Planar Building Units Ling Qin,†,‡ Hai-Lang Jia,† Zi-Jian Guo,† and He-Gen Zheng*,† †
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, P. R. China ‡ Xuancheng Campus, Hefei University of Technology, Xuancheng 242000, Anhui, P. R. China S Supporting Information *
ABSTRACT: Assembly of the 4-connected building units leads to three threedimensional frameworks, {[Cd(TPPBDA)(OH)2]·2H2O·4DMA}n (1), {[Cd(TPPBDA)1/2(tpdc)]·DMF}n (2), and {[Zn(TPPBDA)1/2(bpdc)]·3H2O·3DMF}n (3) (TPPDBA = N,N,N′,N′-tetrakis(4-(4-pyridine)-phenyl) biphenyl-4,4′-diamine, H2tpdc = 4,4″-dicarboxyl-(1,1′,3′,1″)-terphenyl), H2bpdc = biphenyldicarboxylic acid, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacteamide), which are based on different ratios of tetrahedral (T) and square-planar (S) building units. For compound 1, T and S nodes are in the ratio of 1:1, which is the feature of pts. While T/S is 2:1 in compound 2 to form a bbf framework, for compound 3, the TPPBDA ligand and the metal center are both in tetrahedral configuration, which constructs a dia net with the ratio of 2:0 (T/S). In addition, the compound 2 exhibits high selectivity for CO2 over CH4, showing a hysteretic sorption− desorption loop.
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INTRODUCTION Recent extensive studies have been focused on molecular designs of the three-dimensional (3D) network structures and their applications such as catalysis,1 optics,2 ferroelectricity,3 sensors,4 and separations.5 Crystal engineering based on predesigned organic linkers and metal ions/clusters with specific coordination geometries is an important approach in the preparation of coordination materials.6,7 Some different 3D metal−organic frameworks have been engineered. Threeconnected nets corresponding to the topologies of SrSi2,8−10 ThSi2,11,12 4-connected nets with diamond,13 NbO,14 quartz,15 bbf,16 and pts,17 6-connected compounds with cubic topologies,18,19 and many higher-connected or mixed-connected nets20−24 have been reported. Some factors tend to affect the structures and topologies of the desired MOFs, such as the counteranions of metal salts, geometric requirements of metal atoms, metal−ligand ratio, pH, solvent, temperature, and the structure of the organic ligand.25−30 However, little attention has been paid to the factor by regulating the ratios of different building blocks up to now. This prompted us to study this interesting and challenging field. Many reported works indicate that the assembly of 4-connected metal ions or cluster nodes with ditopic linkers would ensure the formation of a four-connected framework.31−33 Inspired by these results and the success in the construction of potentially useful metal−organic frameworks, we present herein a designed tetratopic pyridyl ligand TPPBDA, that is, N,N,N′,N′-tetrakis (4-(4-pyridine)-phenyl) biphenyl-4,4′-diamine © 2014 American Chemical Society
(Scheme S1 in the Supporting Information) and the systematic construction of three 3D porous coordination polymers with V-type (H2tpdc = 4,4″-dicarboxyl-(1,1′,3′,1″)-terphenyl or H2bpdc = biphenyldicarboxylic acid) linear linkers, that is {[Cd(TPPBDA)(OH)2]·2H2O·4DMA}n (1), {[Cd(TPPBDA)1/2(tpdc)]·DMF}n (2), and {[Zn(TPPBDA)1/2(bpdc)]·3H2O·3DMF }n (3).
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RESULTS AND DISCUSSION As shown in Scheme 1, the coordination polymers built up of 4-connecting tetrahedral or planar-symmetric metal ions and TPPBDA ligands are precisely equivalent to the pts, bbf, and dia networks. In addition, the interpentration forms are also different (Table 1). In complex 1, the TPPBDA ligand connects four Cd(II) cations in tetrahedral configuration. The Cd(II) ion center coordinated by four TPPBDA ligands can be considered as square-planar nodes. Finally the ratio of tetrahedral (T) and square-planar (S) nodes is 1:1, which is the feature of pts. For compound 2, two carboxylates of the V-shape ligand tpdc2− adopt bidentate chelating coordination modes. There are two N atoms from two square-planar TPPBDA ligands occupying two vertices of the tetrahedral metal center, which results in a bbf framework with the ratio (T/S) of 2:1. While linear linker bpdc2− takes place of V-shape ligand for compound 3, the TPPBDA ligand and the metal center are both in tetrahedral Received: October 9, 2014 Revised: November 7, 2014 Published: November 13, 2014 6607
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the TPPBDA nodes, thus giving a short vertex symbol 42.84, which is that of the pts topology,34 as shown in Figure 1c. It is worth noting that there are 3D channels running along the a-, b-, and c-axes in the structure of 1, as shown in Figure S1, Supporting Information. Such a large cavity causes 4-fold interpenetration of the networks, which can be best described as two sets of a normal 2-fold net that is a [2 + 2] mode of interpenetration (Figure 1d). The adjacent nets (A1 and A2) are related by inversion center, and alternate nets (A1 and A3; A1 and A4) are related by translation along the [010] direction. According to Blatovs’ classification, which is mainly based on the symmetric relationships between the interpenetrating nets,35,36 the interpenetration of 1 can be classified as type IIIa, Z = 4[2*2] (Zt = 2; Zn = 2). Though a rich variety of topologies of interpenetration is evident in the polymeric networks, the 4-fold interpenetration with [2 + 2] mode of 1 (class IIIa) is unprecedented. All of the reported pts cases are almost classified as type Ia or IIa.37−39 Crystal Structure of {[Cd(TPPBDA)1/2(tpdc)]·DMF}n (2). X-ray crystallography reveals the 3D net 2 adopts a bbf topology. The asymmetric unit of 2 contains one Cd(II) cation, half a TPPBDA ligand, one tpdc2− anion, and one DMF molecule (Figure 2a). The tetradentate TPPBDA ligands and tpdc2− anions bridge the Cd(II) ions into a 3D network containing one-dimensional (1D) channels along the b-axis (Figure 2b). Considering the Cd(II) cations and the TPPBDA ligands as T and S nodes, respectively, 2 can be defined as a four-connected net with T and S nodes in the ratio of 2:1, giving a short vertex symbol {64.82}{66}2, which is that of the bbf topology40 as shown in Figure 2c. In order to minimize the presence of large cavities and to stabilize the framework during the assembly process, four other identical networks are filled in the cavities giving a 5-fold interpenetrating 3D architecture (class Ia) (Figure 2d). The adjacent nets are related by the translation vector [100]. As far as we know, many interpenetrated networks with four-coordinate nodes are reported,41−45 such as
Scheme 1. Different Ratios of the Tetrahedral and SquarePlanar Nodes Assembling Three 4-Connected MOFs with Different Topological Types in Compounds 1−3
configuration, which constructs a dia net with the ratio of 2:0. The compounds all exhibit 4-connected nets, while there are some differences in the interpenetration forms. Compounds 1 and 3 are 4-fold interpenetrating pts and dia networks, respectively, while 2 is a 5-fold interpenetrating bbf framework. Crystal Structure of {[Cd(TPPBDA)(OH) 2 ]·2H 2 O· 4DMA}n (1). The asymmetric unit of 1 contains one Cd(II) cation, one TPPBDA ligand, two OH− anions, two water and four DMA molecules, which are evident from the elemental analysis and thermogravimetric analysis (Figure 1a). The Cd(II) ion is six-coordinated by four N atoms from four TPPBDA ligands and two OH− anions. The tetradentate TPPBDA ligands bridge the Cd(II) ions into a 3D network (Figure 1b). By considering the Cd(II) and the TPPBDA ligands as square-planar (S) and tetrahedral (T) nodes, respectively, 1 can be defined as a four-connected net with S and T nodes in the ratio of 1:1. The long topological vertex symbol is 4.4.87.87.87.87 for the Cd nodes and 4.4.82.82.88.88 for
Table 1. Crystal Data and Structure Refinements Parameters of Complexes 1−3
a
complex
1
2
3
formula Mr cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρcaled (g cm−3) μ (mm−1) F (000) rflns collected uniq rflns R(int) GOF (F2) R1[I > 2σ(I)]a wR2[I > 2σ(I)]b
C72H82CdN10O8 1327.91 orthorhombic Pbcn 28.5893(10) 41.9618(15) 12.0642(4) 90.00 90.00 90.00 14472.9(9) 8 1.219 0.360 5605 13430 7506 0.0798 0.952 0.0448 0.1263
C52H41CdN4O5 914.29 monoclinic P21/c 8.8305 19.9787(15) 25.7425(19) 90.00 96.8210(10) 90.00 4509.4(6) 4 1.347 0.536 1876 25124 5471 0.0742 1.029 0.0431 0.1072
C51H55N6O10Zn 977.42 orthorhombic Pnna 13.7355(12) 40.624(4) 20.8303(19) 90.00 90.00 90.00 11623.1(19) 8 1.117 0.477 4104 83426 6022 0.1016 1.055 0.0782 0.2045
R1 = Σ∥F0| − |Fc∥/|Σ|F0|. bwR2 = {Σ[w(F02 − Fc2)2]/Σ[w(F02)2]}1/2; where w = 1/[σ2(Fo2) + (aP)2 + bP] and P = (Fo2 + 2Fc2)/3. 6608
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Figure 1. (a) Coordination environment of 1 with 30% ellipsoid probability (hydrogen atoms and solvent molecules are omitted for clarity). Symmetry code: #1 = 0.5 + x, 0.5 + y, 0.5 − z. #2 = 0.5 + x, −0.5 + y, 0.5 − z. (b) A perspective of 3D framework along the a axis. (c) Schematic representation of 4-connected pts topology net. (d) The 4-fold interpenetrating frameworks represented by [2 + 2] mode of interpenetration.
Figure 2. (a) Coordination environment of 2 with 30% ellipsoid probability (hydrogen atoms and DMA molecules are omitted for clarity). Symmetry code: #1 = 1 − x, 0.5 + y, 1.5 − z; #2 = −x, 0.5 + y, 2.5 − z. (b) View of 3D net with 1D channels along the b axis. (c) A view of 4-connected bbf topology. (d) Schematic representation of 5-fold interpenetrating framework. 6609
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Figure 3. (a) Coordination environment of 3 with 30% ellipsoid probability (hydrogen atoms and solvent molecules are omitted for clarity). Symmetry code: #1 = 1.5 − x, 2 − y, −1 + z; #2 = 0.5 + x, 1.5 − y, −0.5 + z. (b) A view of 3D framework along the c axis. (c) A view of 4-connected dia topology. (d) Schematic representation of 4-fold interpenetrating framework.
also can be described as a [2 + 2] mode of interpenetration (Figure 3d). Gas Uptake. The porosity of sample 2 was probed via gas sorption measurements. There is little or no adsorption of N2 up to 1 atm. Compound 2 takes up different amounts of CO2 (41.29 cm3 g−1) and CH4 (3.28 cm3 g−1) at 273 K and 850 mbar (Figure 4). The lower CH4 adsorption may be attributed to its smaller quadrupole moment, lower polarizability, and bigger gas molecule diameter than that of CO2.46−48 The adsorption of CO2 follows a linear pathway without reaching a plateau up to 1 atm. The desorption trace is different from that of adsorption, leading to hysteretic adsorption−desorption loop.49 The results suggest that compound 2 shows high selectivity for CO2 over CH4.50,51 To explore the interaction between CO2 and the surface of the compound 2, we calculated the isosteric heat of adsorption
diamondoid net involved in interpenetrating phenomena with a range from 2- up to 18-fold, while the bbf net with 5-fold interpenetration has not been reported. Crystal Structure of {[Zn(TPPBDA)1/2(bpdc)]·3H2O· 3DMF}n (3). Different from 1 and 2, 3 is a 3D 4-fold interpenetrating diamondoid network and crystallizes in the orthorhombic space group Pnna. As shown in Figure 3a, each Zn(II) is coordinated tetrahedrally by two nitrogen atoms from different TPPBDA ligands and two monodentate carboxylate groups from different bpdc anions. Furthermore, the tetradentate TPPBDA and bpdc2− link the tetrahedral Zn(II) into a 3D network (Figure 3b), giving a short vertex symbol 66 of dia topology (Figure 3c). The adjacent nets are related by an inversion center (C1 and C2) and pure translations (C2 and C3; C1 and C4). Therefore, the overall interpenetration of 3 6610
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Figure 4. CO2 (black) and CH4 (red) sorption isotherms at 273 K.
(Qst) based on the Clausius−Clapeyron equation using CO2 sorption isotherms measured at 273 and 298 K (Figure S11, Supporting Information). A plot of the isosteric heat of adsorption (Qst) as a function of CO2 adsorbed quantity is shown in Figure S14, Supporting Information. At the onset of adsorption, Qst is ∼29 kJ/mol, which is similar to the values for some other MOF materials.52−54 As expected, the heat of adsorption decreases to 5 kJ/mol at higher CO2 uptake and remains steady at this value throughout the adsorption process.
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CONCLUSIONS In summary, we have designed and synthesized a geometryvariable TPPBDA ligand, nearly tetrahedral or planarsymmetric configuration. Furthermore, we have first reported three MOFs with the different interpentration forms and topologies related to cooperite, bbf, and diamond by regulating the ratios of 4-connected building blocks. In addition, the compound 2 adsorbs CO2 selectively over CH4, showing hysteretic sorption−desorption loops. Extension of this 4-connected ligand to other metal salts and a further systematic investigation of their network connectivity and function is in progress.
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ASSOCIATED CONTENT
S Supporting Information *
Crystallographic data in CIF format, selected bond lengths and angles, IR, TGA, PXRD, patterns of photochemistry, and gas adsorption data. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: 86-25-83314502. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by grants from the Natural Science Foundation of China (Nos. 21371092 and 91022011) and National Basic Research Program of China (2010CB923303). Dedicated to Professor Xinquan Xin on the occasion of his 80th birthday.
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