Four 3D Porous MetalâOrganic Frameworks with Various Layered and

Four 3D Porous Metal-Organic Frameworks with Various Layered and Pillared Motifs Wen-Guan Lu,†,‡ Long Jiang,† Xiao-Long Feng,† and Tong-Bu Lu*,† MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, State Key Laboratory of Optoelectronic Materials and Technologies, and School of Chemistry and Chemical Engineering, Sun Yat-Sen UniVersity, Guangzhou 510275, China, and Department of Chemistry, Shaoguan UniVersity, Shaoguan, 512005 China

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 3 986–994

ReceiVed October 7, 2007; ReVised Manuscript ReceiVed NoVember 22, 2007

ABSTRACT: Hydrothermal reactions of imidazole-4,5-dicarboxylic acid (H3IDC), 4,4′-bipyridine (bpy), and Cd(NO3)2 · 4H2O under different conditions yielded four novel three-dimensional (3D) porous metal-organic frameworks (MOFs) of {[Cd5(IDC)2(HIDC)(bpy)3(py)2(H2O)3] · 2NO3 · 2H2O}n (1), [Cd5(HIDC)2(IDC)2(py)2]n (2), {[Cd5(IDC)3(bpy)2(H2O)2] · NO3 · 3.5H2O}n (3), and {[KCd4(IDC)2.5(bpy)2(H2O)2] · 1.5NO3 · 3H2O}n (4). X-ray single-crystal structural analyses revealed that IDC3- and HIDC2in 1–4 exhibit six different types of coordination modes, among them two modes are first reported in this presentation. In 1 and 4, the cadmium ions are interconnected by µ5-IDC3- in two different asymmetrical coordination modes to produce two different infinite two-dimensional (2D) layers, which are further pillared by µ2-bpy (in 1) or µ5-IDC3- and µ2-bpy alternately (in 4) to form 3D porous MOFs of 1 and 4, in which the two asymmetrical coordination modes of µ5-IDC3- have not been reported. In 2 and 3, the cadmium ions are interconnected by µ5-IDC3- in a symmetrical coordination mode to form similar infinite 2D layers, and the 2D layers are further pillared by µ4-HIDC2- (in 2) or µ4-IDC3- and µ2-bpy alternately (in 3) to form 3D porous MOFs of 2 and 3. There are two different sizes of pores in 3 and 4, while the porous sizes are uniform in 1 and 2. Compounds 1, 2, and 4 display blue fluorescent emissions in the solid state at room temperature. Introduction The investigation of the assembly of porous metal-organic frameworks (MOFs) has attracted great interest due to their versatile architecture and promising applications for ionexchange, gas storage, separation, and catalysis.1–6 One of the most effective approaches to synthesizing novel porous MOFs with unique structures and properties is hydrothermal/solvothermal synthesis by incorporating appropriate metal ions (connectors) with multifunctional bridging ligands (linkers). In a special reaction environment with higher temperature and pressure, the reaction becomes faster, thus leading to a higher degree of reversibility in the process of crystal growth.7 However, hydrothermal synthesis is a relatively complex process, and the final products under a given set of conditions are often unpredictable. Generally, many factors can affect the structures of MOFs containing carboxylate ligands, such as counteranions,8 the pH values of the reaction solutions,9 temperature,10 and molar ratio between metal salts and ligands,11 and reaction solvent system.12 Therefore, by using the same building blocks, a series of MOFs with different structures can be constructed by changing various reaction conditions.7–13 Recently, imidazole-4,5-dicarboxylic acid (H3IDC), a planar rigid ligand containing two nitrogen and four oxygen atoms, has attracted much interest in coordination chemistry. H3IDC can be partially or fully deprotonated to generate H2IDC-, HIDC2-, and IDC3- anions at different pH values. Therefore, H3IDC can potentially afford various coordination modes in multicoordinated ways with metal ions to form a series of MOFs with different structures and useful properties.5g,h,6d,8a,10d,11b,12a,14–19 On the other hand, many MOFs containing polynuclear d10 metal ions exhibit intriguing photoluminescent properties.8,9a,11b,18,19b,20 * To whom correspondence should be addressed. Fax: +86-20-84112921. E-mail: [email protected]. † Sun Yat-Sen University. ‡ Shaoguan University.

We are also interested in the coordination chemistry of H3IDC, and we have found that this ligand is effective in promoting noninterpenetrated porous MOFs due to its multiple coordination interactions with metal ions,8a,18a,e which show novel structures and useful adsorption and luminescent properties. As an extension of our previous investigations on non-interpenetrated porous MOFs based on H3IDC and d10 metal ions, a series of new three-dimensional (3D) porous MOFs have been constructed. Herein, we reported on the synthesis and crystal structures of four 3D porous MOFs of {[Cd5(IDC)2(HIDC)(bpy)3(py)2(H2O)3] · 2NO3 · 2H2O}n (1) (bpy ) 4,4′bipyridine, py ) pyridine), [Cd5(HIDC)2(IDC)2(py)2]n (2), {[Cd5(IDC)3(bpy)2(H2O)2] · NO3 · 3.5H2O}n (3),and{[KCd4(IDC)2.5(bpy)2(H2O)2] · 1.5NO3 · 3H2O}n (4), which exhibit various layered and pillared motifs. Experimental Section General Remarks. H3IDC was prepared from benzoimidazole in 75% yield. All of other chemicals are commercially available and used without further purification. Elemental analyses were determined using an Elementar Vario EL elemental analyzer. The IR spectra were recorded in the 4000–400 cm-1 region using KBr pellets and a Bruker EQUINOX 55 spectrometer. Photoluminescent measurements were conducted on a Shimadzu RF-5301PC fluorescence spectrophotometer, at room temperature for the solid polycrystalline samples. Thermal gravimetric analysis (TGA) data were collected on a Netzsch TG-209 instrument under air atmosphere in the temperature range 20–600 °C with a heating rate of 10 °C/min. The variation temperature powder X-ray diffraction (XPRD) measurements were recorded on a RIGAKU D/MAX 2200 VPC diffractometer. {[Cd5(IDC)2(HIDC)(bpy)3(py)2(H2O)3] · 2NO3 · 2H2O}n (1). A mixture of Cd(NO3)2 · 4H2O (0.308 g, 1.0 mmol), H3IDC (0.078 g, 0.50 mmol), bpy (0.156 g, 1.0 mmol), py (1.0 mL), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 170 °C for 7 days, and then cooled to room temperature at a rate of 10 °C/h. The pH values of the solution in the starting and ending reactions are ca. 6. Pale block-shaped crystals of 1 were collected, washed with distilled water, and dried in air. Yield: 0.238 g, 63% base on Cd(NO3)2 · 4H2O. Anal. Calcd for C55H52Cd5N16O25: C, 34.78; H, 2.76;

10.1021/cg700979r CCC: $40.75  2008 American Chemical Society Published on Web 01/11/2008

3D Porous Metal-Organic Frameworks

Crystal Growth & Design, Vol. 8, No. 3, 2008 987 Table 1. Crystal Data and Structure Refinements for 1-4

compound

1

2

3

4

formula formula weight crystal system, space group a /Å b /Å c /Å R/° β/° γ/° V /Å3, Z F(000) crystal size/mm3 θ range for data collection/° reflections collected/unique (Rint) obsd reflns [I g 2σ(I)] data/restraints/parameters Dc/Mg · m-3 goodness-of-fit on F2 final R indices [I g 2σ(I)] R1, wR2 R indices (all data) R1, wR2

C55H48Cd5N16O23 1863.12 orthorhombic, Cmma 19.041(4) 23.089(5) 15.056(3) 90 90 90 6619(2), 4 3656 0.25 × 0.25 × 0.10 1.35 to 26.00 16107/3396 (Rint ) 0.0601) 2740 3396/436/316 1.866 1.176 0.0954, 0.2002 0.1157, 0.2113

C30H16Cd5N10O16 1334.53 orthorhombic, Pnma 14.4247(17) 16.2067(19) 15.7309(18) 90 90 90 3677.5(7), 4 2536 0.41 × 0.35 × 0.31 1.80 to 27.06 30193/4168 (Rint ) 0.0250) 3666 4168/1/296 2.410 1.090 0.0202, 0.0479 0.0252, 0.0500

C35H30Cd5N11O20.5 1494.73 orthorhombic, Cmca 16.6207(7) 15.3719(12) 37.354(3) 90 90 90 9543.7(12), 8 5768 0.12 × 0.08 × 0.07 4.09 to 62.04 13884/3727 (Rint ) 0.0674) 2838 3727/252/342 2.065 1.040 0.0915, 0.2009 0.1090, 0.2088

C32.5H28.5Cd4KN10.5O19.5 1366.86 monoclinic, P2/c 19.374(2) 14.8874(18) 15.3721(18) 90 111.753(2) 90 4118.0(8), 4 2656 0.32 × 0.18 × 0.01 1.13 to 27.06 24277/8961 (Rint ) 0.0486) 5552 8961/96/569 2.205 1.072 0.0681, 0.2085 0.1113, 0.2444

N, 11.80%. Found: C, 34.58; H, 2.82; N, 11.93%. IR data (KBr, cm-1): 3403m, 3067m, 1576s, 1533s, 1474s, 1443s, 1398s, 1368s, 1289m, 1250s, 1220m, 1101s, 1067m, 1005m, 867m, 829m, 811m, 759w, 703w, 665m, 628m, 519w, 485w. [Cd5(HIDC)2(IDC)2(py)2]n (2). A mixture of Cd(NO3)2 · 4H2O (0.308 g, 1.0 mmol), H3IDC (0.156 g, 1.0 mmol), bpy (0.156 g, 1.0 mmol), py (1.0 mL), KOH (0.112 g, 2.0 mmol), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 180 °C for 3 days, followed by cooling to 100 °C at a rate of 10 °C/h, and held at this temperature for 10 h, then cooled to room temperature. The pH values of the solution before and after reactions are ca. 8 and 6, respectively. Pale block-shaped crystals of 2 were collected, washed with distilled water, and dried in air. Yield: 0.134 g, 50% based on Cd(NO3)2 · 4H2O. Anal. Calcd for C30H16N10O16Cd5: C, 27.00; H, 1.21; N, 10.50%. Found: C, 26.22; H, 1.59; N, 10.76%. IR data (KBr, cm-1): 3162w, 3070w, 1681m, 1600s, 1461s, 1379s, 1281m, 1233s, 1093s, 1012m, 857s, 829s, 783s, 663w, 627w, 521w, 490m, 440w. It is noteworthy that bpy is not incorporated into 2. However, without adding bpy, a different compound of [Cd(HIDC)(py)]n was formed.16d {[Cd5(IDC)3(bpy)2(H2O)2] · NO3 · 3.5H2O}n (3). A mixture of Cd(NO3)2 · 4H2O (0.308 g, 1.0 mmol), H3IDC (0.078 g, 0.50 mmol), bpy (0.078 g, 0.50 mmol), KOH (0.084 g, 1.5 mmol), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 170 °C for 7 days, and then cooled to room temperature at a rate of 10 °C/h. The pH values of the solution before and after reactions remain ca. 6. Pale cuboid crystals of 3 were collected, washed with distilled water, and dried in air. Yield: 0.190 g, 63% based on Cd(NO3)2 · 4H2O (the flake-shaped crystals of 4 were simultaneously formed with a yield less than 2%, which were separated by hand). Anal. Calcd for C35H30Cd5N11O20.5: C, 28.12; H, 2.02; N, 10.31%. Found: C, 27.89; H, 1.74; N, 10.54%. IR data (KBr, cm-1): 3427m, 1599s, 1468s, 1414m, 1369s, 1287s, 1070w, 834m, 810m, 666m, 631m, 543w. {[KCd4(IDC)2.5(bpy)2(H2O)2] · 1.5NO3 · 3H2O}n (4). A mixture of Cd(NO3)2 · 4H2O (0.308 g, 1.0 mmol), H3IDC (0.039 g, 0.25 mmol), bpy (0.078 g, 0.50 mmol), KOH (0.042 g, 0.75 mmol), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 170 °C for 7 days, and then cooled to room temperature at a rate of 10 °C/h. The pH values of the solution before and after the reactions remained ca. 6. Colorless flake-shaped crystals of 4 were collected, washed with distilled water, and dried in air. Yield: 0.056 g, 21% based on Cd(NO3)2 · 4H2O. Anal. Calcd for C32.5H28.5Cd4KN10.5O19.5: C, 28.56; H, 2.10; N, 10.76. Found: C, 29.03; H, 2.26; N, 11.03. IR data (KBr, cm-1): 3361m, 3090m, 1611s, 1532s, 1463s, 1361s, 1240m, 1222m, 1087s, 845m, 805s, 667m, 631m, 543m, 502m. X-ray Crystallography. Single crystal data for 1, 2, and 4 were collected on a Bruker Smart 1000 CCD diffractometer, with Mo KR radiation (λ ) 0.71073 Å). The empirical absorption corrections were applied using the SADABS program.21 Single crystal data for 3 were collected on a CrysAlis CCD, Gemini S Ultra (Oxford Diffraction Ltd.), with Cu KR radiation (λ ) 1.5418 Å). The empirical absorption corrections were applied using spherical harmonics, implemented in

SCALE3 ABSPACK scaling algorithm. The structures were solved using direct methods, and refined with the full-matrix least-squares technique using the SHELXTL program.22 Anisotropic thermal parameters were applied to all nonhydrogen atoms. All the hydrogen atoms of the ligands were placed in calculated positions with fixed isotropic thermal parameters and included in the structure factor calculations in the final stage of full-matrix least-squares refinement. The aqua hydrogen atoms in 1, 3, and 4 were not included from difference maps. The positions of pyridine and µ2-HIDC2- in 1, NO3- in 1 and 4, and potassium ions in 4 are disordered and were refined with the constraint. The crystal data are summarized in Table 1. The selected bond lengths and angles are given in Table 2.

Results and Discussion Syntheses. The hydrothermal reactions of Cd(NO3)2 · 4H2O with H3IDC and bpy under different conditions in water yielded four 3D porous MOFs. First, the stoichiometry of starting materials is important for the formations of these compounds. The reactions of Cd(NO3)2 · 4H2O, H3IDC, and bpy in a molar ratio of 2:1:2, 1:1:1, 2:1:1, and 4:1:2 produced the crystals of 1–4, respectively, while other stoichiometries failed to produce suitable crystals or gave products with low yields (about 2%). Second, the final pH values of the solutions are another crucial factor for the formation of crystalline products, as the crystals could not be obtained at a final pH value higher than 7 or lower than 6. Third, all the crystals of 1–4 were obtained by cooling the vessel at a rate of 10 °C/h. If the vessel was cooled to room temperature directly, the quality of isolated crystals is not good enough for structural analysis. All 1–4 are stable in air and insoluble in common solvents. All the peaks displayed in the measured powdered X-ray diffraction (PXRD) patterns for the samples of 1–4 can closely match those in the simulated patterns generated from single-crystal diffraction data (Figures S1 and S2, Supporting Information), indicating a single phase for each compound is formed. The existences of uncoordinated NO3anions in 1, 3, and 4 are supported by the results of IR spectra measurements, which exhibit strong peaks around 1360–1370 cm-1. {[Cd5(IDC)2(HIDC)(bpy)3(py)2(H2O)3] · 2NO3 · 2H2O}n (1). As illustrated in Figure 1a, the asymmetrical unit in 1 contains four Cd(II) ions, in which Cd(1) shows a distorted N2O5 pentagonal bipyramidal geometry, and the other three Cd(II) ions show a distorted octahedral geometry. Cd(1) is seven-coordinated with four oxygen atoms (O(1), O(2), O(1i), and O(2i)) from two individual asymmetrical µ5-IDC3- (Scheme 1a) and one water

988 Crystal Growth & Design, Vol. 8, No. 3, 2008

Lu et al.

Table 2. Selected Bond Lengths (Å) and Angles (°) for 1–4a 1 Cd(1)-N(5)#1 Cd(1)-O(2) Cd(1)-O(1)#1 Cd(2)-O(1) Cd(3)-N(3)#1 Cd(3)-O(2) Cd(4)-O(4)#4 Cd(4)-O(5) N(5)#1-Cd(1)-N(5) O(1W)-Cd(1)-O(2)#1 O(1)-Cd(1)-O(1)#1 N(1)#2-Cd(2)-O(1) N(3)#1-Cd(3)-N(3) N(2)-Cd(4)-O(4)#4

2.300(15) 2.379(11) 2.547(11) 2.363(11) 2.28(2) 2.287(11) 2.282(13) 2.483(18) 174.2(8) 145.1(3) 173.6(5) 106.9(4) 178.2(10) 135.2(5)

Cd(1)-N(5) Cd(1)-O(2)#1 Cd(2)-N(1)#2 Cd(2)-O(2W) Cd(3)-O(3) Cd(3)-N(3) Cd(4)-N(6) Cd(4)-N(7) O(1W)-Cd(1)-O(1) O(1W)-Cd(1)-O(2) N(1)#2-Cd(2)-N(1) O(1)#2-Cd(2)-O(1) O(3)-Cd(3)-O(2)#1 N(6)-Cd(4)-O(4)

2.300(15) 2.379(11) 2.201(13) 2.345(19) 2.252(12) 2.28(2) 2.218(13) 2.359(2) 93.2(2) 145.1(3) 180.000(3) 180.000(2) 154.5(4) 159.05(14)

Cd(1)-O(1W) Cd(1)-O(1) Cd(2)-N(1) Cd(2)-O(1)#2 Cd(3)-O(3)#1 Cd(3)-O(2)#1 Cd(4)-N(2) Cd(4)-O(4) O(2)-Cd(1)-O(1)#1 O(2)#1-Cd(1)-O(1) N(1)-Cd(2)-O(1)#2 O(3)-Cd(3)-O(3)#1 O(3)#1-Cd(3)-O(2) N(7)-Cd(4)-O(5)

2.30(2) 2.547(11) 2.201(13) 2.363(11) 2.252(12) 2.287(11) 2.262(14) 2.382(14) 121.8(4) 121.8(4) 106.9(4) 124.1(6) 154.5(4) 162.6(4)

2.242(2) 2.3643(18) 2.274(2) 2.4204(18) 2.224(2) 2.320(4) 106.01(8) 107.45(8) 126.82(7) 162.39(7) 175.30(7)

Cd(1)-O(7) Cd(1)-O(3)#1 Cd(2)-N(1) Cd(2)-O(3)#1 Cd(3)-O(6)#5 Cd(3)-N(5) N(2)#1-Cd(1)-O(7)#2 O(7)-Cd(1)-N(4)#2 O(5)#3-Cd(2)-O(1) N(1)-Cd(2)-O(3)#1 N(6)-Cd(3)-N(5)

2.2695(19) 2.694 2.292(2) 2.4252(19) 2.271(2) 2.355(4) 119.65(8) 134.70(7) 109.99(7) 136.26(7) 176.90(12)

2.255(12) 2.326(15) 2.314(14) 2.372(11) 2.205(13) 2.24(3) 112.6(4) 113.3(5) 139.1(5) 176.8(5)

Cd(1)-N(2)#3 Cd(1)-O(2) Cd(2)-N(3)#5 Cd(2)-O(6)#5 Cd(3)-O(5)#2 Cd(3)-O(2W) O(3)#3-Cd(1)-O(1) N(4)-Cd(1)-O(2) O(1)-Cd(2)-O(6)#5 O(1W)-Cd(3)-O(2W)

2.270(13) 2.462(12) 2.310(14) 2.408(10) 2.244(12) 2.27(3) 146.3(4) 162.8(5) 172.2(4) 176.0(12)

2.253(8) 2.335(7) 2.236(7) 2.452(11) 2.237(7) 2.449(10) 2.235(8) 2.304(7) 104.1(4) 107.4(3) 165.9(4) 169.2(4) 116.1(4) 109.4(3)

Cd(1)-O(1) Cd(1)-O(9) Cd(2)-O(5) Cd(2)-O(2) Cd(3)-O(2) Cd(3)-O(5) Cd(4)-O(6) Cd(4)-O(9)#4 O(1)-Cd(1)-O(9) O(4)#1-Cd(1)-O(9) O(8)#3-Cd(2)-O(2) O(4)#1-Cd(3)-O(5) O(6)-Cd(4)-O(9)#4 O(8)#3-Cd(4)-O(9)#4

2.268(7) 2.525(8) 2.257(7) 2.456(7) 2.286(7) 2.488(7) 2.245(7) 2.586(8) 122.1(3) 149.2(2) 166.7(2) 165.0(2) 118.5(3) 148.0(2)

2 Cd(1)-O(1) Cd(1)-N(4)#2 Cd(2)-O(5)#3 Cd(2)-O(5) Cd(3)-O(8) Cd(3)-O(6)#3 O(1)-Cd(1)-N(2)#1 O(1)-Cd(1)-O(7)#2 O(5)#3-Cd(2)-N(3) N(3)-Cd(2)-O(1) O(8)-Cd(3)-O(6)#5

2.2365(18) 2.285(2) 2.2486(18) 2.3858(18) 2.224(2) 2.2707(19) 124.72(7) 115.08(7) 135.71(7) 109.93(7) 175.30(7)

Cd(1)-N(2)#1 Cd(1)-O(7)#2 Cd(2)-N(3) Cd(2)-O(1) Cd(3)-O(8)#4 Cd(3)-N(6) O(1)-Cd(1)-O(7) N(2)#1-Cd(1)-N(4)#2 N(1)-Cd(2)-O(5) O(5)-Cd(2)-O(1) O(8)#4-Cd(3)-O(6)#3

Cd(1)-O(6) Cd(1)-O(1) Cd(2)-N(1) Cd(2)-O(1) Cd(3)-O(4) Cd(3)-O(5) O(6)-Cd(1)-N(2)#3 N(2)#3-Cd(1)-O(1) N(1)-Cd(2)-N(5)#4 O(4)-Cd(3)-O(5)#2

2.129(11) 2.256(12) 2.200(14) 2.357(12) 2.205(13) 2.244(11) 143.2(5) 100.4(5) 152.3(5) 176.8(5)

Cd(1)-O(3)#3 Cd(1)-N(4) Cd(2)-N(5)#4 Cd(2)-O(3) Cd(3)-O(4)#2 Cd(3)-O(1W) O(6)-Cd(1)-O(1) O(1)-Cd(1)-N(4) N(3)#5-Cd(2)-O(3) O(4)#2-Cd(3)-O(5)

3

4 Cd(1)-N(5) Cd(1)-N(9)#2 Cd(2)-N(1) Cd(2)-N(6) Cd(3)-N(3) Cd(3)-N(8) Cd(4)-O(10)#4 Cd(4)-N(7)#5 N(2)#1-Cd(1)-O(1) N(5)-Cd(1)-N(9)#2 N(1)-Cd(2)-O(5) N(3)-Cd(3)-O(2) N(4)#3-Cd(4)-O(6) O(10)#4-Cd(4)-N(7)#5

2.199(10) 2.294(10) 2.199(8) 2.403(9) 2.202(8) 2.411(10) 2.226(9) 2.266(9) 156.3(3) 148.3(4) 143.7(3) 141.5(3) 157.8(3) 134.5(4)

Cd(1)-N(2)#1 Cd(1)-O(4)#1 Cd(2)-O(8)#3 Cd(2)-O(1W) Cd(3)-O(4)#1 Cd(3)-O(2W) Cd(4)-N(4)#3 Cd(4)-O(8)#3 N(5)-Cd(1)-O(4)#1 N(9)#2-Cd(1)-O(4)#1 N(6)-Cd(2)-O(1W) N(8)-Cd(3)-O(2W) O(10)#4-Cd(4)-O(8)#3 N(7)#5-Cd(4)-O(8)#3

a Symmetry transformations used to generate equivalent atoms: #1 -x + 1, -y + 3/2, z. #2 -x + 1/2, -y + 3/2, -z + 2. #3 x, -y + 3/2, z. #4 -x + 1/2, -y + 3/2, -z + 1 for 1; #1 -x + 3/2, -y + 1, z + 1/2. #2 -x + 1, -y + 1, -z + 2. #3 -x + 2, -y + 1, -z + 2. #4 x, -y + 3/2, z. #5 -x + 2, y + 1/2, -z + 2 for 2; #1 -x + 1/2, y, -z + 3/2. #2 -x + 1, y, z. #3 -x + 1/2, y + 1/2, z. #4 x, -y, -z + 1. #5 -x + 1/2, y - 1/2, z. for 3; #1 x, -y + 2, z + 1/2. #2 -x + 1, -y + 2, -z, #3 x, -y + 1, z - 1/2. #4 x, y - 1, z. #5 -x + 1, -y + 1,-z for 4.

molecule (O(1W)) in the equatorial plane, and two nitrogen atoms (N(5) and N(5i)) from two µ2-bpy in axial positions. To our knowledge, the asymmetrical µ5-IDC3- coordination mode has not been found in the reported MOFs containing IDC3ligands. In 1, Cd(2) is six-coordinated with two oxygen atoms (O(1) and O(1ii)) and two nitrogen atoms (N(1) and N(1ii)) from two individual µ5-IDC3- in the equatorial plane, and two water molecules (O(2W) and O(2Wii)) in axial positions. The coordination environment of Cd(3) is similar to that of Cd(2), being ligated by four oxygen atoms (O(2), O(3), O(2i), and O(3i)) from two individual µ5-IDC3- in the equatorial plane, and two nitrogen atoms (N(3) and N(3i)) from two monodentate bpy in axial positions. Cd(4) is ligated by two oxygen atoms

(O(4) and O(4iv)) and one nitrogen atom (N(2) from two individual µ5-IDC3-, and nitrogen atom (N(6) from a µ2HIDC2- (Scheme 1b) in the equatorial plane, and one pyridine nitrogen atom (N(7)) and one oxygen atom (O(5)) from the µ2HIDC2- in axial positions. In 1, the Cd(II) ions are connected via µ5-IDC3- and µ2HIDC2- bridges to form a 2D sheet along the ac plane (Figure 1b). The 2D sheets are further pillared by µ2-bpy (through the connection of two Cd(1) belong to two adjacent sheets) to form a novel 3D porous MOF of 1 (Figure 1c). The porous sizes are 15.1 × 11.6 and 11.6 × 9.5 Å (measured by the Cd · · · Cd distances) along the a and c axis, respectively. The pores are filled with coordinated py (to Cd(4)), monodentate coordinated


Crystal Growth & Design, Vol. 8, No. 3, 2008 989

Figure 1. (a) The coordination environments of cadmium and bridging modes of µ5-IDC3- and µ2-HIDC2- in 1. (b) The 2D sheet along the ac plane. (c) The 3D MOF with 1D channels along the a (left) and c (right) axis, the coordinated py and water molecules, monodentate coordinated bpy, and uncoordinated NO3- anions and lattice–water molecules are omitted for clarity.

bpy (to Cd(3)), and coordinated water molecules (to Cd(2)), as well as uncoordinated NO3- anions and lattice–water molecules. There are π · · · π interactions between monodentate coordinated bpy molecules and adjacent µ2-bpy pillars, with a distance of 3.51 Å. It should be noted that coordinated py and monodentate

bpy molecules, as well as uncoordinated NO3- may be exchanged by other molecules or anions, and this investigation is ongoing. [Cd5(HIDC)2(IDC)2(py)2]n (2). Compound 2 consists of three Cd(II) with different coordination environments (Figure 2a), and


Lu et al.

Scheme 1. The various coordination modes of HIDC2- and IDC3- in 1–4, in which the modes of a and f are new

two kinds of symmetrical coordination modes of µ4-HIDC2(Scheme 1c) and µ5-IDC3- (Scheme 1d). All three Cd(II) display distorted octahedral geometries, in which each Cd(1) and Cd(2) is six-coordinated by two individual µ4-HIDC2- and two individual µ5-IDC3- via monodentate and N,O-chelating bidentate modes, while Cd(3) is coordinated by four oxygen atoms from two individual µ5-IDC3- and two pyridine molecules. The coordination environments of Cd(3) is different from that in a recent reported compound of {[Cd5(IDC)2(HIDC)2(H2O)] · 6H2O}n,11b in which Cd(1) and Cd(2) are six-coordinated with octahedral geometries, while Cd(3) is five-coordinated with square pyramidal geometry. In 2, the Cd(II) ions are connected via µ5-IDC3- bridges to form an undulated 2D sheet along the ab plane (Figure 2b).

The 2D sheets are then pillared by µ4-HIDC2- to form a 3D porous MOF of 2 (Figure 2c). The pores are opened along the a axis, with the porous size of 6.7 × 6.0 Å (measured by the Cd · · · Cd distances), which are filled with coordinated pyridine molecules. The framework of 2 is similar to those of recent reported compounds of [Zn5(IDC)2(HIDC)2(DMF)4]n,18f and {[Cd5(IDC)2(HIDC)2(H2O)] · 6H2O}n,11b whose channels are occupied by coordinated DMF and water molecules, respectively. {[Cd5(IDC)3(bpy)2(H2O)2] · NO3 · 3.5H2O}n (3). As illustrated in Figure 3a, there are two kinds of symmetrical coordination modes of µ5-IDC3- (Scheme 1d) and µ4-IDC3- (Scheme 1e), and one asymmetrical unit of 3 contains two and halfcrystallographically independent Cd(II) ions, and each Cd(II)

Figure 2. (a) The coordination environments of cadmium and bridging modes of µ5-IDC3- and µ4-HIDC2- in 2 (each py molecule connected to Cd(3) ion was drawn as one nitrogen atom for clarity). (b) The 2D sheet along the ab plane. (c) The 3D MOF with 1D channels along a axis (all py molecules are omitted for clarity).



Figure 3. (a) The coordination environments of cadmium and bridging modes of symmetrical µ5-IDC3- and µ4-IDC3- in 3 (bpy molecule connected to Cd(2) was drawn as one nitrogen atom for clarity). (b) The 2D sheet along the ab plane. (c) The 3D MOF with two different sizes of 1D open channels along the b axis (uncoordinated NO3-, coordinated and lattice–water molecules are omitted for clarity).

shows a distorted octahedral geometry. Cd(1) is ligated by two oxygen and one nitrogen atoms (O(6), O(3iii), N(2iii)) from two individual µ5-IDC3-, two oxygen atoms (O(1) and O(2)) from a µ4-IDC3-, and one nitrogen atom (N(4)) from µ2-bpy. Cd(2) is six-coordinated to two oxygen and one nitrogen atoms (O(3), O(6v), N(3v)) from two individual µ5-IDC3-, one oxygen and nitrogen atoms (O(1), N(1)) from a µ4-IDC3-, and one nitrogen atom (N(5iv)) from µ2-bpy. Cd(3) is coordinated to four oxygen atoms (O(4), O(4ii), O(5), and O(5ii)) from two individual µ5-IDC3-, and two water molecules (O(1W) and O(2W)). In 3, each µ5-IDC3- bridges five Cd(II) ions to generate an undulated 2D sheet along the ab plane (Figure 3b). The structural motif of 2D sheet is similar to those in 2 and {[Cd5(HIDC)2(IDC)2(H2O)] · 6H2O}n,11b while it is different from that in 1. The 2D sheets are further pillared alternately by µ4-IDC3- and µ2-bpy (through the bridging Cd(1) and Cd(2) in one sheet and Cd(1) and Cd(2) in adjacent sheet) to give a novel 3D porous MOF of 3 (Figure 3c), with two different sizes of one-dimensional (1D) open channels along the b axis. The porous sizes are approximately 11.7 × 6.7 Å and 6.7 × 6.6 Å (measured by the Cd · · · Cd distances), in which the larger pores are occupied by coordinated and lattice–water molecules, and uncoordinated NO3-, and the smaller pores are filled with coordinated and lattice–water molecules only. {[KCd4(IDC)2.5(bpy)2(H2O)2] · 1.5NO3 · 3H2O}n (4). As illustrated in Figure 4a, IDC3- exhibits two kinds of coordina-

tion modes of symmetrical µ4-IDC3- (Scheme 1e) and asymmetrical µ5-IDC3- (Scheme 1f), in which the latter has not been reported before. The asymmetrical unit in 4 contains four crystalographically independent Cd(II) ions with distorted octahedral geometry, in which Cd(1) is ligated by three oxygen and three nitrogen atoms from two individual µ5IDC3-, one µ4-IDC3-, and one µ2-bpy, respectively; Cd(2) and Cd(3) show similar N2O4 coordination environments with three oxygen and one nitrogen atoms from three individual µ5-IDC3- occupying the equatorial plane, and one nitrogen atom from µ2-bpy, and one coordinated water molecule occupying the axial positions; Cd(4) is coordinated by four oxygen and two nitrogen atoms from two individual µ5IDC3-, one µ4-IDC3- and one µ2-bpy, respectively. The Cd(II) ions in 4 are connected by µ5-IDC3- to produce an infinite 2D sheet containing [Cd(IDC)]4 rings along the bc plane (Figure 4b). The motif of 2D sheet is different from those in 1–3. Similar to 3, the planar 2D sheets are further pillared alternately by µ2-bpy and µ4-IDC3- to generate a 3D porous MOF with two different sizes of 1D open channels along the b axis (Figure 4c). The porous size are approximately 11.7 × 8.1 Å and 8.1 × 6.6 Å (measured by the Cd · · · Cd distances), in which the larger pores are occupied by lattice–water molecules and uncoordinated NO3-, and the smaller pores are filled with coordinated and lattice–water molecules. The potassium ions are located at the surfaces of the smaller pores and are weakly interacted with the oxygen atoms (O(10)) of µ4-IDC3-. It should


Lu et al.

Figure 4. The coordination environments of cadmium and bridging modes of asymmetrical µ5-IDC3- and symmetrical µ4-IDC3- in 4 (bpy molecules connected to Cd(1) and Cd(4) were drawn as one nitrogen atom for clarity). (b) The 2D sheet along the bc plane. (c) The 3D MOF with two different sizes of 1D open channels along the b axis (uncoordinated NO3-, coordinated and lattice–water molecules and K+ are omitted for clarity).

be pointed out that construction of a porous MOF whose pore surfaces immobilize regularly ordered and available alkali cations is one of the challenges toward materials with high performance pores.4f Thus 4 has a potential use for hydrocarbon transformation since alkali cations in zeolites have been demonstrated to serve as catalytic sites for hydrocarbon transformation. XPRD, Thermal Stability, and Luminescent Properties. The XPRD patterns at different temperatures (Figure S1, Supporting Information) indicate that the MOFs of 1 and 2 are stable up to 250 and 300 °C, respectively. Compounds 1 and 2 show similar thermal behaviors, which are different from those of 3 and 4 (Figure 5). The TGA curves of 1 exhibit an initial weight loss from room temperature to 156 °C, with the observed weight loss of 6.9% corresponding to the release of coordinated and lattice–water molecules (calcd 6.6%). After that an additional weight loss of 4.3% up to 250 °C may be attributed to the gradual release of coordinated py or monodentate bpy molecules. The TGA diagram of 2 displays a gradual weight loss of 12.0% up to 300 °C, corresponding to the loss of two coordinated py molecules per formula unit (calcd. 11.9%). The TGA curves of 3 and 4 display an initial weight loss around 250 °C for 3 and 150 °C for 4. The observed weight losses (5.5% for 3 and 5.8% for 4) are smaller than the calculated values for the loss of coordinated and lattice–water molecules

Figure 5. The TGA curves for 1-4.

(6.6% for 3 and 6.6% for 4). The deviations may be due to the easy loss of lattice–water molecules under ambient temperature. The frameworks are stable up to 380 and 350 °C for 3 and 4, respectively, and then began to decompose upon further heating.



References

Figure 6. The photoluminescent spectra of 1, 2, and 4 in the solid state at the room temperature.

The fluorescent emissions properties of 1-4 in the solid state at room temperature were investigated. Compound 3 exhibits very weak fluorescent emission under our experimental conditions. As shown in Figure 6, compounds 1, 2, and 4 exhibit blue photoluminescence with emission maxima at 437, 441, and 455 nm upon excitation at 339, 351, and 389 nm, respectively. For excitation wavelengths between 280 and 480 nm, a rather weak photoluminescence emission is observed for H3IDC (λem ) 410 nm) and bpy (λem ) 486 nm). Therefore, these emission bands can be attributed to the emission of ligand-to-metal charge transfer (LMCT), which have been found in many reported MOFs.8,9a,11b,18,19b,20 The different maximum emission positions may be attributed to the different coordination modes of IDC3and HIDC2- (Scheme 1) and coordination environments around cadmium ions, as photoluminescent behavior is closely associated with the metal ions and the ligands coordinated around them.20 Conclusions 18e

As we expected, imidazole-4,5-dicarboxylate, a rigid planar ligand containing multiple coordination sites, is beneficial for the construction of porous MOFs, as the multiple coordination interactions of HIDC2- and IDC3- to Cd(II) are effective in promoting non-interpenetrated MOFs. Therefore, using Cd(NO3)2 · 4H2O, H3IDC, and bpy as building blocks, we have successfully assembled four novel 3D non-interpenetrated porous MOFs with various layered and pillared motifs. In these 3D porous MOFs, IDC3-, and HIDC2- exhibit six different types of coordination modes, among them two asymmetrical µ5-IDC3- modes (Scheme 1a,f) are first found. The different coordination modes of IDC3- and HIDC2- lead to the formation of different layered structures, which are further connected by µ2-bpy, µ4-HIDC2-, µ4-IDC3-, and µ5-IDC3- pillars to construct four 3D porous MOFs of 1-4. Our results revealed that the structures of 3D porous MOFs are very affected by the reaction conditions such as the Cd(II)/H3IDC/bpy molar ratio, pH value, and the temperature, though the same building blocks were used. Thus, it still has a long way to approach the controlled synthesis of a defined structure. Acknowledgment. This work was supported by NSFC (20625103) and 973 Program of China (2007CB815305). Supporting Information Available: X-ray crystallographic file in CIF format; XPRD patterns of 1–4. This material is available free of charge via the Internet at http://pubs.acs.org.

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