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Novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-cyclohexanedicarboxylate and various bipyridyl ligands
Journal of Molecular Structure 994 (2011) 335–342
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-cyclohexanedicarboxylate and various bipyridyl ligands Eun Young Kim a, Hyun Min Park a, Ha-Yeong Kim b, Jin Hoon Kim a, Min Young Hyun a, Ju Hoon Lee a, Cheal Kim a,⇑, Sung-Jin Kim b,⇑, Youngmee Kim b a b
Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 February 2011 Received in revised form 17 March 2011 Accepted 18 March 2011 Available online 25 March 2011 Keywords: CdII complexes Bipyridyl ligands Photoluminescence 1,2-Cyclohexanedicarboxylate Coordination polymers
a b s t r a c t Four CdII-(e,a-cis-1,2-chdc) complexes, [Cd(H2O)(1,2-chdc)(2,20 -bpy)] 1, [Cd(1,2-chdc)(bpe)]n 2, [Cd2(1,2chdc)(4,40 -bpy)2]n 3A, and [Cd(H2O)(1,2-chdc)(4,40 -bpy)2]n3n(H2O) 3B (1,2-chdc = 1,2-cyclohexanedicarboxylate), with different assistant ligands (2,20 -bipyridine (2,20 -bpy), 1,2-bis(4-pyridyl)ethene (bpe), and 4,40 -bipyridine (4,40 -bpy)) have been synthesized and their structures were determined. Depending on the assistant ligands, the structures and dimensionalities of CdII-(e,a-cis-1,2-chdc) complexes have been varied. Two carboxylates in e,a-cis-1,2-chdc coordinate to CdII ions in chelating (g1:g1), bridging (g1:g1:l2), and chelating/bridging (g2:g1:l2) modes. Photoluminescence study of the compounds 1 and 2 showed that emission spectrum of compound 1 was observed at 348 nm, while relatively weak luminescence was displayed at 516 nm for 2. The thermal stabilities of these complexes were also examined. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Carboxylate-including ligands have provided a variety of metal– organic frameworks (MOFs) with several metal ions [1–7]. Their structures with various dimensionalities can control the coordination modes and the pore sizes. Recently, coordination polymers with flexible multicarboxylates, such as 1,4-cyclohexanedicarboxylate (1,4-chdc) [8–22], 1,3-cyclohexanedicarboxylate (1,3-chdc) [23], 1,2,3,4,5,6-cyclohexanehexacarboxylate (chhc) [24–27], and cyclohexane-1,2,4,5-tetracarboxylate (cht) [28], which can control conformation and configuration conversion in coordination networks, have been synthesized and intensively studied [29]. Compare to metal-(1,4-chdc) complexes, few metal complexes with 1,2-cyclohexanedicarboxylate (1,2-chdc) have been reported in the literature [30–35]. While there are a few reports that different assistant ligands can have profound effects on coordination geometry [36,6,37–42], however, such an effect was only once reported in the system of zinc nitrate with 1,2-chdc that showed six novel ZnII coordination polymers (0-D, 1-D, 2-D to 3-D) constructed from 1,2-chdc and various bipyridyl ligands [43]. Significantly, the use of assistant ligands influenced coordination modes of carboxylates: two carboxylates coordinate to ZnII ions in chelating, bridging, and ⇑ Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim), tel.: +82 2 3277 3589; fax: +82 2 3277 3419 (S.-J. Kim). E-mail addresses: [email protected] (C. Kim), [email protected] (S.-J. Kim). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.03.046
monodentate coordination modes while the chelating/bridging mode was not observed in ZnII-(1,2-chdc) system with the assistant ligands. These results suggested that further study is necessary to see which factor (the assistant ligand vs the metal ion) influences the whole structure including coordination modes of carboxylates. For a further systematic investigation of the relationship between the metal ions and the nature of the different assistant ligands in the system with M-(1,2-chdc) unit, therefore, we have employed CdII-(1,2-chdc) unit with three different assistant ligands, 2,20 -bipyridine (2,20 -bpy), 4,40 -bipyridine (4,40 -bpy), 1,2bis(4-pyridyl)ethene (bpe). Depending on the assistant ligands, the dimensionality of CdII-(1,2-chdc) complexes has also been varied as shown in the ZnII-(1,2-chdc) system. We report here the syntheses, structures, thermal stabilities, and photoluminescence of four novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-chdc and three different bipyridyl ligands. 2. Experimental 2.1. Materials 2,20 -Bipyridine, cis-1,2-cyclohexanedicarboxylic acid, 1,2-bis(4pyridyl)ethene, 4,40 -bipyridine, acetonitrile, acetone, methanol, para-substituted phenyl acetate, para-substituted phenyl benzoate, methyl acetate, methyl benzoate, ammonium hydroxide,
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and Cd(NO3)26H2O were purchased from Aldrich and were used as received. 2.2. Instrumentation Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using a vario MACRO (Elemental Analysensysteme, Germany) in the Laboratory Center of Seoul National University of Science and Technology, Korea. IR spectra were measured on a BIO RAD FTS 135 spectrometer as KBr pellets. Thermogravimetric analyses (TGA) were carried out on a Shimadzu TA50 integration thermal analyzer. The emission/excitation spectra were recorded on a Perkin Elmer LS45 fluorescence spectrometer. 2.3. 1-D chain of [Cd(H2O)(1,2-chdc)(2,20 -bpy)]n (1) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetone solution of 2,20 -bipyridine (25.24 mg, 0.16 mmol). Suitable crystals of compound 1 for X-ray analysis were obtained in 2 weeks. The yields were 10.98 mg (30.1%). Purity of bulk sample of 1 was checked by powder XRD (see Fig. S1 in Supporting information). Anal. Calcd. for C18H20CdN2O5 (456.76), 1: C, 47.33; H, 4.42; N, 6.13. Found: C, 47.57; H, 4.36; N, 5.81%. IR (KBr): m(cm1) = 3417(brs), 3066(m), 2973(m), 2900(m), 2850(m), 1680(w), 1580(s), 1536(s), 1477(m), 1440(m), 1407(s), 1291(m), 1157(m), 1018(m), 928(w), 843(w), 780(s), 737(w), 652(w), 581(w), 415(w).
was solved and refined using SHEXTL V6.12 [44]. All hydrogen atoms were placed in the calculated positions. The crystallographic data for compounds 1–3 are listed in Table 1. Structural information was deposited at the Cambridge Crystallographic Data Center (CCDC Reference Numbers 790089, 790090, 790091, and 812938 for 1, 2, 3A, and 3B respectively).
3. Results and discussion 3.1. Syntheses and general characterization Complexes 1–3 were obtained as colorless crystalline materials by the reaction of 1,2-H2chdc and cadmium(II) nitrate with various bipyridyls in aqueous medium in a molar ratio of 1:1:2 except for 2 with the ratio of 2:1:2, respectively. In addition, they are air stable, and can retain their crystalline integrity at ambient conditions for a considerable length of time. It should be noted that 1,2-chdcH2 used in the experiments is cis-conformer, and the 1,2-chdc dianion in all four compounds possesses only e,a-cis conformation. The infrared spectra of 1–3 were fully consistent with their formulations. Asymmetric and symmetric C@O stretching modes of the ligated benzoate moieties were evidenced by very strong, slightly broadened bands at 1600 cm1 and 1400 cm1 [45–47]. The absence of any bands in the area of 1710 cm1 indicates full deprotonation of all carboxylate groups in 1–3 [45–47], which is consistent with the results of the X-ray analysis. Scheme 1 shows all four structures constructed by CdII-(e,a-cis-1,2-chdc) and different assistant bipyridyl ligands.
2.4. 2-D sheet of [Cd(1,2-chdc)(bpe)]n (2) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetonitrile solution of 1,2-bis(4-pyridyl)ethylene (30.06 mg, 0.16 mmol). Suitable crystals of compound 2 for X-ray analysis were obtained in 3 weeks. The yields were 26.24 mg (70.6%). Purity of bulk sample of 2 was checked by powder XRD (see Fig. S2 in Supporting information). Anal. Calcd. for C20H20CdN2O4 (464.78) 2: C, 51.68; H, 4.35; N, 6.03. Found: C, 51.54; H, 4.12; N, 6.47%. IR (KBr): m(cm1) = 3058(m), 2927(m), 1607(s), 1548(s), 1427(s), 1342(m), 1308(m), 1014(m), 967(m), 892(w), 840(s), 827(s), 764(m), 623(w), 551(s). 2.5. 3-D of [Cd2(NO3)2(1,2-chdc)(4,40 -bpy)2]n (3A) and 1-D of [[Cd(H2 O)(1,2-chdc)(4,40 -bpy)2]3(H2O)]n (3B) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetone solution of 4,40 -dipyridine (25.24 mg, 0.16 mmol). Two kinds of crystals 3A (small block, 0.08 0.08 0.05) and 3B (big block, 0.20 0.20 0.08) for X-ray analysis were obtained in 2 weeks. IR (KBr) for the mixture of 3A and 3B: m(cm1) = 3453(brs), 3243(brs), 2970(w), 2923(s), 2839(m), 1664(s), 1599(w), 1558(s), 1446(w), 1400(s), 1310(w), 1258(w), 1218(s), 1040(m), 1010(m), 990(w), 930(w), 894(w), 812(s), 666(w), 610(s), 505(s). 2.6. X-ray crystallography The X-ray diffraction data for all four compounds were collected on a Bruker SMART APX diffractometer equipped with a monochromater in the Mo Ka (k = 0.71073 Å) incident beam. Each crystal was mounted on a glass fiber. The CCD data were integrated and scaled using the Bruker-SAINT software package, and the structure
3.2. Structure description of 1, 1-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, a water ligand, and a 2,20 -bpy ligand, and symmetry operations (x + 3/2, y + 1/2, z + 1/4) and (x + 3/2, y 1/2, z + 1/4) produce a onedimensional chain 1 (Fig. 1). The CdII ion is seven-coordinated with four O atoms from two chelating 1,2-chdc, two N atoms from a bidentate 2,20 -bpy, and an O atom from a water. CdII ions are bridged by e,a-cis-1,2-chdc ligands to form a one-dimensional chain (Fig. 1). The coordination mode for two carboxylates in 1,2chdc is the asymmetric chelating (g1:g1) [30–35,48]. The intramolecular hydrogen bond between water hydrogen atom and next carboxylate oxygen atom in a chain makes the one-dimensional chain structure stronger (green dotted lines in Fig. 1). The CdAO1,2-chdc distances of asymmetric chelating carboxylates are 2.259(4), 2.283(4) Å and 2.537(5), 2.620(4) Å. The CdAOwater distance is 2.518(5) Å, and the CdAN bond distances are 2.322(4) and 2.372(4) Å (Table S1). The Cd Cd distance is 6.197(1) Å. 3.3. Structure description of 2, 2-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc and a bpe ligand, and symmetry operations (x + 1, y + 1, z), (x + 2, y + 1, z), (x, y 1, z + 1), and (x, y + 1, z 1) produce a twodimensional sheet 2 (Fig. 2). Two carboxylates of e,a-cis-1,2-chdc ligands bridge CdII ions to form one-dimensional chains, and bpe ligands bridge those chains to form a two-dimensional sheet (Fig. 2). Two carboxylates in 1,2-chdc show two different coordination modes: the chelating (g1:g1) and the bridging (g1:g1:l2). The coordination geometry of CdII ion is distorted octahedral constructed by two O atoms from a chelating cis-1,2-chdc, two O atoms from two bridging cis-1,2-chdc, and two N atoms from two bpe ligands. The CdAO1,2-chdc bond distances range from 2.2394(18) to 2.4455(19) Å, and the CdAN bond distances are 2.342(2) and 2.363(2) Å (Table S1). The Cd Cd distances in a
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E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342 Table 1 Crystallographic data for compounds 1–3.
Empirical formula Formula weight Temperature (K) Wavelength (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z Density (calc.) (Mg/m3) Absorption coeff. (mm1) Crystal size (mm3) Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Largest diff. peak and hole (e Å3)
1
2
3A
3B
C18H20CdN2O5 456.76 293(2) 0.71073 P41212 10.3296(5) 10.3296(5) 90.00 90.00 90.00 91.366(2) 3466.8(4) 8 1.750 1.293 0.25 0.10 0.10 19,284 4169 [R(int) = 0.0812] 4169/2/242 0.944 R1 = 0.0444, wR2 = 0.1136 R1 = 0.0567, wR2 = 0.1217 0.721 and 0.821
C20H20CdN2O4 464.78 293(2) 0.71073 P1 7.7115(6) 9.7515(7) 12.6997(10) 76.4650(10) 76.8020(10) 88.1130(10) 903.74(12) 2 1.708 1.237 0.30 0.10 0.10 5046 3469 [R(int) = 0.0307] 3469/0/244 1.015 R1 = 0.0267, wR2 = 0.0668 R1 = 0.0290, wR2 = 0.0674 0.430 and 0.891
C14H13CdN3O5 415.67 170(2) 0.71073 C2/c 20.835(4) 10.177(2) 16.014(3) 90.00 106.12(3) 90.00 3262.1(11) 8 1.693 1.366 0.08 0.08 0.05 8972 3212 [R(int) = 0.0630] 3212/5/201 0.940 R1 = 0.0379, wR2 = 0.0890 R1 = 0.0569, wR2 = 0.0919 1.808 and 0.833
C28H32CdN4O8 664.98 293(2) 0.71073 C2/c 26.740(4) 10.4638(15) 21.003(3) 90.00 97.270(2) 90.00 5829.4(15) 8 1.515 0.804 0.20 0.20 0.08 15,785 5705 [R(int) = 0.0827] 5705/6/388 0.877 R1 = 0.0318, wR2 = 0.0738 R1 = 0.0489, wR2 = 0.0770 0.478 and 0.588
Scheme 1. Structures from CdII-(e,a-cis-1,2-chdc) with assistant bipyridyl ligands.
one-dimensional chain are 3.930(2) and 5.737(3), and the Cd Cd distance between chains is 14.086(9) Å. 3.4. Structure description of 3A, 3-D Asymmetric unit contains a CdII ion, half of e,a-cis-1,2-chdc, a 4,4 -bpy ligand, and a nitrate, and symmetry operations (x 1/2, 0
y 1/2, z), (x, y, z + 2), (x + 1/2, y + 1/2, z), and (x, y, z + 3/ 2) produce a three-dimensional structure 3A (Fig. 3a). The cyclohexyl group is disordered as shown in Fig. 3b. Two Cd(NO3)+ are bridged by two e,a-cis-1,2-chdc to form dinuclear units, and these dinuclear units are connected by 4,40 -bpy ligands to form a threedimensional structure 3A (Fig. 3). Assuming the cadmium dimers act as nodes, the complete Schläfli symbol of the 4-connected unin-
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2.381(3) Å, and the CdAOnitrate distances are 2.420(4) and 2.455(4) Å. The CdAN bond distances are 2.268(4) and 2.280(4) Å (Table S1). The Cd Cd distance in a dinuclear unit is 3.70(5) Å.
3.5. Structure description of 3B, 1-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, two 4,4 -bpy ligands, a water ligand, and three water solvent molecules, and symmetry operations (x + 1/2, y + 1/2, z + 1/2) and (x + 1/ 2, y 1/2, z + 1/2) produce a one-dimensional structure 3B (Fig. 4a). The e,a-cis-1,2-chdc ligands bridge CdII to form a onedimensional structure, and the coordination mode for carboxylates in 1,2-chdc is the chelating (g1:g1). The 4,40 -bpy ligands act as a monodentate dangling ligand in 3B while they do as a bridging ligand in 3A. The CdII is seven-coordinated by four O atoms from two chelating cis-1,2-chdc ligands, two N atoms from two 4,40 -bpy ligands, and an O atom from a water ligand to form a distorted pentagonal bipyramid. Inter- and intra-molecular OAH O hydrogen bonding interactions provide a two-dimensional sheet (Fig. 4b, see Table S2). The CdAO1,2-chdc bond distances are 2.37585(18) and 2.4626(17) Å, and the CdAOwater distance is 2.330(2) Å. The CdAN bond distances are 2.361(2) and 2.389(2) Å (Table S1). The Cd Cd distance is 6.756(3) Å. 0
Fig. 1. Structure of 1-D chain of [Cd(H2O)(1,2-chdc)(2,20 -bpy)] 1. All hydrogen atoms were omitted for clarity. Intra-molecular hydrogen bonds are shown in green lines (OwaterAH Ocarboxylate 2.134 Å (141.54°)). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
odal net was calculated as 658 network topology based on the TOPOS analysis. The coordination mode of carboxylates is the chelating/bridging (g2:g1:l2). The CdII ion is seven-coordinated by two O atoms from one e,a-cis-1,2-chdc, an O atom from the other e,a-cis1,2-chdc, two O atoms from a nitrate, and two N atoms from two 4,40 -bpy to form a distorted pentagonal bipyramid in which five O atoms are in the equatorial positions and two N atoms are in axial positions. The CdAO1,2-chdc bond distances are 2.358(3) and
Fig. 2. Structure of 2-D sheet of [Cd(1,2-chdc)(bpe)]n 2. All hydrogen atoms were omitted for clarity.
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Fig. 3. (a) 3-D structure of [Cd2(NO3)2(1,2-chdc)(4,40 -bpy)2]n 3A. (b) The dinuclear unit of 3A with disordered 1,2-chdc in green color. All hydrogen atoms were omitted for clarity.
Like ZnII-(a,e-cis-1,2-chdc) system, we have also systematically investigated CdII complexes containing particularly 1,2-chdc ligand with different assistant bipyridyl ligands, 2,20 -bpy, bpe, and 4,40 bpy. According to the change of assistant bipyridyl ligands, CdII(e,a-cis-1,2-chdc) provides 1-D, 2-D and 3-D compounds as shown in Scheme 1. Only one conformer (a,e-cis) has also been observed in 1,2-chdc ligands of all four CdII compounds as shown in ZnII compounds. The observed coordination modes of two carboxylates in CdII-(a,e-cis-1,2-chdc) complexes are shown in Scheme 2. For 1, two carboxylates coordinate to CdII ions, and both carboxylates are in chelating (g1:g1) modes. For 2, two carboxylates also coordinate to CdII ions: one carboxylate is in the chelating (g1:g1) mode and the other one is in the bridging (g1:g1:l2) mode. For 3A, carboxylates show the chelating/bridging (g2:g1:l2) modes,
and for 3B, they show the chelating (g1:g1) modes. From the previous work of ZnII-(a,e-cis-1,2-chdc), it was noted that carboxylates of a,e-cis-1,2-chdc with chelating, bridging, and monodentate coordination modes have been observed in all six compounds, but for this CdII system, their chelating/bridging (g2:g1:l2) mode has also been observed as well as chelating (g1:g1) and bridging (g1:g1:l2). The chelating/bridging (g2:g1:l2) mode of carboxylates has been observed in recent literatures [25–31], and M-(1,2chdc) system without assistant ligands can provide favorably metal–oxygen–metal networks [25–35]. In the previous work of ZnII-(1,2-chdc) system, it was suggested that construction of metal–oxygen–metal linkages might be prevented if assistant ligands were employed to M-(1,2-chdc) system, and that they can provide various structures according to the change of the assistant ligands
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Fig. 4. (a) 1-D structure of [[Cd(H2O)(1,2-chdc)(4,40 -bpy)2]3(H2O)]n 3B. All hydrogen atoms were omitted for clarity. (b) Two-dimensional sheet through hydrogen bonds in 3B. All pyridyl and cyclohexyl hydrogen atoms were omitted for clarity. The hydrogen bonds are shown in the green dotted lines. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Scheme 2. Coordination modes in CdII-(a,e-cis-1,2-chdc) complexes.
[43]. Also, it was showed that the use of assistant ligands may influence coordination modes of carboxylates in the previous ZnII-(1,2chdc) system. Carboxylates in chelating/bridging (g2:g1:l2) modes provide dinuclear Cd2 units which could not be observed in the ZnII-(1,2-chdc) system. From these results, it is noted that the metal ion as well as the assistant ligand can influence both the whole structure and coordination modes of carboxylates.
3.6. Photoluminescence property We have examined the emission spectra of CdII complexes 1 and 2, since coordination polymers containing cadmium and zinc exhibited excellent photoluminescent properties [49,50]. The emission spectra of CdII complexes 1 and 2, together with those of the ligands 2,20 -bpy, bpe, and cis-1,2-chdcH2, were measured in the solid state at room temperature (see Fig. 5). Emission of
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1000
Intensity
800
600
400
200
0 280
330
380
430
480
530
580
630
Wavelength (nm) Fig. 5. Emission spectra of complexes 1, 2, and ligands (2,20 -bpy, bpe, and cis-1,2-chdc) at room temperature.
compound 1 was observed at 348 nm (kex = 267 nm), while relatively weak luminescence was observed at 516 nm (kex = 441 nm) for 2 under the same experimental conditions. Such emission of complex 2 can be tentatively assigned to the intraligand transition of bpe ligand, since the similar emissions were observed for the ligand (511 nm for bpe (kex = 413 nm)) [51–53]. The emission band of complex 1 is blue-shifted compared to the corresponding ligands (390 nm for 2,20 -bpy (kex = 340 nm) or 403 nm for cis-1,2chdc (kex = 263 nm)). In addition, it is noteworthy that compound 1 showed an intense emission compared with that of compound 2 at room temperature, which may be attributed to effective increase of the rigidity of the complex and reduces the loss of energy by radiationless decay. This suggests that 1 may be a good candidate for a potential hybrid inorganic–organic photoactive material [54]. 3.7. Thermogravimetric analysis To study the thermal stabilities of these complexes, thermal gravimetric analysis (TGA) of compounds 1 and 2 was performed (see Supporting information: Figs. S3 and S4). Compound 1 first lost its coordinated one OH between 131 and 237 °C; the observed weight loss of 3.5% was consistent with that calculated (3.9%). After this, the 1-D framework was stable up to 237 °C and then began to decompose upon further heating. The second gradual weight loss of 31.1% in the temperature range of 237–296 °C corresponds to the loss of a coordinated 2,20 -bpy ligand (calcd. 34.2%). The third weight loss of 40.8% from 336 to 434 °C may be attributed to the loss of one coordinated cis-1,2-chdc ligand (calcd. 37.3%). The TGA curve of compound 2 showed that it underwent a rapid and significant weight loss of 38.0% in the temperature range of 225–378 °C, which corresponds to the loss of one bpe ligand (calcd. 39.2%). The second gradual weight loss of 33.2% from 378 to 425 °C may be attributed to the loss of coordinated cis-1,2-chdc ligand (calcd 33.2%). The residue started to decompose completely to CdO upon further heating. 4. Conclusion Four CdII-(a,e-cis-1,2-chdc) complexes with different assistant ligands (2,20 -bpy, bpe, and 4,40 -bpy) have been synthesized and their structures were determined. Depending on the assistant ligands, the dimensionality of 1,2-chdc complexes has been varied. In 1,2-chdc, only (e,a-cis) conformer has been observed in all cases,
and two carboxylates coordinate to CdII ions in chelating (g1:g1), bridging (g1:g1:l2), and chelating/bridging (g2:g1:l2) modes. This study indicates that the structures and dimensionalities of CdII-(a,e-cis-1,2-chdc) compounds could be controlled by changing of assistant bipyridyl ligands. Moreover, the present CdII and the previous ZnII systems suggest that both assistant ligands and metal ions could influence the whole structures and coordination modes of carboxylates. Photoluminescence study suggested that the photoluminescence property of the CdII complexes could be tuned by the change of the assistant ligands, and that they may be good candidates for luminescent materials. Acknowledgements Financial support from the Korean Science & Engineering Foundation (R01-2008-000-20704-0 and 2009-0074066), the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0082832), and the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Womans University (Grant R11-2005-008-00000-0) is gratefully acknowledged. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2011.03.046. References [1] S. Noro, S. Kitagawa, M. Kondo, K. Seki, Angew. Chem., Int. Ed. 39 (2000) 2081– 2084. [2] Z.L. Huang, M. Drillon, N. Masciocchi, A. Sironi, J.T. Zao, P. Rabu, P. Panissod, Chem. Mater. 12 (2000) 2805–2812. [3] L. Pan, N. Ching, X. Huang, J. Li, Inorg. Chem. 39 (2000) 5333–5340. [4] L. Pan, B.S. Finkel, X. Huang, J. Li, Chem. Commun. (2001) 105–106. [5] P.S. Mukherjee, N. Das, Y.K. Kryshenko, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 126 (2004) 2464–2473. [6] N.L. Rosi, J. Kim, M. Eddaoudi, B. Chen, M. O’Keeffe, O.M. Yaghi, J. Am. Chem. Soc. 127 (2005) 1504–1518. [7] Z. Wang, G. Chen, K. Ding, Chem. Rev. 109 (2009) 322–359. [8] W.H. Bi, R. Cao, D.F. Sun, D.Q. Yuan, X. Li, Y.Q. Wang, X.J. Li, M.C. Hong, Chem. Commun. (2004) 2104–2105. [9] M. Yu, L. Xie, S. Liu, C. Wang, H. Cheng, Y. Ren, Z. Su, Inorg. Chim. Acta 360 (2007) 3108–3112. [10] J. Yang, J.-F. Ma, Y.-Y. Liu, J.-C. Ma, S.R. Batten, Cryst. Growth Des. 9 (2009) 1894–1911.
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Novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-cyclohexanedicarboxylate and various bipyridyl ligands Eun Young Kim a, Hyun Min Park a, Ha-Yeong Kim b, Jin Hoon Kim a, Min Young Hyun a, Ju Hoon Lee a, Cheal Kim a,⇑, Sung-Jin Kim b,⇑, Youngmee Kim b a b
Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 February 2011 Received in revised form 17 March 2011 Accepted 18 March 2011 Available online 25 March 2011 Keywords: CdII complexes Bipyridyl ligands Photoluminescence 1,2-Cyclohexanedicarboxylate Coordination polymers
a b s t r a c t Four CdII-(e,a-cis-1,2-chdc) complexes, [Cd(H2O)(1,2-chdc)(2,20 -bpy)] 1, [Cd(1,2-chdc)(bpe)]n 2, [Cd2(1,2chdc)(4,40 -bpy)2]n 3A, and [Cd(H2O)(1,2-chdc)(4,40 -bpy)2]n3n(H2O) 3B (1,2-chdc = 1,2-cyclohexanedicarboxylate), with different assistant ligands (2,20 -bipyridine (2,20 -bpy), 1,2-bis(4-pyridyl)ethene (bpe), and 4,40 -bipyridine (4,40 -bpy)) have been synthesized and their structures were determined. Depending on the assistant ligands, the structures and dimensionalities of CdII-(e,a-cis-1,2-chdc) complexes have been varied. Two carboxylates in e,a-cis-1,2-chdc coordinate to CdII ions in chelating (g1:g1), bridging (g1:g1:l2), and chelating/bridging (g2:g1:l2) modes. Photoluminescence study of the compounds 1 and 2 showed that emission spectrum of compound 1 was observed at 348 nm, while relatively weak luminescence was displayed at 516 nm for 2. The thermal stabilities of these complexes were also examined. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Carboxylate-including ligands have provided a variety of metal– organic frameworks (MOFs) with several metal ions [1–7]. Their structures with various dimensionalities can control the coordination modes and the pore sizes. Recently, coordination polymers with flexible multicarboxylates, such as 1,4-cyclohexanedicarboxylate (1,4-chdc) [8–22], 1,3-cyclohexanedicarboxylate (1,3-chdc) [23], 1,2,3,4,5,6-cyclohexanehexacarboxylate (chhc) [24–27], and cyclohexane-1,2,4,5-tetracarboxylate (cht) [28], which can control conformation and configuration conversion in coordination networks, have been synthesized and intensively studied [29]. Compare to metal-(1,4-chdc) complexes, few metal complexes with 1,2-cyclohexanedicarboxylate (1,2-chdc) have been reported in the literature [30–35]. While there are a few reports that different assistant ligands can have profound effects on coordination geometry [36,6,37–42], however, such an effect was only once reported in the system of zinc nitrate with 1,2-chdc that showed six novel ZnII coordination polymers (0-D, 1-D, 2-D to 3-D) constructed from 1,2-chdc and various bipyridyl ligands [43]. Significantly, the use of assistant ligands influenced coordination modes of carboxylates: two carboxylates coordinate to ZnII ions in chelating, bridging, and ⇑ Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim), tel.: +82 2 3277 3589; fax: +82 2 3277 3419 (S.-J. Kim). E-mail addresses: [email protected] (C. Kim), [email protected] (S.-J. Kim). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.03.046
monodentate coordination modes while the chelating/bridging mode was not observed in ZnII-(1,2-chdc) system with the assistant ligands. These results suggested that further study is necessary to see which factor (the assistant ligand vs the metal ion) influences the whole structure including coordination modes of carboxylates. For a further systematic investigation of the relationship between the metal ions and the nature of the different assistant ligands in the system with M-(1,2-chdc) unit, therefore, we have employed CdII-(1,2-chdc) unit with three different assistant ligands, 2,20 -bipyridine (2,20 -bpy), 4,40 -bipyridine (4,40 -bpy), 1,2bis(4-pyridyl)ethene (bpe). Depending on the assistant ligands, the dimensionality of CdII-(1,2-chdc) complexes has also been varied as shown in the ZnII-(1,2-chdc) system. We report here the syntheses, structures, thermal stabilities, and photoluminescence of four novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-chdc and three different bipyridyl ligands. 2. Experimental 2.1. Materials 2,20 -Bipyridine, cis-1,2-cyclohexanedicarboxylic acid, 1,2-bis(4pyridyl)ethene, 4,40 -bipyridine, acetonitrile, acetone, methanol, para-substituted phenyl acetate, para-substituted phenyl benzoate, methyl acetate, methyl benzoate, ammonium hydroxide,
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and Cd(NO3)26H2O were purchased from Aldrich and were used as received. 2.2. Instrumentation Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using a vario MACRO (Elemental Analysensysteme, Germany) in the Laboratory Center of Seoul National University of Science and Technology, Korea. IR spectra were measured on a BIO RAD FTS 135 spectrometer as KBr pellets. Thermogravimetric analyses (TGA) were carried out on a Shimadzu TA50 integration thermal analyzer. The emission/excitation spectra were recorded on a Perkin Elmer LS45 fluorescence spectrometer. 2.3. 1-D chain of [Cd(H2O)(1,2-chdc)(2,20 -bpy)]n (1) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetone solution of 2,20 -bipyridine (25.24 mg, 0.16 mmol). Suitable crystals of compound 1 for X-ray analysis were obtained in 2 weeks. The yields were 10.98 mg (30.1%). Purity of bulk sample of 1 was checked by powder XRD (see Fig. S1 in Supporting information). Anal. Calcd. for C18H20CdN2O5 (456.76), 1: C, 47.33; H, 4.42; N, 6.13. Found: C, 47.57; H, 4.36; N, 5.81%. IR (KBr): m(cm1) = 3417(brs), 3066(m), 2973(m), 2900(m), 2850(m), 1680(w), 1580(s), 1536(s), 1477(m), 1440(m), 1407(s), 1291(m), 1157(m), 1018(m), 928(w), 843(w), 780(s), 737(w), 652(w), 581(w), 415(w).
was solved and refined using SHEXTL V6.12 [44]. All hydrogen atoms were placed in the calculated positions. The crystallographic data for compounds 1–3 are listed in Table 1. Structural information was deposited at the Cambridge Crystallographic Data Center (CCDC Reference Numbers 790089, 790090, 790091, and 812938 for 1, 2, 3A, and 3B respectively).
3. Results and discussion 3.1. Syntheses and general characterization Complexes 1–3 were obtained as colorless crystalline materials by the reaction of 1,2-H2chdc and cadmium(II) nitrate with various bipyridyls in aqueous medium in a molar ratio of 1:1:2 except for 2 with the ratio of 2:1:2, respectively. In addition, they are air stable, and can retain their crystalline integrity at ambient conditions for a considerable length of time. It should be noted that 1,2-chdcH2 used in the experiments is cis-conformer, and the 1,2-chdc dianion in all four compounds possesses only e,a-cis conformation. The infrared spectra of 1–3 were fully consistent with their formulations. Asymmetric and symmetric C@O stretching modes of the ligated benzoate moieties were evidenced by very strong, slightly broadened bands at 1600 cm1 and 1400 cm1 [45–47]. The absence of any bands in the area of 1710 cm1 indicates full deprotonation of all carboxylate groups in 1–3 [45–47], which is consistent with the results of the X-ray analysis. Scheme 1 shows all four structures constructed by CdII-(e,a-cis-1,2-chdc) and different assistant bipyridyl ligands.
2.4. 2-D sheet of [Cd(1,2-chdc)(bpe)]n (2) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetonitrile solution of 1,2-bis(4-pyridyl)ethylene (30.06 mg, 0.16 mmol). Suitable crystals of compound 2 for X-ray analysis were obtained in 3 weeks. The yields were 26.24 mg (70.6%). Purity of bulk sample of 2 was checked by powder XRD (see Fig. S2 in Supporting information). Anal. Calcd. for C20H20CdN2O4 (464.78) 2: C, 51.68; H, 4.35; N, 6.03. Found: C, 51.54; H, 4.12; N, 6.47%. IR (KBr): m(cm1) = 3058(m), 2927(m), 1607(s), 1548(s), 1427(s), 1342(m), 1308(m), 1014(m), 967(m), 892(w), 840(s), 827(s), 764(m), 623(w), 551(s). 2.5. 3-D of [Cd2(NO3)2(1,2-chdc)(4,40 -bpy)2]n (3A) and 1-D of [[Cd(H2 O)(1,2-chdc)(4,40 -bpy)2]3(H2O)]n (3B) 14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid, 10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of Cd(NO3)26H2O were dissolved in 4 mL H2O and carefully layered by 4 mL acetone solution of 4,40 -dipyridine (25.24 mg, 0.16 mmol). Two kinds of crystals 3A (small block, 0.08 0.08 0.05) and 3B (big block, 0.20 0.20 0.08) for X-ray analysis were obtained in 2 weeks. IR (KBr) for the mixture of 3A and 3B: m(cm1) = 3453(brs), 3243(brs), 2970(w), 2923(s), 2839(m), 1664(s), 1599(w), 1558(s), 1446(w), 1400(s), 1310(w), 1258(w), 1218(s), 1040(m), 1010(m), 990(w), 930(w), 894(w), 812(s), 666(w), 610(s), 505(s). 2.6. X-ray crystallography The X-ray diffraction data for all four compounds were collected on a Bruker SMART APX diffractometer equipped with a monochromater in the Mo Ka (k = 0.71073 Å) incident beam. Each crystal was mounted on a glass fiber. The CCD data were integrated and scaled using the Bruker-SAINT software package, and the structure
3.2. Structure description of 1, 1-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, a water ligand, and a 2,20 -bpy ligand, and symmetry operations (x + 3/2, y + 1/2, z + 1/4) and (x + 3/2, y 1/2, z + 1/4) produce a onedimensional chain 1 (Fig. 1). The CdII ion is seven-coordinated with four O atoms from two chelating 1,2-chdc, two N atoms from a bidentate 2,20 -bpy, and an O atom from a water. CdII ions are bridged by e,a-cis-1,2-chdc ligands to form a one-dimensional chain (Fig. 1). The coordination mode for two carboxylates in 1,2chdc is the asymmetric chelating (g1:g1) [30–35,48]. The intramolecular hydrogen bond between water hydrogen atom and next carboxylate oxygen atom in a chain makes the one-dimensional chain structure stronger (green dotted lines in Fig. 1). The CdAO1,2-chdc distances of asymmetric chelating carboxylates are 2.259(4), 2.283(4) Å and 2.537(5), 2.620(4) Å. The CdAOwater distance is 2.518(5) Å, and the CdAN bond distances are 2.322(4) and 2.372(4) Å (Table S1). The Cd Cd distance is 6.197(1) Å. 3.3. Structure description of 2, 2-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc and a bpe ligand, and symmetry operations (x + 1, y + 1, z), (x + 2, y + 1, z), (x, y 1, z + 1), and (x, y + 1, z 1) produce a twodimensional sheet 2 (Fig. 2). Two carboxylates of e,a-cis-1,2-chdc ligands bridge CdII ions to form one-dimensional chains, and bpe ligands bridge those chains to form a two-dimensional sheet (Fig. 2). Two carboxylates in 1,2-chdc show two different coordination modes: the chelating (g1:g1) and the bridging (g1:g1:l2). The coordination geometry of CdII ion is distorted octahedral constructed by two O atoms from a chelating cis-1,2-chdc, two O atoms from two bridging cis-1,2-chdc, and two N atoms from two bpe ligands. The CdAO1,2-chdc bond distances range from 2.2394(18) to 2.4455(19) Å, and the CdAN bond distances are 2.342(2) and 2.363(2) Å (Table S1). The Cd Cd distances in a
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E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342 Table 1 Crystallographic data for compounds 1–3.
Empirical formula Formula weight Temperature (K) Wavelength (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z Density (calc.) (Mg/m3) Absorption coeff. (mm1) Crystal size (mm3) Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Largest diff. peak and hole (e Å3)
1
2
3A
3B
C18H20CdN2O5 456.76 293(2) 0.71073 P41212 10.3296(5) 10.3296(5) 90.00 90.00 90.00 91.366(2) 3466.8(4) 8 1.750 1.293 0.25 0.10 0.10 19,284 4169 [R(int) = 0.0812] 4169/2/242 0.944 R1 = 0.0444, wR2 = 0.1136 R1 = 0.0567, wR2 = 0.1217 0.721 and 0.821
C20H20CdN2O4 464.78 293(2) 0.71073 P1 7.7115(6) 9.7515(7) 12.6997(10) 76.4650(10) 76.8020(10) 88.1130(10) 903.74(12) 2 1.708 1.237 0.30 0.10 0.10 5046 3469 [R(int) = 0.0307] 3469/0/244 1.015 R1 = 0.0267, wR2 = 0.0668 R1 = 0.0290, wR2 = 0.0674 0.430 and 0.891
C14H13CdN3O5 415.67 170(2) 0.71073 C2/c 20.835(4) 10.177(2) 16.014(3) 90.00 106.12(3) 90.00 3262.1(11) 8 1.693 1.366 0.08 0.08 0.05 8972 3212 [R(int) = 0.0630] 3212/5/201 0.940 R1 = 0.0379, wR2 = 0.0890 R1 = 0.0569, wR2 = 0.0919 1.808 and 0.833
C28H32CdN4O8 664.98 293(2) 0.71073 C2/c 26.740(4) 10.4638(15) 21.003(3) 90.00 97.270(2) 90.00 5829.4(15) 8 1.515 0.804 0.20 0.20 0.08 15,785 5705 [R(int) = 0.0827] 5705/6/388 0.877 R1 = 0.0318, wR2 = 0.0738 R1 = 0.0489, wR2 = 0.0770 0.478 and 0.588
Scheme 1. Structures from CdII-(e,a-cis-1,2-chdc) with assistant bipyridyl ligands.
one-dimensional chain are 3.930(2) and 5.737(3), and the Cd Cd distance between chains is 14.086(9) Å. 3.4. Structure description of 3A, 3-D Asymmetric unit contains a CdII ion, half of e,a-cis-1,2-chdc, a 4,4 -bpy ligand, and a nitrate, and symmetry operations (x 1/2, 0
y 1/2, z), (x, y, z + 2), (x + 1/2, y + 1/2, z), and (x, y, z + 3/ 2) produce a three-dimensional structure 3A (Fig. 3a). The cyclohexyl group is disordered as shown in Fig. 3b. Two Cd(NO3)+ are bridged by two e,a-cis-1,2-chdc to form dinuclear units, and these dinuclear units are connected by 4,40 -bpy ligands to form a threedimensional structure 3A (Fig. 3). Assuming the cadmium dimers act as nodes, the complete Schläfli symbol of the 4-connected unin-
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2.381(3) Å, and the CdAOnitrate distances are 2.420(4) and 2.455(4) Å. The CdAN bond distances are 2.268(4) and 2.280(4) Å (Table S1). The Cd Cd distance in a dinuclear unit is 3.70(5) Å.
3.5. Structure description of 3B, 1-D Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, two 4,4 -bpy ligands, a water ligand, and three water solvent molecules, and symmetry operations (x + 1/2, y + 1/2, z + 1/2) and (x + 1/ 2, y 1/2, z + 1/2) produce a one-dimensional structure 3B (Fig. 4a). The e,a-cis-1,2-chdc ligands bridge CdII to form a onedimensional structure, and the coordination mode for carboxylates in 1,2-chdc is the chelating (g1:g1). The 4,40 -bpy ligands act as a monodentate dangling ligand in 3B while they do as a bridging ligand in 3A. The CdII is seven-coordinated by four O atoms from two chelating cis-1,2-chdc ligands, two N atoms from two 4,40 -bpy ligands, and an O atom from a water ligand to form a distorted pentagonal bipyramid. Inter- and intra-molecular OAH O hydrogen bonding interactions provide a two-dimensional sheet (Fig. 4b, see Table S2). The CdAO1,2-chdc bond distances are 2.37585(18) and 2.4626(17) Å, and the CdAOwater distance is 2.330(2) Å. The CdAN bond distances are 2.361(2) and 2.389(2) Å (Table S1). The Cd Cd distance is 6.756(3) Å. 0
Fig. 1. Structure of 1-D chain of [Cd(H2O)(1,2-chdc)(2,20 -bpy)] 1. All hydrogen atoms were omitted for clarity. Intra-molecular hydrogen bonds are shown in green lines (OwaterAH Ocarboxylate 2.134 Å (141.54°)). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
odal net was calculated as 658 network topology based on the TOPOS analysis. The coordination mode of carboxylates is the chelating/bridging (g2:g1:l2). The CdII ion is seven-coordinated by two O atoms from one e,a-cis-1,2-chdc, an O atom from the other e,a-cis1,2-chdc, two O atoms from a nitrate, and two N atoms from two 4,40 -bpy to form a distorted pentagonal bipyramid in which five O atoms are in the equatorial positions and two N atoms are in axial positions. The CdAO1,2-chdc bond distances are 2.358(3) and
Fig. 2. Structure of 2-D sheet of [Cd(1,2-chdc)(bpe)]n 2. All hydrogen atoms were omitted for clarity.
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Fig. 3. (a) 3-D structure of [Cd2(NO3)2(1,2-chdc)(4,40 -bpy)2]n 3A. (b) The dinuclear unit of 3A with disordered 1,2-chdc in green color. All hydrogen atoms were omitted for clarity.
Like ZnII-(a,e-cis-1,2-chdc) system, we have also systematically investigated CdII complexes containing particularly 1,2-chdc ligand with different assistant bipyridyl ligands, 2,20 -bpy, bpe, and 4,40 bpy. According to the change of assistant bipyridyl ligands, CdII(e,a-cis-1,2-chdc) provides 1-D, 2-D and 3-D compounds as shown in Scheme 1. Only one conformer (a,e-cis) has also been observed in 1,2-chdc ligands of all four CdII compounds as shown in ZnII compounds. The observed coordination modes of two carboxylates in CdII-(a,e-cis-1,2-chdc) complexes are shown in Scheme 2. For 1, two carboxylates coordinate to CdII ions, and both carboxylates are in chelating (g1:g1) modes. For 2, two carboxylates also coordinate to CdII ions: one carboxylate is in the chelating (g1:g1) mode and the other one is in the bridging (g1:g1:l2) mode. For 3A, carboxylates show the chelating/bridging (g2:g1:l2) modes,
and for 3B, they show the chelating (g1:g1) modes. From the previous work of ZnII-(a,e-cis-1,2-chdc), it was noted that carboxylates of a,e-cis-1,2-chdc with chelating, bridging, and monodentate coordination modes have been observed in all six compounds, but for this CdII system, their chelating/bridging (g2:g1:l2) mode has also been observed as well as chelating (g1:g1) and bridging (g1:g1:l2). The chelating/bridging (g2:g1:l2) mode of carboxylates has been observed in recent literatures [25–31], and M-(1,2chdc) system without assistant ligands can provide favorably metal–oxygen–metal networks [25–35]. In the previous work of ZnII-(1,2-chdc) system, it was suggested that construction of metal–oxygen–metal linkages might be prevented if assistant ligands were employed to M-(1,2-chdc) system, and that they can provide various structures according to the change of the assistant ligands
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Fig. 4. (a) 1-D structure of [[Cd(H2O)(1,2-chdc)(4,40 -bpy)2]3(H2O)]n 3B. All hydrogen atoms were omitted for clarity. (b) Two-dimensional sheet through hydrogen bonds in 3B. All pyridyl and cyclohexyl hydrogen atoms were omitted for clarity. The hydrogen bonds are shown in the green dotted lines. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Scheme 2. Coordination modes in CdII-(a,e-cis-1,2-chdc) complexes.
[43]. Also, it was showed that the use of assistant ligands may influence coordination modes of carboxylates in the previous ZnII-(1,2chdc) system. Carboxylates in chelating/bridging (g2:g1:l2) modes provide dinuclear Cd2 units which could not be observed in the ZnII-(1,2-chdc) system. From these results, it is noted that the metal ion as well as the assistant ligand can influence both the whole structure and coordination modes of carboxylates.
3.6. Photoluminescence property We have examined the emission spectra of CdII complexes 1 and 2, since coordination polymers containing cadmium and zinc exhibited excellent photoluminescent properties [49,50]. The emission spectra of CdII complexes 1 and 2, together with those of the ligands 2,20 -bpy, bpe, and cis-1,2-chdcH2, were measured in the solid state at room temperature (see Fig. 5). Emission of
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1000
Intensity
800
600
400
200
0 280
330
380
430
480
530
580
630
Wavelength (nm) Fig. 5. Emission spectra of complexes 1, 2, and ligands (2,20 -bpy, bpe, and cis-1,2-chdc) at room temperature.
compound 1 was observed at 348 nm (kex = 267 nm), while relatively weak luminescence was observed at 516 nm (kex = 441 nm) for 2 under the same experimental conditions. Such emission of complex 2 can be tentatively assigned to the intraligand transition of bpe ligand, since the similar emissions were observed for the ligand (511 nm for bpe (kex = 413 nm)) [51–53]. The emission band of complex 1 is blue-shifted compared to the corresponding ligands (390 nm for 2,20 -bpy (kex = 340 nm) or 403 nm for cis-1,2chdc (kex = 263 nm)). In addition, it is noteworthy that compound 1 showed an intense emission compared with that of compound 2 at room temperature, which may be attributed to effective increase of the rigidity of the complex and reduces the loss of energy by radiationless decay. This suggests that 1 may be a good candidate for a potential hybrid inorganic–organic photoactive material [54]. 3.7. Thermogravimetric analysis To study the thermal stabilities of these complexes, thermal gravimetric analysis (TGA) of compounds 1 and 2 was performed (see Supporting information: Figs. S3 and S4). Compound 1 first lost its coordinated one OH between 131 and 237 °C; the observed weight loss of 3.5% was consistent with that calculated (3.9%). After this, the 1-D framework was stable up to 237 °C and then began to decompose upon further heating. The second gradual weight loss of 31.1% in the temperature range of 237–296 °C corresponds to the loss of a coordinated 2,20 -bpy ligand (calcd. 34.2%). The third weight loss of 40.8% from 336 to 434 °C may be attributed to the loss of one coordinated cis-1,2-chdc ligand (calcd. 37.3%). The TGA curve of compound 2 showed that it underwent a rapid and significant weight loss of 38.0% in the temperature range of 225–378 °C, which corresponds to the loss of one bpe ligand (calcd. 39.2%). The second gradual weight loss of 33.2% from 378 to 425 °C may be attributed to the loss of coordinated cis-1,2-chdc ligand (calcd 33.2%). The residue started to decompose completely to CdO upon further heating. 4. Conclusion Four CdII-(a,e-cis-1,2-chdc) complexes with different assistant ligands (2,20 -bpy, bpe, and 4,40 -bpy) have been synthesized and their structures were determined. Depending on the assistant ligands, the dimensionality of 1,2-chdc complexes has been varied. In 1,2-chdc, only (e,a-cis) conformer has been observed in all cases,
and two carboxylates coordinate to CdII ions in chelating (g1:g1), bridging (g1:g1:l2), and chelating/bridging (g2:g1:l2) modes. This study indicates that the structures and dimensionalities of CdII-(a,e-cis-1,2-chdc) compounds could be controlled by changing of assistant bipyridyl ligands. Moreover, the present CdII and the previous ZnII systems suggest that both assistant ligands and metal ions could influence the whole structures and coordination modes of carboxylates. Photoluminescence study suggested that the photoluminescence property of the CdII complexes could be tuned by the change of the assistant ligands, and that they may be good candidates for luminescent materials. Acknowledgements Financial support from the Korean Science & Engineering Foundation (R01-2008-000-20704-0 and 2009-0074066), the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0082832), and the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Womans University (Grant R11-2005-008-00000-0) is gratefully acknowledged. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2011.03.046. References [1] S. Noro, S. Kitagawa, M. Kondo, K. Seki, Angew. Chem., Int. Ed. 39 (2000) 2081– 2084. [2] Z.L. Huang, M. Drillon, N. Masciocchi, A. Sironi, J.T. Zao, P. Rabu, P. Panissod, Chem. Mater. 12 (2000) 2805–2812. [3] L. Pan, N. Ching, X. Huang, J. Li, Inorg. Chem. 39 (2000) 5333–5340. [4] L. Pan, B.S. Finkel, X. Huang, J. Li, Chem. Commun. (2001) 105–106. [5] P.S. Mukherjee, N. Das, Y.K. Kryshenko, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 126 (2004) 2464–2473. [6] N.L. Rosi, J. Kim, M. Eddaoudi, B. Chen, M. O’Keeffe, O.M. Yaghi, J. Am. Chem. Soc. 127 (2005) 1504–1518. [7] Z. Wang, G. Chen, K. Ding, Chem. Rev. 109 (2009) 322–359. [8] W.H. Bi, R. Cao, D.F. Sun, D.Q. Yuan, X. Li, Y.Q. Wang, X.J. Li, M.C. Hong, Chem. Commun. (2004) 2104–2105. [9] M. Yu, L. Xie, S. Liu, C. Wang, H. Cheng, Y. Ren, Z. Su, Inorg. Chim. Acta 360 (2007) 3108–3112. [10] J. Yang, J.-F. Ma, Y.-Y. Liu, J.-C. Ma, S.R. Batten, Cryst. Growth Des. 9 (2009) 1894–1911.
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