A Series of 2D and 3D MetalâOrganic ... - ACS Publications

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A Series of 2D and 3D MetalOrganic Frameworks Based on a Flexible Tetrakis(4-pyridyloxymethylene)methane Ligand and Polycarboxylates: Syntheses, Structures, and Photoluminescent Properties Jiao Guo, Jian-Fang Ma,* Bo Liu, Wei-Qiu Kan, and Jin Yang* Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People's Republic of China

bS Supporting Information ABSTRACT: A series of structurally diverse metalorganic frameworks (MOFs), [Co 4 (TPOM)2 (L1)4 (H 2 O)4 ] 3 H 2 O (1), [Ni 2 (TPOM)(L2)2 (H2O)2] 3 2H2O (2), [Co2(TPOM)(L2)2(H2O)2] 3 H2O (3), [Cu4(TPOM)2(L3)4] 3 3H2O (4), [Co2(TPOM)0.5(L4)] (5), and [Cd(TPOM)(L3)3] 3 7H2O (6), where TPOM = tetrakis(4-pyridyloxymethylene)methane, H2L1 = 1,3benzenedicarboxylic acid, H2L2 = 5-hydroxyisophthalic acid, H3L3 = 1,3,5benzenetricarboxylic acid, and H4L4 = 1,2,4,5-benzenetetracarboxylic acid, have been hydrothermally synthesized. These complexes were structurally characterized by X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 shows a 3D 4-connected framework with a rare (84 3 62) topology. Compounds 2 and 3 are isostructural and display 3D 2-fold interpenetrating frameworks with (64 3 82)(66)2 topologies. Compound 4 exhibits a 2-fold interpenetrating structure with a scarce trinodal (3,4,5)-connected (4 3 62)(4 3 69)66 topology. Compound 5 possesses a 3D 4-connected net with the TPOM ligands located in the 3D channels. Compound 6 features 2D square layers (sql). The free TPOM ligands and L3 anions form discrete fragments through hydrogen bonds and ππ interactions. Interestingly, the fragments penetrate the 2D networks above and below to yield a unique 2D f 3D polythreading framework. The structural differences among such compounds show the effects of the carboxylates and central metals on the complex structures. The UVvis absorption spectra, optical energy gap, and luminescent properties were also investigated for the compounds.

’ INTRODUCTION The design and synthesis of metalorganic frameworks (MOFs) are of great interest not only for their potential applications in sorption,1 photochemical areas,2 magnetism,3 and catalysis4 but also for their intriguing variety of architectures and fascinating new topologies.5 So far, a large number of mixedligand MOFs with 1D, 2D, and 3D structures have been rationally designed and physically characterized.6,7 In this regard, metalpolycarboxylate complexes, in the presence of rigid N-donor bridging ligands, such as pyridine, 4,40 -bipyridine (bpy),8 1,2-bis(4-pyridyl)-ethane (bpe),9 1,2-di(4-pyridyl)-ethylene (dpe),10 and 1,3-bi(4-pyridyl)-propane (bpp),11 have been widely reported. However, metalpolycarboxylate compounds with flexible N-donor bridging ligands have not been well investigated.12 Among the N-donor bridging ligands, tetrakis(4-pyridyloxymethylene)methane (TPOM),13 an important flexible N-donor ligand, is a good candidate for the construction of MOFs with diverse structures. Because of the special arrangement of the four r 2011 American Chemical Society

pyridy N atoms, TPOM offers intriguing characteristics: On one hand, four pyridy N atoms of the TPOM ligand can act as four potential coordination nodes; on another hand, the four pyridy groups can freely twist around the quaternary carbon atom (Ccenter) and four CH2 groups with different bond angles to meet the requirements. Up to now, only several mixed-ligand MOFs containing TPOM have been reported.8,13 In this paper, six new MOFs based on TPOM and different carboxylates (Scheme 1) have been synthesized under hydrothermal conditions: [Co4(TPOM)2(L1)4(H2O)4] 3 H2O (1), [Ni2(TPOM)(L2)2(H2O)2] 3 2H2O (2), [Co2(TPOM)(L2)2(H2O)2] 3 H2O (3), [Cu4(TPOM)2(L3)4] 3 3H2O (4), [Co2(TPOM)0.5(L4)] (5), and [Cd(TPOM)(L3)3] 3 7H2O (6). These compounds are characterized by X-ray crystallography, elemental analysis, infrared spectra (IR), powder X-ray diffraction (PXRD), and Received: May 7, 2011 Revised: June 5, 2011 Published: June 24, 2011 3609

dx.doi.org/10.1021/cg200581w | Cryst. Growth Des. 2011, 11, 3609–3621

Crystal Growth & Design

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thermogravimetric (TG) analyses. The structures and topological analyses of these compounds, as well as the effects of coordination modes of TPOM ligands, carboxylates, and metal ions on the structures of the MOFs, have been discussed in detail. In addition, the photoluminescent property for compound 6 has been discussed in detail.

(TGA) was performed on a Perkin-Elmer TG-7 analyzer heated from 40 to 800 °C under nitrogen gas. The photoluminescent property and the quantum yield of compound 6 were measured on a Perkin-Elmer FLS-920 spectrometer. The excitation wavelength in photoluminescence quantum yield measurement was set as 340 nm, and the scan range of emission spectrum was 360675 nm with a scan step of 1 nm. Diffuse reflectivity spectra were collected on a finely ground sample with a Cary 500 spectrophotometer equipped with a 110 mm diameter integrating sphere. Diffuse reflectivity was measured from 200 to 2000 nm using barium sulfate as a standard with 100% reflectance. Crystal Structure Determination. Single-crystal X-ray diffraction data for 16 were recorded on a Oxford Diffraction Gemini R Ultra diffractometer with graphite-monochromated Mo KR radiation (λ = 0.71073 Å) at 293 K. Absorption corrections were applied using multiscan technique. All of the structures were solved by Direct Method of SHELXS-97 and refined by full-matrix least-squares techniques using the SHELXL-97 program.15,16 All nonhydrogen atoms were easily found from the Fourier difference maps and refined anisotropically, whereas the hydrogen atoms of the organic molecules were placed by geometrical considerations and were added to the structure factor calculation. All H atoms bound to carbon were refined using a riding model with d(CH) = 0.93 Å, Uiso = 1.2 Ueq(C) for aromatic and d(CH) = 0.97 Å, Uiso = 1.5 Ueq(C) for CH2 atoms. Some water H atoms and hydroxyl H atoms were located in a difference Fourier map and refined as riding atoms with d(OH) = 0.850.89 Å and Uiso = 1.5Ueq(O). The hydrogen atoms of the disordered atoms and some water O atoms in compounds 14 and 6 were not included in the models. The disordered C atoms of compound 2 (C19, C190 ; C20, C200 ; and C21, C210 ) were refined using C atoms split over two sites, with a total occupancy of 1. The topologies of compounds 15 were analyzed by using OLEX program.17 The detailed crystallographic data and structure refinement parameters for these compounds are summarized in Table 1. Selected bond distances and angles are listed in Tables S1S6 (Supporting Information). Synthesis of [Co4(TPOM)2(L1)4(H2O)4] 3 H2O (1). A mixture of CoCO3 (23.8 mg, 0.2 mmol), H2L1 (33.2 mg, 0.2 mmol), TPOM (22.2 mg, 0.05 mmol), and water (8 mL) was sealed in a Teflon reactor (15 mL), which was heated at 150 °C for 3 days, and then, it was cooled to 10 °C h1. Purple crystals of 1 were collected in a 64% yield (based on CoCO3). Anal. calcd for C82H74Co4N8O29 (Mr = 1871.20): C, 52.63; H, 3.99; N, 5.99. Found: C, 52.55; H, 4.03; N, 5.90. IR (KBr, cm1): 3446 (s),

’ EXPERIMENTAL SECTION Materials and Methods. The TPOM ligand was synthesized in accordance with the procedure reported.14 Reagents and solvents employed were commercially available and used as received without further purification. Physical Measurements. The C, H, and N elemental analysis was conducted on a Carlo Erba 1106 elemental analyzer. The FT-IR spectra were recorded from KBr pellets in the range 4000400 cm1 on a Mattson Alpha-Centauri spectrometer. Thermogravimetric analysis

Scheme 1. Polycarboxylate Ligands and N-Donor TPOM

Table 1. Crystal Data and Structure Refinements for Compounds 16

a

1

2

3

4

5

6

formula

C82H74Co4N8O29

C41H35N4Ni2O18

C41H37Co2N4O17

C86H70Cu4N8O35

C45H28Co2N4O20

C52H54CdN4O29

Mr

1871.20

989.07

975.60

2029.65

1062.51

1311.25

space group a (Å)

C2/c 18.1284(7)

P2/c 9.9686(12)

Pc 10.1977(8)

P21212 16.8478(8)

I41/acd 16.272(5)

P21/n 14.8271(7)

b(Å)

8.8472(3)

9.3686(7)

9.3925(7)

17.0353(9)

16.272(5)

14.2870(7)

c(Å)

26.6561(9)

24.551(3)

24.4616(17)

8.0615(5)

29.936(5)

27.5557(14) 90

R (°)

90

90

90

90

90

β (°)

108.349(4)

90.215(11)

91.926(7)

90

90

97.689(5)

γ (°)

90

90

90

90

90

90

V (Å3)

4057.9(2)

2292.9(4)

2341.7(3)

2313.7(2)

7926(4)

5784.8(5)

Z Dc(g/cm3)

2 1.530

2 1.427

2 1.374

1 1.452

8 1.767

4 1.484

GOF on F2

0.7250

0.810

0.7680

0.707

0.788

1.1550

R1 [I > 2σ(I)]a

0.0291

0.0598

0.0668

0.0441

0.0365

0.0845

wR2 (all data)b

0.0397

0.1442

0.1797

0.1099

0.0758

0.1844

Rint

0.0347

0.0550

0.0725

0.0610

0.0693

0.0992

R1 = Σ||Fo| |Fc||/Σ|Fo|. b wR2 = |Σw(|Fo|2 |Fc|2)|/Σ|w(Fo2)2|1/2. 3610

dx.doi.org/10.1021/cg200581w |Cryst. Growth Des. 2011, 11, 3609–3621

Crystal Growth & Design 2499 (w), 1696 (m), 1650 (m), 1608 (s), 1566 (m), 1509 (m), 1464 (w), 1436 (m), 1389 (m), 1293 (s), 1248 (m), 1208 (m), 1153 (w), 1036 (s), 926 (w), 863 (s), 830 (w), 739 (s), 679 (m), 536 (m). Synthesis of [Ni2(TPOM)(L2)2(H2O)2] 3 2H2O (2). A mixture of NiCO3 (23.6 mg, 0.2 mmol), H2L2 (33.2 mg, 0.2 mmol), TPOM (22.2 mg, 0.05 mmol), and water (8 mL) was sealed in a Teflon reactor (15 mL), which was heated at 150 °C for 3 days, and then, it was cooled to 10 °C h1. Green needle crystals of 2 were collected in a 55% yield (based on NiCO3). Anal. calcd for C41H35N4Ni2O18 (Mr = 989.07): C, 49.78; H, 3.56; N, 5.66. Found: C, 49.87; H, 3.47; N, 5.70. IR (KBr, cm1): 3423 (w), 1614 (w), 1544 (w), 1507 (m), 1463 (m), 1382 (w), 1295 (w), 1211 (w), 1038 (m), 974 (s), 927 (s), 878 (s), 830 (s), 784 (m), 725 (m), 673 (s), 540 (s). Synthesis of [Co2(TPOM)(L2)2(H2O)2] 3 H2O (3). The preparation of 3 was similar to that of 2 except that CoCO3 (23.8 mg, 0.2 mmol) was used instead of NiCO3. Purple needle crystals of 3 were collected in a 40% yield (based on CoCO3). Anal. calcd for C41H37Co2N4O17 (Mr = 975.60): C, 50.47; H, 3.82; N, 5.74. Found: C, 50.49; H, 3.80; N, 5.69. IR (KBr, cm1): 3420 (w), 1613 (w), 1578 (w), 1506 (m), 1463 (m), 1382 (w), 1296 (m), 1210 (m), 1037 (s), 878 (s), 830 (s), 830 (s) 781 (m), 723 (m), 644 (s), 539 (s), 466 (s). Synthesis of [Cu4(TPOM)2(L3)4] 3 3H2O (4). A mixture of Cu2(OH)2CO3 (22.2 mg, 0.1 mmol), H3L3 (28.0 mg, 0.13 mmol), TPOM (22.2 mg, 0.05 mmol), and water (8 mL) was sealed in a Teflon reactor (15 mL), which was heated at 150 °C for 3 days, and then, it was cooled to 10 °C h1. Blue block crystals of 4 were collected in a 43% yield (based on Cu2(OH)2CO3). Anal. calcd for C86H70Cu4N8O35 (Mr = 2029.65): C, 50.89; H, 3.48; N, 5.52. Found: C, 51.00; H, 3.39; N, 5.50. IR (KBr, cm1): 3546 (m), 3443 (m), 3076 (m), 1615 (w), 1575 (w), 1508 (w), 1483 (m), 1436 (w), 1362 (w), 1295 (m), 1210 (m), 1093 (m), 1061 (s), 1035 (m), 938 (s), 876 (s), 826 (m), 753 (w), 724 (w), 593 (s), 537 (s), 472 (s), 419 (s). Synthesis of [Co2(TPOM)0.5(L4)] (5). A mixture of CoCO3 (23.8 mg, 0.2 mmol), H4L4 (25.4 mg, 0.10 mmol), TPOM (22.2 mg, 0.05 mmol), and water (8 mL) was sealed in a Teflon reactor (15 mL), which was heated at 150 °C for 3 days, and then, it was cooled to 10 °C h1. Purple needle crystals of 5 were collected in a 49% yield (based on CoCO3). Anal. calcd for C45H28Co2N4O20 (Mr = 1062.51): C, 50.86; H, 2.66; N, 5.27. Found: C, 51.01; H, 2.34; N, 5.30. IR (KBr, cm1): 3376 (w), 2544 (m), 1861 (s), 1680 (m), 1613 (w), 1551 (w), 1435 (w), 1367 (w), 1282 (m), 1200 (m), 1109 (m), 933 (s), 842 (s), 811 (s), 738 (w), 690 (m), 627 (s), 526 (m), 458 (s), 421 (s). Synthesis of [Cd(TPOM)(L3)3] 3 7H2O (6). The preparation of 6 was similar to that of 4 except that Cd(OH)2 (29.2 mg, 0.2 mmol) was used instead of Cu2(OH)2CO3. Colorless crystals of 6 were collected in a 62% yield [based on Cd(OH)2]. Anal. calcd for C52H54CdN4O29 (Mr = 1311.25): C, 47.62; H, 4.15; N, 4.27. Found: C, 47.59; H, 4.19; N, 4.32. IR (KBr, cm1): 3862 (s), 3731 (s), 3438 (w), 1625 (w), 1577 (m), 1504 (m), 1461 (s), 1383 (m), 1317 (s), 1130 (m), 991 (s), 922 (s), 809 (m), 567 (w), 407 (w).

’ RESULTS AND DISCUSSION Structure of [Co4(TPOM)2(L1)4(H2O)4] 3 H2O (1). As shown in Figure 1a, the structure of 1 contains one crystallographically unique Co(II) atom, half TPOM ligand, one L1 anion, one coordination water molecule, and a half lattice water molecule. Each Co(II) ion is six-coordinated by one nitrogen atom from one TPOM ligand [Co1N1 = 2.1065(18) Å], four carboxylate oxygen atoms from three L1 anions [Co1O1 = 2.0885(13), Co1O1#2 = 2.1741(13), Co1O3#1 = 2.1951(16), and Co1O4#1 = 2.1161(14) Å], and one water oxygen atom [Co1O1W = 2.0893(16) Å] in an octahedral coordination geometry.

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Figure 1. (a) Coordination environment of the Co(II) ion in 1 (30% probability displacement ellipsoids). Symmetry codes: #1 = x 1/2, y 1/2, z; #2 = x + 3/2, y + 3/2, z + 1; and #4 = x + 2, y, z + 3/2 (all of the lattice water molecules and H atoms are omitted for clarity). (b) The 1D double chain constructed by L1 anions and Co(II) atoms along the b-axis. (c) Schematic representation (left) and the plywoodlike packing mode (right) of the 1D chains (constructed by the Co(II) atoms and the L1 anions) spanning two different directions. (d) Schematic representation of the 4-connected net with a (84 3 62) topology (the L1 anion is given in red and yellow, and the TPOM is given in green).

Notably, the two carboxylate groups of L1 anion exhibit two different coordination modes: One links one Co(II) atom in a chelating mode, while the other connects two Co(II) atoms in a bridging mode. In this way, L1 anions linked neighboring Co(II) atoms to yield an 1D double chain (Figure 1b). Interestingly, these chains arranged on parallel levels in different propagating directions to give rise to a plywoodlike packing mode (Figure 1c).18 It is noted that only two pyridyl nitrogen atoms of TPOM ligand coordinate to the Co(II) atoms (mode I). In this mode, the TPOM ligand further connects the Co(II) atoms of neighboring double chains to yield a 3D framework. From a 3611



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Figure 2. (a) Coordination environments of the Ni(II) ions in 2 (10% probability displacement ellipsoids). Symmetry codes: #1 = x + 2, y, z + 1/2; #2 = x + 3, y + 2, z; #3 = x + 3, y, z + 1/2; #4 = x, y + 2, z + 1/2; and #5 = x + 2, y, z (all of the lattice water molecules and H atoms are omitted for clarity). (b) The 1D helical chain constructed by L2 anions and Ni(II) atoms along the a-axis. (c) View of the 2D layer extended by the TPOM and the Ni1 and Ni2 ions. (d) Coordination environment of the TPOM ligand. (e) View of the 3D framework built from 2D layers and L2 anions along the b-axis. (f) Schematic representation of 3D 2-fold interpenetrating framework of compound 2.

topological perspective, binuclear Co(II) clusters can be considered as 4-connected nodes, and both L1 anion and TPOM ligand can be viewed as linkers, so the net of 1 can be best described as a (84 3 62) topology (Figure 1d). Structure of [Ni2(TPOM)(L2)2(H2O)2] 3 2H2O (2). The asymmetric unit of 2 contains two half Ni(II) atoms, half TPOM ligand, one L2 anion, one and two half water molecules. As depicted in Figure 2a, the two Ni(II) atoms exhibit the same coordination geometries. Each Ni(II) atom is six-coordinated by two nitrogen atoms from two TPOM ligands (N1, N1#3 for Ni1;

N2, N2#5 for Ni2), and four oxygen atoms (O6#2, O6#4, O7#2, and O7#4 for Ni1; O4, O4#5, O1W, and O1W#5 for Ni2), showing a distorted octahedral coordination geometry. One carboxylate of the L2 adopts a μ1-η0:η1 mode, while the other shows a μ2-η1:η1 mode. In 2, each L2 anion links two Ni(II) atoms to form an infinite helical chain (Figure 2b). Unlike compound 1, four pyridyl nitrogen atoms of TPOM ligand in 2 coordinate to four Ni(II) atoms (mode II), yielding a 2D layer along the b-axis (Figure 2c,d). Moreover, the 2D networks and the 1D helical chains form a 3D framework via sharing the Ni(II) atoms (Figure 2e). 3612



Figure 3. Coordination environments of the Co(II) ions in 3 (30% probability displacement ellipsoids). Symmetry codes: #5 = x + 1, y + 2, z + 1/2; #6 = x 1, y, z; #7 = x 1, y, z 1/2; and #8 = x 1, y + 2, z (all of the lattice water molecules and H atoms are omitted for clarity).

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Topologically, both Ni1 and Ni2 can be reduced to 4-connected nodes, and the TPOM ligand can also be viewed as a 4-connected node. Therefore, the structure of 2 becomes a 4-connected net with the Schl€afli symbol of (64 3 82)(66)2. The most striking feature of compound 2 is that two identical 3D frameworks interlock each other, resulting in a 3D 2-fold interpenetrating architecture (Figure 2f). Structure of [Co2(TPOM)(L2)2(H2O)2] 3 H2O (3). The structure of compound 3 is essentially isostructural with 2 (Figure 3). There are small differences between compounds 2 and 3. The coordination number of the metal center is different. The asymmetric unit of 3 consists of two Co(II) ions, two kinds of L2 anions, one TPOM ligand, two coordination water molecules,

Figure 4. (a) Coordination environment of the Cu(II) ion in 4 (10% probability displacement ellipsoids). Symmetry codes: #1 = x + 2, y, z; #2 = x 1/2, y + 1/2, z + 3; #3 = x 1/2, y + 1/2, z + 1; #4 = x + 1/2, y + 1/2, z + 1; #5 = x + 2, y + 1, z; and #6 = x + 1/2, y + 1/2, z + 3 (all of the lattice water molecules and H atoms are omitted for clarity). (b) View of the 2D sheet extended by the TPOM and Cu(II) atoms. (c) View of the 2D layer with 4- and 8-membered rings. (d) Schematic representation of a single 3D framework of compound 4. (e) Schematic representation of 3D 2-fold interpenetrating framework of compound 4. 3613


Crystal Growth & Design and two half lattice water molecules. For convenience, the L2 anions containing the oxygen atoms labeled O5 and O10 are designated L2A and L2B, respectively. As depicted in Figure 3, there are two types of coordination environments around the Co(II) ions. Co1 is five-coordinated and resides in a distorted tetrahedral pyramid coordination environment defined by two nitrogen atoms from two TPOM ligands and three oxygen atoms from one L2A and one L2B anions. Co2 is in an octahedral coordination sphere, which is defined by two coordinated nitrogen atoms from two TPOM ligands, two coordination water oxygen atoms at the equatorial position, and the other two carboxylic oxygen atoms from one L2A and one L2B anions, at the axial positions. However, in compound 2, Ni1 is six-coordinated in an octahedral coordination environment. In addition, the coordination modes of the carboxylate ligands in 2 and 3 are different. In 3, the two carboxylate groups of L2A display monodentate coordination modes, while those of L2B exhibit a monodentate mode and a bis-chelating mode, respectively. It should be pointed out that although the starting materials used for syntheses of 3 and [Co2(TPOM)(L2)2(H2O)2] 3 (H2O)5 (M)13a are the same, their solvents (water for 3 and DMF:water = 1:2 for M) and temperatures (150 °C for 3 and 110 °C for M) are different. As compared with M, the coordination number of the metal center (five and six for 3; four and six for M) is different. However, their frameworks are the same with the Schl€afli symbol of (64 3 82)(66)2. Structure of [Cu4(TPOM)2(L3)4] 3 3H2O (4). Compound 4 contains one crystallographically unique Cu(II) atom, half TPOM ligand, one L1 anion, and three-quarter water molecules. As shown in Figure 4a, each Cu(II) cation is five-coordinated by two nitrogen atoms from two TPOM ligands [Cu1N1 = 2.007(5) and Cu1N2#2 = 1.999(5) Å] and three carboxylate oxygen atoms from three L3 anions [Cu1O3 = 1.973(4), Cu1O8#1 = 1.955(3), and Cu1O5#3 = 2.237(4) Å] in a tetragonal pyramid coordination geometry. Like compound 2, the TPOM ligand connects four Cu(II) atoms in mode II to form one type of 2D layer, which has rhombic windows with a side length of 12.0188(9) Å and a approximately diagonal measurement of 17.0353(9) 16.8478(8) Å2 based on the C7 3 3 3 C7 distances (Figure 4b). Each carboxylate group of L3 shows a monodentate coordination mode. In this mode, each L3 anion links three Cu(II) ions to form another type of 2D layer with 4- and 8-membered rings (Figure 4c). Moreover, the two types of 2D networks form a 3D framework via sharing the Cu(II) atoms. From a topological point of view, if the L3 anions are considered as 3-connected nodes, TPOM ligands are viewed as 4-connected nodes, and Cu(II) ions are regarded as 5-connected nodes, then the 3D framework of 4 becomes a trinodal (3,4,5)-connected net with Schl€afli symbol of (4 3 62)(4 3 69)66 (Figure 4d). The void space in the single framework is so large that two identical 3D frameworks interpenetrate each other to form a unique 2-fold interpenetrating architecture, leaving a small space for the inclusion of solvent molecules as shown in Figure 4e (15.5% of the cell volume calculated by PLATON19). Structure of [Co2(TPOM)0.5(L4)] (5). When L1 anion was replaced by L4 anion, a quite different structure of 5 was obtained. As shown in Figure 5a, compound 5 contains one crystallographically unique Co(II) atom, a quarter TPOM ligand, and half L1 anion. Each Co(II) ion is four-coordinated with four carboxylate oxygen atoms from four L4 anions [Co1O1 = 1.9419(17), Co1O1#1 = 1.9419(17), Co1O4#2 = 1.9672(18),

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Figure 5. (a) Coordination environment of the Co(II) ion in 5 (10% probability displacement ellipsoids). Symmetry codes: #1 = y + 3/4, x 3/4, z + 1/4; #2 = y + 5/4, x + 3/4, z + 1/4; #3 = x + 3/2, y + 1/2, z; #4 = x + 3/2, y, z; #6 = y + 3/4, x + 3/4, z 1/4; #7 = y + 5/ 4, x 5/4, z 1/4; and #8 = x + 2, y 1/2, z (all of the H atoms are omitted for clarity). (b) Views of 3D framework (left) of 5 constructed by L4 anions and Co(II) atoms along the c-axis and schematic representation of the 4-connected topology with the (42 3 84)2 network. (c) Views of the 3D channels occupied by the TPOM ligands across from each other.

and Co1O4#3 = 1.9672(18) Å] in a tetragonal coordination geometry. As illustrated in Figure 5b, each L4 anion acts as a μ4-bridge to link four Co(II) ions with its four carboxylate groups to furnish a 3D framework with large open windows. The window dimensions of the cavities within the 3D open frameworks are approximately 17.0363 17.0363 Å2 viewed along the b-axis. PLATON calculations show that the void is 4927.4 Å3 per unit cell volume (53.9% of the cell volume). A striking feature of 5 is that there are two kinds of crystallographically independent TPOM ligands located inside the channels in opposite positions (mode III) (Figure 5c). From a topological view, if L4 anions and Co(II) ions are considered to be 4-connected nodes, and then, the framework of 5 becomes a 4-connected net with a Schl€afli symbol of (42 3 84)2 (Figure 5c). Structure of [Cd(TPOM)(L3)3] 3 7H2O (6). When Cu(II) ions was replaced by Cd(II) ions, a quite different structure of 6 was 3614



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Figure 6. (a) Coordination environment of the Cd(II) ion in 6 (10% probability displacement ellipsoids). Symmetry codes: #1 = x + 1/2, y 1/2, z + 3/2; #2 = x 1/2, y + 1/2, z + 3/2; #3 = x 1/2, y 1/2, z + 3/2; #4 = x + 1/2, y + 1/2, z + 3/2 (all the lattice water molecules and H atoms are omitted for clarity). (b) View of the 2D sql layer extended by the L3A and L3B anions and Cd(II) atoms. (c) Schematic representation of the 3D porous framework of 6 with the TPOM ligands and the L3 anions. (d) View of the fragment constructed through hydrogen-bonding and ππ interactions between the free TPOM ligands and the L3 anions. (e) View of the 3D framework. (f) Schematic representation of the unique 2D f 3D polythreading framework of 6.

obtained. The asymmetric unit of 6 contains one crystallographically unique Cd(II) atom, one TPOM ligand, three L3 anions, and seven lattice water molecules. For convenience, the L3 anions containing the oxygen atoms O1, O7, and O13 are designated L3A, L3B, and L3C, respectively. As shown in Figure 6a, each Cd(II) atom is six-coordinated by six carboxylate oxygen atoms from four L3 anions [Cd1O1 = 2.264(6), Cd1O2 = 2.540(7), Cd1O7 = 2.238(6), Cd1O11#4 = 2.280(6),

Cd1O12#4 = 2.523(6), and Cd1O8#4 = 2.735(10) Å] in an octahedral coordination geometry. Both L3A and L3B anions are partly deprotonated, and only two carboxylate groups coordinate to the Cd(II) centers in a monodentate mode and a bis-chelating mode, respectively. In this way, L3A and L3B anions link neighboring Cd(II) atoms to yield a 2D sql network (Figure 6b). Notably, the sql network has large square windows with approximate dimensions of 10.2211 10.3710 Å 2 (Figure 6b). 3615



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Table 2. θ Angles in Compounds 16 (θ1θ6 Represent Angles of N 3 3 3 Ccenter 3 3 3 N, and θ7θ10 Represent angles of CcenterCH2OC) compound

θ1

θ2

θ3

θ4

θ5

θ6

θ7

θ8

θ9

θ10

1

88.31

92.73

118.16

118.16

121.22

121.22

173.28

173.28

179.78

179.78

2 3

69.06 70.16

92.24 91.16

122.66 122.66

124.29 124.40

125.36 125.97

125.36 126.76

163.88 164.13

163.88 164.31

177.15 167.92

177.15 176.34

4

88.26

103.49

115.77

115.77

117.01

117.01

174.59

174.59

178.89

178.89

5

53.51

53.51

136.03

136.03

151.04

151.04

52.84

52.84

52.84

52.84

6

77.26

89.53

114.23

125.47

126.67

127.82

155.91

170.53

172.19

176.87

An interesting aspect of the structure is that the 2D porous sheets are stacked in an ABAB fashion along the a direction (Figure S1 in the Supporting Information). It should be pointed out that there are channels viewed along the c-axis, which are occupied by the fully protonated TPOM ligands and the partly protonated L3C anions. Notably, among most of the known porous MOFs, the channels are mainly occupied by the solvents molecules. To the best of our knowledge, both the N-donor ligands and the carboxylates located in the 2D pores are exceedingly rare.13 In addition, there exist hydrogen-bonding interactions between the uncoordinated pyridyl nitrogen atoms and the oxygen atoms. As shown in Figure 6d, the free TPOM ligand and the L3 anion form a discrete fragment through both hydrogen-bonding [N1H1 3 3 3 O16 = 2.691(13) Å] and ππ interactions (centroid-to-centroid distance of 3.68 Å and face-to-face distance of 3.67 Å). The most peculiar feature of 6 is that each [Cd4(L3A)2(L3B)2] window of the blue layer is threaded by one red fragment, and each red fragment passes through two windows above and below (Figure 6e). As a result, a unique 2D f 3D polythreading framework is generated. It is noteworthy that the present 2D f 3D polythreading framework of 6 is completely different from the reported ones.2022 In those reported 2D f 3D polythreading frameworks, the 2D networks are all penetrated by infinite chains. As far as we know, the present 3D polythreading framework is unique in MOFs. The supramolecular assembly of the fragments and 2D grids is further stabilized by other NH 3 3 3 O [N2H2 3 3 3 O6W = 2.601(18), N4H2 3 3 3 O3 = 2.728(13)] and OH 3 3 3 O [O14 H4A 3 3 3 O6 = 2.762(8), O17H17 3 3 3 O8 = 2.573(10), and N3H3A 3 3 3 O10 = 2.667(12) Å] hydrogen-bonding interactions. Distortion and Coordination Modes of TPOM. According to the report,23 the distortion can be estimated by comparing the N 3 3 3 Ccenter 3 3 3 N angles defined by the central carbon atom of the pentaerythrityl center (Ccenter) and the nitrogen atoms of the pyridyl groups. From Table 2, we can see that in 14 and 6, the TPOM ligand adopts a conformation holding the four pyridyl groups in an irregular orientation. The N 3 3 3 Ccenter 3 3 3 N angles range from 88.31(34) to 121.223(29)° for 1, 69.06(61) to 125.361(63)° for 2, 70.16(39) to 126.76(28)° for 3, 88.26(62) to 117.005(62)° for 4, and 77.26(18) to 127.82(23)° for 6, respectively, showing slightly distorted tetrahedral geometries. The CH2O spacers are fully extended with CcenterCH2 OC torsion angles of 173.28(194) to 179.78(17)° for 1, 163.88(60) to 177.15(48)° for 2, 164.13(19) to 176.34(17)° for 3, 174.59(43) to 178.89(45)° for 4, and 155.91(11) to 176.87(11)° for 6, respectively. However, the conformation of TPOM in 5 is substantially different from those in 14 and 6. The flexible ligand TPOM

Scheme 2. Coordination Modes of the TPOM Ligand

adopts a highly distorted tetrahedral orientation, and two pairs of pyridyl groups are almost in parallel. The angles of N 3 3 3 Ccenter 3 3 3 N are 2 53.51(39)°, 2 136.04(39)°, and 2 151.04(39)°, showing a extremely distorted tetrahedral geometry. The CH2O spacers, which connect each pyridyl group to the core, adopt orientations that are not fully extended with CcenterCH2OC torsion angles of 4 52.84(18)°. From the discussion above, we can see that the TPOM ligands can bend and rotate freely when coordinating to the central metals or free due to the flexible nature of the spacers between the four pyridyl rings. As shown in Scheme 2, in compound 1, only two pyridyl nitrogen atoms of TPOM ligand coordinate to the metals (mode I), while, in compounds 24, four pyridyl nitrogen atoms of TPOM ligand coordinate to the metals (mode II). In compounds 5 and 6, the free TPOM molecules are located inside the 3D and 2D pores, respectively (mode III). The variety of coordination modes of the TPOM ligands in compounds 16 results in the structural difference. Effect of the Carboxylate Anions on the Framework. The carboxylate anions act as key roles in determining the structures of the resultant complexes. Through varying the carboxylate anions (H2L1, H2L2, and H4L4) under similar synthetic conditions, three Co(II) compounds with different structures were successfully obtained. The H2L1 and H2L2 anions are dicarboxylic acid ligands, while the H4L4 anion is a tetracarboxylic acid ligand. 3616



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Figure 7. UVvis absorption spectrum of compounds 16.

The compounds 1, 3, and 5 show the effect of carboxylate anions on their complex structures. In 1, each L1 anion connects two Co(II) atoms with one of the carboxylate groups in a chelating mode and the other in a bridging mode, yielding a 1D double chain. These chains are further extended by the TPOM ligands to form a 3D framework. In 3, the two carboxylate groups of L2A display monodentate coordination modes, while those of L2B exhibit a monodentate mode and a bis-chelating mode, respectively. The two kinds of L2 anions link the Co(II) to form a 1D helical chain, which is further extended by the TPOM ligands to afford a 3D 2-fold interpenetrating framework with the Schl€afli symbol of (64 3 82)(66)2. In 5, each carboxylate group of L4 anion connects the central metals in a monodentate mode, resulting in a 3D porous framework with discrete TPOM ligands located in the channels across from each other. Accordingly, we can see that the different carboxylate anions have a remarkable effect on the structures of the MOFs. Effect of the Central Metals on the Framework. It should be noted that the central metals also have an important function in

the formation of the final structures. For example, the structural differences of 4 and 6 are mainly caused by changes of the metal ions. The different coordination environments of the central metals are the main reasons for the structural differences in 4 and 6. In 4, each Cu(II) ion adopts a distorted tetragonal pyramid coordination geometry, which is connected by the L3 anions and the TPOM ligands to give a (3,4,5)-connected net with the Schl€afli symbol of (4 3 62)(4 3 69)66. In 6, each Cd(II) ion displays a octahedral coordination geometry. The six-coordinated Cd(II) ions are bridged by the L3 (L3A and L3B) anions to furnish a 2D sql network. Notably, the 2D channels are occupied by the TPOM ligands and the L3C anions. In addition, through hydrogen-bonding interactions and strong ππ interactions, a unique 2D f 3D polythreading framework is generated. Thermal Analysis and PXRD Results. To characterize the compounds more fully in terms of thermal stability, their thermal behaviors were studied by TGA. The experiments were performed on samples consisting of numerous single crystals of 16 3617



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Figure 8. Diffuse reflectance UVvis-NIR spectra of KM functions vs energy (eV) of compounds 16.

under N2 atmosphere with a heating rate of 10 °C/min, as shown in Figure S2 in the Supporting Information. For compound 1, a small weight loss of 0.8% (calcd 0.96%) is observed from 33 to 59 °C due to the release of one lattice water molecule. The following weight loss from 65 to 142 °C (obsd, 3.1%; calcd, 3.85%) corresponds to the release of four coordinated molecules. The residual composition decomposed at 357 °C. The remaining weight is assigned to Co2O3 (obsd, 16.2%; calcd, 17.73%). For compound 2, the first weight loss corresponding to the release of two lattice water molecules (obsd, 3.3%; calcd, 3.64%) is observed in the temperature range of 3562 °C, and the following weight loss from 70 to 137 °C (obsd, 3.9%; calcd, 3.64%) can be attributed to the release of two coordinated water molecules. The removal of the organic components occurs in the range of 331495 °C. The remaining weight is attributed to the formation of NiO (obsd, 15.7%; calcd, 15.10%). For compound 3, the first weight loss from 32 to 54 °C

(obsd, 1.3%; calcd, 1.85%) corresponds to the loss of one lattice water molecule. The second weight loss from 67 to 102 °C (obsd, 4.0%; calcd, 3.69%) can be attributed to the release of two coordinated water molecules. The third gradually weight loss from 345 to 490 °C corresponds to the collapse of the framework. The Co2O3 was formed as the remaining residue (obsd, 17.9%; calcd, 17.00%). For compound 4, the first weight loss of 3.0% (calcd, 2.66%) in the temperature range of 49157 °C can be assigned to the release of three lattice water molecules. The decomposition of the residual composition begins from 245 to 430 °C. The departure of the structure finally leads to the formation of CuO (obsd, 14.8%; calcd, 15.68%). For 5, the anhydrous compound begins to decompose from 275 to 496 °C. The remaining weight can be attributed to the formation of Co2O3 (obsd, 16.1%; calcd, 15.61%). For 6, the weight loss in the range of 132272 °C corresponds to the departure of seven lattice water molecules, free TPOM ligands, and L3 anions (obsd, 3618



Figure 9. Solid-state photoluminescent spectra of 6 at room temperature.

Figure 10. Fitted decay curve monitored at 433 nm for compound 6 in the solid state at room temperature. The sample was excited at 340 nm (the black circles represent experimental data, and the solid red lines represent fitting results).

59.1%; calcd, 59.68%), and the anhydrous compound begins to decompose at 385 °C, leading to the formation of CdO as the residue (obsd, 9.6%; calcd, 9.79%). To confirm whether the crystal structures are truly representative of the bulk materials, PXRD experiments were carried out for 16. The PXRD experimental and computer-simulated patterns of the corresponding complexes are shown in the Supporting Information. They show that the synthesized bulk materials and the measured single crystals are the same (Figure S3 in the Supporting Information). Optical Energy Gap. The UVvis absorption spectra of compounds 16 were carried out in the crystalline state at room temperature (Figure 7). According to the report, the TPOM ligands exhibits a strong absorption band in the range of 220260 nm, which can be ascribed to π* f π transitions of the ligands.12 Energy bands of complex 1 from 500 to 520 nm, complex 2 from 660 to 680 nm, complex 3 from 510 to 530 nm, complex 4 from 680 to 700 nm, and complex 5 from 580 to 600 nm are assigned as dd transitions, while lower energy

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bands from 200 to 220 nm for 1, from 200 to 220 nm for 2, from 245 to 265 nm for 3, from 230 to 260 nm for 4, from 240 to 260 nm for 5, and from 250 to 270 nm for 6 are considered as intraligand transitions. To explore the conductivity of compounds 16, the measurements of diffuse reflectivity for powder samples were used to obtain their band gaps (Eg), which were determined as the intersection point between the energy axis and the line extrapolated from the linear portion of the adsorption edge in a plot of the KubelkaMunk function F against E.24 As shown in Figure 8, the Eg values assessed from the steep absorption edge are 3.28 eV for 1, 3.59 eV for 2, 3.18 eV for 3, 3.40 eV for 4, 2.98 eV for 5, and 3.67 eV for 6. The reflectance spectra reveal the presence of an optical band gap and the nature of semiconductivity for compounds 16, which indicates that these compounds are potential wide gap semiconductor materials. Luminescent Properties. Luminescent properties of compounds with d10 metal centers have attracted intense interests because of their potential applications in chemical sensors, photochemistry, and electroluminescent display.25,26 The solid-state photoluminescent property of compound 6 has been investigated in the solid state at room temperature. The emission and excitation peaks are shown in Figure 9. The emission peaks of free TPOM ligand13 and H3L312 are at 450 and 363 nm, respectively, which are probably attributable to the π* f n or π* f π transitions. The emission peak of compound 6 at 433 nm (λex = 340 nm) exhibits a red shift with respect to the free ligand H3L3 (403 nm). Because the Cd(II) ions are difficult to oxidize or to reduce, the emission of compound 6 is neither metal-toligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature.27 As a result, the emission can be assigned to intraligand transitions.28 The luminescence decay curve of 6 at room temperature (Figure 10) is well fit into a single-exponential function as I = A + B1 exp(t/τ1) + B2 exp(t/τ2). The emission decay lifetimes of compound 6 are τ1 = 2.50 ns (64.95%) and τ2 = 5.95 ns (35.05%) (χ2 = 1.069). The luminescence lifetimes of 6 are much shorter than ones from a triplet state (>103 s), so the emissions should arise from a singlet state.29,30 The photoluminescence quantum yield of compound 6 in the solid state is 0.10.31

’ CONCLUSION Six new MOFs with different structures have been isolated through varying the polycarboxylates and metal centers. By comparison with their compound structures, we can see that the coordination modes of TPOM ligands, the carboxylate anions, and the central metals play dominant roles in the assembly of their final topologies. The optical energy gaps of 16 imply that these compounds are potential wide gap semiconductor materials. The photoluminescent emission of the compound 6 indicates that this complex may be a good candidate for optical materials. ’ ASSOCIATED CONTENT

bS

Supporting Information. X-ray crystallographic data in CIF format, selected bond lengths and angles, view of the sheets stacked in ABAB fashion in compound 6, and TG and PXRD patterns of the compounds 16. This material is available free of charge via the Internet at http://pubs.acs.org.

3619



’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (J.-F.M.). E-mail: yangjinnenu@ yahoo.com.cn (J.Y.).

’ ACKNOWLEDGMENT We thank the National Natural Science Foundation of China (Grant Nos. 21071028 and 21001023), the Science Foundation of Jilin Province (20090137 and 20100109), the Fundamental Research Funds for the Central Universities, the Specialized Research Fund for the Doctoral Program of Higher Education, the China Postdoctoral Science Foundation (20080431050 and 200801352), and the Training Fund of NENU’s Scientific Innovation Project. ’ REFERENCES (1) (a) Ferey, G.; Latroche, M.; Serre, C.; Millange, F.; Loiseau, T.; Guegan, A. P. Chem. Commun. 2003, 2976. (b) Rowsell, J. L. C.; Millward, A. R.; Park, K. S.; Yaghi, O. M. J. Am. Chem. Soc. 2004, 126, 5666. (c) Maji, T. K.; Mostafa, G.; Chang, H. C.; Kitagawa, S. Chem. Commun. 2005, 2436. (d) Wong-Foy, A. G.; Matzger, A. J.; Yaghi, O. M. J. Am. Chem. Soc. 2006, 128, 3494. (e) Lin, X.; Jia, J.; Zhao, X.; Thomas, K. M.; Blake, A. J.; Walker, G. S.; Champness, N. R.; Hubberstey, P.; Schr€oder, M. Angew. Chem., Int. Ed. 2006, 45, 7358. (f) Liu, Y.-L.; Eubank, J. F.; Cairns, A. J.; Eckert, J.; Kravtsov, V. C.; Luebke, R.; Eddaoudi, M. Angew. Chem., Int. Ed. 2007, 46, 3278. (g) Thallapally, P. K.; Tian, J.; Kishan, M. R.; Fernandez, C. A.; Dalgarno, S. J.; McGrail, P. B.; Warren, J. E.; Atwood, J. L. J. Am. Chem. Soc. 2008, 130, 16842. (h) Zhang, Y.-B.; Zhang, W.-X.; Feng, F.-Y.; Zhang, J.-P.; Chen, X.-M. Angew. Chem., Int. Ed. 2009, 48, 5287. (i) Ma, L.-Q.; Jin, A.; Xie, Z.-G.; Lin, W.-B. Angew. Chem., Int. Ed. 2009, 48, 9905. (2) (a) Pang, J.; Marcotte, E. J. P.; Seward, C.; Brown, R. S.; Wang, S. Angew. Chem., Int. Ed. 2001, 40, 4042. (b) Liang, K.; Zheng, H.-G.; Song, Y.-L.; Lappert, M. F.; Li, Y.-Z.; Xin, X.-Q.; Huang, Z.-X.; Chen, J.-T.; Lu, S.-F. Angew. Chem., Int. Ed. 2004, 43, 5776. (c) Huang, Y.-Q.; Ding, B.; Song, H.-B.; Zhao, B.; Ren, P.; Cheng, P.; Wang, H.-G.; Liao, D.-Z.; Yan, S.-P. Chem. Commun. 2006, 4906. (d) Bauer, C. A.; Timofeeva, T. V.; Settersten, T. B.; Patterson, B. D.; Liu, V. H.; Simmons, B. A.; Allendorf, M. D. J. Am. Chem. Soc. 2007, 129, 7136. (e) Zheng, X.-L.; Liu, Y.; Pan, M.; L€u, X.-Q.; Zhang, J.-Y.; Zhao, C.-Y.; Tong, Y.-X.; Su, C.-Y. Angew. Chem., Int. Ed. 2007, 46, 7399. (f) Allendorf, M. D.; Bauer, C. A.; Bhaktaa, R. K.; Houka, R. J. T. Chem. Soc. Rev. 2009, 38, 1330. (3) (a) Brechin, E. K.; Harris, S. G.; Harrison, A.; Parsons, S.; Whittaker, A. G.; Winpenny, R. E. P. Chem. Commun. 1997, 653. (b) Lu, J.-Y.; Lawandy, M. A.; Li, J. Inorg. Chem. 1999, 38, 2695. (c) Kumagai, H.; Kepert, C. J.; Kurmoo, M. Inorg. Chem. 2002, 41, 3410. (d) Cao, R.; Shi, Q.; Sun, D.-F.; Hong, M.-C.; Bi, W.-H.; Zhao, Y.-J. Inorg. Chem. 2002, 41, 6161. (e) Gavrilenko, K. S.; Punin, S. V.; Cador, O.; Golhen, S.; Ouahab, L.; Pavlishchuk, V. V. J. Am. Chem. Soc. 2005, 127, 12246. (f) Pan, Z. R.; Zheng, H.-G.; Wang, T.-W.; Song, Y.; Li, Y.-Z.; Guo, Z.-J.; Batten, S. R. Inorg. Chem. 2008, 47, 9528. (g) Bi, Y.-F.; Wang, X.-T.; Wang, B.-W.; Liao, W.-P.; Wang, X.-F.; Zhang, H.-J.; Gao, S.; Lia, D.-Q. Dalton Trans. 2009, 2250. (4) (a) Wu, C.-D.; Hu, A.-G.; Zhang, L.; Lin, W.-B. J. Am. Chem. Soc. 2005, 127, 8940. (b) Alaerts, L.; Seguin, E.; Poelman, H.; Starzyk, F. T.; Jacobs, P. A.; Vos, D. E. D. Chem.—Eur. J. 2006, 12, 7353. (c) Cho, S.-H.; Ma, B.; Nguyen, S. T.; Hupp, J. T.; Albrecht-Schmitt, T. E. Chem. Commun. 2006, 2563. (d) Xamena, F. X. L.; Abad, A.; Corma, A.; Garcia, H. J. Catal. 2007, 250, 294. (e) Liao, Z.-L.; Li, G.-D.; Bi, M.-H.; Chen, J.-S. Inorg. Chem. 2008, 47, 4844. (f) Wu, J.; Hou, H.-W.; Guo, Y.-X.; Fan, Y.-T.; Wang, X. Eur. J. Inorg. Chem. 2009, 19, 2796. (5) (a) Zang, B.; Clearfield, A. J. Am. Chem. Soc. 1997, 119, 2751. (b) Li, J.-R.; Kuppler, R. J.; Zhou, H.-C. Chem. Soc. Rev. 2009, 38, 1477. (c) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y.; Eddaoudi, M.;

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