Inorganic Chemistry Communications 48 (2014) 94–98

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Inorganic Chemistry Communications

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3D pillared-layer coordination frameworks constructed from4-(1,2,4-triazole)benzoic acid and different [M(HCOO)]n layers

Yu-Hai Mu, Zhi-Wei Ge, Cheng-Peng Li ⁎College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, MOE Key Laboratory of Inorganic–Organic Hybrid Functional Material Chemistry,Tianjin Normal University, Tianjin 300387, PR China

⁎ Corresponding author.E-mail address: tjnulicp@gmail.com (C.-P. Li).

http://dx.doi.org/10.1016/j.inoche.2014.08.0271387-7003/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 24 July 2014Received in revised form 25 August 2014Accepted 28 August 2014Available online 29 August 2014

Keywords:Pillared-layer frameworkIn situ synthesis4-(1,2,4-Triazole)benzoic acidStructural diversityNetwork topology

Twodistinct pillared-layer frameworks [M(HCOO)(4-tba)]n (M=Cd for 1 andPb for 2) have beenprepared from4-(1,2,4-triazole)benzoic acid (4-Htba) andM(NO3)2 salts by using the solvothermal method in DMF. During thereaction, formate anion is in situ obtained as the hydrolyzate of DMF. Single crystal X-ray diffraction reveals that 1displays a 3D self-interpenetrating (3,3,4,6)-connected network of (4.6.8)(4.64.8)(4.66.87.10)(4.82) topologywhereas 2 presents a 3D unusual (3,3,6,6)-connected network with the point symbol of (4.62)2(42.6)2(42.66.87)(44.66.85). Their structural divergences should be properly attributed to the fact that the similar[M2(HCOO)2] secondary building units were arranged in different directions along the b axis to result in different[M(HCOO)]n+ layers in 1 and 2. In addition, thermal stability and luminescent properties of both complexes arealso studied.

© 2014 Elsevier B.V. All rights reserved.

1 Synthesis of 1 and 2. The ligand 4-Htba (0.1 mmol) was dissolved in DMF (5 mL), towhich a DMF solution (5 mL) of Cd(NO3)2·4H2O (0.1 mmol) was added with stirring forca. 30 min. Then, the solution was sealed in a Teflon-linear autoclave and heated at100 °C for 3 days, after cooling to room temperature at a rate of 10 °C/h, colorless blockcrystals of complex 1were obtained in 58% yield (20.0 mg). Anal. Calcd for C10H7CdN3O4:C, 34.75; H, 2.04; N, 12.16%. Found: C, 34.71; H, 2.06; N, 12.14%. IR (KBr, cm−1): 1606vs,1575vs, 1542vs, 1449m, 1410vs, 1368s, 1337s, 1303s, 1281s, 1229m, 1149m, 1051m,994w, 975m, 873w, 854m, 812w, 781m, 724w, 698w, 669w, 646w, 541w. The same syn-

Recent years have witnessed prosperous development of researchon the synthesis of hybrid materials named metal–organic frameworks(MOFs) or coordination polymers (CPs), using diverse pre-designed li-gands with different metal ions [1–4]. As a subclass of functional mate-rials, they have shown extensive application in gas storage/separation,magnetism, catalysis, optics, and drug delivery. [5–11]. Therefore, therational design and construction of novel MOFs with specific networkshave been of particular importance as a topic subject. Towards this di-rection, many efforts have been paid on the research of the optimumstrategy and manipulation in the self-assembly of MOF, which is still abig challenge. Outstandingly, pillared-layer assembling strategy hasbeen proved to be one of the most effective approaches to fabricatethe desired MOFs, in which the metal-involved polymeric layers canbe pillared by various organic struts to produce multifarious porouschannels and network topology [12–15]. In essence, the central metalions play an extremely significant role in directing the polymeric layersand connectivity of organic struts, and thus the resultant frameworks[16–18].

In this work, our synthetic strategy includes the use of two distinctmetal ions of Cd(II) and Pb(II) with different coordination geometriesand atom radii as the metal nodes. Furthermore, formate anions, insitu synthesized from the hydrolysis of DMF solvent, combine with

Cd(II) and Pb(II) centers to form the different 2D [M(HCOO)]n+ layers,which comprise the similar [M2(HCOO)2] secondary building unit butin different arrangements. In addition, the organic ligand 4-(1,2,4-triazole)benzoic acid (4-Htba) is introduced as the strut to constructthe pillared-layer MOFs [M(HCOO)(4-tba)]n (M = Cd for 1 and Pbfor 2),1 which were characterized by elemental analysis, IR spectra,and powder X-ray diffraction (PXRD) techniques (see Fig. S1 for PXRDpatterns). Interestingly, due to the diverse coordination characteris-tics of Cd(II) and Pb(II), these two MOFs show the various polymericstructures, including a 3D self-interpenetrating (3,3,4,6)-connectednetwork of (4.6.8)(4.64.8)(4.66.87.10)(4.82) topology and a 3Dunusual (3,3,6,6)-connected network with the point symbol of(4.62)2(42.6)2(42.66.87)(44.66.85).

thetic procedure as that for 1 was used except that Cd(NO3)2·4H2O was replaced byPb(NO3)2 (0.1 mmol), forming colorless block crystals of 2 in 54% yield (23.8 mg). Anal.Calcd for C10H7PbN3O4: C, 27.27; H, 1.60; N, 9.54%. Found: C, 27.22; H, 1.64; N, 9.49%. IR(KBr, cm−1): 1603s, 1557vs, 1383vs, 1340s, 1305m, 1277m, 1222m, 1143w, 1050w,964w, 848w, 782m, 719w, 696w, 666w, 641w, 541w.

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Single crystal X-ray diffraction study shows that complex 12 has a 3Dpillared-layer framework,which crystallizes in the orthorhombic crystalsystem with Pbcm space group. The asymmetric unit consists of twohalf-occupied CdII ions, a pair of half-occupied HCOO− anions, and one4-tba− anion. As shown in Fig. 1a, Cd1 center is six-coordinated byfour oxygen atoms from four HCOO− anions and two nitrogen atomsfrom two 4-tba− in the trans-positions, to complete a distorted octahe-dral geometry. Cd2 ion is eight-coordinated by four pairs of carboxylatesfrom two HCOO− anions and two 4-tba− anions. The two independentHCOO− anions act as the μ3-bridging linker to form a binuclear motif[Cd2(HCOO)2], which is further interconnected by additional Cd\Obonds to afford a 2D polymeric [Cd(HCOO)]n+ layer along the abplane (Fig. 1b). Interestingly, within this layer, the binuclear motifsalong the b axis arrange in an anti-parallel fashion. With regard to the4-tba− ligands, the pyridyl ring and carboxylate adopt themonodentateand chelating coordination modes to ligate CdII centers, respectively(Scheme 1a). As a result, 4-tba− ligands function as the μ2-linkers tointerconnect the layers to afford a 3D pillared-layered framework(Fig. 1c). Topologically, on the one hand, Cd1, Cd2, HCOO− anion, and4-tba− ligand can be considered as the 6-, 4-, 3-, and 3-connectednodes, respectively. And thus, the overall framework can be simplifiedas a tetranodal (3,3,4,6)-connected network (as calculated by TOPOS)with the point symbol of (4.6.8)(4.82)(4.64.8)(4.66.87.10) [19,20], whichinterestingly reveals a self-interpenetrating entangled net (Fig. 1d). Onthe other hand, if considering each binuclear [Cd2(HCOO)2] motif as a6-connected node, the framework of 1 features a msw architecturewith the point symbol of (48.67) (Fig. S2) [21].

When a more bulky atom of Pb(II) is used instead of Cd(II), another3D pillared-layer framework 22 is achieved, which crystallizes in themonoclinic crystal system with C2/c space group. The asymmetric unitcomprises two half-occupied PbII ions, one HCOO− anion, and one4-tba− anion. As shown in Fig. 2a, Pb1 is eight-coordinated to eight ox-ygen atoms from two 4-tba− anions and four HCOO− anions, while Pb2is eight-coordinated to six oxygen atoms from two 4-tba− anions andtwo HCOO− anions, and two nitrogen atoms from two 4-tba− anions.Similar to that of 1, HCOO− anion in 2 acts as the μ3-bridging linker toform binuclear motif [Pb2(HCOO)2], which is also extended by theadditional Pb\O bonds to afford a 2D polymeric [Pb(HCOO)]n+ layeralong the ab plane (Fig. 2b). Different to those of 1, these [Pb2(HCOO)2]units arrange in a parallel fashion along the b direction (Fig. 2b), and the4-tba− ligands act as the μ3-linkers (monodentate pyridyl and μ-O,O-μ-O,O′ carboxylate) (Scheme 1b). In this way, another 3D pillared-layerframework of 2 is generated (Fig. 2c). In order to understand the structur-al divergence between 1 and 2, similar topological simplification ap-proach is performed. On the one hand, by taking Pb1, Pb2, HCOO−

anion and 4-tba− anion as the 6-, 6-, 3-, 3-connected nodes, respectively,this network shows a tetranodal (3,3,6,6)-connected architecture withthe point symbol of (42.6)2(4.62)2(44.66.85)(42.66.87) (Fig. 2d). On theother hand, if each binuclear [Pb2(HCOO)2] unit is considered as a node,each can connect to six 4-tba− anions and four [Pb2(HCOO)2] units torepresent a 10-connected node. In combination with the 3-connected4-tba− node, this network suggests a (3,10)-connected architecturewith the point symbol of (43)2(418.624.83) (see Fig. S3).

2 Single crystal X-ray diffraction data for complexes 1 and 2were collected on a BrukerAPEX II CCD diffractometer equipped with a graphite monochromated Mo Kα radiation.The structures were solved by direct methods and refined anisotropically on F2 for allnon-H atoms by full-matrix least-squaresmethods using SHELXTL. H atoms of the ligandswere located geometrically with assigned isotropic thermal parameters. Crystallographicdata for 1: C10H7CdN3O4, M = 345.59, 0.15 × 0.14 × 0.13 mm3, orthorhombic, Pbcm,a = 6.7987(4), b = 13.1320(9), c = 23.1349(15) Å, V = 2065.5(2) Å3, Z = 8,Dc = 2.223 g/cm3, F(000) = 1344, GOF = 1.097, μ = 2.126 mm−1, Rint = 0.0257, finalR indices [I N 2σ(I)] R1 = 0.0184 and wR2 = 0.0466. Crystallographic data for 2:C10H7PbN3O4, M = 440.38, 0.18 × 0.14 × 0.13 mm3, monoclinic, C2/c, a = 10.7467(7),b = 8.8429(5), c = 23.529(2) Å, β = 99.0800(10)°, V = 2208.0(3) Å3, Z = 8,Dc = 2.650 g/cm3, F(000) = 1616, GOF= 1.037, μ= 15.293 mm−1, Rint = 0.1014, finalR indices [I N 2σ(I)] R1 = 0.0445 and wR2 = 0.1124.

The structural differences between the pillared-layer frameworks 1and 2 are mainly due to the metal-independent effect on the structuresof MII-formate polymeric layers and coordination modes of the 4-tba−

pillar. In the [M(HCOO)]n+ layers, the building tectons of [Cd2(HCOO)2]in 1 and [Pb2(HCOO)2] in 2 were arranged in different directions alongthe a axis, to afford diverse polymeric structures (see Figs. 1b and 2b).And as for 4-tba− pillars, they adopt the μ2-bridging mode in 1 andμ3-linking fashion in 2 (Scheme 1), respectively. As a result, two distinct3D pillared-layer frameworks with a self-interpenetrating and a non-entangled network in 1 and 2 are extended (Figs. 1c and 2c).

In the TGA curve of 1, it keeps stable until heating to 218 °C, whichfollows with a series of continuous weight loss till heating to 800 °C(Fig. S4a). As for 2, the polymeric framework starts to collapse until194 °C and multi-steps of weight loss are observed during heating to800 °C (Fig. S4b). Solid-state fluorescent measurements indicate thatexcitation of microcrystalline sample of 4-Htba at 324 nm results inthe maximum fluorescent emission at 456 nm, while those for 1 and 2similarly appear at 496 nm under the same condition. By comparingthe locations and profiles of their emission peaks, the significantred-shift (Δ = 40 nm) and different types of emission profiles of 1 or2 to 4-Htba are found. Obviously, these emissions in 1 and 2 are notthe intra-ligand π→ π* transitions of Htba, but can be properly ascribedto either metal-to-ligand charge transfer (LMCT) or ligand-to-metalcharge transfer (MLCT) between the 4-tba− and the metal centers inthe 3D networks.

In summary, two distinct 3D pillared-layer frameworks can beassembled by combining the different MII-formate polymeric layers(CdII for 1 and PbII for 2) with 4-tba− pillars, which show the self-interpenetrating (4.6.8)(4.82)(4.64.8)(4.66.87.10) network and theentangled (4.62)2(42.6)2(42.66.87)(44.66.85) structure, respectively.It is revealed that, the delicate modulation on the metal nodes inthe layers with the same organic pillar can significantly affect thetopology of the overall pillared-layer framework. This work willpromote us to further systematically explore the effective modifica-tion on the pillar-layer strategy to fabricate interesting coordinationassembled systems.

Acknowledgments

This work was financially supported by the National Natural ScienceFoundation of China (no. 21101116) and Tianjin Normal University.

Appendix A. Supplementary Material

CCDC 1011681 and 1011682 contain the crystallographic data for 1and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-ciated with this article can be found, in the online version, at doi: http://dx.doi.org/10.1016/j.inoche.2014.08.027. This data include MOL filesand InChiKeys of the most important compounds described in thisarticle.

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Fig. 1. Views of 1. (a) Coordination environment of CdII centers (symmetry codes for A: x, y, −z + 3/2; B: x − 1, y, z; C: −x + 1, y + 1/2, −z + 3/2; D: −x + 2, −y, z + 1/2;E: −x + 2, −y, −z + 1). (b) 2D [Cd(HCOO)]n− polymeric layer. (c) 3D pillared-layer network. (d) Topological view of the 3D self-interpenetrating (3,3,4,6)-connectednetwork with the point symbol of (4.6.8)(4.64.8)(4.66.87.10)(4.82).

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Scheme 1. Coordination modes of the 4-tba− ligand in 1 (a) and 2 (b).

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(a)

(b)

(c) (d)

Fig. 2.Views of 2. (a) Coordination environment of PbII centers (symmetry codes for A:−x, y,−z+1/2; B:−x,−y+1,−z; C: x,−y+1, z+1/2; D: x− 1/2, y− 1/2, z; E:−x+1/2, y−1/2,−z+ 1/2; F:−x, y− 1,−z+ 1/2; G: x, y− 1, z). (b) 2D [Pb(HCOO)]n− polymeric layer. (c) 3D pillared-layer network. (d) Topological view of the 3D (3,3,6,6)-connected networkwith the point symbol of (4.62)2(42.6)2(42.66.87)(44.66.85).

98 Y.-H. Mu et al. / Inorganic Chemistry Communications 48 (2014) 94–98