Cd(II) Terephthalate Coordination Polymers ... - ACS Publications

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Zn(II)/Cd(II) Terephthalate Coordination Polymers Incorporating Bi‑, Tri‑, and Tetratopic Phenylamine Derivatives: Crystal Structures and Photoluminescent Properties Zhenzhen Shi,† Zhaorui Pan,†,‡ Hailang Jia,† Shuguang Chen,† Ling Qin,† and Hegen Zheng*,† †

State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R. China ‡ School of Environmental Science, Nanjing Xiaozhuang University, Nanjing 211171, P. R. China S Supporting Information *

ABSTRACT: Using reticular chemistry allowed the design and construction of four novel Zn(II)/Cd(II) coordination polymers, {[Zn(BTPA)(TPA)]·H2O}n (1), {[Zn(TTPA)(TPA)]·H2O}n (2), {[Cd2(TTPA)2(TPA)2(DMF)]·2H2O}n (3), and {[Cd(TTPBDA)(TPA)]0.5·DMF·H2O}n (4). They were successfully synthesized from bi-, tri-, and tetratopic phenylamine derivatives (BTPA = bis(4-(1H1,2,4-triazol-1-yl)phenyl)amine, TTPA = tris(4-(1H-1,2,4-triazol-1yl)phenyl)amine, TTPBDA = N4,N4,N4′,N4′-tetrakis(4-(1H-1,2,4triazol-1-yl)phenyl)-(1,1′-biphenyl)-4,4′-diamine) incorporating a linear terephthalic acid (H2TPA) ligand and Zn(II)/Cd(II) nitrate salts. These transparent crystals present gradually increasing dimensionality and complexity upon extension of the denticity of the phenylamine organic building blocks, as clearly supported by single-crystal X-ray analysis, infrared spectroscopy, elemental analysis, powder X-ray diffraction, and thermogravimetric analysis. Complex 1 shows two-dimensional (2D) threefold-interpenetrating layers (2D + 2D → 2D) with the sql topology that are further formed into a three-dimensional (3D) supramolecular structure by interlayer π···π stacking and hydrogen-bonding interactions. Complex 2 displays 2D layers with the hcb topology that are further assembled into a 3D fourfold-interpenetrating supramolecular framework with the 3,4,4T25 topology by hydrogen-bonding interactions. Complex 3 possesses a fourfold-interpenetrating 3D (3,4,5)-connected architecture with the 3,4,5T86 topology. Complex 4 features an interesting and unusual new self-penetrating (4,6)-connected 3D topological network with the point symbol of (414· 8)(66), which contains a fourfold-interpenetrated 3D dia network linked by TPA2− ligands. The results suggest that these diverse coordination networks mainly can be adjusted by the number of 1,2,4-triazole substituents on the aniline backbones and the coordination geometries of the metal ions. Furthermore, the photoluminescence spectra and emission decay lifetimes of complexes 1−4 were examined.

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INTRODUCTION Metal−organic frameworks (MOFs) or porous coordination polymers (PCPs) are constructed by connecting metal centers or clusters as nodes with organic linkers to make extended crystalline structures. Since a reticular synthesis approach that requires the use of secondary building units (SBUs) to direct the assembly of ordered frameworks was suggested by Yaghi and co-workers,1 more than 20 000 different MOFs, largely composed of a limited number of different kinds of building units, have been reported and studied over the last 15 years.2 They have been also utilized for many potential applications such as photoluminescence,3−5 chemical sensors,6−9 gas storage and separation,10,11 biomedicine,12 and heterogeneous catalysis.13 However, it is a long-standing challenge to design and synthesize new crystalline coordination polymers with fascinating topologies from polytopic linkers and/or multiple building units.14 Among many developments made in this respect, © XXXX American Chemical Society

ditopic or polytopic organic carboxylates as organic linkers connecting metal ions or SBUs have yielded extensive architecturally robust crystalline MOF structures with permanent and high porosity.15 For instance, in the classical MOF5,16 MOF-177,17 and HKUST-118 MOFs, Zn4O(CO2)6 and Cu2(CO2)4 paddlewheel SBUs are joined by ditopic or tritopic carboxylate linkers to form pcu and tbo topologies, respectively. Other tetratopic,19−21 pentatopic,22,23 hexatopic,24−26 and octatopic27,28 carboxylates have also been widely utilized as multidentate linkers, generating various topological structures with potential properties. At the same time, ditopic and tritopic N-donor ligands based on 1,2,4triazoles, which combine the coordination geometries of both Received: January 13, 2016 Revised: April 6, 2016

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DOI: 10.1021/acs.cgd.6b00056 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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requirements. In addition, a bitopic H2TPA ligand was also employed as a bridging ligand to construct coordination polymers in this work. Four new Zn(II)/Cd(II) coordination polymers were prepared: {[Zn(BTPA)(TPA)]·H2O}n (1), {[Zn(TTPA)(TPA)]·H 2 O}n (2), {[Cd 2 (TTPA) 2 (TPA) 2 (DMF)]·2H2O}n (3), and {[Cd(TTPBDA)(TPA)]0.5·DMF· H2O}n (4). With the increase in the number of triazole rings in the phenylamine derivatives, the structural dimensionality and complexity of these complexes are extended. In addition, we also describe their characterizations and photoluminescent properties in detail.

imidazoles and pyrazoles to arrange their three heteroatoms, have been extensively studied.29−37 However, to the best of our knowledge, coordination polymers based on polytopic 1,2,4triazole-containing ligands with phenylamine backbones have not been investigated systematically much to date.38 According to the reticular synthesis approach, we introduced different numbers of 1,2,4-triazole rings into the phenylamine system and prepared three different-shaped ligands, namely, Vshaped BTPA, triangular TTPA, and quadrangular TTPBDA ligands (Scheme 1). The phenyl and triazole rings in these

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Scheme 1. Structures of the H2TPA, BTPA, TTPA, and TTPBDA Ligands

RESULTS AND DISCUSSION The experimental section is included in the Supporting Information. Crystallographic data and experimental details for complexes 1−4 are given in Table 1. Selected bond lengths and angles of these complexes are listed in Table S1 in the Supporting Information, and hydrogen-bonding distance and angle data for complexes 1−4 are listed in Table S2. Description of the Crystal Structures. {[Zn(BTPA)(TPA)]· H2O}n (1). The single-crystal X-ray structure of complex 1 was solved in the triclinic P1̅ crystal system. The structure of 1 contains a Zn(II) ion, a BTPA ligand, a deprotonated H2TPA ligand, and a lattice water molecule (removed by PLATON39). Each Zn ion is four-coordinated by two nitrogen atoms from two different BTPA ligands and two oxygen atoms from two different TPA2− ligands to form a distorted {ZnN2O2} tetrahedral geometry (Figure 1a). The Zn−N bond lengths are 2.004(2) and 2.028(2) Å, and the Zn−O bond lengths are 1.9548(19) and 1.9564(19) Å.

ligands rotate freely through C−N bonds to coordinate the metal ions and meet the geometric and conformational

Table 1. Crystal Data and Structural Refinement Parameters of Complexes 1−4 empirical formula formula weight T (K) 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, θmax/deg total, unique data Rint observed data [I > 2σ(I)] Nref, Npar GOF on F2 R1, wR2 [I > 2σ(I)]b R1, wR2 (all data) min, max residual density/e·Å−3

1a

2

3

4a

C24H19N7O5Zn 550.86 293(2) triclinic P1̅ 9.6198(10) 10.7405(12) 12.4473(13) 72.1150(10) 70.342(2) 71.2690(10) 1118.0(2) 2 1.583 1.147 544 1.78, 27.25 9940, 4926 0.0258 4277 4926, 325 1.071 0.0395, 0.1343 0.0455, 0.1421 −0.487, 0.439

C32H24N10O5Zn 693.98 293(2) triclinic P1̅ 9.6786(16) 11.867(2) 14.149(2) 77.930(3) 88.773(2) 88.770(3) 1588.6(4) 2 1.451 0.831 712 1.47, 26.67 13300, 6426 0.0688 5184 6426, 439 1.055 0.0549, 0.1622 0.0692, 0.1867 −0.860, 0.675

C67H55Cd2N21O11 1555.12 296(2) triclinic P1̅ 12.2673(16) 16.452(2) 16.597(2) 92.251(2) 90.256(2) 101.757(2) 3276.6(8) 2 1.576 0.728 1576 1.23, 26.37 19978, 13010 0.0743 11717 13010, 912 1.099 0.0660, 0.2096 0.0696, 0.2118 −1.725, 4.459

C29H27Cd0.5N8O4 607.78 293(2) monoclinic C2/c 18.535(4) 27.031(6) 10.995(3) 90 103.158(4) 90 5364(2) 8 1.280 0.463 2104 1.36, 27.67 18009, 6208 0.067 4582 6208, 321 1.066 0.0506, 0.1211 0.0725, 0.1280 −0.721, 0.841

The residual electron densities were flattened by using the SQUEEZE option of PLATON. bR1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = {∑[w(Fo2 − Fc2)2]/ ∑[w(Fo2)2]}1/2, where w = 1/[σ2(Fo2) + (aP)2 + bP], in which P = (Fo2 + 2Fc2)/3. a

B



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Figure 1. (a) Coordination environment of the Zn(II) ions in 1. The hydrogen atoms have been omitted for clarity. Symmetry code: #1 = x − 1, y − 1, z. (b) Two 1D chains constructed by Zn(II) ions and BTPA or TPA2− ligands along different directions (left); a single 2D layer (middle); the sql topology (right). (c) Schematic view of the threefold-interpenetrating 2D layer. (d) Perspective view of the 3D supramolecular structure resulting from π···π stacking (green dashed lines) and hydrogen-bonding interactions (orange dashed lines).

BTPA ligands adopting a μ2-bridging coordination mode (Figure S1a in the Supporting Information) link Zn ions to form 1D chains, and TPA2− ligands adopting a μ1-η1:η0 coordination mode (Figure S2a) also connect Zn ions to generate 1D chains (Figure 1b, left). In this way, these 1D chains are further connected to form a single 2D layer (Figure 1b, middle). Topological analysis of the crystal structure of 1 was performed using TOPOS 4.0 software.40 Thus, the single 2D layer can be described as a 4-connected (42·62)-sql topology (Figure 1b, right). To stabilize the crystal structure during the assembly process, three identical layers are interlaced with one another in the spaces, yielding a threefold-interpenetrating 2D layer (2D + 2D → 2D), as shown in the Figure 1c. In complex 1, interlayer π···π interactions exist between benzene rings of different BTPA ligands with centroid−centroid distances of 3.677 Å. Furthermore, adjacent layers are packed into a 3D supramolecular structure by π···π stacking and hydrogenbonding interactions (N7−H7A···O4#5 = 2.918 Å; symmetry code #5 = −x, −y + 1, −z) (Figure 1d and Table S2). {[Zn(TTPA)(TPA)]·H2O}n (2). Complex 2 crystallizes the same triclinic crystal system as 1, with space group P1̅ . However, the crystal structure of 2 exhibits a 2D layer with the 63-hcb topology. The asymmetric unit consists of one Zn(II) ion, one TTPA ligand, one deprotonated H2TPA ligand, and one lattice water molecule. As shown in Figure 2a, each Zn(II) ion is four-

coordinated by two carboxylate oxygen atoms from two TPA2− ligands and two nitrogen atoms from two TTPA ligands, resulting in a slightly distorted tetrahedral {ZnN 2O 2} coordination geometry. The Zn−O bond lengths are 1.923(3) and 1.945(3) Å, and the Zn−N ones are 2.005(3) and 2.007(3) Å. The deprotonated carboxylic groups of the H2TPA ligand adopt a μ1-η1:η0 coordination mode (Figure S2a) and link Zn(II) ions to form 1D zigzag chains. These adjacent 1D chains are connected by μ2-bridging TTPA ligands (Figure S1b) to yield a 2D layer (Figure 2b). Adjacent 2D layers are further extended into a 3D supramolecular network by hydrogenbonding interactions between carboxylate oxygen atoms and nitrogen atoms or solvent water molecules (O5−H5A···N8#4 = 2.901 Å and O5−H5B···O4#5 = 2.785 Å; symmetry codes: #4 = −x + 2, −y + 1, −z + 1; #5 = −x + 1, −y + 1, −z) (Figure 2c and Table S2). Analysis of the 2D layer topology revealed that each Zn(II) ion acts as a 3-connected node, and the simplified layer is shown in Figure 2d. Thus, it can be represented as a 3connected hcb topology. In order to better identify the nature of the complicated supramolecular network of 2 when considering hydrogen-bonding interactions, suitable nodes and linkers can be defined by using a topological approach. Each TTPA ligand links two Zn ions and one TPA2− ligand, so C



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Figure 2. (a) Coordination environment of the Zn(II) ions in 2. The hydrogen atoms and lattice water molecules have been omitted for clarity. Symmetry code: #1 = x − 1, y − 1, z. (b) A single 2D layer constructed by Zn(II) ions, TTPA ligands, and TPA2− ligands. (c) Perspective view of the 3D supramolecular network resulting from hydrogen-bonding interactions (pink dashed lines). (d−f) Schematic views of (d) the hcb topology, (e) the 3,4,4T25 topology, and (f) the fourfold-interpenetrating net.

it can be regarded as a 3-connected node. Each TPA2− ligand bridges two Zn ions and two TTPA ligands, while the Zn(II) ion links one Zn ion joined by the TPA2− ligand, one TPA2− ligand, and two TTPA ligands; these can be regarded as two different kinds of 4-connected nodes. Therefore, the final topology of 2 is a 3-nodal (3,4,4)-connected 3,4,4T25 topological net with the point symbol (62·84)(63)2(64·82)2, as shown in Figure 2e. The potential voids are large enough to be filled via mutual interpenetration of four independent 3D frameworks, generating a fourfold-interpenetrating 3D structure (Figure 2f). To our knowledge, this 3D supramolecular network represents the first example of a Zn(II) MOF with the 3,4,4T25 topology sustained by the interplay of the coordinative and hydrogen-bonding interactions.41,42

{[Cd2(TTPA)2(TPA)2(DMF)]·2H2O}n (3). Complex 3 also crystallizes the same triclinic crystal system as 1 and 2, with space group P1̅ . The asymmetric unit contains two crystallographically independent Cd(II) ions, two TTPA ligands, two deprotonated H2TPA ligands, a coordinated DMF molecule, and two lattice water molecules. As shown in Figure 3a, both of the crystallographically independent Cd(II) ions are six-coordinated with a distorted octahedral environment ({CdN3O3} for Cd1; {CdN2O4} for Cd2). Cd1 is coordinated by three oxygen atoms from two different TPA2− ligands and a nitrogen atom from a TTPA ligand at the equatorial positions and by two other nitrogen atoms from two different TTPA ligands at the axial positions with an N(6)#2− Cd(1)−N(1) angle of 175.9(2)°. In contrast to Cd1, in Cd2 D



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Figure 3. (a) Coordination environment of the Cd(II) ions in 3. The lattice water molecules and hydrogen atoms have been omitted for clarity. Symmetry codes: #1 = x, y + 1, z + 1; #2 = x − 1, y − 1, z; #3 = x − 1, y, z − 1; #4 = x + 1, y + 1, z. (b) Two 1D chains constructed by Cd(II) ions and TTPA or TPA2− ligands along different directions. (c) A single 3D framework constructed by Cd(II) ions and TTPA and TPA2− ligands in the bc plane. (d) The fourfold-interpenetrating network with the 3,4,5T86 topology.

shown in Figure 4a, each Cd(II) ion is six-coordinated with a slightly distorted octahedral {CdN4O2} coordination geometry involving four nitrogen atoms from four different TPPBDA ligands at the equatorial positions and two carboxylate oxygen atoms from two deprotonated H2TPA ligands at the axial positions with an O(1)−Cd(1)−O(1)#1 angle of 175.0(2)°. The Cd−O bond length is 2.272(3) Å, and the Cd−N bond lengths are 2.360(3) and 2.367(3) Å. TTPBDA ligands adopting a μ4-bridging coordination mode (Figure S1e) link Cd ions to generate a single 3D framework (Figure 4b). Interestingly, different shapes of channels are generated in the ab, bc, and ac planes in the single net, as shown in Figures 4b and S3a,b. From the topological point of view, both the TTPBDA ligands and Cd(II) ions can be considered as 4-connected nodes. Thus, the single 3D framework can be abstracted into a 4-connected 66-dia topological network (Figure 4c). In order to minimize the presence of cavities and stabilize the framework during the assembly process, three other identical networks are filled in the voids, generating a fourfold-interpenetrating 3D network, as shown in Figure 4d. The interpenetration can be also classified as type IIIa, Z = 2 × 2 = 4 (Zt = 2; Zn = 2),43,44 and the interpenetrating nets are generated by [0,0,1] TIVs (10.99 Å) and nontranslating interpenetration symmetry elements. The resulting 3D net is composed practically of 26membered rings and 58-membered rings constructed from TTPBDA ligands and Cd ions and contains two alternately arranged kinds of intertwined left- and right-handed doublehelical chains (labeled as L1/R1 and L2/R2) running along the crystallographic 21 axis with a long pitch of 21.99 Å (Figure 4e). The two kinds of symmetry-related double helices coexist in the centrosymmetric solid, in which they appear in the left- and right-handed enantiomorphs, respectively. However, the L1,R2type and R1,L2-type double-helical chains are arranged

one equatorial coordination site is occupied by an oxygen atom from one DMF molecule instead of a nitrogen atom from one TTPA ligand. The apical positions are occupied by two nitrogen atoms with an N(15)#4−Cd(2)−N(11) angle of 168.2(2)°. The Cd−N distances range from 2.336(6) to 2.353(6) Å, and the Cd−O distances range from 2.192(5) to 2.505(5) Å. TTPA ligands adopting μ2- and μ3-bridging coordination modes (Figure S1c,d) link Cd1 and Cd2 ions to form 1D chains (Figure 3b, top). Two carboxylate groups of the H2TPA ligands adopting μ1-η1:η1 and μ1-η1:η0 coordination modes are deprotonated (Figure S2b) and link Cd1 and Cd2 ions to generate 1D chains (Figure 3b, bottom). Finally, a single 3D network (Figure 3c) is constructed from Cd(II) ions and TTPA and TPA2− ligands in the bc plane. From the topological view, μ3-bridging TTPA ligands, Cd2 ions, and Cd1 ions can be simplified as 3-connected, 4-connected, and 5-connected nodes, respectively, while both μ2-bridging TTPA and TPA2− ligands acting as 2-connected nodes are ignored. Therefore, the whole structure can be represented as a 3-nodal (3,4,5)-connected 3,4,5T86 topological network with the point symbol (53)(55· 6)(56·84). The potential spaces are large enough to be filled via mutual interpenetration of four independent 3D frameworks, generating a fourfold-interpenetrating 3D structure (Figure 3d). The interpenetration can be classified as type IIIa, Z = 2 × 2 = 4 (Zt = 2; Zn = 2),43,44 and the interpenetrating nets are generated by [1,0,0] translating interpenetration vectors (TIVs) (12.27 Å) and nontranslating interpenetration symmetry elements. {[Cd(TTPBDA)(TPA)]0.5DMF·H2O}n (4). Crystal structure determination revealed that complex 4 crystallizes in the monoclinic crystal system with space group C2/c. The asymmetric unit contains half a Cd(II) cation, half a TTPBDA ligand, half a TPA2− anion, a DMF solvent molecule, and a lattice water molecule (squeezed by PLATON software). As E



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Figure 4. (a) Coordination environment of the Cd(II) ions in 4. The lattice water molecules and hydrogen atoms have been omitted for clarity. Symmetry codes: #1 = −x + 1, y, −z + 3/2; #2 = x + 1/2, y + 1/2, z + 1; #3 = −x + 1/2, y + 1/2, −z + 1/2. (b) A single 3D framework constructed from Cd(II) ions and TTPBDA ligands in the ab plane. (c) The dia topology. (d) The fourfold-interpenetrating framework. (e) View of the two intertwined left-handed and right-handed helices, marked as L1 and R1 and L2 and R2, respectively. (f) The fourfold-interpenetrating topological net. (g) The (4,6)-connected self-penetrating network (TPA2− acting as blue linkers).

Effect of the Organic Ligands and Metal Ions on the Networks. From the above discussion, it can be seen that the organic ligands and metal ions play a critical role in assembling the resulting networks with diverse topologies,1,15,45 as summarized in Figure 5 and Table S3. The carboxylic groups of the H2TPA ligands in all of the complexes are fully deprotonated and adopt bridging or chelating coordination modes, so H2TPA ligands are only considered as linkers. Upon the introduction of Zn(II) centers in 1 and 2, it is observed that each Zn(II) ion shows a four-coordinated slightly distorted tetrahedral {ZnN2O2} coordination geometry, while in 3 and 4 each Cd(II) ion introduced shows a six-coordinated slightly distorted octahedral geometry. These crystal structures indicate

alternately (Figure S3c,d), which indicates achirality, as is further confirmed by the achiral space group C2/c. When TPA2− ligands as linkers are introduced into the complicated fourfold-interpenetrating 3D network (Figure 4f), the final obtained 3D structure exhibits an interesting and unusual new binodal (4,6)-connected 3D topological network (Figure 4g) with the point symbol (414.8)(66), in which Cd(II) ions and TTPBDA ligands are denoted as 6-connected and 4connected nodes, respectively. It is worth noting that the whole structure can be seen as a self-penetrating network (Figure S4) because the final structure can be easily simplified to a fourfoldinterpenetrated net by omitting the TPA2− linkers. F



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Figure 5. Schematic representation illustrating the different topologies resulting from the introduction of multitopic ligands in complexes 1−4.

that the dimensionality and complexity mainly can be adjusted by the number of 1,2,4-triazole substituents on the phenylamine backbones. In these complexes, coordinated nitrogen atoms of the triazole rings in these ligands display different degrees and bridging fashions (Figure S1: a for 1, b for 2, c and d for 3, e for 4). When the bitopic BTPA ligand is introduced, the simple threefold-interpenetrating 2D layer (2D + 2D → 2D) of 1 with the sql topology is obtained. The tritopic TTPA ligand is added in 2, but it in fact adopts a μ2-bridging mode just as the BTPA ligand does. Thus, 2 displays a 2D layer with the hcb topology. As the tritopic TTPA ligand added in 3 adopts μ2- or μ3-bridging coordination modes, 3 possesses a complicated (3,4,5)-connected fourfold-interpenetrating 3D architecture with the 3,4,5T86 topology. When the TTPBDA ligand is used, 4 features an unusual self-penetrating (4,6)connected 3D new topological network with the point symbol (414.8)(66) that contains a fourfold interpenetrating 3D dia topological network linked by TPA2− ligands. Of course, 1 and 2 are further formed into 3D supramolecular structures by interlayer π···π stacking and/or hydrogen-bonding interactions. Powder X-ray Diffraction and Thermogravimetric Analyses. In order to confirm the purities of complexes 1− 4, powder X-ray diffraction (PXRD) analyses of all four complexes were carried out at room temperature. As shown in Figures S5−S8, the main peak positions of the experimental patterns of complexes 1−4 are almost consistent with their simulated ones, demonstrating the single-phase purities of the products. To examine the thermal stabilities of complexes 1−4, thermogravimetric (TG) analyses were carried out (Figure 6). The TG curves indicate that there are weight losses of approximately 2.89% from room temperature to 235 °C for 1 and 2.67% between room temperature and 140 °C for 2, corresponding to the loss of guest molecule (3.27% calcd and

Figure 6. TG diagrams of complexes 1−4.

2.60% calcd for one lattice water molecule per formula unit for 1 and 2, respectively). Then the TG curves present a plateau until approximately 378 °C for 1 and 358 °C for 2. Finally, rapid weight losses are observed, which are attributed to decomposition of the coordination frameworks for complexes 1 and 2. Complex 3 loses two lattice water molecules and one coordinated DMF molecule below 180 °C (7.02% calcd, 7.64% exptl), and then TG curve presents a plateau until approximately 340 °C, where the structure begins to collapse. The TG study of complex 4 shows an initial weight loss of 3.04% (2.96% calcd) from 25 to 90 °C, suggesting the loss of one water molecule per formula unit. Then one DMF solvent molecule is gradually lost in the range of 90−340 °C (14.99% calcd, 14.41% exptl), after which the observed rapid weight loss suggests that decomposition of the structure begins. Photoluminescent Properties. Coordination polymers, especially with d10 metal centers, have been investigated for photoluminescent properties because of their potential G



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applications as luminescent materials.3−5 The solid-state photoluminescence of complexes 1−4 was determined at room temperature, as shown in Figure 7 and Table S4. The

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CONCLUSIONS We successfully synthesized four Zn(II)/Cd(II) complexes that were constructed from a linear H2TPA ligand and bi-, tri-, or tetratopic phenylamine derivatives under hydrothermal conditions. Complex 1 shows threefold-interpenetrating 2D layers with the sql topology that are further formed into a 3D supramolecular structure by interlayer π···π stacking and hydrogen-bonding interactions. Complex 2 displays 2D layers with the hcb topology that can be further assembled into a fourfold-interpenetrating 3D supramolecular framework with the 3,4,4T25 topology by hydrogen-bonding interactions. Complex 3 possesses a fourfold-interpenetrating 3D architecture with the 3,4,5T86 topology. Complex 4 features an interesting and unusual self-penetrating (4,6)-connected 3D (414·8)(66) topological network that contains fourfold-interpenetrating 3D dia topological networks linked by TPA2− ligands. The structural dimensions and complexity of these complexes mainly may be attributed to the different numbers of 1,2,4-triazole substituents on the phenylamine building blocks. The potential spaces in these complexes allow individual nets to interpenetrate with one another, which may be the different degrees between coordinated nitrogen atoms of multitopic ligands. Furthermore, the photoluminescence spectra and emission decay lifetimes of complexes 1−4 reveal that they may be candidates for photoluminescent materials.

Figure 7. Photoluminescence emission spectra of complexes 1−4 at room temperature.

emission peaks were observed at 420 nm (λex = 397 nm) for complex 1, 407 nm (λex = 369 nm) for complex 2, 413 nm (λex = 380 nm) for complex 3, and 428 nm (λex = 397 nm) for complex 4. In order to understand the nature of such emission bands, the photoluminescent properties of the free ligands were also measured. Upon excitation at ca. 362 nm for H2TPA, 363 nm for BTPA, 388 nm for TTPA, and 404 nm for TTPBDA, emissions were observed at ca. 417, 396, 416, and 430 nm, respectively, which can be assigned to the π* → π or π* → n electronic transitions. In comparison with those of the corresponding free multitopic ligands, the emission maxima of complex 1 are slightly red-shifted while the emission bands of complexes 2−4 are slighty blue-shifted. The differences in the band positions of these complexes might be related to the differences in the metal centers and coordination environments or the degree of π-electron overlap of the multitopic organic linkers in these structures. The interactions between solvent molecules and complex frameworks often affect the emission spectra of the as-made complexes.46 In order to eliminate solvent effects, complexes 1-4 were evacuated by heating, giving rise to complexes 1′−4′. The solid-state photoluminescence of complexes 1′−4′ was also measured at room temperature, as shown by the red lines in Figures S9−S12, and the PXRD patterns of complexes 1′−4′ were also measured at room temperature, as shown in Figures S13−S16. Apart from complex 3′, the emission spectra of the others are red-shifted to different degrees compared with the corresponding nonevacuated complexes. The structure of complex 3 contains coordinated DMF molecules, and the solvent effect may not have been fully eliminated, so the emission spectrum of complex 3′ continued to blue-shift. Furthermore, the emission decay lifetimes of these complexes were measured, and the curves (Figures S17−S20) were best fitted by biexponentials in the solid.47,48 The emission decay lifetimes are τ1 = 1.20 μs (44.91%) and τ2 = 11.41 μs (55.09%) (χ2 = 1.316) for complex 1, τ1 = 2.24 μs (9.78%) and τ2 = 14.27 μs (90.22%) (χ2 = 1.545) for complex 2, τ1 = 1.21 μs (42.76%) and τ2 = 9.51 μs (57.24%) (χ2 = 1.385) for complex 3, and τ1 = 1.22 μs (42.65%) and τ2 = 11.22 μs (57.35%) (χ2 = 1.406) for complex 4.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b00056. Detailed experimental procedures; conformations of the BTPA, TTPA, and TTPBDA ligands; coordination modes of the TPA2− ligands; some additional figures showing the networks in 4; IR spectra, PXRD patterns, photoluminescence spectra, and emission decay curves and lifetimes; and selected bond lengths and angles for 1−4 (PDF) Accession Codes

CCDC 1446963−1446966 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 86-25-83314502. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by grants from the National Natural Science Foundation of China (21371092 and 91022011), the National Science Foundation for Young Scientists of China (21301094), and the National Basic Research Program of China (2010CB923303).

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