Structure, Hydrogen Storage, and Luminescence Properties of Three 3D Metal-Organic Frameworks with NbO and PtS Topologies Ming Xue, Guangshan Zhu,* Yangxue Li, Xiaojun Zhao, Zhao Jin, Enhua Kang, and Shilun Qiu*
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 7 2478–2483
State Key Laboratory of Inorganic Synthesis & PreparatiVe Chemistry, Jilin UniVersity, Changchun 130012, China ReceiVed January 29, 2008; ReVised Manuscript ReceiVed April 7, 2008
ABSTRACT: Three 3D multifunctional microporous metal-organic frameworks (MOFs), Cu2(ABTC)(H2O)2 · (DMF)2(H2O) (JUC62), Cd2(ABTC)(DMF)3 · (DMF)2 (JUC-63), and Mn(H2ABTC)(DMF)2 (JUC-64) (H4ABTC ) 3,3′,5,5′-azobenzenetetracarboxylic acid, DMF ) N,N′-dimethylformamide, and JUC ) Jilin University China) have been synthesized by self-assembly of a rigid tetra-carboxylate ligand H4ABTC and corresponding transition metal salts under mild conditions. X-ray crystallography reveals that their topologies are based on NbO (JUC-62) and PtS (JUC-63 and JUC-64) nets, constructed of 4-connected rectangular ABTC4units with 4-connected square paddle-wheel Cu2(CO2)4(H2O)2 secondary building units (SBUs), tetrahedral bimetallic Cd2(CO2)4(DMF)3 SBUs, and tetrahedral monometallic Mn(CO2)4(DMF)3 SBUs, respectively. High-pressure hydrogen sorption of the activated JUC62 reveals a type I profile at 77 K, which is saturated at 40 bar with a hydrogen uptake of about 4.71 wt%. Photoluminescence investigations reveal that JUC-62 and JUC-63 display strong main emission spectra peaks at 392 and 402 nm, respectively. Introduction Metal-organic framework (MOF) design and construction is currently a flourishing field of research owing to the intriguing molecular topologies and the potentially exploitable adsorption, catalytic, fluorescence, and magnetic properties.1 The recent discovery that MOFs take up significant amounts of hydrogen has spurred interest in these materials as possible storage media for hydrogen fuel cell vehicles.2 Meanwhile an important aspect of this relatively new chemistry is the analysis and direction of network topologies of the MOFs, which is a precondition to make true and significant development.3 In particular, exploring highly symmetrical multifunctional organic ligands and suitable metal salts in a design strategy to construct coordination complexes with special topologies is of higher interest, due to the predictability of the resulting networks.4 Some structures of minerals, such as quartz diamond, rutile, perovsktie, NbO, PtS, and feldspar, have been artificially produced by replacing monatomic anions (O2-, S2-) with polyatomic organic ligands as linkers and utilizing the well-defined coordination geometries of metal centers as nodes.5 Among an infinite number of possibilities, the three-dimensional (3-D) NbO network was identified as the default using square-planar 4-connected nodes, and PtS networks could be constructed when using both squareplanar and tetrahedral 4-connected nodes.6 Recently, we designed a tetra-carboxylate ligand, 3,3′,5,5′azobenzenetetracarboxylic acid (H4ABTC),7 which can act as a rigid rectangular-planar 4-connected ligand. We expect to prepare some microporous MOFs with 4-connected topologies from different coordination geometric transition metal ions with this ligand. During the course of our work, three metal-organic frameworks were reported on this ligand.8 Herein, we will describe three compounds Cu2(ABTC)(H2O)2 · (DMF)2(H2O) (JUC-62), Cd2(ABTC)(DMF)3 · (DMF)2 (JUC-63), and Mn(H2ABTC)(DMF)2 (JUC-64) (H4ABTC ) 3,3′,5,5′-azobenzenetetracarboxylic acid, DMF ) N,N′-dimethylformamide, and JUC ) Jilin University China), possessing NbO and PtS net * Author to whom all correspondence should be addressed. Fax: (+86) 431 85168331. E-mail:
[email protected] (S.L.Q.);
[email protected] (G.S.Z.).
topologies, respectively, from Cu2+, Cd2+, or Mn2+ ions with the H4ABTC ligand. Of further interest, the high-pressure hydrogen storage and fluorescence properties have been examined. Experimental Section Materials and Measurements. All reagents and solvents were used as received from commercial suppliers without further purification. Fluorescence spectroscopy data were recorded on a LS55 luminescence spectrometer. Analyses for C, H, and N were carried out on a PerkinElmer 240C analyzer. Thermal gravimetric analyses (TGA) were performed under oxygen atmosphere with a heating rate of 5 °C/min using a Perkin-Elmer TGA 7 thermogravimetric analyzer. Powder X-ray diffraction (PXRD) data were collected on a Siemens D5005 diffractometer with Cu KR radiation (λ ) 1.5418 Å). Synthesis of Cu2(ABTC)(H2O)2 · (DMF)2(H2O) (JUC-62). A mixture of Cu(NO3)2 · (H2O)2.5 (24 mg, 0.1 mmol) and H4ABTC (18 mg, 0.05 mmol) was dissolved in DMF/ethanol/H2O (5:3:1) at room temperature in a 25 mL beaker. Sufficient 2 M HNO3 was added until the mixture became clear. The mixture was left undisturbed at 60 °C for 2 days to give blue-green, polyhedral crystals. Yield: 61% (based on H4ABTC). Elemental anal. Calcd C22H26N4O13Cu2 (680): C, 38.82; H, 3.85; N, 8.24. Found: C, 38.91; H, 3.78; N, 8.32. Synthesis of Cd2(ABTC)(DMF)3 · (DMF)2 (JUC-63). A mixture of Cd(NO3)2 · (H2O)4 (30 mg, 0.1 mmol) and H4ABTC (11 mg, 0.03 mmol) was dissolved in DMF/ethanol/H2O (12:3:1) at room temperature in a 25 mL beaker. Sufficient 2 M HNO3 was added until the mixture became clear. The mixture was left undisturbed at room temperature for 1 week to give yellowy, block-shaped crystals. Yield: 56% (based on H4ABTC). Elemental anal. Calcd C31H27N7O13Cd2 (932.97): C, 39.87; H, 2.92; N, 10.51. Found: C, 39.72; H, 2.81; N, 10.68. Synthesis of Mn(H2ABTC)(DMF)2 (JUC-64). A mixture of MnCl2 · (H2O)4 (40 mg, 0.2 mmol) and H4ABTC (11 mg, 0.03 mmol) was dissolved in DMF/glycol/H2O (8:2:1) at room temperature in a 25 mL beaker. Sufficient 2 M HCl was added until the mixture became clear. The mixture was left undisturbed at 55 °C for 2 days to give orange, block-shaped crystals. Yield: 73% (based on H4ABTC). Elemental anal. Calcd C22H22N4O10Mn (557.07): C, 47.39; H, 3.98; N, 10.05. Found: C, 47.26; H, 3.82; N, 10.16. X-ray Crystallographic Study. Diffraction intensities for JUC-62, JUC-63, and JUC-64 were collected on a computer-controlled Bruker SMART CCD diffractometer equipped with graphite-monochromated Mo KR (λ ) 0.71073 Å) radiation at room temperature by using the ω-scan technique. Raw data for all structures were processed using SAINT and absorption corrections were applied using SADABS.9 The structures were solved by direct methods and refined with the full-
10.1021/cg8001114 CCC: $40.75 2008 American Chemical Society Published on Web 06/07/2008
MOFs with NbO and PtS Topologies
Crystal Growth & Design, Vol. 8, No. 7, 2008 2479
Table 1. Crystallographic Data for JUC-62, JUC-63, and JUC-64
formula Fw crystal syst space group a [Å] b [Å] c [Å] R [deg] β [deg] γ [deg] V [Å3] Z T (K) λ (Å) Fcalcd (Mg/m3) µ (mm-1) GOF on F2 Ra [I > 2σ(I)] Rwb a
JUC-62
JUC-63
JUC-64
C32H12N4O20Cu4 1026.62 trigonal R-3 (No. 148) 45.571(6) 45.571(6) 20.270(4) 90.00 90.00 120.00 36455(10) 18 293(2) 0.71073 0.842 1.078 0.952 0.0923 0.1383
C31H27N7O13Cd2 930.40 orthorhombic Pna2(1) (No. 33) 23.5160(11) 15.1207(7) 12.8597(6) 90.00 90.00 90.00 4572.6(4) 4 293(2) 0.71073 1.351 0.988 1.001 0.0582 0.1501
C18H22N4O10Mn 509.34 monoclinic P2(1)/c (No. 14) 11.3667(10) 22.1056(19) 9.6677(9) 90.00 102.986(2) 90.00 2367.1(4) 4 293(2) 0.71073 1.429 0.616 1.003 0.0394 0.0779
R ) Σ|Fo| - | Fc|/Σ|Fo|. b Rw ) [Σw(Fo2 - Fc2)/ Σw(Fo2)2]1/2.
Table 2. Selected Bond Lengths (Å) for JUC-62, JUC-63, and JUC-64 JUC-62a Cu(1)-O(7)#1 Cu(1)-O(9) Cu(1)-O(17) Cu(2)-O(10) Cu(2)-O(8)#1 Cu(3)-O(3) Cu(3)-O(14)#4 Cu(3)-O(20) Cu(4)-O(6)#5 Cu(4)-O(13)#4
1.931(8) 2.008(6) 2.178(7) 2.005(6) 1.927(7) 1.821(9) 1.918(6) 2.111(7) 1.918(7) 2.046(6)
Cu(1)-O(1) Cu(1)-O(11)#2 Cu(2)-O(12)#2 Cu(2)-O(18) Cu(2)-O(2) Cu(3)-O(15)#3 Cu(3)-O(5)#5 Cu(4)-O(4) Cu(4)-O(16)#3 Cu(4)-O(19)
1.969(7) 2.029(7) 1.786(7) 2.183(7) 1.987(6) 1.867(8) 1.998(6) 1.877(8) 1.934(6) 2.163(6)
JUC-63b Cd(1)-O(9) Cd(1)-O(11) Cd(1)-O(3)#2 Cd(2)-O(6)#1 Cd(2)-O(4)#2 Cd(2)-O(2)
2.216(10) Cd(1)-O(5)#1 2.254(9) Cd(1)-O(10) 2.283(11) Cd(1)-O(2) 2.198(11) Cd(2)-O(7)#3 2.218(10) Cd(2)-O(1) 2.409(9) Cd(2)-O(8)#3 JUC-64c
2.244(10) 2.258(11) 2.289(9) 2.212(10) 2.393(9) 2.501(10)
Mn(1)-O(1) Mn(1)-O(9) Mn(1)-O(10)
2.1390(19) 2.165(2) 2.175(2)
2.162(2) 2.174(2) 2.204(2)
Mn(1)-O(6)#1 Mn(1)-O(3)#2 Mn(1)-O(8)#3
a Symmetry transformations used to generate equivalent atoms: #1 y + 1/3, -x + y + 2/3, -z + 2/3; #2 -x + y + 2/3, -x + 1/3, z + 1/3; #3 -y + 1/3, x - y - 1/3, z - 1/3; #4 x - y, x, -z; #5 -x + y + 1, -x + 1, z. b Symmetry transformations used to generate equivalent atoms: #1 -x + 1/2, y - 1/2, z - 1/2; #2 -x + 1, -y + 1, z - 1/2; #3 x + 1/2, -y + 1/2, z. c Symmetry transformations used to generate equivalent atoms: #1 -x + 1, y - 1/2, -z + 3/2; #2 -x + 1, -y, -z + 1; #3 x - 1, -y + 1/2, z + 1/2.
matrix least-squares technique using the program SHELXTL.10 Anisotropic thermal parameters were assigned to all non-hydrogen atoms. The hydrogen atoms were set in calculated positions. For JUC-62, guest solvent molecules were highly disordered and were impossible to refine using conventional discrete-atom models. To resolve these issues, the contribution of solvent electron density was removed by the SQUEEZE routine in PLATON.11 Pertinent crystallographic data and structure refinement parameters were summarized in Table 1, and the selected bond lengths and bond angles of JUC-62, JUC-63, and JUC-64 are listed in Table 2 and Tables S1-S3 in Supporting Information, respectively. Crystal drawings were produced by Cerius2 soft. CCDC666395 (JUC-62), CCDC-666396 (JUC-63), and CCDC-666397 (JUC64) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/ retrieving.html (or from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB21EZ, U.K.; fax: (44) 1223-336-003; e-mail:
[email protected]).
Figure 1. The single-crystal X-ray structure of JUC-62: (a) The Cu2(CO2)4(H2O)2 paddle-wheel unit, which can be viewed as a 4-connected node (yellow, square SBU); (b) the organic linker ABTC4- unit, which coordinates to four Cu2(CO2)4(H2O)2 units can act as a 4-connected node (blue, rectangular SBU); (c) view along the c axes showing hexagonal channels with a pore diameter of about 9.6 Å; (d) square SBUs (yellow) and rectangular SBUs (blue) form the NbO network. Color code: Cu, yellow; O, red; C, gray; N, blue. (Hydrogen atoms, guest molecules, and terminal H2O molecules have been omitted for clarity.)
High-Pressure Hydrogen Sorption Measurement. High-pressure hydrogen sorption isotherm measurements on JUC-62 were recorded using a RUBOTHERM magnetic suspension balance (Ankersmid B.V., Netherlands). High purity hydrogen (99.999%) was used for the measurement. About 150 mg of as-synthesized blue-green crystalline sample of JUC-62 was immersed in acetone for 2 h, and fresh acetone was added after the extract was decanted, which was operated at least five times. Then the crystals were allowed to immerse in acetone for 24 h to remove the guest solvates (DMF and H2O). After the removal of acetone by decanting, the sample was dried under a dynamic vacuum (
