Crystal Structures and Spectroscopic Properties of MetalâOrganic

Article pubs.acs.org/crystal

Crystal Structures and Spectroscopic Properties of Metal−Organic Frameworks Based on Rigid Ligands with Flexible Functional Groups Chuanlei Zhang, Mingdao Zhang, Ling Qin, and Hegen 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 S Supporting Information *

ABSTRACT: Two rigid linear ligands with alkoxy functional groups (L1 = 4,4′-(2,5-dimethoxy-1,4-phenylene) dipyridine; L2 = 4,4′-(2,5-diethoxy-1,4phenylene) dipyridine) incorporating carboxyl-containing auxiliary ligands (isophthalic acid = H2IPA; terephthalic acid = H2TPA; biphenyl-4,4′dicarboxylate = H2BPDC) have been adopted to build a series of complexes with M(II) (M = Zn, Co, Cd) under solvothermal conditions. The formula of these complexes are {[Zn(L1)(IPA)]}n (1), {[Zn(L1)(TPA)]·DMF}n (2), {[Co(L1)(TPA)(H2O)2]·2DMF}n (3), {[Cd(L1)(TPA)(H2O)2]·2DMF}n (4), and {[Co(L2)(BPDC)]·0.5H2O}n (5). Five complexes have been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. Topological analyses reveal that complex 2 is a 6-connected pcu net with point symbol {412·63}, while complex 5 is a 6connected rob net with point symbol {48·68·8}, the other complexes 1, 3, and 4 can be simplified as 4-connected sql nets with point symbol {44.62}. Complexes 1, 3, and 4 are 2D layer motifs, 2 and 5 are both 2-fold interpenetrating 3D frameworks. The optical absorption spectra of 3 and 5 indicate the nature of semiconductivity. The strong fluorescence emissions and long emission lifetimes of 1, 2, and 4 display that they are promising phosphorescent materials.

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INTRODUCTION To build various structures of MOFs (metal−organic frameworks) is not only an important content in the research of molecular field but also the basis for exploring their properties. More and more studies show that MOFs have extensive applications in luminescence,1 molecular magnet,2 ionexchange,3 drug delivery,4 heterogeneous catalysis,5 physical gas storage,6 sensing, and separation.7 However, how to construct appropriate crystal structures is the primary issue. Using mixed ligands to create MOFs is an important tactics these years.8 From the previous studies, it can be seen that rigid ligands are easier to project distinctive structures than the flexible ones. Rigid ligands containing pyridyl group were studied intensely recently.9 Linear rigid ligands with more than two benzene rings often have strong fluorescence properties for π···π conjugation effect, and also have other unexpected nature after proper modification. To date, many functional MOFs have been constructed via modification of a traditional rigid pyridine ligand 1,4-bis(4-pyridyl)benzene (L). For instance, S. Kitagawa and co-workers10 in 2011 reported a soft SBU with regenerative properties constructed by fluorine replaced L ligand; M. Fujita and co-workers11 reported a modified ligand based on L, which contained ethylene glycol side chains, and observed an apicalligand-exchange reaction at a cobalt ion within a square-grid coordination network. Recent researches show that the introduction of hybrid ligands is a very effective way to construct novel metal−organic frameworks.12 © 2013 American Chemical Society

In this paper, we introduce methoxyl and ethoxyl to 1,4bis(4-pyridyl)benzene) (L) to synthesize two rigid linear ligands (L1 = 4,4′-(2,5-dimethoxy-1,4-phenylene)dipyridine; L2 = 4,4′-(2,5-diethoxy-1,4-phenylene)dipyridine). Alkoxy functional groups have good solubility and flexibility, so ligands L1 and L2 are beneficial for construction of novel complexes. The two ligands incorporate aromatic carboxylates (isophthalic acid = H2IPA; terephthalic acid = H2TPA; biphenyl-4,4′dicarboxylate = H2BPDC) and transition metal ions (Zn2+/ Co2+/Cd2+) to construct five 2D or 3D metal−organic frameworks, namely, {[Zn(L1)(IPA)]}n (1), {[Zn(L1)(TPA)]·DMF}n (2), {[Co(L1)(TPA)(H2O)2]·2DMF}n (3), {[Cd(L1)(TPA)(H 2 O) 2 ]·2DMF} n (4), and {[Co(L2)(BPDC)]·0.5H2O}n (5). All complexes are characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction, and thermogravimetry measurements. Furthermore, the crystal and topological structures, UV−visible and photoluminescent spectra are investigated in detail.

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RESULTS AND DISCUSSION The experimental section has been listed in the Supporting Information. The detailed information of complexes 1−5 is summarized in Table 1 and 2. Received: July 29, 2013 Revised: December 13, 2013 Published: December 16, 2013 491

dx.doi.org/10.1021/cg401149h | Cryst. Growth Des. 2014, 14, 491−499

Crystal Growth & Design

Article

ligands from nearly perpendicular direction to furnish a 2D layer (Figure 1c). Moreover, the packing diagram exhibits that the 2D networks are stacking parallelly, as depicted in Figure 1d. Because these layers do not overlap with one another, there are no channels in the crystal structure. From a topological perspective, the 2D layers can be simplified to (4,4)-connected sql nets with point symbol {44·62}. Description of the Crystal Structure of {[Zn(L1)(TPA)]· DMF}n (2). Complex 2 is a 3D supramolecular structure. The asymmetric unit contains one Zn(II) ion, half a L1 ligand, one deprotonated terephthalic acid and one lattice DMF molecule squeezed by PLATON software. As shown in Figure 2a, each Zn(II) is square-pyramidally coordinated by four carboxylate oxygen atoms from four symmetrical TPA ligands at the basal positions and one nitrogen atom from one L1 ligand at the apical position. The Zn−N bond distance is 2.037(2) Å, and the Zn−O bond distances are vary in the range of 2.024(2)− 2.112(2) Å; the N−Zn−O angles are in the range of 90.52(9)− 110.55(10)°, and the O−Zn−O angles are in the range of 86.48(8)−159.06(8)°, which deviated from normal bond angles found in other Zn complexes.13 Two crystallographically equivalent Zn(II) cations are bridged by four carboxylate groups adopting a bis-bidentate coordination mode to generate a distorted dinuclear Zn(II) “paddle-wheel” secondary building unit (SBU) with a Zn···Zn distance of 2.9782(6) Å. The paddle-wheel is bridged by TPA ligands to form a 2D (4, 4) flat network with square grids. Because of the tortile “paddlewheel” SBU, the TPA forms a rectangle with a size of 10.955 × 10.906 Å2 (Figure 2b). There are also rectangular grids in complex 2 with a size of 16.599 × 10.955 Å2 (Figure 2c), which are built by TPA and L1 ligands and Zn(II) cations. The layers of square grids are further connected by the L1 ligands to form a 3D coordination polymer network. From the topological perspective, the SBU [Zn2(CO2)4] can be regarded as a 6-connected node; thus, the framework of 2

Scheme 1. Structures of the Carboxylic Acids and L1/L2 Ligands Used in This Work

Description of the Crystal Structure of {[Zn(L1)(IPA)]}n (1). Complex 1 crystallizes in the triclinic space group P1̅. The Zn ions are six-coordinated by four carboxylate oxygen atoms from three different IPA ligands and two nitrogen atoms belonging to two L1 ligands (Figure 1a). The Zn−N bond lengths are 2.174(3) and 2.179(3) Å, and Zn−O bond distances are in the range of 2.030(2)−2.210(3) Å. Two carboxyl groups of IPA adopt two different coordination modes, one adopts bidentate bridging node to combine two Zn(II) ions, the other adopts bidentate chelating mode to link one Zn(II) ion. The IPA ligands link the Zn(II) ions to form a 1D chain with the adjacent Zn···Zn distance of 4.5304 Å (Figure 1b). Such 1D chains are further extended through L1

Table 1. Crystal Data and Structural Refinements Parameters of Complexes 1−5a empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ (mm−1) F(000) θmin−max (deg) tot., uniq. data R(int) Nref, Npar R1, wR2 [I > 2σ(I)] GOF on F2 min. and max residue density (e·Å−3) a

1

2

3

4

5

C26H20N2O6Zn 521.81 triclinic P1̅ 9.6191(10) 10.0535(11) 12.8335(14) 71.6760(10) 87.048(2) 75.9160(10) 1142.3(2) 2 1.517 1.122 536 1.67, 27.10 9107, 4890 0.0481 4890, 318 0.0672, 0.1974 1.006 −1.477, 1.048

C17H12NO5Zn 375.65 monoclinic P2/c 10.9063(4) 10.9553(4) 16.5990(7) 90.00 101.6550(10) 90.00 1942.39(13 4 1.285 1.286 764 1.86, 28.31 13803, 4842 0.0778 4842, 274 0.0384, 0.1036 1.005 −0.790, 0.700

C32H36CoN4O10 695.58 triclinic P1̅ 7.2562(14) 10.207(2) 11.423(2) 108.061(2) 92.203(3) 99.553(3) 789.5(3) 1 1.463 0.608 363 1.88, 27.40 7081, 3528 0.0496 3528, 246 0.0500, 0.1271 1.014 −0.630, 0.827

C32H24CdN4O10 736.95 triclinic P1̅ 7.3036(3) 10.4501(4) 11.5545(4) 108.2510(10) 94.8050(10)0) 98.4340(10) 820.52(5) 1 1.491 0.727 372 1.87, 26.37 5176, 3327 0.0685 3327, 249 0.0346,0.0913 1.044 −0.760, 0.673

C34H29CoN2O6.5 628.52 monoclinic P2/ic 10.2536(5) 11.9941(6) 25.9444(12) 90.00 105.733(2) 90.00 3071.2(3) 4 1.359 0.608 1304 1.63, 26.37 18872, 6293 0.0934 6293, 423 0.0454, 0.0992 1.002 −0.364, 0.472

R1 = Σ∥Fo| − |Fc∥/|Σ|Fo|; wR2 ={Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}1/2, where w = 1/[σ2(Fo2) + (aP)2 + bP], P = (Fo2 + 2Fc2)/3. 492



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Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 1−5a complex 1 Zn(1)−O(9)#1 Zn(1)−N(2) Zn(1)−O(1) O(9)#1−Zn(1)−O(8) #2 O(8)#1−Zn(1)−N(2)

2.030(2) 2.174(3) 2.205(2) 104.93(10)

O(8)#2−Zn(1)−N(1) O(9)#1−Zn(1)−O(1)

82.90(11) 151.67(10)

N(2)−Zn(1)−O(1) O(9)#1−Zn(1)−O(2)

88.24(10) 92.96(10)

N(2)−Zn(1)−O(2) O(1)−Zn(1)−O(2)

93.08(12) 59.36(10) complex 2

89.92(11)

Zn(1)−O(3) Zn(1)−O(1) Zn(1)−O(4)#1 O(3)−Zn(1)−N(1)

2.024(2) 2.0394(18) 2.112(2) 110.55(10)

N(1)−Zn(1)−O(1)

100.15(9)

N(1)−Zn(1)−O(2)

99.67(9)

O(3)−Zn(1)−O(4) #1 O(1)−Zn(1)−O(4) #1 O(3)−Zn(1)−Zn (1)#1 O(1)−Zn(1)−Zn (1)#1 O(4)#1−Zn(1)−Zn (1)#1

158.92(9) 86.48(8) 93.21(7) 79.58(6)

Zn(1)−O(8)#2 Zn(1)−N(1) Zn(1)−O(2) O(9)#1−Zn(1)−N (2) O(9)#2−Zn(1)−N (1) N(2)−Zn(1)−N(1) O(8)#2−Zn(1)−O (1) N(1)−Zn(1)−O(1) O(8)#2−Zn(1)−O (2) N(1)−Zn(1)−O(2)

Zn(1)−N(1) Zn(1)−O(2) Zn(1)−Zn(1)#1 O(3)−Zn(1)−O (1) O(3)−Zn(1)−O (2) O(1)−Zn(1)−O (2) N(1)−Zn(1)−O (4)#1 O(2)−Zn(1)−O (4)#1 N(1)−Zn(1)−Zn (1)#1 O(2)−Zn(1)−Zn (1)#1

complex 3 2.085(3) 2.179(3) 2.210(3) 100.08(11)

O(2)−Co(1)−N (1) O(3)#1−Co(1)− N(1) O(2)−Co(1)−N (1)#1 O(3)#1−Co(1)− N(1)#1 N(1)−Co(1)−N (1)#1

91.48(11) 167.67(12) 102.09(10)

88.48(6) 91.52(6)

Co(1)−O(2)#1 Co(1)−O(3) Co(1)−N(1)#1 O(2)−Co(1)−O (3)#1 O(2)−Co(1)−O (3) O(3)#1−Co(1)− O(3)

95.01(7) 89.76(7) 84.99(7)

89.76(7) 84.99(7) 90.24(7) 95.01(7)

180.00(8)

2.283(2) 2.340(3) 2.361(3) 180.00(14)

Cd(1)−O(2)#1 Cd(1)−N(1)#1 Cd(1)−O(1) O(2)−Cd(1)−N(1)

2.283(2) 2.340(3) 2.361(3) 90.56(10)

89.44(10)

90.52(9)

N(1)−Cd(1)−O(1)

96.69(10)

O(2)−Cd(1)−N(1) #1 N(1)−Cd(1)−N(1) #1 O(2)#1−Cd(1)−O (1)#1 N(1)#1−Cd(1)−O (1)#1 O(2)#1−Cd(1)−O (1) N(1)#1−Cd(1)−O (1)

89.44(10)

159.06(8)

Cd(1)−O(2) Cd(1)−N(1) Cd(1)−O(1)#1 O(2)−Cd(1)−O(2) #1 O(2)#1−Cd(1)−N (1) O(2)#1−Cd(1)−N (1)#1 O(2)−Cd(1)−O(1) #1 N(1)−Cd(1)−O(1) #1 O(2)−Cd(1)−O(1)

86.64(8)

O(1)#1−Cd(1)−O (1)

180.00(12)

Co(1)−O(1) Co(1)−O(3) Co(1)−N(1) O(1)−Co(1)−O(2) O(2)−Co(1)−O(3)

1.988(2) 2.033(2) 2.174(3) 121.48(9) 97.72(12)

O(2)−Co(1)−N(2) #1 O(1)−Co(1)−N(1) O(3)−Co(1)−N(1)

91.13(10)

90.58(11)

2.037(2) 2.0403(18) 2.9782(6) 89.81(8) 89.54(8)

90.56(10) 91.09(9) 83.31(10) 88.91(9)

180.0 88.91(9) 96.69(10) 91.09(9) 83.31(10)

complex 5

156.24(7) 79.56(6)

65.72(6)

2.0949(15) 2.1213(17) 2.1555(19) 180.0

O(2)#1−Co(1)− N(1) O(3)−Co(1)−N (1) O(2)#1−Co(1)− N(1)#1 O(3)−Co(1)−N (1)#1

complex 4

83.51(10) 161.06(11)

complex 3 Co(1)−O(2) Co(1)−O(3)#1 Co(1)−N(1) O(2)−Co(1)−O (2)#1 O(2)#1−Co(1)− O(3)#1 O(2)#1−Co(1)− O(3)

90.24(7)

2.0949(15) 2.1213(17) 2.1555(19) 91.52(6) 88.48(6)

86.47(11) 86.02(10)

Co(1)−O(2) Co(1)−N(2)#1 O(1)−Co(1)−O(3) O(1)−Co(1)−N(2) #1 O(3)−Co(1)−N(2) #1 O(2)−Co(1)−N(1) N(2)#1−Co(1)−N (1)

2.009(2) 2.144(3) 139.74(11) 92.08(11) 96.26(11) 88.08(10) 177.66(11)

a Symmetry codes: for 1: #1 = x, y − 1, z; #2 = −x+1, − y + 1, − z + 1; for 2: #1= −x + 1, y, − z + 1/2; for 3: #1 = −x + 1, − y + 1, − z + 1; for 4: #1 = −x + 1, − y + 1, − z; for 5: #1 = x + 1, y − 1, z

180.000(1)

can be topologically represented as a 6-connected pcu net with the point symbol of {412·63} (Figure 2d). Description of the Crystal Structure of {[Co(L1)(TPA)(H2O)2]·2DMF}n (3) and {[Cd(L1)(TPA)(H2O)2]·2DMF}n (4). Complexes 3 and 4 are isostructural and crystallize in the triclinic crystal system of P-1 space group. Only structure 3 is described here in detail (Coordination environment of the Cd(II) ion in 4 was listed in Supporting Information Figure S20). X-ray diffraction reveals that only half of the crystallographically independent Co(II) center is contained in the asymmetric unit. The Co(II) sites in distorted octahedral geometry, defined by two nitrogen atoms and four oxygen atoms. The axial positions are occupied by two oxygen atoms from coordinated water molecules while the equatorial plane consists of two nitrogen atoms from two L1 ligands and two oxygen atoms from two TPA ligands (Figure 3a). The two kinds of ligands are coordinated to the Co(II) ion to form a 2D rectangular grid with planar layers. These layers are held

together by different types of hydrogen bonding (d(C3···O1) = 2.774(3) Å, ∠C3−H3A···O1 = 100°; d(C12···O2) = 3.139(9) Å, ∠C12−H12A···O2 = 121°; d(C14···O3) = 3.343(7) Å, ∠C14−H14A···O3 = 155°, etc.) and π···π stacking interactions (the distance between two parallel layers is 3.324 Å) in the structure to yield a 3D network. One prominent structural feature of 3 is the presence of channels formed by the accumulation of 2D layers. For a single 2D layers, the dimensions of the rectangular grids is about 15.684 × 11.500 Å2. Despite such a big cavity, the layers are noninterpenetrated. When the parallel layers are stacking in an AAA··· mode (Figure 3b), infinite one-dimensional channels are created along the a-axis (Figure 3c). The solvent-accessible volume of these channels, calculated with the PLATON program, is 244.5 Å3 or 31.0% of the total unit cell volume. These channels are occupied by many disordered DMF solvent molecules, which have been crystallographically identified and well refined. 493



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Figure 1. (a) Coordination environment of the Zn(II) ions in 1. The hydrogen atoms are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = x, −1 + y, z, #2 = 1 − x, 1 − y, 1 − z. (b) View of the 1D chain constructed by IPA ligands and Zn(II) ions. (c) Polyhedral view of a single 2D coordination network of 1 along (1 0 1) plane. (d) Topological representation of the parallel stacking 2D layers of 1.

These are similar to values found in other complexes.14 Two crystallographically equivalent Co(II) cations are bridged by two carboxylate groups adopting a bis-bidentate coordination mode to generate a dinuclear Co(II) secondary building unit (SBU) with a Co···Co distance of 4.006 Å (Figure 4a). On the basis of plane Co2(CO2)2 SBU, four BPDC ligands assemble with up−up−down−down way to extend, and four L2 ligands extend in a direction perpendicular to this plane. Due to the four BPDC ligands are not in the same plane and the stretching direction of L2 ligands are decided by Co2(CO2)2 SBU, so there is no obvious layer in the whole structure. Actually, two BPDC ligands in a diagonal position of the Co2(CO2)2 SBU connect upward and downward SBU respectively to form a ladder structure (Supporting Information Figure S21). The

Description of the Crystal Structure of {[Co(L2)(BPDC)]·0.5H2O}n (5). X-ray analysis reveals that complex 5 crystallizes in the monoclinic space group P2/c. Its asymmetric unit consists of one crystallographically independent Co(II) ion, one L2 ligand, one deprotonated BPDC ligand and half of solvent water molecule. Each Co(II) is coordinated by four carboxylate oxygen atoms from three BPDC ligands in a flat position, and two nitrogen atoms from two L2 ligands distribution in the plane of the upper and lower position, which forms octahedral coordination mode. The Co−N bond distances are 2.144(3) and 2.174(3) Å, and the Co−O bond distances are 1.988(2), 2.009(2), and 2.033(2) Å; the N−Co− O angles are in the range of 86.02(10)−96.26(11)°, and the O−Co−O angles are in the range of 97.72 (12)−139.74 (11)°. 494



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Figure 2. (a) Coordination environment of the Zn(II) ions in 2. The hydrogen atoms and solvent molecules are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = 1 − x, y, 0.5 − z. (b) 2D flat network with square grids constructed by TPA ligands and Zn(II) ions in 2. (c) The rectangular grid built by TPA and L1 ligands. (d) Schematic representation of 2-fold interpenetrating 3D framework with pcu topology of 2.

ladder chains extend in the cross direction to form a 2D network, then combine the L2 ligands from vertical direction to construct 3D framework (Figure 4b). It can be regarded the binuclear cobalt as a network node, and each node connects to six adjacent ones. Thus, the 3D

coordination polymer lattice for complex 5 can be characterized as a 6-connected 2-fold interpenetrating rob network with the point symbol of {48·66·8} (Figure 4c). X-ray Powder Diffraction Results. From the PXRD patterns of complexes 1−5 (Figures S1−S5, Supporting 495



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Figure 3. (a) Coordination environment of the Co(II) ions in 3. The hydrogen atoms and solvent molecules are omitted for clarity (30% ellipsoid probability). Top right corner is the view of octahedral geometry of Co(II) center. Symmetry codes: #1 = 1 − x, 1 − y, 1 − z. (b) The AAA··· stacking 2D layers structure of 3 viewed along c axis. (c) One-dimensional channels along the a-axis.

analyses (Supporting Information Figure S13) were studied in detail. For complex 1, it does not contain guest molecules, the TG curve is almost flat until 409 °C, then appears a significant skeleton decomposition. From 25 to 151 °C, the weightlessness 12.13% for complex 2 is equivalent of lossing one lattice DMF molecule (calcd 11.62%), then the curve presents a gravity platform until 375 °C, after this, the framework starts to decompose. The TGA curves of 3 and 4 are very similar for their similar structure. From 25 to 700 °C, there are several apparent weightlessness steps. A weight loss of approximately

Information), the peak positions are agree well with their simulated ones, which indicating that the products have been successfully obtained as pure crystalline phases. To further examine the framework stability of complex 3, variable temperature PXRD patterns were tested, and the sample was heated in a series of temperatures in nitrogen atmosphere. The result reveals that this structure is stable until at least 275 °C (Supporting Information Figure S3). Thermogravimetric Analyses. To characterize the thermal stability of these complexes, thermogravimetric (TG) 496



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Figure 4. (a) Views of the coordination mode for the dinuclear Co(II) along the c axis. The hydrogen atoms and lattice solvent molecules are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = 2 − x, 1 − y, − z; #2 = 1 + x, − 1 + y, z; #3 = 1 − x, 2 − y, − z. (b) Perspectives of single 3D framework along the a axis (left) and c axis (right). (c) Schematic representation of 2-fold interpenetrating 3D framework with rob topology of 5.

25.82% between 107 and 187 °C for 3 (22.90% between 90 and 192 °C for 4) is equivalent of lossing the free DMF and H2O molecules (calcd 26.18% for 3, 23.43% for 4). From 278 °C, the skeleton of complex 3 begins to collapse, which shows a rapid weight loss. There is a slight weightlessness 1.51% before 368 °C for 5, which is equivalent to the loss of the solvent water molecule (calcd 1.43%). Above 368 °C, the ligands begin

to decompose, at the same time the framework begins to collapse. UV−visible Spectra. The UV−visible spectra of ligands L1, L2 and complexes 3 and 5 are presented in Supporting Information Figure S14a. The spectra of L1 and L2 ligands have distinct low energy absorption maxima (341 and 349 nm, respectively), which can be attributed to π−π* transitions. The subtle difference for 8 nm is the characteristic of methoxyl and 497



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connected rob topology with point symbol {48·68·8}, from the latest CCDC upgrade package, this type of topology based on rigid linear ligand is rare, it enriches the structure of this kind of MOFs. The above studies indicate that organic ligands and the central metal atoms have a great effect on the final structures. The optical absorption spectra of 3 and 5 indicate the nature of semiconductivity. The strong fluorescence emissions and long emission lifetimes of 1, 2, and 4 display that they are promising phosphorescent materials.

ethoxyl on ligands. There are two bands at 300−400 nm and 400−600 nm for compound 3 and 5. The band at 300−400 nm is π−π* transitions of ligands, and the lower energy band at 400−600 nm can be seen as metal-to-ligand charge-transfer (MLCT) transitions. The Kubelka−Munk function15 can be used to study the semiconductor properties of complexes 3 and 5 F (R ) =

(1 − R )2 K = 2R S

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with R representing the reflectance, K the absorption, and S the scattering. In a K/S versus E (eV) plot, extrapolating the linear part of the rising curve to zero provides the onset of absorption. The band gap of L1 and L2 at 2.86 and 2.65 eV display a good semiconductor property (Supporting Information Figure S14b). The Eg value at 1.94 and 2.93 eV for 3, 1.91 and 2.79 eV for 5, while it is only 1.10 eV for the semiconductor silicon material. Luminescent Properties. Luminescent complexes are of great interest due to their various application in chemical sensors, photochemistry, and light-emitting diode (LED).16 Complexes 1, 2, and 4 are difficult to dissolve in general solvents, so their fluorescence properties were tested in the form of solid state, as well as the free L1 ligand (Supporting Information Figure S15). The fluorescent emission band at λmax = 428 nm under 335 nm excitation of L1 ligand can be ascribed to the π* → n or π* → π electronic transitions. The emissions of 1 (λem = 420 nm, λex = 350 nm), 2 (λem = 461 nm, λex = 340 nm), and 4 (λem = 418 nm, λex = 350 nm) can be probably assigned to the intraligand charge transfer transitions.17 Because the Zn2+ and Cd2+ ion is difficult to oxidize or reduce due to its d10 configuration,18 metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT) is impossible essentially. The differences among the spectra of these compounds are due to their different structures. Compared with ligand, the fluorescences of complexes are stronger, which is mainly attributed to the coordination effect.19 Besides, the emission decay lifetimes of these complexes were also investigated. The luminescent decay curves (Figures S16− 19, Supporting Information) can be fitted with a doubleexponential decay function. The emission decay lifetimes of 1, 2, 4 and L1 ligand are as follows: L1 ligand, τ1 = 9.71 μs (50.88%), τ2 = 1.30 μs (49.12%) (χ2 = 1.141); complex 1, τ1 = 9.85 μs (49.91%), τ2 = 1.24 μs (50.09%) (χ2 = 1.075); complex 2, τ1 = 10.62 μs (48.11%), τ2 = 1.30 μs (51.89%) (χ2 = 1.133); complex 4, τ1 = 9.43 μs (54.97%), τ2 = 1.13 μs (45.03%) (χ2 = 1.105). As we know, emission lifetime value of many metal− organic frameworks is nanosecond,20 the lifetime of complexes 1, 2, and 4 is longer than this value. Complexes with the life span at the microsecond level are classified as phosphorescent materials.

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data in CIF format, selected bond lengths and angles, patterns of photochemistry, TGA and PXRD in PDF format. This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: 86-25-83314502. E-mail: [email protected]. 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. 91022011, 21371092, 20971065, and 21021062) and National Basic Research Program of China (2010CB923303).

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REFERENCES

(1) (a) Tanabe, K. K.; Allen, C. A.; Cohen, S. M. Angew. Chem., Int. Ed. 2010, 49, 9730. (b) Su, C. Y.; Cai, Y. P.; Chen, C. L.; Smith, M. D.; Kaim, W.; Zur Loye, H. C. J. Am. Chem. Soc. 2003, 125, 8595. (c) Perry, J. J.; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev. 2009, 38, 1400. (d) Desiraju, G. R. J. Am. Chem. Soc. 2013, 135, 9952. (e) Zhang, Y.; Yang, J.; Yang, Y.; Guo, J.; Ma, J. F. Cryst. Growth Des. 2012, 12, 4060. (2) (a) Chen, B. L.; Zhao, X. B.; Putkham, A.; Hong, K. L.; Lobkovsky, E. B.; Hurtado, E. J.; Fletcher, A. J.; Thomas, K. M. J. Am. Chem. Soc. 2008, 130, 6411. (b) Uemura, K.; Yamasaki, Y.; Komagawa, Y.; Tanaka, K.; Kita, H. Angew. Chem., Int. Ed. 2007, 46, 6662. (c) Streb, C.; Long, D. L.; Cronin, L. Chem. Commun. 2007, 471. (3) (a) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y. B.; Eddaoudi, M.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004, 427, 6974. (b) Wang, X. L.; Qin, C.; Wang, E. B.; Su, Z. M. Chem. Eur. J. 2006, 12, 2680. (c) Mahata, P.; Sundaresan, A.; Natarajan, S. Chem. Commun. 2007, 4471. (4) (a) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y.; Eddaoudi, M.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004, 427, 523. (b) Farha, O. K.; Shultz, A. M.; Sarjeant, A. A.; Nguyen, A. T.; Hupp, J. T. J. Am. Chem. Soc. 2011, 133, 5652. (c) Murray, L. J.; Dinca, M.; Long, J. R. Chem. Soc. Rev. 2009, 38, 1294. (d) Li, J. R.; Sculley, J.; Zhou, H. C. Chem. Rev. 2012, 112, 869. (e) Shimomura, S.; Higuchi, M.; Matsuda, R.; Yoneda, K.; Hijikata, Y.; Kubota, Y.; Mita, Y.; Kim, J.; Takata, M.; Kitagawa, S. Nat. Chem. 2010, 2, 633. (5) (a) Sun, Q. F.; Iwasa, J.; Ogawa, D.; Ishido, Y.; Sato, S.; Ozeki, T.; Sei, Y.; Yamaguchi, K.; Fujita, M. Science 2010, 328, 1144. (b) Alam, M. A.; Tsuda, A.; Sei, Y.; Yamaguchi, K.; Aida, T. Tetrahedron. 2008, 64, 8264. (6) (a) Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Angew. Chem., Int. Ed. 2009, 48, 3418. (b) Liu, S.; Russell, D. H.; Zinnel, N. F.; Gibb, B. C. J. Am. Chem. Soc. 2013, 135, 4314. (c) Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O’Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1257. (d) Yuan, D. Q.; Zhao, D.; Sun, D. F.; Zhou, H. C. Angew. Chem., Int. Ed. 2010, 49, 5357.

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CONCLUSIONS Five metal−organic frameworks have been obtained successfully based on the reaction of rigid ligands and carboxylcontaining auxiliary ligands with corresponding transition metal ions. Different metal centers may obtain different structures under the same condition. The reaction condition is much the same except metal ions for 2−4, complex 2 is 2-fold interpenetrating 3D framework, but complexes 3 and 4 are both 2D motifs. Structural diversity induced by metal ion will be one of the highlights of our future research. Complex 5 is 6498



Article

(7) (a) Sun, C. Y.; Wang, X. L.; Qin, C.; Jin, J. L.; Su, Z. M.; Huang, P.; Shao, K. Z. Chem.Eur. J. 2013, 19, 3639. (b) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Duyne, R. P. V.; Hupp, J. T. Chem. Rev. 2012, 112, 1105. (c) Lu, Z. Z.; Zhang, R.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G. J. Am. Chem. Soc. 2011, 133, 4172. (d) Kong, X. J.; Long, L. S.; Zheng, Z. P.; Huang, R. B.; Zheng, L. S. Acc. Chem. Res. 2010, 43, 201. (8) (a) Ji, C. C.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G. Cryst. Growth Des. 2011, 11, 480. (b) Liu, Y. Y.; Ma, J. F.; Yang, J.; Su, Z. M. Inorg. Chem. 2007, 46, 3027. (9) (a) Cui, J. H.; Lu, Z. Z.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G. Cryst. Growth Des. 2012, 12, 1022. (b) Hijikata, Y.; Horike, S.; Sugimoto, M.; Sato, H.; Matsuda, R.; Kitagawa, S. Chem.Eur. J. 2011, 17, 5138. (10) Seo, J.; Bonneau, C.; Matsuda, R.; Takata, M.; Kitagawa, S. J. Am. Chem. Soc. 2011, 133, 9005. (11) Takaoka, K.; Kawano, M.; Tominaga, M.; Fujita, M. Angew. Chem., Int. Ed. 2005, 44, 2151. (12) (a) Yao, X. Q.; Hu, J. S.; Zhang, M. D.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G. Cryst. Growth Des. 2013, 13, 3381. (b) Farha, O. K.; Malliakas, C. D.; Kanatzidis, M. G.; Hupp, J. T. J. Am. Chem. Soc. 2010, 132 (3), 950. (c) Li, T.; Kozlowski, M. T.; Doud, E. A.; Blakely, M. N.; Rosi, N. L. J. Am. Chem. Soc. 2013, 135, 11688. (d) Li, S. L.; Lan, Y. Q.; Qin, J. S.; Ma, J. F.; Liu, J.; Yang, J. Cryst. Growth Des. 2009, 9 (3), 4142. (13) (a) Wei, H. X.; Chen, Y. W.; Gao, D. Z.; Sun, Y. Q.; Zhang, G. Y.; Xu, Y. Y. Inorg. Chim. Acta 2011, 375, 298. (b) Yang, E. C.; Zhao, H. K.; Ding, B.; Wang, X. G.; Zhao, X. J. Cryst. Growth Des. 2007, 7, 2009. (c) Che, G. B. Acta Crystallogr., Sect. E (Struct. Rep. Online) 2006, 62, 1378. (d) Qi, Y. J.; Li, H.; Cao, M. H.; Zhang, Q.; Hu, C. W.; Wang, E. B. J. Mol. Struct. 2006, 782, 32. (e) Gong, Y.; Hu, C. W.; Li, H.; Huang, K. L.; Tang, W. J. Solid State Chem. 2005, 178, 3152. (14) (a) Hu, J. S.; Huang, L. F.; Yao, X. Q.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G.; Xue, Z. L. Inorg. Chem. 2011, 50, 2404. (b) Alborés, P.; Rentschler, E. Dalton Trans. 2009, 2609. (c) Song, J. L.; Zhao, H. H.; Mao, J. G.; Dunbar, K. R. Chem. Mater. 2004, 16, 1884. (15) Kubelka, P.; Munk, F. Z. Tech. Phys. 1931, 12, 593. (16) (a) Hu, J. S.; Shang, Y. J.; Yao, X. Q.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G.; Xue, Z. L. Cryst. Growth Des. 2010, 10, 2676. (b) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330. (c) Yang, J.; Yue, Q.; Li, G. D.; Cao, J. J.; Li, G. H.; Chen, J. S. Inorg. Chem. 2006, 43, 2857. (17) Hu, T. L.; Zou, R. Q.; Li, J. R.; Bu, X. H. Dalton Trans. 2008, 10, 1302. (18) Kurtz, S. K.; Perry, T. T. J. Appl. Phys. 1968, 39, 3798. (19) (a) Wang, S. Coord. Chem. Rev. 2001, 215, 79. (b) Wen, L. L.; Dang, D. B.; Duan, C. Y.; Li, Y. Z.; Tian, Z. F.; Meng, Q. J. Inorg. Chem. 2005, 44, 7161. (20) (a) Zhang, M. D.; Qin, L.; Yang, H. T.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G. Cryst. Growth Des. 2013, 13, 1961. (b) Jin, F.; Zhang, Y.; Wang, H. Z.; Zhu, H. Z.; Yan, Y.; Zhang, J.; Wu, J. Y.; Tian, Y. P.; Zhou, H. P. Cryst. Growth Des. 2013, 13, 1978.

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