Coligand Modulated Six-, Eight-, and Ten ... - ACS Publications

Coligand Modulated Six-, Eight-, and Ten-Connected Zn/ Cd-1,2,4-Triazolate Frameworks Based on Mono-, Bi-, Tri-, Penta-, and Heptanuclear Cluster Units Quan-Guo Zhai,† Can-Zhong Lu,*,† Xiao-Yuan Wu,† and Stuart R. Batten‡

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 11 2332–2342

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, P.R. China, and School of Chemistry, Monash UniVersity, Victoria 3800, Australia ReceiVed June 27, 2007; ReVised Manuscript ReceiVed August 7, 2007

ABSTRACT: Using nonsubstituted 1,2,4-triazole and the second bridging ligands as coligands, a series of three-dimensional metal–organic frameworks based on different secondary building units (SBUs), namely, Zn2(trz)3(SCN) (1), Zn2(trz)2(ox) (2), Cd3(trz)2(suc)Cl2(3), [Cd5(trz)6(OAc)2Cl2(H2O)2] · 2H2O (4), and [Zn7(trz)6(1,2,4,5-BTC)2(H2O)6] · 8H2O (5) (trz ) 1,2,4-triazole, ox ) oxalate, suc ) succinic acid, 1,2,4,5-BTC ) 1,2,4,5-benzenetetracarboxylate), have been synthesized and structurally characterized with the aid of single-crystal X-ray diffraction. The SBUs in 1–5 vary from mononuclear, binuclear, linear trinuclear, linear pentanuclear to heptanuclear d10-1,2,4-triazolate polynuclear clusters. Compound 1 presents a complicated 3,6-connected topology based on three nonequivalent nodes. Compound 2 adopts a 6-connected 3D network of distorted R-Po topology that is built from dizinc units. The structure of 3 consists of two intersecting (4,4) grids which generate a novel self-penetrating 4,8-connected net with (456)(412616) topology when the tricadmium cores and succinic acid ligands are regarded as eight-connected and four-connected nodes, respectively. Compound 4 can be described as an 8-connected CsCl-type net utilizing unprecedented linear pentacadmium cores as eight-connected nodes and trz ligands as linkers. The microporous structure of 5 exhibits a novel 4,10-connected net constructed from ten-connected heptanuclear [Zn7(trz)6]8+ cluster and four-connected 1,2,4,5-BTC ligand. Detailed structural comparison of these complexes indicated that the increase in the length of the second bridging ligands induces the progressive increase in the metal nuclearity and the increase in the connectivities of the ultimate nets: that is, the length of the second bridging ligand plays a significant role in tuning the nuclearity of metal-1,2,4-triazolate clusters and the connectivity of a specific network. All the complexes exhibit high thermal stability and strong fluorescence properties. Introduction In the past decade, the remarkable progress in crystal engineering has provided a wide range of metal–organic frameworks (MOFs) with interesting framework topologies and potential applications in areas such as ion-exchange,1 catalysis,2 luminescence,3 and gas storage.4 To date, many MOFs have been prepared on the basis of the connector and linker approach.5 Connectors are inorganic units, often clusters or chains of transition metal ions, that can yield different coordination geometries. Linkers are typically functionalized organic molecules such as carboxylate-type O-donors and amine- or pyridine-type N-donors. By combining connectors with linkers, extended structures are formed with well-defined pores or channels. Although a large number of organic molecules have been investigated as potential linkers, MOFs incorporating polycarboxylate and polypyridine ligands have witnessed the most important development.6 However, organic ligands offering different charge-balance requirements, alternative linking modes, and orientation of donor groups are closely related to the structures and applications of materials. So, the development of new ligand systems is continuously an important aspect for the chemistry of hybrid inorganic–organic materials. Simple organic molecules, 1,2,4-triazole and its derivatives, which are usually studied as precursors of compounds with importance in medicine biology and industry, have gained more and more interest as ligands to bridge metal ions because of their potential bridging modes: µ1,2, µ2,4, and µ1,2,4. These ligands * E-mail: [email protected]; Fax: +86-591-83714946; Tel.: +86-59183705794. † Chinese Academy of Sciences. ‡ Monash University.

unite the coordination of both pyrazole and imidazole and exhibit an extensively documented ability to bridge metal ions to afford polynuclear clusters. To date, many triazole-based polynuclear compounds have been reported, including dinuclear, linear trinuclear, cyclic trinuclear, tetranuclear, and hexanuclear ring complexes.7 However, coordination polymers constructed from metal–triazole polynuclear units are rare, especially high dimensional networks.8 As an extension of our study of TM/ 1,2,4-triazole/ polyoxometalates hybrid systems, we have been focusing on using hydrothermal or solvothermal synthesis to discover new high-dimensional metal–organic frameworks with metal-1,2,4-triazolate polynuclear clusters as connectors. Previously, by controlling the molar ratios of copper dichloride dihydrate and nonsubstituted 1,2,4-triazole, we first obtained a series of three-dimensional MOFs constructed from µ3-oxo or µ3-Cl bridged trinuclear clusters.9 We also reported a novel 3D hybrid architecture consisting of hexanuclear Cu6(datrz)6 ring and (H2O)6 encircling Cu4I4–O–Cu4I4 cluster.10 Herein, we used nonsubstituted 1,2,4-triazole and the second bridging ligands as coligands to synthesize a series of novel three-dimensional Zn/Cd-1,2,4-triazolate frameworks, namely, Zn2(trz)3(SCN) (1), Zn2(trz)2(ox) (2), Cd3(trz)2(suc)Cl2 (3), [Cd5(trz)6(OAc)2Cl2(H2O)2] · 2H2O (4), and [Zn7(trz)6(1,2,4,5- BTC)2(H2O)6] · 8H2O (5) (trz ) 1,2,4-triazole, ox ) oxalate, suc ) succinic acid, 1,2,4,5-BTC ) 1,2,4,5- benzenetetracarboxylate). The basic building units in these complexes are mononuclear, binuclear, linear trinuclear, linear pentanuclear, and heptanuclear Zn/Cdtrz clusters, respectively. To the best of our knowledge, the pentanuclear and heptanuclear clusters are the first two examples in the whole coordination chemistry of 1,2,4-triazole and its derivatives. Moreover, these frameworks provide new examples

10.1021/cg070593q CCC: $37.00  2007 American Chemical Society Published on Web 10/13/2007

Coligand Modulated Zn/Cd-1,2,4-Triazolate Frameworks

of highly connected systems and illustrate again the aesthetic diversity of coordination network chemistry. Detailed structural comparison of these complexes indicated that the increase in the bulk of the second bridging ligands induces the increase in the separations between two clusters and leads to the increase in the metal nuclearity (1 f 2 f 3 f 5 f 7), which further induces the gradual increase in connectivity of the resultant 3D net (3,6 f 6 f 4,8 f 8 f 4,10). In other words, the bulk of the second carboxylate ligands influences the metal nuclearity and hence the connectivity of the ultimate net. These complexes may be excellent candidates for potential photoactive materials, because they all exhibit high thermal stability and strong fluorescence properties. Experimental Section Materials and Methods. All chemicals were obtained from commercial sources and used without further purification. The IR spectra (KBr pellets) were recorded on a Magna 750 FT-IR Spectrophotomer. C, H, and N elemental analyses were determined on an Elementar Vario EL III elemental analyzer. X-ray powder diffraction data were recorded on a Rigaku MultiFlex diffractometer with a scan speed of 5°/min. TGA-DTA measurements were performed by heating the sample from 40 to 900 °C at a heating rate of 10°/min in air or nitrogen on a NETSCHZ STA-449C thermoanalyzer. The fluorescence spectra were measured on powder samples at room temperature using an Edinburgh Analytical instrument FLS920. The excitation slit was 2.5 nm, the emission slit was 2.5 nm, and the response time was 2 s. Synthesis of Zn2(trz)3(SCN) (1). A mixture of Zn(OAc)2 · 2H2O (0.22 g, 1.0 mmol), trz (0.11 g, 1.5 mmol), KSCN (0.049 g, 0.50 mmol), and H2O (10 mL) was heated at 180 °C for 5 days under autogenous pressure. The mixture was cooled to room temperature at a rate of 0.5 °C min-1. Pure colorless prismatic crystals were collected, washed with H2O, and air-dried (yield 0.15 g, 78% based on Zn). Anal. Calcd for C7H6N10Zn2S: C, 21.40; H, 1.54; N, 35.63. Found: C, 21.33; H, 1.59; N, 35.41%. IR (KBr pellets, λ, cm-1): 3410 (br), 3137 (m), 3013 (w), 2887 (w), 2480 (w), 2067 (s), 1786 (w), 1758 (m), 1745 (w), 1619 (w), 1570 (w), 1509 (s), 1439 (w), 1428 (w), 1353 (w), 1279 (s), 1206 (w), 1157 (s), 1005 (s), 947 (w), 896 (w), 887 (s), 874 (w), 664 (s), 494 (m). Synthesis of Zn2(trz)2(ox) (2). A mixture of ZnCl2 (0.14 g, 1.0 mmol), trz (0.069 g, 1.0 mmol), Na2C2O4 (0.067 g, 0.50 mmol), and H2O (10 mL) was heated at 180 °C for 5 days under autogenous pressure. The mixture was cooled to room temperature at a rate of 0.5 °C min-1. Almost pure colorless prismatic crystals were collected, washed with H2O, and air-dried (yield 0.11 g, 64% based on Zn). Anal. Calcd for C6H4N6Zn2O4: C, 21.30; H, 1.14; N, 23.68. Found: C, 21.33; H, 1.49; N, 24.11. IR (KBr pellets, λ, cm-1): 3387 (s), 3181 (w), 3104 (m), 2949 (w), 2446 (w), 1631 (m), 1532 (s), 1466 (w), 1425 (w), 1359 (m), 1312 (s), 1266 (w), 1213 (w), 1180 (w), 1156 (m), 1100 (w), 1080 (w), 1058 (w), 1045 (w), 1028 (w), 1007 (m), 889 (w), 796 (s), 645 (s), 534 (w), 495 (s). Synthesis of Cd3(trz)2(suc)Cl2(3). A mixture of Cd(OAc)2 · 2H2O (0.40 g, 1.5 mmol), trz (0.069 g, 1.0 mmol), succinic acid (0.06 g, 0.50 mmol), KCl (0.075 g, 1.0 mmol), and H2O (10 mL) was heated at 165 °C for 5 days under autogenous pressure after adjustment of pH to ca. 8.0 by addition of dilute NaOH solution. The mixture was cooled to room temperature at a rate of 0.5 °C min-1. Pure light yellow block crystals were collected, washed with H2O, and air-dried (yield 0.24 g, 80% based on Cd). Anal. Calcd for C8H8N6Cd3Cl2O4: C, 14.55; H, 1.22; N, 12.73. Found: C, 14.86; H, 1.09; N, 12.80. IR (KBr pellets, λ, cm-1): 3437 (br), 3156 (w), 3131 (w), 2931 (w), 2577 (w), 2485 (w), 1765 (w), 1748 (w), 1525 (s), 1506 (s), 1461 (m), 1413 (m), 1395 (s), 1294 (m), 1287 (m), 1262 (w), 1204 (m), 1156 (s), 1065 (s), 1013 (m), 993 (m), 949 (m), 886 (m), 875 (w), 770 (w), 683 (s), 660 (s), 492 (w). Synthesis of [Cd5(trz)6(OAc)2Cl2(H2O)2] · 2H2O (4). A mixture of Cd(OAc)2 · 2H2O (0.40 g, 1.5 mmol), trz (0.11 g, 1.5 mmol), KCl (0.038 g, 0.50 mmol), and H2O (10 mL) was heated at 180 °C for 5 days under autogenous pressure. The mixture was cooled to room temperature at a rate of 0.5 °C min-1. Almost phase-pure colorless prismatic crystals were collected, washed with H2O, and air-dried (yield 0.27 g, 73% based on Cd). Anal. Calcd for C16H26N18Cd5Cl2O8: C, 15.61; H, 2.13;

Crystal Growth & Design, Vol. 7, No. 11, 2007 2333 N, 20.47. Found: C, 15.72; H, 1.99; N, 20.68. IR (KBr pellets, λ, cm-1): 3445 (br), 2561 (w), 2432 (w), 1621 (w), 1544 (m), 1504 (s), 1417 (m), 1378 (w), 1281 (s), 1199 (w), 1154 (s), 1012 (w), 991 (s), 945 (w), 881 (w), 669 (s), 622 (w). Synthesis of [Zn7(trz)6(1,2,4,5-BTC)2(H2O)6] · 8H2O (5). A mixture of Zn(OAc)2 · 2H2O (0.33 g, 1.5 mmol), trz (0.11 g, 1.5 mmol), 1,2,4,5benzenetetracarboxylate (1,2,4,5-BTC) (0.13 g, 0.5 mmol), and H2O (10 mL) was heated at 180 °C for 5 days under autogenous pressure. The mixture was cooled to room temperature at a rate of 0.5 °C min-1. The resulting colorless block crystals were collected, washed with H2O, and air-dried (yield: 0.30 g, 86% based on Zn). Anal. Calcd for C32H44N18Zn7O30: C, 23.72; H, 2.86; N, 15.56. Found: C, 23.55; H, 2.94; N, 15.50. IR (KBr pellets, λ, cm-1): 3444 (br), 1609 (s), 1517 (m), 1435 (w), 1375 (m), 1327 (w), 1284 (w), 1213 (w), 1158 (m), 1139 (w), 1083 (m), 1070 (w), 1008 (m), 833 (w), 767 (w), 700 (w), 666 (m), 590 (w), 531 (w). X-ray Crystallography. Suitable single crystals of compounds 1–5 were carefully selected under an optical microscope and glued to thin glass fibers. Crystallographic data for all compounds were collected with a Siemens Smart CCD Diffractometer with graphite-monochromated Mo kR radiation (λ ) 0.71073 Å) at T ) 293(2) K. Absorption corrections were made using SADABS program.11 The structures were solved using direct method and refined by full-matrix least-squares methods on F2 by using Shelx-97 program package.12 All nonhydrogen atoms were refined anistropically. Positions of the hydrogen atoms attached to carbon and nitrogen atoms were fixed at their ideal positions and those attached to water oxygen atoms were not located. Crystal data as well as details of data collection and refinement for 1–5 are summarized in Table 1. Selected bonded lengths and angles are listed in Table 2. CCDC-610319 (1), 610320 (2), 610321 (3), 610322 (4), and 607907 (5) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/ data_request/cif.

Results and Discussion Preparations of the Complexes. It should be noted that although unsubstituted 1,2,4-triazole is an ideal organic linker, coordination polymers based on this ligand are rare compared with those based on its derivatives. This is most likely caused by the fact that it almost always immediately produces insoluble precipitates with nearly all transition metal ions.7b Hydrothermal techniques, which are widely used in the synthesis of inorganic materials and coordination polymers, can effectively get over the solublity problem. Several inorganic–organic hybrid solids obtained using this method have proved that 1,2,4-triazole and its derivatives are stable under hydrothermal reaction conditions. In our experiments, a series of anions including Cl–, SCN–, OAc–, oxalate, succinate, and 1,2,4,5-benzenetetracarboxylate were chose as the second or third bridging ligands to be added to the reacting system of 1,2,4-triazole and zinc or cadmium salts. The structural features of compounds 1–5 clearly demonstrate that the length of the second ligands plays an important role in the formation of the fundamental polynuclear SBUs and further influences the connectivity of the ultimate topological nets. Description of Crystal Structures. The SCN– anion is a highly versatile bidentate ligand with two donor atoms, which gives rise to linkage isomers or polymers and forms a variety of different coordination modes in coordination polymers. When SCN – was first chosen as the second ligand in our experiments, complex 1 was obtained with an unusual 3,6-connected topology. X-ray crystallographic analysis revealed that the structure contains two distinct Zn(II) ions, one SCN– and three trz ligands (Figure 1a). Zn(1) is coordinated to six N1 (or N2) atoms from six different trz ligands to form a [ZnN6] octahedral geometry (Zn–N ) 2.134(5)–2.203(8) Å). The Zn(1) atoms are linked via µ1,2-bridging triazoles to generate [Zn(trz)3]nn– chains running

2334 Crystal Growth & Design, Vol. 7, No. 11, 2007

Zhai et al.

Table 1. Crystal Data and Structure Refinements for Complexes 1-5

empirical formula fw space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z, dcalcd (g/cm3) µ(Mo-KR) (mm-1) F(000) no. of reflns collected/unique R(int) params GOF on F2 R1,a wR2 [I > 2δ(I)] R1, wR2 (all data) a

1

2

3

4

5

C7H6N10Zn2S 393.02 Pnma 7.7740(10) 10.2050(13) 17.143(2) 90 90 90 1360.0(3) 4, 1.919 3.686 776 9717/1633 0.0601 106 1.033 0.0687, 0.1603 0.0763, 0.1659

C6H4N6Zn2O4 354.89 Pna21 9.7119(8) 7.6320(5) 13.4698(10) 90 90 90 998.40(13) 4, 2.361 4.823 696 7156/2287 0.0196 164 0.990 0.0168, 0.0360 0.0180, 0.0364

C8H8N6Cd3Cl2O4 660.30 P21/c 6.8109(5) 14.1240(15) 8.1723(2) 90 111.186(7) 90 733.02(10) 2, 2.983 4.704 612 5498/1674 0.0241 106 1.024 0.0205, 0.0484 0.0227, 0.0496

C16H26N18Cd5Cl2O8 1231.45 P21/c 8.5173(5) 22.4055(14) 9.7615(5) 90 92.285(2) 90 1861.35(19) 2, 2.197 3.016 1172 14231/4250 0.0282 223 1.086 0.0337, 0.0810 0.0387, 0.0855

C32H46N18Zn7O30 1620.46 C2/c 25.192(2) 14.2036(9) 18.7190(16) 90 119.594(2) 90 5824.1(8) 4, 1.848 2.936 3256 22247/6676 0.0423 384 1.061 0.0595, 0.1616 0.0713, 0.1707

R1 ) Σ(|Fo| – |Fc|) / Σ|Fo|, wR2 ) [Σw(Fo2 – Fc2)2/Σw(Fo2)2]0.5.

along the a-axis direction (Figure S1). The Zn(1) · · · Zn(1) distance is 3.904(2) Å. Each Zn(2) atom bridges three adjacent [Zn(trz)3]nn– chains via three N4 atoms of triazole ligands (Zn–N ) 1.991(8)–1.998(5) Å) to form the three-dimensional structure of 1 (Figure 1b). The SCN– anion acts not as bridging ligand as expected but a terminal coordinated ligand to complete the distorted tetrahedral geometry of the Zn(2) atom (Zn–N ) 2.009(9) Å). It should be noted that the cobalt(II) triazolate magnet reported by Zubieta13 has a similar structure to compound 1. We have also obtained the similar structure when SCN– was changed as Cl–.13 To analyze the net, we can define the trz ligand as a three-connected node. This means that there are three kinds of nodes in the structure of 1: a six-connected node for Zn(1), a three-connected node for Zn(2), and a threeconnected node for the trz anion. These three nonequivalent nodes lead to an unusual network topology which depicted in Scheme 1. The Schläfli symbol for the net is (482)3(83)(4686103), representing the nodes trz, Zn(2), and Zn(1), respectively. This net can be derived from the binodal 6-connecting NiAs (or nia) net14 by replacing the trigonal prismatic 6-connecting center (As) in nia by four 3-connecting nodes such that a central 3-connecting node (Zn(2) in 1) is connected to three other 3-connecting nodes (trz in 1) orientated perpendicular to it. In other words, the network becomes nia if Zn(1) is treated as one node and Zn2(trz)3 moieties are treated as the other node. Alternatively, Yaghi et al.15 have recently demonstrated a concept of infinite rodlike secondary building units in the design and synthesis of metal–organic frameworks. According to this concept, the 3D net of 1 exhibits a rather simple topological framework based on 1D rod-shaped [Zn(1)(trz)3]- building blocks and three-connected Zn(2) nodes (Scheme 1). Compound 2, obtained by using oxalate under the same reaction conditions as 1, adopts a 6-connected 3D network structure of R-Po topology that is built from dinuclear Zn2 units. Figure 2a illustrates the coordination environments of the Zn atoms and the 6-fold connectivity of the bimetallic unit. The two zinc atoms are crystallographically independent. Zn(1) is coordinated by four carboxylic oxygen atoms of two different oxalate ligands (Zn–O ) 2.0842(17)–2.1805(16) Å) and two N1 (or N2) atoms from two trz ligands (Zn–N ) 2.060(2) and 2.1248(19) Å) to furnish a distorted octahedral geometry. Zn(2) is bonded by three nitrogen atoms from three different trz ligands and one µ-oxygen atom of oxalate ligand to generate a slightly enlonged tetrahedral geometry. The two Zn(II) atoms are bridged by one triazole ligand in a µ1,2 fashion, and one µ2-O. This

connectivity makes the Zn–O–Zn angle 120.14(8)° and Zn · · · Zn distance of 3.632(12) Å. Each dinuclear SBU, which acts as a node, is connected to six others (Figure S2) through four bridging trz and two µ3-ox ligands to generate an extended neutral 3D network (Figure 2b), which can also be considered as being constructed from distorted 2D square-grid (4,4) layers of [Zn2(ox)(µ1,2,4-trz)] (Figure S3) linked by µ1,4-trz ligands. The overall topology of the 3D frame can be described as a distorted R-Po net because parallel (4,4) nets are cross-linked by zigzag chains (Scheme 1). The node–node distances are 6.499(4), 7.974(1), and 5.879(6) Å, respectively. It should be noted that among the currently known MOFs of R-Po topology, the majority are 2-fold or 3-fold interpenetrated frameworks.16 However, compound 2 presents a noninterpenetrated structure due to the bulk of the SBU nodes relative to the length of the connections between the nodes. This does not give sufficient room to allow the formation of subsequent networks. Complex 3 exhibits an interesting self-penetrating threedimensional framework based on two sets of intersecting 2D (4,4) nets. Figure 3a shows that two independent Cd atoms both have distorted octahedral geometries. The first 2D net is built from linear trinuclear Cd3 units (Figure 3b), which has a simple (4,4) topology when [Cd3(trz)2Cl2] subunits is regarded as square-planer four-connected nodes. The fundamental centrosymmetric trinuclear unit, containing two µ1,2-bridging trz ligands and two µ2-Cl–, is completely different from those linear trinuclear reported previously.7b, 7h This bonding mode makes the Cd–Cl–Cd angle 103.71(3)° and the Cd · · · Cd separation 4.049(6) Å. As shown in Figure S4, the third bridging ligand, succinic acid, leads to the formation of the second 2D layer in 3. Each succinate group presents trans-configuration, just like fumarate, and adopts a unique eight-connected bridging mode to link six Cd(II) atoms. This novel µ6-bridge has been rarely reported and may offer a new kind of bridging mode in the chemistry of carboxylate-bridged metal clusters. The eight links orient in four different directions and each pair chelates to a single adjoining trinuclear Cd3 unit (Figure 3b). So each succinate ligand only connects to four adjacent subunits. On this basis, the second 2D sheet in 3 also exhibits (4,4) topology when the trinuclear Cd3 units and succinate groups are regarded as four-connected nodes. Furthermore, the two types of (4,4) grids link each other via sharing of the trimer nodes, to generate a three-dimensional architecture (Figure 3c). These two kinds of nodes in the 3D net of 3 are four- and eight-connected, respectively. The molar ratio of these two kinds of nonequivalent


Crystal Growth & Design, Vol. 7, No. 11, 2007 2335

Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compounds 1–5a Zn2(trz)3(SCN) (1) Zn(1)–N(2) Zn(1)–N(6) Zn(1)–N(1) N(2)–Zn(1)–N(2)#1 N(2)–Zn(1)–N(6) N(2)–Zn(1)–N(1)#1 N(6)–Zn(1)–N(1)#1 N(2)–Zn(1)–N(1)

2.134(5) 2.160(8) 2.201(5) 88.1(3) 94.5(2) 176.4(2) 88.9(2) 90.6(2)

Zn(1)–N(3) Zn(2)–N(7) Zn(2)–N(5) N(6)–Zn(1)–N(1) N(1)#1–Zn(1)–N(1) N(2)–Zn(1)–N(3) N(6)–Zn(1)–N(3) N(1)–Zn(1)–N(3)

Zn(1)–N(5) Zn(1)–O(4) Zn(1)–O(3) Zn(1)–-N(2) N(5)–Zn(1)–O(4) N(5)–Zn(1)–O(3) O(4)–Zn(1)–O(3) N(5)–Zn(1)–N(2) O(4)–Zn(1)–N(2) O(3)–Zn(1)–N(2) N(5)–Zn(1)–O(1)

2.060(2) 2.0842(17) 2.1156(16) 2.1248(19) 97.23(7) 93.17(7) 169.31(6) 98.41(8) 96.22(7) 84.65(7) 90.98(7)

Zn(1)–O(1) Zn(1)–O(2) Zn(2)–N(3) Zn(2)–N(6) O(4)–Zn(1)–O(1) O(3)–Zn(1)–O(1) N(2)–Zn(1)–O(1) N(5)–Zn(1)–O(2) O(4)–Zn(1)–O(2) O(3)–Zn(1)–O(2) N(2)–Zn(1)–O(2)

Cd(1)–N(1) Cd(1)–N(3) Cd(1)–O(1)#1 N(1)–Cd(1)–N(3) N(1)–Cd(1)–O(1)#1 N(3)–Cd(1)–O(1)#1 N(1)–Cd(1)–O(1)#2 N(3)–Cd(1)–O(1)#2 O(1)#1–Cd(1)–O(1)#2 N(1)–Cd(1)–O(2)#2 N(3)–Cd(1)–O(2)#2

2.261(3) 2.291(3) 2.309(2) 165.08(10) 89.19(9) 100.15(9) 87.01(9) 80.01(10) 158.28(6) 84.41(9) 81.89(9)

Cd(1)–O(1)#2 Cd(1)–O(2)#2 Cd(1)–Cl(1) O(1)#1–Cd(1)–O(2)#2 O(1)#2–Cd(1)–O(2)#2 N(1)–Cd(1)–Cl(1) N(3)–Cd(1)–Cl(1) O(1)#1–Cd(1)–Cl(1) O(1)#2–Cd(1)–Cl(1) O(2)#2–Cd(1)–Cl(1) N(2)#3–Cd(2)–N(2)

Cd(1)–N(2) Cd(1)–N(1) Cd(1)–N(9) Cd(1)–N(5) Cd(1)–O(3) N(2)–Cd(1)–N(1) N(2)–Cd(1)–N(9) N(1)–Cd(1)–N(9) N(2)–Cd(1)–N(5) N(1)–Cd(1)–N(5) N(9)–Cd(1)–N(5) N(2)–Cd(1)–O(3) N(1)–Cd(1)–O(3) N(9)–Cd(1)–O(3) N(5)–Cd(1)–O(3) N(2)–Cd(1)–O(2) N(1)–Cd(1)–O(2) N(9)–Cd(1)–O(2)

2.290(4) 2.296(3) 2.339(4) 2.340(3) 2.360(3) 96.38(14) 175.81(13) 86.41(14) 91.60(14) 170.47(13) 85.35(13) 93.91(14) 94.57(14) 88.97(14) 90.04(13) 90.58(12) 93.07(12) 86.14(12)

Cd(1)–O(2) Cd(2)–N(7) Cd(2)–N(8) Cd(2)–N(6) Cd(2)–O(2) N(5)–Cd(1)–O(2) O(3)–Cd(1)–O(2) N(7)–Cd(2)–N(8) N(7)–Cd(2)–N(6) N(8)–Cd(2)–N(6) N(7)–Cd(2)–O(2) N(8)–Cd(2)–O(2) N(6)–Cd(2)–O(2) N(7)–Cd(2)–O(1) N(8)–Cd(2)–O(1) N(6)–Cd(2)–O(1) O(2)–Cd(2)–O(1) N(7)–Cd(2)–Cl(1)

Zn(1)–N(8) Zn(1)–N(1) Zn(1)–N(9) Zn(2)–N(6) Zn(2)–O(6) Zn(2)–N(5) N(8)#1–Zn(1)–N(8) N(8)#1–Zn(1)–N(1) N(8)-Zn(1)-N(1) N(1)-Zn(1)-N(1)#1 N(8)–Zn(1)–N(9)#1 N(1)–Zn(1)–N(9)#1 N(8)–Zn(1)–N(9) N(1)–Zn(1)–N(9) N(9)#1–Zn(1)–N(9) N(6)–Zn(2)–O(6) N(6)–Zn(2)–N(5) O(6)–Zn(2)–N(5) N(6)–Zn(2)–O(9) O(6)–Zn(2)–O(9)

2.115(4) 2.178(4) 2.214(4) 1.975(4) 1.984(4) 1.984(4) 180 89.88(17) 90.12(17) 180 89.57(17) 88.59(17) 90.43(17) 91.41(17) 180 100.16(17) 113.29(19) 110.88(19) 124.83(18) 101.6(2)

Zn(2)–O(9) Zn(3)–O(7) Zn(3)–O(4) Zn(3)–N(4) Zn(3)–O(3) Zn(3)–O(5) N(5)–Zn(2)–O(9) O(7)–Zn(3)–O(4) O(7)–Zn(3)–N(4) O(4)–Zn(3)–N(4) O(7)–Zn(3)–O(3) O(4)–Zn(3)–O(3) N(4)–Zn(3)–O(3) O(7)–Zn(3)–O(5) O(4)–Zn(3)–O(5) N(4)–Zn(3)–O(5) O(3)–Zn(3)–O(5) N(3)–Zn(4)–N(7)#2 N(3)–Zn(4)–N(2) N(7)#2–Zn(4)–N(2)

2.203(8) 1.991(8) 1.998(5) 88.9(2) 90.5(3) 89.4(2) 174.5(3) 87.3(2)

Zn(2)–N(4)

2.1775(17) 2.1805(16) 1.948(2) 1.981(2) 100.51(6) 76.77(6) 159.62(7) 173.28(7) 78.46(6) 90.96(6) 87.24(8)

Zn(2)–N(4) Zn(2)–O(3)

N(7)–Zn(2)–N(5) N(5)–Zn(2)–N(5)#2 N(7)–Zn(2)–N(4) N(5)–Zn(2)–N(4)

2.009(9) 114.92(17) 120.7(3) 101.8(4) 99.7(2)

Zn2(trz)2(ox) (2) 2.0078(19) 2.0757(16)

O(1)–Zn(1)–O(2) N(3)–Zn(2)–N(6) N(3)–Zn(2)–N(4) N(6)–Zn(2)–N(4) N(3)–Zn(2)–O(3) N(6)–Zn(2)–O(3) N(4)–Zn(2)–O(3)

84.81(7) 126.16(8) 127.51(8) 104.85(8) 95.02(7) 98.19(7) 88.59(7)

Cd(2)–N(2) Cd(2)–O(2) Cd(2)–Cl(1) N(2)–Cd(2)–O(2)#3 N(2)–Cd(2)–O(2) O(2)#3–Cd(2)–O(2) N(2)#3–Cd(2)–Cl(1) N(2)–Cd(2)–Cl(1) O(2)#3–Cd(2)–Cl(1) O(2)–Cd(2)–Cl(1) Cl(1)–Cd(2)–Cl(1)#3

2.279(3) 2.467(2) 2.6019(8) 87.04(9) 92.96(9) 180 91.07(7) 88.93(7) 93.38(6) 86.62(6) 180

Cd(2)–O(1) Cd(2)–Cl(1) Cd(3)–N(3)#1 Cd(3)–N(4) Cd(3)–Cl(1) N(8)–Cd(2)–Cl(1) N(6)–Cd(2)–Cl(1) O(2)–Cd(2)–Cl(1) O(1)–Cd(2)–Cl(1) N(3)#1–Cd(3)–N(3)#2 N(3)#1–Cd(3)–N(4) N(3)#2–Cd(3)–N(4) N(4)–Cd(3)–N(4)#3 N(3)#1–Cd(3)–Cl(1)#3 N(3)#2–Cd(3)–Cl(1)#3 N(4)–Cd(3)–Cl(1)#3 N(4)–Cd(3)–Cl(1) Cl(1)#3–Cd(3)–Cl(1)

2.514(3) 2.5258(12) 2.280(3) 2.330(3) 2.7689(11) 91.28(10) 117.56(10) 158.13(8) 105.34(9) 180 91.08(13) 88.92(13) 180 90.08(10) 89.92(10) 88.89(9) 91.11(9) 180

Zn(4)–N(3) Zn(4)–N(7)#2 Zn(4)–N(2) Zn(4)–O(1) Zn(4)–O(2) Zn(4)–O(11) N(3)–Zn(4)–O(1) N(7)#2–Zn(4)–O(1) N(2)–Zn(4)–O(1) N(3)–Zn(4)–O(2) N(7)#2–Zn(4)–O(2) N(2)–Zn(4)–O(2) O(1)–Zn(4)–O(2) N(3)–Zn(4)–-O(11) N(7)#2–Zn(4)–O(11) N(2)–Zn(4)–O(11) O(1)–Zn(4)–O(11) O(2)–Zn(4)–O(11)

2.080(4) 2.087(4) 2.101(4) 2.158(4) 2.166(4) 2.242(6) 166.4(2) 94.21(18) 94.24(19) 87.39(17) 176.21(19) 92.39(18) 84.36(17) 90.4(3) 87.1(3) 172.6(2) 78.7(3) 89.2(3)

Cd3(trz)2(suc)Cl2 (3) 2.421(2) 2.505(2) 2.5468(9) 105.67(8) 52.67(7) 96.73(8) 93.40(7) 98.47(6) 103.20(6) 155.85(5) 180

[Cd5(trz)6(OAc)2Cl2(H2O)2] · 2H2O (4) 2.375(3) 2.304(3) 2.306(4) 2.314(4) 2.377(3) 81.63(11) 170.65(13) 172.33(14) 83.93(14) 89.93(15) 89.55(12) 85.24(13) 84.08(12) 93.37(13) 88.00(15) 137.09(13) 53.03(11) 95.63(10)

[Zn7(trz)6(1,2,4,5-BTC)2(H2O)6] · 8H2O (5) 1.989(4) 1.948(4) 1.994(4) 2.006(4) 2.030(5) 2.465(7) 104.97(19) 102.27(17) 109.35(17) 93.09(18) 134.1(2) 104.3(2) 105.8(2) 97.10(18) 159.50(18) 86.7(2) 56.4(2) 93.33(18) 96.90(18) 91.22(17)

a Symmetry codes: 1, #1 x, -y + 1/2, z. 3, #1 x, y, z - 1; #2 x, -y + 1/2, z - 1/2; #3 -x + 1, -y + 1, -z + 1. 4, #1 x + 1, y, z; #2 -x + 1, -y + 1, -z + 1; #3 -x + 2, -y + 1, -z + 1. 5, #1 - x, -y + 1, -z; #2 x + 1/2, y + 1/2, z.


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Figure 1. (a) Drawing with atomic labeling showing the basic coordination environments in compound 1. (b) Polyhedral diagram of 1 viewed along the a-axis direction.

Scheme 1. Schematic Drawing of Reaction and Topology of Compounds 1–5

nodes is 1:1, and the 3D 4,8-connected structure (Scheme 1) of 3 has the Schläfli symbol (456)(412616). Some of the “shortest circuits” of the network are penetrated by rods of the same net (Figure 3d), making it a self-penetrating network.17 To the best of our knowledge, only one 4,8-connected MOF example with CaF2-type topology based on regular cubic and tetrahedral building blocks has been reported to date.18 The discovery of this completely new eight-connected topology of 3 is useful at the basic level in the crystal engineering of coordination networks. The structure of compound 4 can be described as a CsCltype net utilizing linear pentanuclear cadmium clusters as eightconnected nodes and trz ligands as linkers. As depicted in Figure 4a, three crystallographically unique Cd(II) atoms are linked by three kinds of bridging ligands, trz, OAc– and Cl–, to form the unprecedented linear pentanuclear cluster. The three independent Cd atoms all exhibit distorted octahedral geometry. Cd(1) atom is coordinated by two N4 atoms from different trz

ligands (Cd–N ) 2.290(4) and 2.296(3) Å), two N1 (or N2) atoms from another two trz ligands (Cd–N ) 2.339(4) and 2.340(3) Å), one acetate oxygen atom (Cd–O ) 2.375(3) Å), and one oxygen atom from a coordinated water molecule (Cd–O ) 2.360(3) Å). The Cd(1) atom links to Cd(2) via two µ1,2bridging trz ligands and one µ2-bridging acetate ligand. Another µ1,2-bridging trz and one chloride ion complete the coordination geometry of the distorted octahedral Cd(2) ion in the unit. The bond lengths are: Cd–N ) 2.304(3)–2.314(4) Å, Cd–O ) 2.377(3)–2.514(3) Å, and Cd–Cl ) 2.5258(12) Å. The Cd(3) atom lies at a center of symmetry, and coordinates to four trz ligands (Cd–N ) 2.280(3) and 2.330(3) Å) and two chloride ions (Cd–Cl ) 2.7689(11) Å). One Cl– ion together with a µ1,2bridging trz ligand link the adjoining Cd(2) atoms. Thus, two kinds of bridging fashions between cadmium atoms exist in the pentanuclear cluster: (i) two µ1,2-triazole and one µ2-O; (ii) one µ1,2-triazole and one µ2-Cl. The bridging angles Cd(1)–O–Cd(2) and Cd(2)–Cl–Cd(3) are 104.38(1) and 104.22(4)°, respectively.



Figure 2. (a) Coordination environments for the dinuclear zinc unit in compound 2. (b) Polyhedral diagram of 2.

Figure 3. (a) Coordination environments for the tricadmium unit in compound 3. (b) Two kinds of 2D (4,4) layers. (c) Polyhedral diagram of the three-dimensional structure of 3. (d) Self-penetrating 4,8-connected net.

The distances of Cd(1) · · · Cd(2) and Cd(2) · · · Cd(3) are 3.754(4) and 4.181(3) Å. To the best of our knowledge, this novel linear

pentanuclear cluster is the first example in the whole coordination chemistry of 1,2,4-triazole and its derivatives. Each


Zhai et al.

Figure 4. (a) Coordination environments for the pentanuclear cadmium unit in 4. (b) Perspective view of the linkage of a pentanuclear core (orange) with eight adjacent neighbors (red). (c) Polyhedral diagram of the three-dimensional structure of compound 4.

pentanuclear metal cluster is surrounded by 12 triazole ligands and linked to eight nearest neighbors through triazole ligands (Figure 4b) to give a novel three-dimensional architecture of 4 (Figure 4c). This, therefore, defines an eight-connected node. As shown in Scheme 1, the 3D eight-connected net consists of parallel (4,4) nets cross-linked by zigzag chains. The zigzag chains are distributed on both sides of a (4,4) net in a parallel fashion and bridge across the diagonal of the (4,4) net. The node–node distances are of three types: I 12.697(1) Å, II 8.517(1) Å, and III 12.220(1) Å. Thus, the overall 3D structure of 4 can be viewed as a distorted CsCl-type, with 42464 topology. This example indicates again that topological analysis is a useful tool for the description and comparison of networks in the crystal engineering, especially for those high-connected architectures. The single-crystal X-ray structural analysis reveals that 5 has a three-dimensional 4,10-connected porous structure constructed from 10-connected Zn-triazole heptanuclear cluster and fourconnected 1,2,4,5-benzenetetracarboxylate (1,2,4,5-BTC). As shown in Figure 5a, seven zinc atoms are linked by six 1,2,4triazole ligands via µ1,2 and µ1,2,4 linking fashions to generate an interesting heptanuclear [Zn7(trz)6]8+ cluster. Four independent Zn atoms exhibit three different coordination geometries. The Zn(1) atom lies at a center of symmetry and coordinates to six N1 (or N2) atoms from six different trz ligands (Zn-N ) 2.115(4)–2.214(4) Å), giving a distorted octahedral geometry. The Zn(2) atom is coordinated to two N4 atoms from different trz ligands (Zn–N ) 1.975(4) and 1.984(4) Å) and two oxygen atoms from different 1,2,4,5-BTC ligands (Zn–O ) 1.984(4) and 1.989(4) Å) to complete a distorted tetrahedral environment, whereas Zn(3) exists in an approximately tetragonal-pyramidal geometry, being ligated by one N4 atom and four oxygen atoms from three different 1,2,4,5-BTC ligands (Zn–N ) 2.006(4) Å and Zn–O ) 1.948(4)–2.465(7) Å). The Zn(4) atom is bound to three triazole nitrogen atoms and three water molecules to

generate the second octahedral geometry. Thus, this unique pentanuclear zinc cluster includes all the common coordination numbers of the Zn(II) ion. The Zn · · · Zn separations controlled by the triazole-bridging mode are 3.756(2) Å for µ1,2 and 6.038(2)–6.252(3) Å for µ1,2,4. It should be noted that in this heptanuclear cluster, the linking mode between Zn(1), Zn(4), and six trz ligands is similar to the {Fe(Htrz)2(trz)}nn– chain of [FeII(Htrz)2(trz)](BF4),19 the {Co(trz)3}nn– chain of [Co2(trz)3Cl]13 or the {Zn(trz)3}nn– chain of compound 1; however, three terminal coordinated water molecules prevent the formation of chain structure. This novel heptanuclear cluster represents the highest nuclearity example in the coordination chemistry of triazole to date. Figure 5b shows that one heptanuclear cluster is surrounded by eight 1,2,4,5-BTC ligands. First, each heptazinc core connects to two adjacent clusters via coordination of the two triazole N4 position nitrogens not used to construct the cluster (N(6)) to the Zn(2) atoms of adjoining clusters and vice versa. This generates a 1D [Zn7(trz)6]n8n+ column structure along the c-axis direction (Figure 5c). Each column is then linked to six adjacent neighbors by µ5-bridging 1,2,4,5-BTC ligands to give the 3D microporous supramolecular framework of 5 (Figure 5d). There are two types of open channels in the structure: 12.5 Å × 10.5 Å cross section channels along the c-axis and 7.8 Å × 8.2 Å channels along the b-axis. Taking the van der Waals radii into account, however, the channels are only about 4 Å × 6 Å along the c-axis and 3 Å × 4 Å along the b-axis. Calculations by PLATON reveal that the van der Waals free space per unit cell (after the solvent–water molecules have been removed) is approximately 1374.2 Å3, corresponding to 23.6% of the crystal volume. To classify the network topology, we can define the 1,2,4,5BTC ligands as a four connected node (Figure S5); each µ5 ligand connects to four clusters. On the other hand, each [Zn7(trz)6]8+ cluster coordinates to eight 1,2,4,5-BTC ligands



Figure 5. (a) Coordination environments for the heptazinc core in 5. (b) View of the linkage of 1,2,4,5-BTC ligands and the heptanuclear core. (c) 1D [Zn7(trz)6]8n+ column structure. (d) 3D microporous framework of 5 viewed along the b- (right) and c-axis (left) directions, respectively.

(Figure 5b) and links to two adjacent heptanuclear neighbors via two N4-position triazole ligands, as described above. This, therefore, defines a 10-connected node. These two nodes link each other to result in a unique 3D 4,10-connected framework (Scheme 1), which, to the best of our knowledge, represents the highest-connected net based on mixed nodes. An alternative description of the complicated net of 5 can be obtained if we divide the 10-connecting heptanuclear cluster into three parts: six-connecting Zn3(trz)6(H2O)6 clusters, four-connecting Zn(2) atom, and four-connecting Zn(3) atom. Thus, complex 5 may be described as 2D sheets of Zn2(1,2,4,5-BTC) linked by Zn3(trz)6(H2O)6 pillars into 3D network. One such sheet is shown in Figures S6 and S7. The Zn(2) and Zn(3) metals are bridged by five-connecting 1,2,4,5-BTC 4– ligands. These sheets lie parallel to the yz plane, and are bridged by Zn3(trz)6(H2O)6 clusters, which act as pillars between the layers (Figure S8). Two of the three water ligands coordinated to each Zn(4) ion reinforce the network by hydrogen bonding to carboxylate oxygens (Figure S9, O1 · · · O3#1 ) 2.818(4) Å, #1 ) x + 1/2, -y + 1/2, z + 1/2; O1 · · · O9 ) 2.950(2) Å; O10 · · · O2#2 ) 2.697(1) Å, #2 ) x - 1/2, -y + 1/2, z - 1/2). The Zn3(trz)6(H2O)6 clusters are connected to two Zn(2) atoms and

one Zn(3) atom in each of two adjoining Zn2(1,2,4,5-BTC) sheets via the 4-position nitrogen atoms of the triazole ligands. Thus the Zn3(trz)6(H2O)6 cluster acts as a six-connecting (SBU). The overall 3D network formed is shown in Figure S10, with 1,2,4,5-BTC4- ligands and Zn3(trz)6(H2O)6 SBUs represented schematically. The resultant topology contains five-connecting 1,2,4,5-BTC4- ligands, four-connecting Zn(2) and Zn(3) atoms, and six-connecting SBUs. Moreover, this complicated topological net can also be considered as being formed from 1D rodshape [Zn7(trz)6]n8n+ subunits according to the principles of rodpacking. It should be noted that the rod-packing diagram of 5 is similar to that of compound 1 as described in Scheme 1. These two examples fully demonstrate the usefulness of the concept of rod packing in simplifying the metal-organic coordination polymers. Effect of Metal Nuclearity and the Bulk of the Second Bridging Ligands. The first information worthy of note is that by controlling synthesis, we obtain five types of highly connected 3D nets based on a series of d10-1,2,4-triazolate polynuclear cluster. The structural results of these novel complexes show that the nuclearity of the metal-triazolate clusters is clearly critical in determining the connectivities of


the metal-organic coordination frameworks. From the trend observed for compounds 1–5 (Scheme 1), we can see that the increase in metal nuclearity (1 f 2 f 3 f 5 f 7) induces the gradual increase in connectivity of the resultant net (3,6 f 6 f 4,8 f 8 f 4,10). Thus, we can conclude that the metal nuclearity of the SBUs is a key factor to controlling the connectivity of a 3D net because polynuclear-cluster-based nodes generally have larger surface areas and have more coordination sites but cause less steric hindrance when coordinated with organic ligands. These examples demonstrate again that the utilization of polynuclear metal clusters as SBUs to construct highly connected frameworks is a feasible route. In the past decades, a large number of examples have shown that the second or third bridging ligands play a controlling role in tuning the molecular structure based on 1,2,4-triazole ligands. However, most of the second or third bridging ligands investigated to date are small inorganic anions, e.g., Cl-, Br-, I-, SCN-, N3-, etc. Although multidentate carboxylate ligands have proven to be good bridging ligands for constructing metal-organic polymers, the combination of carboxylate and 1,2,4-traizole ligands has been rarely investigated to date. Detailed structural comparison of complexes 1–5 indicated that the carboxylate ligands are strongly related to the metal nuclearity of the polynuclear cluster SBUs. In 2, one µ2-oxygen atom from the oxalate ligand helps to form the binuclear units and the whole µ6-coordianted oxalate anion acts as linker to connect the fundamental units. When a longer dicarboxylate ligand, succinic acid, is used in 3, three cadmium atoms are linked by two µ1,2trz and two µ2-chlorine to generate a linear trinuclear cluster. The µ6-coordianted succinate anion serves as a four-connected node to link the trinuclear SBUs. Further, when the larger, bulkier 1,2,4,5-benzenetetracarboxylate ligands used in 5, seven zinc atoms are linked by six trz to give a heptanuclear cluster. Thus, it can be seen that the increase in the bulk of the second bridging carboxylate ligands (oxalate, succinate, and 1,2,4,5BTC) induces the increase in the separations between two clusters, and furthermore, leads to the increase in the metal nuclearity. In other words, the bulk of the carboxylate ligands influences the metal nuclearity and hence the connectivity of the ultimate net. Therefore, it is challenging to continue the investigations in this part of research, because of the extensive choices of multidentate carboxylate ligands and the possibility of new high-nuclear metal-1,2,4-triazolate clusters. Soild-State Emission Spectroscopy. Upon excitation of solid samples of 1–5 at λ ) 340 ( 5 nm, intense bonds in the emission spectra (Figure 6) are observed at 487 nm for 1, 410 nm for 2, 4, and 5, and 415 nm for 3. To more thoroughly understand the nature of the emission band, we also investigated the luminescence of 1,2,4-triazole and carboxylate ligands in the solid state at room temperature. All the organic ligands are nearly nonfluorescent in the range 400–800 nm for excitation wavelengths between 250 and 450 nm. However, in these coordination complexes, the highest occupied molecular orbitals (HOMOs) are presumably associated with the π-bonding orbitals from the aromatic 1,2,4-triazole rings, whereas the lower unoccupied molecular orbitals (LUMOs) are associated mainly with the Cd/Zn-X (X ) O from carboxy, SCN- or Cl-) δ*antibonding orbitals, localized more on the metal centers. Thus, the origin of the emission might be attributed to the ligand-tometal charge transfer (LMCT).20 XRPD, TGA, and Heating–Cooling and Dehydration– Hydration Experiments. As shown in Figure S11 and Figure 7, compounds 1–5 were characterized via X-ray powder diffraction (XRPD). All the XRPD patterns measured for the

Zhai et al.

Figure 6. Emission spectra of 1–5 in the solid state at room temperature. All complexes are excited at 340 ( 5 nm.

Figure 7. XRPD patterns for 5: (a) calculated on the basis of the structure determined by single-crystal X-ray diffraction; (b) assynthesized; (c) after heating at 150 °C for 30 min; (d) after heating at 200 °C for 30 min; (e) after heating at 300 °C for 30 min; (f) after rehydration of the sample for 24 h.

as-synthesized samples were in good agreement with the XRPD patterns simulated from the respective single-crystal X-ray data. TGA-DTA was performed on crystalline samples from 40 to 900 °C at a heating rate of 10°/min under an air atmosphere for 1–3 and a nitrogen atmosphere for 4 and 5. The TG/DTA curves of compounds 1–5 are provided in Figure S12. The framework of compound 1 was stable up to ca. 360 °C; decomposition of organic ligands and thiocyanate occurred between 360 and 850 °C. The remaining weight (45.92%) indicated that the final product should be a 1:1 mixture of ZnO and ZnS (45.51%). No weight losses were observed in the TG curve of compound 2 up to 375 °C; above 375 °C, a sharp weight loss was observed in the range 375-570 °C, corresponding to the decomposition of two trz ligands (exptl 37.31%, calcd 38.34%). The oxalate components decomposed in the temperature range 570-805 °C and ZnO forms as the final product. This conclusion is supported by the percentage of the residues (37.31%), which is in accordance with the expected value (38.34%). The framework of 3 was stable up to 370 °C; sharp decomposition of the trz ligands was observed in the range


370–435 °C (exp, 20.59%; calcd, 20.61%). Further, the succinic acid and chlorine were decomposed in the range 435–700 °C. The remaining weight (39.07%) indicated that the final product was CdO (38.89%, two-thirds of the total Cd). In our opinion, the other one-third of Cd was sublimation in the form of CdCl2. Complex 4 first lost weight corresponding to four water molecules from 40 to 190 °C, leaving a framework of Cd5(trz)6(OAc)2Cl2. This framework was stable up to 315 °C; above 315 °C, the two-step weight loss is 49.12%, which is consistent with the removal of six trz ligands, two acetate anions, and two chlorine ions (calcd 48.51%). The TG curve of 5 shows a weight loss of 15.01% from 40 to 250 °C, corresponding to the release of fourteen guest or bonded water molecules (calcd 15.57%). No weight loss was observed from 250 to 360 °C, and the framework started to decompose at higher temperatures. The weight loss of 55.89% (calcd 56.14%) between 260 and 710 °C corresponds to the elimination of the organic components. Because of the microporous structure of compound 5, heating–cooling and dehydration- hydration experiments were carried out via TGA and monitored by X-ray powder diffraction technique (XRPD, Figure 7). Compared to the original crystals, the dehydrated solid obtained by heating showed basically an identical XRPD pattern, except that several main diffraction peaks shifted slightly to lower 2θ values and the diffraction intensity decreased. This fact shows that a certain structural change or distortion occurs after removal of the water molecules. This conjecture was further supported by the XRPD pattern of the evacuated solid after soaking in water for 24 h, in which the peak positions and their intensities are nearly co-incident to those observed for the assynthesized solid. The thermal stability of 5 was further demonstrated by the almost identical XRPD patterns for the dehydrated solid obtained by heating at 150, 200, and 300 °C for 30 min (curves c–e in Figure 7), respectively. It should be noted that high thermal stability of porous metal-organic frameworks is one of the most desirable qualities for application purposes. However, N2 sorption experiments for 5 unfortunately showed that only surface adsorption had occurred, indicating that nitrogen molecules could not diffuse into the channels at this temperature. Conclusions The use of coligands based on 1,2,4-triazole to react with d10 metals affords a series of interesting self-assembled polymeric architectures based on mononuclear, binuclear, linear trinuclear, linear pentanuclear, and heptanuclear SBUs. These frameworks provide new examples of highly connected systems and illustrate again the aesthetic diversity of coordination network chemistry. Compound 1 presents a novel 3,6-connected topology based on three nonequivalent nodes. Complex 2 exhibits rare noninterpenetrated distorted R-Po topology. 3 shows a novel self-penetrating 4,8-connected topology based on trinuclear units. Although compound 4 has the common CsCl-type topology, the linear pentanuclear cluster is the first example in the coordination chemistry of 1,2,4-triazole. The 4,10-connected microporous structure of compound 5 represents the highest-connected net based on mixed nodes. All the compounds exhibit strong fluorescence emission bands in the solid state at ambient temperature. The isolation of these compounds also demonstrates that the combination of 1,2,4-triazole ligands and polycarboxylate ligands is an effective way to construct metal–organic frameworks with intriguing architectures. On the other hand, we believe that polymers with potential properties in electrical


conductivity and magnetism will be synthesized by using other transition metals (such as Cu(II), Co(II), Ni(II) or Mn(II)). On the basis of this work, further syntheses, structures, and properties studies of the mixed ligand system of 1,2,4-triazole and polycarboxylate with transition metals are under way in our laboratory. Acknowledgment. This work was supported by the 973 key program of the MOST (2006CB932904), the National Science Foundation of China (20425313, 20521101, 20333070, and 90206040), the Chinese Academy of Sciences (KJCX2-YWMO5), the Natural Science Foundation of Fujian Province (2005HZ01-1), and the Australian Research Council. Supporting Information Available: X-ray crystallographic files in CIF format, additional plots of the structures, XRPD and thermogravimetric analysis results in PDF format. This information is available free of charge via the Internet at http://pubs.acs.org.

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