Zn(II) and Cd(II) metal–organic frameworks (MOFs) constructed from a symmetric triangular semirigid multicarboxylate ligand: Synthesis, structures and luminescent properties

Solid State Sciences 14 (2012) 317e323

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Zn(II) and Cd(II) metaleorganic frameworks (MOFs) constructed from a symmetric triangular semirigid multicarboxylate ligand: Synthesis, structures and luminescent properties Ningning Zhao, Wenjun Li*, Changyan Sun, Yongzhong Bian, Hailong Wang, Zhidong Chang, Hongxia Fan Department of Chemistry and Chemical Engineering, University of Science and Technology Beijing, No.30 Xueyuan Road, Haidian District, Beijing 100083, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 October 2011 Received in revised form 10 December 2011 Accepted 20 December 2011 Available online 10 January 2012

Three transition metal coordination polymers [Zn2(H2L)(2,20 -bpy)2(H2O)]n∙2nH2O (1), [Zn2(H2L)(2,20 bpy)2]n (2), and [Cd2(H2L)(2,20 - bpy)2(H2O)2]n∙2nH2O (3), have been assembled from a semirigid triangular multicarboxylate ligand 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalic acid (H6L) with the help of 2,20 bipyridine (2,20 -bpy) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of Pı and displays a one-dimensional (1D) ladder chain structure constructed from 2,20 bpy ligand and H2L ligand, which stacks together in an -ABCABC- motif, featuring a mutually embedded chained structure. In complex 2, the H2L ligands bridge the adjacent Zn(II) atoms into a complicated ribbon chain along the b axis. There is pep stacking interaction between the chains, which results in the formation of a 2D supramolecular structure. Complex 3 also exhibits a 1D ladder-like chain. The different molecular structures for complexes 1 and 2 formed from the same H6L and Zn(NO3)2∙6H2O in different metal-to-ligand ratios in the presence of NaOH, reveals the influence of metaleligand ratio on the structure of the coordination polymer. In contrast, a series of same reaction using Cd(NO3)2∙4H2O as a starting material instead of Zn(NO3)2∙6H2O only led to the formation of 3, illustrating the fact organic ligands display different coordination preferences at different metal ions. In addition, the thermal and luminescent properties of complexes 1e3 were also investigated. Ó 2012 Elsevier Masson SAS. All rights reserved.

Keywords: Triphthalic acid Transition metal Triangular semirigid ligand Luminescent property

1. Introduction Metaleorganic frameworks (MOFs) from self-assembly of metal ions and multifunctional ligands have been developed rapidly in recent years because of their fascinating structural topologies and diverse functional properties [1e6]. It is well-known that the key to successful design of intriguing MOFs should be the proper choice of metal center with preferred coordination geometries and intelligent ligand design [7e9]. Furthermore, factors such as the reaction temperature, solvent system, counterions, pH value, and metal-toligand ratio have been found to exert influence on the formation of coordination frameworks. Therefore, it is still a considerable challenge to predict and accurately control the framework array of the supramolecular structures of MOFs [10]. Most of the reported coordination frameworks are constructed by linking transition metal atoms and multidentate bridging ligands [11e16]. In this context, coordination frameworks with

* Corresponding author. E-mail addresses: [email protected], [email protected] (W. Li). 1293-2558/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2011.12.014

aromatic multicarboxylate ligands such as 1,3-/1,4-benzene dicarboxylate, 1,3,5-benzenetricarboxylate, and so on as functional linkers have been widely studied due to their rigid characters, diverse coordination modes as well as high thermal stability. Recently, the semirigid multicarboxylate ligands with two benzene rings of central molecular framework bridged by a nonmetallic atom (C, O, S, and N atoms) were well used in construction of coordination frameworks and have been becoming an active research field [17e21]. As can be seen, semirigid multidentate carboxylate ligand provides diverse coordination conformations as well as abundant acceptor and donor atoms to form hydrogen bond, leading to interesting molecular structures such as helices and interpenetrating networks. However, these semirigid multidentate O-donor ligands possess semirigid backbone rotating around only one bridged nonmetallic atom at freedom, probably leading to the limitation in generation of the molecular structure and functionality of MOFs. To the best of our knowledge, the semirigid multidentate O-donor ligands with more than one bridged nonmetallic atom have been scarcely explored. Therefore, it seems interesting to prepare new semirigid multidentate Odonor species with more than one bridged nonmetallic atom for

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the purpose of assembling new MOFs with novel structural motifs and properties. In the present work, a new triangular multidentate O-donor ligand 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalic acid (H6L) (Scheme 1) was synthesized. It is worth noting that there are three phthalic acid segments attached at symmetrical positions of the central benzene ring through the linkage of the oxygen atoms, which can bend in some extent and can provide relative flexibility of the structure. In addition, the completely or partly deprotonated H6L ligands may have irregular orientations when they coordinate to metals to compensate the charge or pH adjusters, which may produce various structural topologies, owing to their hexadentate carboxylate arms and their steric bulk. Fortunately, three new coordination polymers [Zn2(H2L)(2,20 -bpy)2(H2O)]n∙2nH2O (1), [Zn2(H2L)(2,20 -bpy)2]n (2), and [Cd2(H2L)(2,20 bpy)2(H2O)2]n∙2nH2O (3) were obtained under hydrothermal condition by utilizing the semirigid multicarboxylate ligand H6L with the help of 2,20 -bipyridine (2,20 -bpy) as auxiliary ligands. The thermal and luminescent properties of these complexes have also been investigated.

the solution was cooled drown to room temperature and filtered. After the pH value of the filtrate was adjusted to about 4e5 with HCl (6.0 mol/L), the filtrate was kept undisturbed at room temperature. After about one day, a large amount of white solid of H6L was collected by filtration with a yield of 4.63 g, 83%. IR/cm1 (KBr): 3432 (m), 1711 (s), 1610 (s), 1578 (s), 1449 (s), 1244 (s), 1124 (s), 1085 (s), 1023 (m). 1HNMR (400 MHz, DMSO-d6): d 7.682 (d, J ¼ 7.6, 3H), d 7.425 (t, J ¼ 8.0, 3H), d 7.234 (d, J ¼ 8, 3H), d 6.173 (s, 3H). 2.2. General synthesis procedure for complexes 1e3 The target complexes were obtained by utilizing the hydrothermal method with the different stoichiometric ratio for the starting materials in the presence of NaOH. A Teflon-lined stainless steel container (25 mL) was employed as a reaction vessel containing all starting materials, which was heated to an appropriate temperature and held for 72 h, then cooled to 100  C at a descent rate of 10  C/h. Finally, the oven was cut off and kept for another 10 h, and perfect crystals were isolated.

2. Experimental section All reagents and solvents employed in the present work were obtained from commercial source and used directly without further purification. 2.1. Synthesis of H6L The ligand of 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalic acid (H6L) was synthesized according to the following procedure, as shown in Scheme 1. To a solution of phloroglucinol (1.26 g, 10 mmol) and anhydrous Na2CO3 (3.18 g, 30 mmol) in DMF (25 ml) stirred for 30 min, 3-nitropthalonitrile (5.19 g, 30 mmol) was added. The resulting mixture was stirred for 48 h. Then the mixture was poured into water (500 ml), and a slightly yellow solid was yielded and isolated by filtration. The crude product was dried in air, yielding 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalonitrile (4.38 g, 87%). 1H NMR (400 MHz, DMSO-d6): d 8.675 (d, J ¼ 8.4, 3H), d 8.526 (d, J ¼ 7.6, 3H), d 8.151 (t, J ¼ 8.4, 3H), d 6.986 (s, 3H). The mixture of 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalonitrile (5.04 g, 10 mmol) and NaOH (4.8 g, 120 mmol) in distilled water (150 ml) was refluxed until the solution turned clear. Then,

OH

NO2

2.2.1. [Zn2(H2L)(2,20 -bpy)2(H2O)]n∙2nH2O (1) The mixture of Zn(NO3)2∙6H2O (0.0595 g, 0.2 mmol), 2,20 -bpy (0.0312 g, 0.2 mmol), H6L (0.0618 g, 0.1 mmol), NaOH (0.008 g, 0.2 mmol), and H2O (15 mL), was sealed in 25 mL Teflon-lined stainless steel reactor, which was heated to 150  C. Colorless block-shaped crystals suitable for X-ray diffraction analysis were separated by filtration with the yield of 0.0649 g, 58.1% (based on ligand). Anal. Calcd. For C50H36N4O18Zn2: C 53.98, H 3.24, N 5.04. Found: C 53.98, H 3.28, N 5.01. IR/cm1 (KBr): 3432 (m, br), 1732 (m), 1605 (s), 1565 (s), 1444 (s), 1391 (s), 1236 (s), 1128 (m), 1028 (m), 766 (m). 2.2.2. [Zn2(H2L)(2,20 -bpy)2]n (2) Complex 2 was synthesized in a similar manner to 1 by using Zn(NO3)2∙6H2O (0.0893 g, 0.3 mmol) instead of Zn(NO3)2∙6H2O (0.0595 g, 0.2 mmol) as starting material. Colorless blocked crystals suitable for X-ray diffraction analysis were obtained after the reactor was cooled to room temperature with the yield of 0.0732 g, 69.2% (based on ligand). Anal. calcd for C50H30N4O15Zn2: C 56.73, H 2.84, N 5.30. Found: C 56.71, H 2.87, N 5.29. IR/cm1 (KBr): 3403 (s, br), 1724 (m), 1601 (s), 1560 (s), 1392 (s), 1238 (s), 1128 (s), 1024 (m), 767 (m).

CN

COOH

CN

COOH O

O CN

Na2CO3

+ 3 HO

OH

1 NaOH 2 HCl

DMF CN

O

CN CN

O

O

COOH

NC CN

Scheme 1. Synthetic route to the hexadentate ligand H6L.

COOH

O

HOOC COOH

N. Zhao et al. / Solid State Sciences 14 (2012) 317e323

2.2.3. [Cd2(H2L)(2,20 - bpy)2(H2O)2]n∙2nH2O (3) By employing the above-described procedure for preparing 1 with Cd(NO3)2∙4H2O (0.0617 g, 0.2 mmol) instead of Zn(NO3)2∙6H2O (0.0595 g, 0.2 mmol) as starting material, colorless block-shaped crystals suitable for X-ray diffraction analysis were obtained after the reactor was cooled to room temperature with the yield of 0.0582 g, 47.6% (based on ligand). Anal. calcd for C50H38N4O19Cd2: C 49.03, H 3.11, N 4.58. Found: C 49.11, H 3.08, N 4.57. IR/cm1 (KBr): 3432 (m, br), 1733 (m), 1606 (s), 1565 (s), 1444 (s), 1393 (s), 1236 (s), 1129 (m), 1026 (m), 767 (m). 2.3. General measurements 1 H NMR spectra were recorded on a Bruker ultrashield AvanceZ 400 spectrometer (400 MHz) in DMSO-d6 using the residual solvent resonance of DMSO-d6 at 2.50 ppm relative to SiMe4 as internal reference. Elemental analyses were carried out with an Elementary Vario El. The infrared spectroscopy on KBr pellets was performed on a Bruker Tensor 37 spectrophotometer in the region of 4000e400 cm1. Thermogravimetric analysis (TGA) was performed on a METTLER TOLEDO STARe TGA/SDTA 851 analyzer heated from 25  C to 700  C under air. Luminescence spectra for the solid samples were recorded with a Hitaichi F-4500 fluorescence spectrophotometer.

2.4. Single crystal X-ray diffraction determination Crystal data for all the three complexes were collected on a Bruker SMART APEXII CCD diffractometer with graphite monochromatic Mo Ka radiation (l ¼ 0.71073 Å) using the SMART and SAINT programs at 298 K. The structures were solved by the direct method (SHELXS-97) and refined by full-matrix least-squares (SHELXS-97) on F2. Anisotropic thermal parameters were used for the non-hydrogen atoms and isotropic parameters for the hydrogen atoms. Hydrogen atoms were added geometrically and refined using a riding model. Crystallographic data and other pertinent information for all the complexes are summarized in Table 1. CCDC 849040e849042 for complexes 1e3 respectively, contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif.

Table 1 Crystal data and structure refinements of complexes 1e3. Complexes

1

2

3

Formula Fw System Space group a/Å b/Å c/Å a/ b/ g/ V/Å3 Z Dcalcd/g cm3 m/mm1 F(000) Rint I > 2q Rw2 I > 2q Rint all Rw2 all S

C50H36N4O18Zn2 1093.54 triclinic Pı 10.9879(3) 13.3574(3) 16.4733(4) 103.902(2) 94.212(2) 95.150(2) 2326.17(10) 2 1.5799(1) 1.116 1126.0 0.0482 0.1146 0.0653 0.1224 1.046

C50H30N4O15Zn2 1057.56 triclinic Pı 9.9463(4) 11.4097(5) 20.8990(9) 95.096(3) 103.663(4) 102.868(3) 2221.53(16) 2 1.5810(1) 1.160 1076.0 0.0359 0.0819 0.0494 0.0865 1.044

C50H38N4O19Cd2 1223.67 triclinic Pı 10.9990(5) 13.6014(6) 17.0316(8) 85.900(4) 89.532(4) 85.018(4) 2531.8(2) 2 1.6052(1) 0.921 1228.0 0.0505 0.1291 0.0716 0.1418 1.071

319

3. Results and discussion 3.1. Synthesis of the multicarboxylate ligand and complexes 1e3 As shown in Scheme 1, the precursor of the multicarboxylate is ligand 3,30 ,300 -(1,3,5-phenylenetri(oxy))triphthalonitrile prepared easily by a nucleophilic replacing reaction of 3nitropthalonitrile and phloroglucinol in the presence of anhydrous Na2CO3 in DMF solution. The resulting precursor is transformed into the target multicarboxylate ligand through a hydrolyzation reaction of cyanide groups. The semirigid multicarboxylate ligand H6L is separated by filtration and employed in a hydrothermal reaction without further purification. In the present study, complexes 1e3 were prepared from the hydrothermal reaction between ligand H6L and nitrate together with 2,20 -bpy as secondary ligand in different molar ratio. A series of reactions were performed to investigate the effect of pH value (from 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, to 11.0), reaction temperature (including 140, 150, and 160  C), and metaleligand ratio (including 1:2:2, 1:3:2) on the formation of coordination polymers from the ligand. The pH value was revealed to play an important role in the formation of MOFs. Hydrothermal reactions gave compounds with good crystal quality and high yields for both 1e3 only when NaOH with a molar ratio 1:3 to the hexacarboxylate ligand was added to deprotonate the ligand (pH ¼ 6.0) again under suitable temperature. This is also true for the reaction temperature. Under all the above mentioned reaction conditions, good crystals for complexes 1e3 can be obtained only at 150  C. The reactions between the multidentate ligand and Zn(NO3)2 salt with two different stoichiometry were carried out, giving two different complexes, respectively. The different structure between 1 and 2 indicates the effect of metaleligand ratio in tuning the structure of coordination polymer. However, only one Cd(II) complex was obtained according to a series of same experiments, showing organic ligands display different coordination preferences at different metal ions. Further study about the influence of metaleligand ratio on the coordination behavior between H6L and Cd(II) ions is in progress. 3.2. IR spectra In the IR spectra of semirigid multidentate ligands, the absorption band at 1711 cm1 for the H6L ligand is attributed to the asymmetric stretching vibration of uncoordinated carboxylic groups. The presence of the characteristic bands at around 1724e1733 cm1 in the IR spectra of complexes 1e3 attributed to the protonated carboxylic groups indicates that deprotonation of the H6L ligand is incomplete, as shown in Fig. S1 (Supporting information). 3.3. Thermal analysis The thermal behavior for complexes 1e3 was studied to reveal their thermal stability. TGA experiments were performed on pure single crystal sample of complexes 1e3 under air atmosphere with a heating rate of 10  C min1 in the range of 25e700  C. The thermal curves are exhibited in Fig. S2 (Supporting information). Complex 1 displays the weight loss by stage owing to the release of water molecules in the range of 58e135  C (obsd 4.96%, calcd 4.86%). The organic spacers then decompose from 234 to 426  C. In TG curve of complex 2, the weight loss is observed owing to the direct decomposition of organic ligands in the range of 295e521  C. For 3, the TGA curve reveals that the lattice water molecules and coordinated water molecules are lost from 32 to 219  C, obsd 5.89%, calcd 5.88%. The residual composition of this complex is then decomposed in the temperature range of 319e417  C.

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3.4. Crystal structure of complex 1 As shown in Fig. 1A, compound 1 is composed of two kinds of crystallographically independent Zn(II) ions. Zn1 ion locates in a square pyramidal coordination geometry completed by two nitrogen atoms of 2,20 -bpy ligands, two oxygen atoms from two different monodentate carboxylic groups, and one oxygen atom of water molecules. The N1, N2, O7, and O16 atoms comprise the basal plane while the O5 atom occupies the apical position. Zn2 possesses a slightly distorted octahedral coordination geometry completed by two nitrogen atoms of 2,20 -bpy ligand, four oxygen atoms from two carboxylic groups in bidentate chelating mode. The ZneO and ZneN bond lengths are in the range of 1.957(4)e2.380(4) and 2.026(3)e2.123(3) Å, respectively. These data are comparable with those of reported compounds containing OeZneN segments [22,23]. The incompletely deprotonated H2L ligand adopts a cis,cis,cis-typed configuration and acts as a m4-bridge linking four Zn(II) atoms (Scheme 2A), in which two carboxylate groups adopt the monodentate fashion and the other two adopt the bidentate chelating mode. Consequently, the Zn(II) cations are bridged by the H2L anions, generating a one-dimensional (1D) ladder structure with the central aromatic rings of H2L ligands as T-shaped nodes. Two phthalic acid segments from different H2L ligands coordinate to two Zn(II) ions to form a dinuclear unit with a distance of 5.211Å, which acts as the rungs of the ladders. 2,20 -bpy ligands locate above and below the corrugated ladder as dangling lateral arms, as shown in Fig. 1B. Furthermore, individual ladder-like chains stack together in an -ABCABC- motif and further assembled into a 2D supramolecular structure via the pep interaction (centroidecentroid distance amounting to 3.900(3) Å) between the 2,20 -bpy ligands of different chains, as shown in Fig. 1C. As a consequence, the 2,20 bpy ligands act as “clamps” by occupying the void spaces of the

neighboring ladder chains, giving a dense structure without any significant overall porosity. 3.5. Crystal structure of complex 2 Complex 2 was synthesized by altering the amount of Zn(NO3)2∙6H2O, which exhibits a different 1D ribbon chain from complex 1. As shown in Fig. 2A, complex 2 is composed of two kinds of crystallographically independent Zn(II) ions. Zn1 ion exhibits a hexa-coordinated geometry built from two nitrogen atoms, two oxygen atoms from two carboxylic groups in monodentate mode, and two oxygen atoms from one chelating carboxylic group. Zn2 ion locates in a distorted trigonal bipyramidal coordination geometry completed by two nitrogen atoms of 2,20 -bpy ligand, two oxygen atoms from one carboxylic group in a bidentate chelating mode, and one oxygen atom from carboxylic group in monodentate mode. The ZneO and ZneN bond lengths are in the range of 1.919(2)e2.2714(19) and 2.046(2)e2.128(2) Å, respectively. Compared with complex 1, the incompletely deprotonated H2L ligand in a cis,cis,trans-typed configuration acts as a m5-bridge linking five Zn(II) atoms (Scheme 2B), and its five carboxylate groups adopt two independent kinds of coordination modes. Three carboxylate groups coordinate to the Zn centers in a monodentate coordination mode, the remaining two adopt the bidentate chelating mode. Two neighboring crystallographically uniform Zn1 ions are linked by four carboxylic groups of two different H2L ligands with a Zn1-Zn1A distance of 5.822 Å, which similar to complex 1. Two adjacent crystallographically equivalent Zn2 ions are bridged by two carboxylic groups of two phthalic acid segments with a Zn2eZn2A separation of 11.410 Å, and Zn1 is linked to the Zn2 through two carboxylic groups of one phthalic acid with a Zn1-Zn2 separation of 6.254 Å, which different from

Fig. 1. (A) Representation of the coordination environment of Zn(II) in 1. (B) Representation of the ladder structure containing cyclic dinuclear rungs in 1. (C) View of the 2D packing of chains showing three adjacent chains.

N. Zhao et al. / Solid State Sciences 14 (2012) 317e323

321

Scheme 2. The coordination modes of multicarboxylate ligands H6L in the complexes 1e3.

complex 1. As a consequence, the H2L ligands bridge the adjacent metal ions into a complicated ribbon chain along the b axis, as shown in Fig. 2B. The individual ribbon chains are further packed into a 2D supramolecular network via intermolecular pep interactions between coordinated 2,20 -bpy ligands, Fig. 2C. The

faceeface distance between the adjacent 2,20 -bpy groups amount to3.771 Å, which is in the normal range to form pep interaction [24,25]. From the above discussion we can see that changing the amount of the Zn(NO3)2 salt can alter the coordination behavior between H6L and Zn(II) ions, both the coordination mode of H6L and the coordination geometry of Zn(II) ions. 3.6. Crystal structure of complex 3

Fig. 2. (A) Representation of the coordination environment of Zn(II) in 2. (B) 1D ribbon chain along the b axis. (C) The 2D supramolecular structures of 2 via intermolecular interactions.

In complex 3, a similar ladder chain as in 1 containing one kind of H2L ligands and two types of Cd(II) ions can be found, as shown in Figs. 3A and 4. Cd1 ion is hexa-coordinated by two nitrogen atoms of 2,20 -bpy ligand, two oxygen atoms from one carboxylic groups in a bidentate chelating mode, one oxygen atom from carboxylic group in a monodentate mode, and one oxygen atom of water molecule. For Cd2 ion, the coordination environment is composed of two nitrogen atoms, four oxygen atoms from two carboxylic groups in a bidentate chelating mode, and one oxygen atom of water molecule. The CdeO and CdeN bond lengths are in the range of 2.200(3)e2.645(3) and 2.293(5)e2.363(5) Å, respectively. These data are comparable with those of reported compounds containing OeCdeN segments [26]. In 3, H2L ligand is incompletely deprotonated and shows a cis,cis,cis-typed configuration with m4-bridging mode (Scheme 2C). As displayed in Fig. 3B, each H2L ligand is connected to four Cd(II) ions through its three chelating carboxylate moieties, as well as one monodentate carboxylate group, which is different from complex 1. Similar to complex 1, the Cd(II) cations are bridged by the H2L ligands, showing a 1D infinite ladder-like chain arranged in the b axis with the central aromatic rings of the H2L ligands as T-shaped nodes and the cyclic dinuclear Cd(II) units playing the role of rungs. Individual ladder-like chains are further arranged in the same manner as in complex 1, with the dangling lateral arms (2,20 -bpy ligands) in each chain deeply penetrating into the rings of two adjacent chains, forming a 2D supramolecular structure via the pep interaction (centroidecentroid separation amounting to 3.705(5) Å) between the 2,20 -bpy ligands of different chains, Fig. 3C.

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typical intraligand pep* or pen electronic transition [28,29]. Excitation of the solid samples at lex ¼ 300 nm produces luminescence peaks with a maximum at 371 nm for 1, 373 nm for 2, and 372 nm for 3, respectively. The three emission bands can be tentatively attributed to the intraligand pep* or pen transition originating from different chromophores in the crystal structures [30e32]. Complexes 1e3 exhibit slightly blue shifted emission bands in comparison with the free ligand H6L, which is considered to be a result of the change of conformation of ligand according to Perkovic’s hypothesis [33,34]. 4. Conclusion In summary, a new triangular semirigid multicarboxylate ligand has been utilized for the first time to construct Zn(II) and Cd(II) coordination polymers with the help of 2,20 -bpy. The present results suggest that the triangular semirigid ligand is a promising candidate for the construction of novel MOFs with interesting structure and functionalities. Acknowledgment This project is supported by National Nature Science Foundation of China (No. 21101013), the Foundation of University of Science and Technology Beijing (No. 00009805), and the Fundamental Research Funds for the Central Universities (No. FRF-BR-10-002A). Appendix. Supplementary data

Fig. 3. (A) Representation of the coordination environment of Cd(II) in 3. (B) A infinite 1D molecular structure of 3. (C) 2D supramolecular network.

Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.solidstatesciences.2011.12.014. References

3.7. Luminescent properties Previous studies have shown that coordination polymers containing cadmium and zinc exhibit photoluminescent properties [27]. Therefore, the emission spectra of complexes 1e3, together with that of the ligand H6L, were measured in the solid state at room temperature. The emission band for the metal free ligand H6L was observed at 381 nm (lex ¼ 300 nm), which is assigned to the

Fig. 4. Emission spectra of 1e3, and free ligand H6L in the solid state at room temperature.

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