Cd

Article pubs.acs.org/crystal

Synthesis, Crystal Structure, and Luminescence of Zn/Cd Coordination Polymers with a New Fuctionalized Terpyridyl Carboxylate Ligand Bing Xu, Juan Xie, Huai-Ming Hu,* Xiao-Le Yang, Fa-Xin Dong, Meng-Lin Yang, and Gang-Lin Xue Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069, China S Supporting Information *

ABSTRACT: Eight new coordination polymers, [Zn(L)Cl]n (1), [Zn2(L)4]n·2nH2O (2), [Zn2(L)2(1,3-bdc)]n (3), [Zn2(L)(1,3-bdc)(OH)] n ·0.5nH 2 O (4), [Zn 9 (L) 4 (1,3-bdc) 6 (OH) 2 ] n ·3nH 2 O (5), [Zn 2 (L) 2 (1,4-bdc)] n ·nH 2 O (6), [Cd 2 (L) 4 ] n ·nH 2 O (7), and [Cd 3 (L) 2 (1,3-bdc) 2 ] n ·nH 2 O (8) [HL = 4′-(2-carboxyphenyl)4,2′:6′,4″-terpyridine, H2(1,3-bdc) = benzene-1,3-dicarboxylic acid, H2(1,4-bdc) = benzene-1,4-dicarboxylic acid] have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, and single crystal X-ray diffraction. Complexes 1, 2, and 7 display a two-dimensional (2D) layer structure. Complex 3 presents a complicated 2D layer structure with paddle-wheel units, which exhibits an interesting (3,4,6)-connected 3-nodal new topological net with the point symbol of (3·4·5·62·7)2(3·6·7)2(32·42·52·62·76·8). Complex 4 is a 2-nodal (3,5)-connected 2D bilayer structure with the gek1 topological net and the point symbol of (3·4·5)(32·4·5·62·74). Complex 5 shows a self-penetrating three-dimensional (3D) framework based on pentanuclear clusters, which features an intriguing (3,3,4,4,12)-connected 5-nodal new topological net with the point symbol of (4·62)2(42·64)4(43)2(48·634·822·102). Complex 6 features a 2-fold interpenetrating (3,4)-connected 3D framework with the ins topological net and the point symbol of (63)(65·8). Complex 8 is a new (4,4,5,6)-connected 3D network built up by a linear Cd3(COO)6 trinuclear cluster with the point symbol of (42·63·8)2(43·63)2(44·64·82)2(48·66·8). The diverse structures indicate that rational adjustment of the second ligand, the pH value, and counteranion are good methods to further design metal−organic compounds with new structures and properties. In addition, the thermal stabilities and photoluminescence properties of 1−8 were also studied.

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INTRODUCTION The design and synthesis of metal−organic frameworks (MOFs) have become a very active area of research, owing to not only their fascinating topological structures1,2 but also their promising applications as functional materials in luminescence, magnetism, absorption, catalysis, ion-exchange, etc.3−6 Although nowadays there exist a variety of coordination polymers which possesses fascinating structures and intriguing properties, it is still a tremendous scientific challenge to predict and synthesize coordination polymers with expected structures and properties due to a number of factors that make a big difference in the formation of MOFs, such as the nature of the metal center and ligand, reaction medium, metal-to-ligand ratio, pH value, and counteranion.7−12 Di- and polycarboxylic acids are widely used as bridging ligands to construct coordination frameworks with versatile structures.13−17 Meanwhile the complexes containing multipyridyl ligands have received much attention in many respects.18−20 At the same time, unprecedented attention has been paid to d 10 metal coordination polymers, as a result of their outstanding photoluminescence.21−23 We are interested in synthesizing © 2014 American Chemical Society

coordination compounds on the basis of multipyridyl ligands and d10 metal ions and have already made advances in this field.24−31 Owing to their electronic and steric versatility and the large π-conjugated structure, 4′-aryl substituted-2,2′:6′,2″terpyridine still acts as a kind of classical ligands in coordination chemistry. Compared with 2,2′:6′,2″-terpyridine, 4,2′:6′,4″terpyridine have an advantage that the terminal pyridyl rings can easily stretch out through the coordination bonds between nitrogen atoms and metal centers, generating high-dimensional MOFs. In this regard, Wen and Ke et al. have reported two porous cadmium(II) frameworks with a polytopic 4-(4carboxyphenyl)- 4,2′:6′,4″-terpyridine ligand.32 Due to high symmetry of this ligand, it enables the formation of microporous metal−organic frameworks (MMOFs). However, 4′-(2-carboxyphenyl)-4,2′:6′,4″-terpyridine (HL, Scheme 1), as an asymmetric ligand, is able to generate a series of new structures, thus, the research system of 4,2′:6′,4″-terpyridine is Received: November 14, 2013 Revised: January 13, 2014 Published: January 24, 2014 1629

dx.doi.org/10.1021/cg4016977 | Cryst. Growth Des. 2014, 14, 1629−1641

Crystal Growth & Design

Article

Scheme 1. Schematic Drawing for Ligand HL

Scheme 2. Sythesis of Complexes 1−8

enriched. As far as we can see, 4′-(2-carboxyphenyl)-4,2′:6′,4″terpyridine has not been reported. It has been selected to construct new MOFs according to the following factors: (a) HL is an asymmetric bifunctional polydentate N,O-donor bridging ligand, which can link adjacent metallic centers through coordination bonding interactions. The terpyridyl and carboxylate groups can both act as bridging groups, while the carboxylate group can also serve as a chelating group. (b) HL has a large π-conjugated structure which markedly makes contribution to form a better connection between the donor and acceptor to fulfill electron transport. On the basis of the above considerations, HL can be extensively employed as a rigid building block to construct MOFs with remarkable structures. In this paper, we have synthesized eight new ZnII/ CdII coordination polymers based on HL, namely, [Zn(L)Cl]n (1), [Zn2(L)4]n·2nH2O (2), [Zn2(L)2(1,3-bdc)]n (3), [Zn2(L)(1,3-bdc)(OH)]n·0.5nH2O (4), [Zn9(L)4(1,3-bdc)6(OH)2]n· 3nH2O (5), [Zn2(L)2(1,4-bdc)]n·nH2O (6), [Cd2(L)4]n·nH2O (7), and [Cd3(L)2(1,3-bdc)2]n·nH2O (8). Meanwhile, their luminescence properties and thermal stabilities are also studied.

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based on Zn. Anal. Calcd (%) for C88H56N12O10Zn2 (1572.19): C, 67.23; H, 3.59; N, 10.69%. Found: C, 67.32; H, 3.64; N, 10.65%. IR (KBr, cm−1): 3423 (s), 1616 (s), 1363(m), 1064 (w), 835 (w), 764 (w), 638 (w). Preparation of [Zn2(L)2(1,3-bdc)] n (3). Complex 3 was synthesized in a similar procedure as 1, except that the metal salt was replaced by Zn(Ac)2·2H2O (21.9 mg, 0.1 mmol) and H2(1,3-bdc) (16.6 mg, 0.1 mmol) was introduced into the reaction system. Colorless quadrate crystals of 3 were obtained. Yield: 34.63 mg, 69.3% based on Zn. Anal. Calcd (%) for C52H32N6O8Zn2 (999.58): C, 62.48; H, 3.23; N, 8.41%. Found: C, 62.59; H, 3.24; N, 8.46%. IR (KBr, cm−1): 3421 (s), 2926 (w), 1616 (m), 1557 (m), 1501 (m), 1394 (s), 1047 (w), 940 (w), 833 (w), 740 (w), 532 (w), 472 (w). Preparation of [Zn2(L)(1,3-bdc)(OH)]n·0.5nH2O (4). A mixture of Zn(NO3)2·6H2O (29.7 mg, 0.1 mmol), HL (35.3 mg, 0.1 mmol), and H2(1,3-bdc) (16.6 mg, 0.1 mmol) in H2O (10 mL) was adjusted to pH = 7 with 0.5 mol L−1 NaOH solution. The mixture were then placed in a Teflon-lined stainless steel vessel (25 mL), heated to 180 °C for 72 h. After cooling to room temperature, colorless block crystals of 4 were obtained. Yield: 25.5 mg, 75.8% based on Zn. Anal. Calcd (%) for C30H19N3O7.5Zn2 (672.22): C, 54.60; H, 2.85; N, 6.25%. Found: C, 54.58; H, 2.83; N, 6.28%. IR (KBr, cm−1): 3421 (s), 3062 (w), 1611 (s), 1564 (m), 1407 (s), 1064 (s), 940 (w), 836 (w), 731 (w), 649 (w), 515 (w). Preparation of [Zn9(L)4(1,3-bdc)6(OH)2] n·3nH2O (5). Complex 5 was obtained by the same procedure used for preparation of 4, except that the pH value of the reaction mixture was adjusted to 5 instead of 7. Colorless prism crystals of 5 were obtained. Yield: 26.8 mg, 77.8% based on Zn. Anal. Calcd (%) for C136H86N12O39Zn9 (3100.5): C, 52.68; H, 2.80; N, 5.42%. Found: C, 52.72; H, 2.91; N, 5.57%. IR (KBr, cm−1): 3427 (s), 3062 (w), 1616 (s), 1564 (m), 1409 (m), 1064 (w), 836 (w), 748 (w), 650 (w), 520 (w) . Preparation of [Zn2(L)2(1,4-bdc)]n·nH2O (6). Complex 6 was synthesized in a similar procedure as 5, except that H2(1,4-bdc) was used as the auxiliary ligand instead of H2(1,3-bdc). Colorless block crystals of 6 were obtained. Yield: 38.4 mg, 75.4% based on Zn. Anal. Calcd (%) for C52 H34 N6 O9 Zn2 (1017.59): C, 61.37; H, 3.37; N, 8.26%. Found: C, 61.38; H, 3.40; N, 8.28%. IR (KBr, cm−1): 3543 (s), 2926 (w), 1573 (s), 1501 (m), 1405 (s), 901 (m), 788 (m), 723 (m), 556 (m). Preparation of [Cd2(L)4]n·nH2O (7). A mixture of CdCl2·2.5H2O (11.4 mg, 0.05 mmol) and HL (17.6 mg, 0.05 mmol) in H2O (10 mL) was adjusted to pH = 5 with the 0.5 mol L−1 NaOH solution. The mixture were then placed in a Teflon-lined stainless steel vessel (25 mL) and heated to 180 °C for 72 h. After cooling to room temperature, colorless quadrate crystals of 2 were obtained. Yield: 29.3 mg, 71% based on HL. Anal. Calcd (%) for C88H56Cd2N12O9 (1650.25): C, 61.37; H, 3.37; N, 8.26%. Found: C, 61.38; H, 3.40;

EXPERIMENTAL SECTION

All commercially available chemicals and solvents are of reagent grade and were used as received without further purification. Ligand HL was synthesized according to the reported procedure with some modification.33 Infrared spectra were obtained from KBr pellets on a Bruker EQUINOX 55 Fourier transform Infrared spectrometer in the 400−4000 cm−1 region. Elemental analyses (C, H, and N) were performed on an elementar Vario EL elemental analyzer. Fluorescence spectra were recorded on a Hitachi F-4500 spectrophotometer at room temperature. Thermal gravimetry analyses (TGA) were carried out with a Universal V2.6 DTA system at a rate of 10 °C/min in a nitrogen atmosphere. Powder X-ray diffraction (PXRD) measurements were measured on a Bruker D8 ADVANCE X-ray powder diffractometer (Cu Kα, 1.5418 Å). The syntheses of complexes 1−8 are shown in Scheme 2. Preparation of [Zn(L)Cl]n (1). A mixture of ZnCl2 (13.6 mg, 0.1 mmol) and HL (35.3 mg, 0.1 mmol) in H2O (10 mL) was adjusted to pH = 4 with 0.5 mol L−1 NaOH solution. The mixture were then placed in a Teflon-lined stainless steel vessel (25 mL) and heated to 180 °C for 72 h. After cooling to room temperature, colorless block crystals of 1 were obtained. Yield: 30.5 mg, 68% based on Zn. Anal. Calcd (%) for C22H14ClN3O2Zn2 (453.18): C, 58.30; H, 3.11; N, 9.27%. Found: C, 58.42; H, 3.07; N, 9.28%. IR (KBr, cm−1): 3422 (s), 1616 (s), 1363 (m), 1062 (w), 835 (w), 764 (w), 671 (w), 638 (w). Preparation of [Zn2(L)4]n·2nH2O (2). A mixture of Zn(Ac)2 (21.9 mg, 0.1 mmol) and HL (35.3 mg, 0.1 mmol) in H2O (10 mL) was adjusted to pH = 4 with 0.5 mol L−1 NaOH solution. The mixture were then placed in a Teflon-lined stainless steel vessel (25 mL) and heated to 180 °C for 72 h. After cooling to room temperature, colorless quadrate crystals of 2 were obtained. Yield: 29.5 mg, 75.2% 1630



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Table 1. Crystal Data and Structural Refinement Parameters for 1−8 compound

1

2

3

4

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρcalcd (g·cm−3) μ (mm−1) F(000) reflections collected reflections unique R(int) parameters S on F2 R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Δρmax and min (e Å−3)

C22H14ClN3O2Zn 453.18 monoclinic P2(1)/n 12.1335(11) 7.9711(7) 20.3084(19) 90 97.4430(10) 90 1947.6(3) 4 1.546 1.422 920 9551 3452 0.0236 262 1.035 0.0301, 0.0727 0.0408, 0.0792 0.309 and −0.231 5

C88H56N12O10Zn2 1572.19 triclinic P1̅ 11.5711(9) 12.1705(9) 14.5802(19) 98.625(2) 94.455(2) 116.5010(10) 1792.3(3) 1 1.457 0.744 808 9141 6281 0.0196 514 1.038 0.0462, 0.1036 0.0635, 0.1129 0.502 and −0.442 6

C52H32N6O8Zn2 999.58 triclinic P1̅ 12.4642(19) 12.5823(17) 15.269(2) 104.357(2) 108.967(2) 90.771(3) 2182.2(5) 2 1.521 1.165 1020 11124 7653 0.046 613 1.046 0.0756, 0.1281 0.1129, 0.1463 0.545 and −0.455 7

C30H19N3O7.5Zn2 672.22 monoclinic C2/c 23.798(8) 19.705(8) 13.445(5) 90 112.564(8) 90 5822(3) 8 1.534 1.701 2720 14522 5160 0.0393 391 1.050 0.0402, 0.1049 0.0537, 0.1118 0.682 and −0.327 8

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρcalcd (g cm−3) μ (mm−1) F(000) reflections collected reflections unique R(int) parameters S on F2 R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Δρmax and min (e Å−3)

C136H86N12O39Zn9 3100.5 triclinic P1̅ 14.198(3) 14.443(3) 18.560(3) 67.524(3) 71.377(3) 65.820(3) 3147.9(10) 1 1.636 1.775 1568 15960 11027 0.0237 898 1.009 0.0421, 0.0903 0.0606, 0.0998 0.0631 and −0.602

C52H34N6O9Zn2 1017.59 monoclinic P2/n 12.5807(16) 9.3402(12) 19.104(3) 90 103.775(3) 90 2180.2(5) 2 1.55 1.17 1040 10610 3841 0.0735 315 1.017 0.0531, 0.1003 0.0925, 0.1159 0.515 and −0.766

C88H56Cd2N12O9 1650.25 triclinic P1̅ 11.605(2) 12.340(2) 14.606(4) 99.002(3) 96.346(4) 116.734(2) 1805.9(7) 1 1.517 0.661 836 9189 6321 0.0160 505 1.035 0.0314, 0.0709 0.0375, 0.0742 0.283 and −0.459

C60H36Cd3N6O12 1370.15 monoclinic P2(1)/n 14.896(3) 9.8043(17) 17.559(3) 90 93.155(3) 90 2560.4(8) 2 1.777 1.309 1356 12205 4505 0.0862 368 0.980 0.0482, 0.0889 0.1050, 0.1080 1.131 and −0.801

N, 8.28%. IR (KBr, cm−1): 3423 (s), 1595 (s), 1542 (s), 1396 (s), 1060(w), 832 (m), 763 (m), 537 (w). Preparation of [Cd3(L)2(1,3-bdc)2]n·nH2O (8). The same synthetic method as that for 7 was used, except for the introduction of H2(1,3-bdc) (16.6 mg, 0.1 mmol) into the reaction system. Colorless block crystals of 8 were obtained. Yield: 36.6 mg, 80.3% based on Cd. Anal. Calcd (%) for C60H36Cd3N6O12 (1370.15): C, 67.23; H, 3.59; N, 10.69%. Found: C, 67.32; H, 3.64; N, 10.65%. IR (KBr, cm−1): 3422 (s), 1610 (s), 1563 (m), 1387 (m), 828 (w), 746 (w), 716 (w), 643 (w). X-ray Crystallography. Intensity data were collected on a Bruker Smart APEX II CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. Empirical

absorption corrections were applied using the SADABS program. The structures were solved by direct methods and refined by the full-matrix least-squares based on F2 using SHELXTL-97.34 All nonhydrogen atoms were refined anisotropically and hydrogen atoms of organic ligands were generated geometrically. Crystal data and structural refinement parameters for 1−8 are summarized in Table1 and selected bond distances and bond angles are listed in Table S1 of the Supporting Information. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 962626−962627 for 1−2, 939307−939309 and 939311 for 3−6, and 962628−962629 for 7−8. These data can be obtained free of charge via www.ccdc.can.ac.uk/conts/retrieving.html (or from the Cambridge 1631



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Crystallographic Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax, (+44) 1223-336033; or e-mail, [email protected]).

occupying the axial positions [Cl1−Zn1−O1 = 159.21(6)°]. The Zn−O and Zn−N bond lengths are 2.444(2)∼1.986(2) Å and 2.062(2)∼2.064(2)Å, respectively. The Zn1−Cl1 distance is 2.2627(8) Å, which is slightly shorter than those reported.35 The three pyridyl rings of L− anion are noncoplanar, and the terminal pyridyl rings (N1 and N3) are twisted with respect to the central pyridyl ring (N2) with the dihedral angles of 30.51° and 28.8°. Two L− anions adopting a μ3-η1:η1:η2 coordination mode (Scheme 3, mode I) link two Zn1 ions to form a [Zn2O2N2C18] 24-membered ring containing a type of pore with a size of 8.732 × 12.452 Å based on Zn1···Zn1 and C16···C16. Then the rings are linked by L− anions to generate a one-dimensional (1D) loop chain (Figure 1b). These chains are further linked by the terminal nitrogen atom (N3B) and carboxylate group of L− anions to give rise to a 2D layer (Figure 1c). Crystal Structure of [Zn2(L)4]n·2nH2O (2). The X-ray structural determination indicates that complex 2 is a 2D layer stucture. The asymmetric unit of 2 consists of one Zn(II) ion, two L− anions, and one lattice water molecule. As shown in Figure 2a, Zn1 is five-coordinated by three oxygen atoms (O1, O3A, and O4A) and two nitrogen atoms (N1B, N4) from four different L− anions, in which O3A and O4A come from the chelating carboxylate group of one L− anion. The coordination geometry of Zn1 can be described as having a distorted trigonal bipyramidal geometry, in which N4 and O3A atoms occupy the axial positions [N4−Zn1−O3A = 148.39(11)°]. Zn−O bond lengths fall in the range of 1.980(2)−2.296(3) Å, and Zn−N bond lengths are 2.066(3) Å (Zn1−N1B) and 2.071(3) Å (Zn1−N4), which are in accordance with the previous report.36 Unlike in complex 1, the L− anions adopt two different coordination fashions: (a) the bimondentate coordination mode (Scheme 3, mode IV) in which both the carboxylate group and one terminal pyridyl ring act as a mondentate coordination mode. (b) The tridentate coordination mode (Scheme 3, mode II) in which the carboxylate group acts as the bidentate-chelating coordination mode, and the terpyridyl moiety acts as the monodentate coordination mode. On the basis of the connection modes, first, each L− anion with coordination mode IV join up two Zn(II) ions to form a 1D zigger chain (Figure 2b). These chains are then further extended into 2D layer (Figure 2c) through L− anions, adopting a coordination mode II. Crystal Structure of [Zn2(L)2(1,3-bdc)]n (3). When H2(1,3-bdc) was introduced into the reaction system, complex 3 was obtained. X-ray single-crystal diffraction analysis reveals that 3 is a 2D framework based on paddle-wheel units. The asymmetric unit of 3 contains two Zn(II) ions, two L−, and one

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RESULTS AND DISCUSSION Crystal Structure of [Zn(L)Cl]n (1). X-ray single-crystal diffraction analysis reveals that 1 is a two-dimensional (2D) framework. The asymmetric unit of 1 contains one Zn(II) ion, one L−, and one Cl− anion. As shown in Figure 1a, Zn1 is

Figure 1. (a) Coordination environment of ZnII ion in 1. The hydrogen atoms are omitted for clarity (symmetry codes: A = −x, −y, −z; B = 0.5 + x, 0.5 − y, −0.5 + z). (b) View of the 1D loop chain of 1 along the b axis. (c) View of the 2D layer structure of 1 along the a axis. (The 1D zigger chain is highlighted.)

surrounded by two nitrogen atoms (N1A and N3B), two oxygen atoms (O1 and O2) from L− anions, and one chlorine atom. The coordination geometry can be described as a distorted trigonal bipyramid geometry with Cl1 and O1 atoms

Scheme 3. Coordination Modes of L− and Auxiliary Ligands in 1−8

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III (Scheme 3) through Zn2−N3 and Zn2−N1 bonds to form a one-dimensional (1D) loop chain (Figure 3c). Further, these 1D loop chains are cross-linked by (1,3-bdc)2− anions to give rise to a 2D framework (Figure 3d). Noticeably, L− anions adopting coordination mode IV (Scheme 3) do not play an indispensable role in the construction of final 2D framework. To further understand the structure of 3, the paddle-wheel Zn(II) unit, L− anion with coodination mode III (Scheme 3) and Zn2 ion can be regarded as 6-, 3-, and 4-connected nodes, respectively. Hence, complex 3 possesses a 3-nodal (3,4,6)connected network with the point symbol of (3·4·5·62·7)2(3·6· 7)2(32·42·52·62·76·8) (Figure 3e). Crystal Structure of [Zn2(L)(1,3-bdc)(OH)]n·0.5nH2O (4). X-ray single crystal diffraction analysis reveals that 4 is a 2D bilayer structure. The asymmetric unit of 4 consists of two Zn(II) ions, one L−, one (1,3-bdc)2−, and one OH− anion and half lattice water molecule. As depicted in Figure 4a, Zn1 is fivecoordinated by one nitrogen (N1A) atom and one oxygen (O1) atom from two L− anions, and three oxygen atoms (O5B, O6B, and O7) from (1,3-bdc)2− and OH− anions to form a slightly distorted trigonal bipyramid geometry, in which N1A and O5B atoms occupy the axial positions [O5B−Zn1−N1A = 150.38(13)°]. Zn2 is four-coordinated by one nitrogen (N3C) and one oxygen (O2) atoms from two L− anions, and two oxygen atoms (O3 and O7) from (1,3-bdc)2− and OH− anions to form a tetrahedral coordination geometry. The Zn−N bond lengths are 2.046(3) and 2.058(3)Å, and the Zn−O bond lengths vary from 1.903(3) to 2.152(3)Å, which are consistent with the corresponding values reported for Zn-pyridyl compounds.37 The three pyridyl rings of the L− ligand are nonplanar, each terminal pyridyl group is twisted with respect to the central one, the dihedral angles between the central and terminal pyridyl rings are 17.21° (N1 pyridyl ring) and 15.57° (N3 pyridyl ring), respectively. Interestingly, it can be observed that Zn1 and Zn2 are connected by an oxgen atom (O7), which comes from a hydroxyl group. It is worth noting that the bidentate-bridging carboxylate group of the L− ligand and a μ2OH group bridge Zn1 and Zn2 to form a dizinc unit, [Zn2(μ2− OH)(μ2-O2CR)]. In the dizinc unit, the Zn1···Zn2 separation is 3.299 Å (Figure 4b). In 4, the L− ligand adopts a μ4-η1:η1:η1:η1bridging coordination mode III (Scheme 3) and the auxiliary (1,3-bdc)2− ligand adopts a μ2-η1:η2-bridging coordination mode VI (Scheme 3). On the basis of these connection modes, the Zn2 units are linked to generate a 2D staggered bilayer structure (Figure 4c). To further understand the structure of 4, the topological analysis was carried out. The L− ligand and dizinc unit can be regarded as 3- and 5-connected nodes, respectively. The (1,3-bdc)2− anion is assigned to a linker. On the basis of the simplification principle,38 complex 4 possesses a 2-nodal (3,5)-connected gek1 net with the point symbol of (3· 4·5)(32·4·5·62·74) (Figure 4d). Crystal Structure of [Zn9(L)4(1,3-bdc)6(OH)2(H2O)2]n· 3nH2O (5). The crystal structure analysis shows that 5 features an unusual 3D framework. The asymmetric unit of 5 contains four and a half Zn(II) ions, two L− anions, three (1,3-bdc)2− anions, one OH− anion, one coordinated water, and one-and-ahalf lattice water molecules. As shown in Figure 5a, Zn1 is fourcoordinated by one nitrogen atom (N1) from L− ligand and three oxygen atoms (O5, O9, and O17) from (1,3-bdc)2− and OH− anions to form a tetrahedral coordination geometry. Zn2 shows a distorted octahedral geometry composed of six oxygen atoms (O17, O17C, O1A, O1B, O6, and O6C) from two μ3OH−, two μ4-L−, and two μ3-(1,3-bdc)2− anions. Zn3 is

Figure 2. (a) Coordination environment of ZnII ion in 2. The hydrogen atoms are omitted for clarity (symmetry codes: A = x, 1 + y, z; B = 1 + x, 1 + y, z). (b) View of the 1D zigger chain of 2. (c) View of the 2D layer structure of 2. (The 1D zigger chain is highlighted.)

(1,3-bdc)2− anions. As shown in Figure 3a, the environment around Zn1 can be described as a distorted square-pyramidal geometry, in which it is coordinated by four oxygen atoms (O1, O2A, O5, and O6A) from two L− and two (1,3-bdc)2− anions in an equatorial plane and one nitrogen atom (N4) from L− anion occupying the axial position. The Zn1−N bond length is 2.023(5) Å, and the Zn1−O distances are in the range of 2.027(4)−2.082(4) Å. Noticeably, the Zn1−O1 [2.034(4) Å] bond length is similar to the Zn1−O2A [2.030(5) Å] bond length, which indicates the symmetrical coordination fashion of the carboxylate in the L− anion. Each Zn2 is coordinated to one oxygen atom (O3) and two nitrogen atoms (N1, N3B) from three different L− anions and one oxygen atom (O7C) from a (1,3-bdc)2− anion, forming a slightly distorted tetrahedral geometry. It is worth noting that the L− anion adopts two different coordination modes in 3: (a) the tetradentate coordination mode in which the carboxylate group adopts the μ2-bridging coordination mode and the two nitrogen atoms of two terminal pyridyl rings act as a mondentate coordination mode (Scheme 3, mode III). (b) The bimondentate coordination mode in which both the carboxylate group and the nitrogen atom of one terminal pyridyl ring act as mondentate coordination modes (scheme 3, mode IV). Meanwhile, (1,3-bdc)2− anion adopts a μ3-η1:η1:η1-bridging coordination mode IX (Scheme 3). Two Zn1 ions are bridged by four carboxylate groups to give a paddle-wheel unit with the Zn1···Zn1 distance of 2.914(1) Å (Figure 3b). The binuclear units are then linked by L− anions, adopting coordination mode 1633



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Figure 3. (a) Coordination environment of ZnII ions in 3. The hydrogen atoms are omitted for clarity (symmetry codes: A = −x + 1, −y, −z + 1; B = +x, +y − 1, +z; C = +x − 1, +y − 1, +z − 1). (b) The paddle-wheel unit in 3. (c) View of the 1D loop chain of 3 along the a axis. (d) View of the 2D layer structure of 3. (The 1D zigger chain is highlighted.) (e) Schemetic view of the 2D topology network: the paddle-wheel Zn(II) unit, L− anion with coodination mode I, and Zn2 ion are marked as blue, green, and red, respectively.

reported examples.39,40 Therefore, five Zn(II) ions within the pentanuclear clusters are totally coplanar, in which the Zn···Zn distances are 3.418 Å (Zn2···Zn5), 3.262 Å (Zn2···Zn1), and 3.522 Å (Zn1···Zn5). Similar to 4, each L− anion adopts μ4η1:η1:η1:η1-coordination mode III (Scheme 3) and links two pentanuclear clusters to generate a 1D loop chain, in which two Zn1, two Zn5 ions, and two L− anions form a new {Zn4O4N2C18} 28-member ring, containing a large pore with a size of ca. 10.063 × 13.212 Å based on the distances of Zn1··· Zn1 and C21···C21. At the same time, a different type of {Zn2O2N2C18} 24-member ring also emerged, which derives from two Zn4 atoms and two L− anions containing a type of pore with size ca. 10.630 × 11.412 Å based on the distances of Zn4···Zn4 and C38···C38. The two kinds of rings are then linked by two carboxylate groups from one (1,3-bdc)2− ligand with coordiantion mode VI (Scheme 3) and arranged in a staggered ABAB pattern, generating a wavelike 2D framework (Figure 5b). The 2D netwoks are further linked by Zn4−O15 and Zn4−O16 bonds to give rise to a 3D framework (Figure

coordinated to one nitrogen atom (N6D) and four oxygen atoms (O7, O8, O4E, and O18) from two μ4-L−, one μ3-(1,3bdc)2− anions, and one coordinated water molecule to show a distorted trigonal bipyramid geometry, in which O4E and O8 atoms occupy the axial positions [O4E−Zn3−O8 = 163.90(12)°]. Zn4 is bound to one nitrogen atom (N4) from one μ4-L− anion and five oxygen atoms (O11, O12, O15G, O16G, and O3F) from one μ4-L− anion and two (1,3-bdc)2− anions to generate a distorted octahedral coordination geometry. The coordination environment of Zn5 is pentacoordinated with a distorted trigonal bipyramid geometry, in which O14 and O2B atoms occupy the axial positions [O14− Zn5−O2B = 153.19(12)°]. In 5, two symmetry-related μ3-OH− groups (symmetry code: −x + 2, −y + 1, −z + 1) connect five Zn(II) ions to form a [Zn5(μ3-OH−)2]8+ cluster unit, which can be regarded as two [Zn3(μ3-OH−)2]4+ triangles sharing a common Zn2 vertex. Such triangles are fit together by four carboxylate groups to make up the pentanuclear [Zn5(μ3OH−)2(COO)4] cluster (Figure 5b), which is similar to some 1634



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Figure 4. (a) Coordination environment of ZnII ions in 4. The hydrogen atoms are omitted for clarity (symmetry codes: A = −x + 1, −y + 1, −z; B = −0.5 + x, 0.5 − y, −0.5 + z; C = 0.5 − x, −0.5 + y, −0.5 − z). (b) A view of the [Zn2(μ2−OH)(μ2-O2CR)] unit. (c) A perspective view of the 2D bilayer structure of 4 along the b axis and the 1D loop chain inside it. (d) Schemetic view of the 2D gek1 net: the L− anions and dizinc units are marked as blue and red, respectively.

new {Zn3O2N5C26} 36-membered ring containing a type of pore with a size of ca. 15.745 × 12.957 Å based on the distances of Zn1···C8 and Zn1···C6. Then such rings are linked through the L− anion forming 2D layers (Figure 6b). Finally, the (1,4bdc)2− anion adopting the μ2-η1:η1-bridging coordination mode X (Scheme 3) link the 2D layers giving rise to the formation of an infinite 3D network, while the L− anions are arranged in a staggered ABAB pattern (Figure 6c). The networks interpenetrate to each other to generate a fascinating 2-fold interpenetrating network. Topologically, Zn1 ion and L− anion can be regarded as 4- and 3-connected nodes, respectively, and complex 6 possesses a 2-nodal (3,4)connected INS-net with the point symbol of (63)(65·8) which is caculated by TOPOS (Figure 6d). Crystal Structure of [Cd2(L)4]n·nH2O (7). Single-crystal Xray crystallography reveals that 7 exhibits a 2D network. The asymmetric unit of 7 contains one Cd(II) ion, two L− anions, and half a lattice water molecule. As illustrated in Figure 7a, Cd1 is six-coordinated by two pairs of chelating oxygen atoms (O1, O2, O3, and O4) and two nitrogen atoms (N1A and N4B) from two different L− anions, forming a distorted octahedral geometry. The O2, O4, N1A, and N4B atoms comprise the equatorial plane, and the O1 and O3 atoms occupy axial positions [O1−Cd1−O3 = 146.96(8)°]. The Cd− O bond lengths are in the range of 2.307(2)−2.4092(19) Å and Cd−N bond lengths are 2.276(2) and 2.290(2) Å, which are consistent with corresponding values reported for Cd(II)

5c). To further understand the structure of 5, topological analysis by reducing complicated structure to simple node-andlinker net was referred. In accordance with the simplification principle,38 each pentanuclear zinc cluster can be regarded as a 12-connected node, Zn3 and Zn4 atoms can be defined as 3and 4-connected nodes, two kinds of L− anions containing different pyridyl rings (N1, N3 and N4, and N6) can be considered as 3- and 4-connected nodes, respectively, while (1,3-bdc)2− anions act as linkers. Hence, the overall structure of 5 is a self-penetrating 5-nodal (3,3,4,4,12)-connected network with the point symbol of (4·62)2(42·64)4(43)2(48·634·822·102) (Figure 5d). Crystal Structure of [Zn2(L)2(1,4-bdc)]n·nH2O (6). To further examine the inflence of the auxiliary ligands on the structure, we used H2(1,4-bdc) instead of H2(1,3-bdc). When H2(1,4-bdc) was used as the auxiliary ligand, a new 2-fold interpenetrating 3D coordination polymer was obtained. The asymmetric unit of 6 contains one Zn(II) cation, one L−, half (1,4-bdc)2− anions, and one lattice water molecule. As show in Figure 6a, Zn1 is four-coordinated to two nitrogen atoms (N1, N3A) of different L− ligands [Zn1−N1=2.043(4) Å and Zn1− N3A = 2.065(4) Å] and two oxygen atoms (O1A, O3) from a L− anion and a (1,4-bdc)2− anion, respectively, in turn, forming a distorted tetrahedral coordination geometry. Apart from the monodentate carboxylate group, two terminal pyridyl rings are all coordinated, thus, the L− anion acts as a tridentate-bridging coordiantion mode V (Scheme 3), linking three Zn1 ions into a 1635



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Figure 5. (a) Coordination environment of Zn(II) ions in 5. The hydrogen atoms are omitted for clarity (symmetry codes: A = +x, +y − 1, +z; B = −x + 2, −y + 2, −z + 1; C = −x + 2, −y + 1, −z + 1; D = −x + 2, −y, −z + 1; E = +x, +y, +z + 1; F = −x + 1, −y + 1, −z; G = −x + 2, −y + 2, −z; H = +x + 1, +y − 1, +z). (b) View of the 2D structure and the pentanuclear [Zn5(μ3-OH−)2(COO)4] cluster units in 5. (c) View of the 3D framework along the b axis. (d) Schemetic view of the 3D topology network: the L− anions are marked as green and light blue. The pentanuclear Zn units are marked as red. The blue and yellow balls represent the Zn4 and Zn3 ions, respectively. And the perspective view of the ring links between 8membered shortest rings inside the net.

Figure 6. (a) Coordination environment of ZnII ion in 6. The hydrogen atoms are omitted for clarity (Symmetry codes: A = −0.5 + x, −y, −0.5 + z). (b) View of the 2D layer in 6. (c) A perspective view of the 3D net of 6 along the a axis. (d) Schemetic view of the 2-fold interpenetrating network: the green spheres represent ZnII ions. 1636



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Figure 7. (a) Coordination environment of Cd(II) ion in 7. The hydrogen atoms are omitted for clarity. (symmetry codes: A = 1+x, 1+y, z; B = x, −1+y, z). (b) View of the 1D zigger chain of 7. (c) View of the 2D layer in 7.

compounds.41 The three pyridyl rings of the L− ligand are nonplanar; each terminal pyridyl group is twisted with respect to the central one, and the dihedral angles between the central and terminal pyridyl rings are 16.22° (N1 pyridyl ring) and 11.42° (N3 pyridyl ring), respectively. Each L− anion adopting μ2-η1:η2 (Scheme 3, mode II) link two Cd(II) ions to form a 1D zigger chain (Figure 7b). The adjacent 1D chains are parallel to each other and are further connected by the nitrogen atom and carboxylate group of L− anions to generate a 2D layer (Figure 7c). Crystal Structure of [Cd3(L)2(1,3-bdc)2]n·nH2O (8). The single-crystal X-ray structural analysis indicates that complex 8 displays a 3D network built up by linear Cd3(COO)6 trinuclear clusters. The asymmetric unit of 8 contains one and a half Cd(II) ions, one L− anion, one (1,3-bdc)2− anion, and a half lattice water molecule. As shown in Figure 8a, the Cd1 is hexacoordinated by four oxygen atoms (O1, O3, O4, and O5C) from two (1,3-bdc)2− anions and one L− anion and two nitrogen atoms (N1A, N3B) from two L− anions. The coordination geometry of Cd1 can be described as a slightly distorted octahedron. The O3, O4, O5C, and N1A atoms comprise the equatorial plane, and the O1 and N3B atoms occupy the apical positions. The Cd1−N bond lengths are 2.348(6) Å and 2.365(5) Å, respectively. The Cd1−O distances fall in the range of 2.240(5)−2.697(5) Å. Cd2 adopts an octahedral [O6] coordination environment and is coordinated by six oxygen atoms (O2, O2D, O3, O3D, O6C, and O6E) from two L− anions and four (1,3-bdc)2− anions, in which O6C and O6E atoms occupy the axial positions [O6C−Cd2−O6E = 180.0(3)°]. The Cd2−O distances are in the range of 2.251(5)2.290(4) Å. The (1,3-bdc)2− anion acts as a μ4-bridge to link one Cd2 and two Cd1 ions, in which two carboxylate groups

adopt μ3-η1:η2:η1 and μ2-η1:η1 coordination fashions, respectively. Cd1, symmetry-related Cd1A (−x, 2 − y, −z) and Cd2 are bridged by six carboxylate groups to form a linear Cd3(COO)6 trinuclear cluster (Figure S1 of the Supporting Information). Each trimer is connected to two others via two pairs of L− anions that show a μ4-η1:η1:η1:η1 coordination mode (Scheme 3, mode III), resulting in the formation of a 1D chain (Figure S2 of the Supporting Information). Then these chains are further linked by the nitrogen atom and carboxylate group of L− anions to give rise to a 2D layer (Figure 8b). Finally, the two-dimensional layers are extended into a 3D network through chelating-bridging (1,3-bdc)2− anions (Figure 8c). To get deep insight into the structure of 8, the topological analysis was carried out. Both the L− and (1,3-bdc)2− anions can be regarded as a 4-connected node. Cd1 ion is attached to four L− anions and one (1,3-bdc)2− anion, which is assigned to a 5-connected node, and the Cd2 ion is coordinated to two L− anions and four (1,3-bdc)2− anions and thus can be considered as a 6-connected node. On the basis of the simplification principle,38 complex 8 possesses a 4-nodal (4,4,5,6)-connected network with the point symbol of (42.63.8)2(43.63)2(44.64.82)2(48.66.8) (Figure 8d). Comparison of Synthetic Conditions and Structures. The syntheses were summarized in Scheme 2. Hydro(solvo)thermal synthesis has proven to be a powerful method in the preparation of coordination polymers. Compounds 1 and 2 were synthesized by using different metal salts without the auxiliary ligand under the same hydrothermal synthesis conditions. When ZnCl2 was used instead of Zn(Ac)2·2H2O, compound 2 was obtained. Although compounds 1 and 2 both show 2D layer frameworks, they possesse different structures and luminescent properties due to the coordination of the 1637



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Figure 8. (a) Coordination environment of CdII ions in 8. The hydrogen atoms are omitted for clarity (symmetry codes: A = −x, 2 − y, 1 − z; B = −0.5 − x, 0.5 + y, 0.5 − z; C = x, −1 + y, z; D = −x, 2 − y, −z; E = −x, 3 − y, −z). (b) View of the 2D structure. (c) View of the 3D framework along the c axis. (d) Schemetic view of the 3D topology network: the L− anion, (1,3-bdc)2− anion, and Cd ion are marked as orange, blue, and green, respectively.

attributed to the different orientations of binding sites in auxiliary ligands. In addition, it is noteworthy that the central metal cations also have significant inflence on the final structures. When CdCl2·2.5H2O was introduced into the reaction system, compounds 7 and 8 were obtained. Compound 7 is a 2D layer structure, while compound 8 displays new 3D network built up by linear Cd3(COO)6 trinuclear clusters. Because the radius of Cd(II) is longer than that of Zn(II), they may have different coordination numbers and geometry, which lead to different structures. Furthermore, we also attempted other second ligands, such as oxalic acid, malic acid, and 1,3,5-benzenetricarboxylic acid instead of H2(1,3-bdc), but only obtained compound 7 not other new structures. These results indicate that reaction conditions such as pH value, counteranion, metal cation, and auxiliary ligand are significant in determining the ultimate structures of the compounds. Meanwhile, we also find that the L− ligand and auxiliary ligand can afford relatively various coordination modes to meet the coordination requirements of the center metal ions. Luminescent Properties. Taking into account the excellent luminescent properties of the terpyridyl species and d10 metal ions compounds,46 the luminescence of the free HL ligand and 1−8 were investigated at room temperature. Unfortunately, compound 1 exhibits very weak emission. As shown in Figure 9, the free ligand exhibits one weak emission band at 384 nm upon excitation at 306 nm. Upon excitation at 310 nm, intense emission is observed at 381, 387, 380, and 392 nm for 2, 3, 4, and 6, respectively, which may be assigned to the intraligand transition of the ligand. Notably, compound 5

chloride atom in compound 1. There is no denying that counteranions are significant in determing the structure of complexes. Anions are able to assist the construction of supramolecular architectures and self-assemblies.42 Apart from that, counteranions do not contribute to the process of construction; they might balance the electric charge of the structure and in turn affect it. Compound 1 was obtained at pH = 4. When the reaction system is weakly acidic, Cl− is easy to coordinate. On the contrary, acetate is protonized, so it is difficult for it to participate in coordination. When H2(1,3-bdc) was introduced into the reaction system, compound 3 was obtained with a 2D layer structure containing paddle-wheel units. When we use Zn(Ac)2·2H2O instead of Zn(NO3)2·6H2O and adjust pH values, compounds 4 and 5 were generated. Compound 4 is a 2D layer structure, while compound 5 displays a 3D network containing pentanuclear Zn(II) clusters. Different pH values in reaction systems lead to various coordination fashions of the ligands and result in distinct ultimate structures. Afterward, in order to investigate the effects of the steric hindrance effect of the substituted group in the auxiliary ligand on the self-assembly of supramolecules and coordination polymers, H2(1,4-bdc) was employed in place of H2(1,3-bdc). As a result, compound 6 was obtained. The nature (coordination ability, mode, and donor character) of the auxiliary ligands is the underlying reason behind the different structures of several complexes.43−45 Belonging to the same kind of bridging ligands in a certain sense, the figuration of H2(1,3-bdc) and H2(1,4-bdc) are quite similar. Nevertheless, 6 shows a 2-fold interpenetrating 3D network, while 4 possesses a 2D bilayer structure. The difference of the structures can be 1638



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7.82%). The remaining weight is assigned to zinc oxide (obsd 17.94%, calcd 17.96%). The TG curve of 2 shows an initial weight loss of 2.42% below 200 °C, corresponding to the removal of lattice water molecules (calcd 2.36%). Then the framework is stable to nearly 400 °C, where a continuous weight loss of 89.71% was observed from 400 to 610 °C, which can be ascribed to the decomposition of L− ligands (calcd 89.65%). The residue product of 10.31% is zinc oxide (calcd 10.35%). Compound 3 was stable to 400 °C and then began to decompose upon further heating. The weight loss of 16.45% in the temperature range of 400−495 °C is attributed to the removal of (1,3-bdc)2− ligands (calcd 16.42%). The weight loss of 70.46% from 580 to 790 °C can be ascribed to the release of L− ligands (calcd 70.50%). The residue product of 16.24% cooresponds to zinc oxide (calcd 16.28%). Compound 4 shows an initial weight loss of 1.36% below 300 °C, corresponding to the removal lattice water molecules (calcd 1.34%). The second step weight loss of 23.60% between 290 and 500 °C indicated the decomposition of (1,3-bdc)2− ligands (calcd 24.41%), and the weight loss of 51.68% between 500 and 790 °C attributed to the loss of L− ligands (calcd 52.42%). The remaining weight may be assigned to the formation of zinc oxide (obsd 23.80%, calcd 24.21%). Compound 5 released its lattice water molecules below 210 °C (obsd 1.78%, calcd 1.74%), and then the compound was stable up to 400 °C and was followed by a twostep weight loss in the temperature range of 400−900 °C, which were assigned to the decomposition of (1,3-bdc)2− and L− ligands (obsd 31.80%, calcd 31.76%; obsd 45.43%, calcd 45.46%), respectively. The remaining weight of 23.59% is zinc oxide (calcd 23.62%). With regard to 6, the first weight loss of 1.79% below 100 °C is consistent with the removal of its lattice water molecules (calcd 1.77%). After this process, a weight loss of 16.19% from 200 to 390 °C was observed, which can be due to the release of (1,3-bdc)2− ligands (calcd 16.13%). The last weight loss of 69.33% in the temperature range of 480−700 °C can be attributed to the decomposition of L− ligands (calcd 69.25%). The final residual weight is likely assigned to zinc oxide (obsd 16.03%, calcd 16.00%). Compound 7 first loses its lattice water molecule below 200 °C (obsd 1.12%, calcd 1.09%), and then the compound was stable up to 480 °C and followed by a continuous weight loss of 85.45% in the temperature range of 480−700 °C (calcd 85.41%), which were attributed to the decomposition of L− ligands. The residue product of 15.61% cooresponds to cadmium oxide (calcd 15.56%). For compound 8, the first weight loss of 1.34% happened below 210 °C corresponds to the removal of lattice water molecules (calcd 1.31%). The second step weight loss of 24.02% between 290 and 500 °C indicated the decomposition of (1,3-bdc)2− ligands (calcd 23.96%), and the weight loss of 51.48% between 500 and 790 °C attributed to the loss of L− ligands (calcd 51.43%). The remaining weight is assigned to the formation of cadmium oxide (obsd 28.16%, calcd 28.12%). TGA results of 1−8 indicate they all possess great thermal stability (Figure S11 of the Supporting Information, shows the TG curves for 1−8).

Figure 9. The solid state emission spectra of the HL and 2−8 at room temperature.

displays a weaker emission band at 389 nm, which can also be attributed to the intraligand transition of the ligand. Meanwhile, the weakened emission peak in 5 may be the result from the weakened conjugacy after coordination. Additionally, compounds 7 and 8 show emssion at 409 nm for 7 and 397 nm for 8, which may also be assigned to the intraligand transition of the ligand. The enhancement of luminescence intensity for compounds 2−8 compared to the free ligand is perhaps a result of the metal−ligand coordination, which effectively increases the rigidity of the ligand and reduces the nonradiative decay of the intraligand (π−π*) excited state.47,48 Furthermore, the emission decay lifetimes of compounds 2−8 were measured and the curves (Figure S3−S9 of the Supporting Information) are best fitted by biexponentials in the solid state.49−51 The emission decay lifetimes of compounds 2−8 are summarized in Table 2. The nanosecond range of lifetime in the solid state at room temperature indicates that the emission is fluorescent in nature. Table 2. Emission Lifetimes of Compounds 2−8 compound

τ1 (ns)

τ2 (ns)

χ2

2 3 4 5 6 7 8

1.26 1.61 1.98 1.50 1.89 1.32 1.50

5.42 5.46 6.68 5.26 6.54 3.95 3.60

1.159 1.091 1.077 0.944 1.066 1.428 1.065

PXRD and Thermogravimetric Analysis. Powder X-ray diffraction experiments were carried out for the primitive samples of complexes 1−8. The observed powder X-ray diffraction (PXRD) patterns are in good agreement with those simulated on the basis of the single-crystal X-ray diffraction data (Figure S10 of the Supporting Information) and indicated the phase purity of the as-synthesized products. To examine thermal stability of these frameworks, thermal gravimetric analysis (TGA) measurements were carried out. Compound 1 was stable to 450 °C and then began to decompose upon further heating. The first continuous weight loss of 77.81% happened in the temperature range of 450−595 °C, which can be attributed to the loss of L− ligands (calcd 77.75%). The second weight loss of 7.79% between 690 and 800 °C was assigned to the release of chloride anions (calcd

■

CONCLUSION In summary, eight new coordination polymers with diverse structures were successfully constructed from the 4′-(2carboxyphenyl)-4,2′:6′,4″-terpyridine ligand under hydrothermal conditions. The compounds 1−8 display intriguing 2D and 3D structures. The result of the present work demonstrates that rational adjustment of the second ligand, the pH value, and the 1639



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counteranion are good methods to further design metal− organic compounds with new structures and properties. Moreover, the thermal stabilities and photoluminenscence properties were also studied. The results indicate that compounds 2−8 possess excellent fluorescence properties and high thermostability, which are likely to be potential luminescent materials.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic files in CIF format, selected bond distances, and bond angles for 1−8, the coordination modes of (1,3-bdc)2− anion and trinuclear CdII subunit of 8, the view of 1D loop chain inside 8, the fitted decay curve of 2−8, PXRD patterns, and thermal analyses. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 20873098 and 21173164). REFERENCES

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