A pair of 3D homochiral helical metal–organic frameworks with hetrometallic chains constructed by proline derivative ligands

Polyhedron 118 (2016) 91–95

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A pair of 3D homochiral helical metal–organic frameworks with hetrometallic chains constructed by proline derivative ligands Zhong-Xuan Xu a,b,⇑, Yu-Lu Ma c, Yang Liu a, Jian Zhang b a

Department of Chemistry, Zunyi Normal College, Zunyi, Guizhou 563002, PR China State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China c School of Chemical Science and Technology, Yunnan University, Kunming 650091, PR China b

a r t i c l e

i n f o

Article history: Received 31 May 2016 Accepted 2 August 2016 Available online 8 August 2016 Keywords: Proline derivative ligands Helical chains Heterometal ions Photoluminescent properties

a b s t r a c t A pair of homochiral metal–organic frameworks based on proline derivative ligands ((S)-H3PIA and (R)-H3PIA), namely [Cd3Na((S)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-L) and [Cd3Na((R)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-D), have been synthesized. Crystallographic analysis indicates complexes 1-L and 1-D contain interesting infinite hetrometallic and homochiral helical chains. Some physical characteristics, such as solid-state circular dichroism (CD), thermal stabilities and photoluminescent properties were also investigated. Our results highlight a feasible synthesis method to construct functional HMOFs from proline derivative ligands and heterometal ions. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Chirality is an essential feature in nature process and life system, which is also an interesting and significant research topic in advanced materials [1]. Of these chiral materials, homochiral metal–organic frameworks (HMOFs) attracted a great deal of attention for their intriguing structures and some potential applications in asymmetric catalysis, chiral separation, nonlinear optics and so on [2]. During the past ten years, great endeavor has been focused on the HMOFs and several approaches have been developed to construct HMOFs with multiple structures and varied functional properties [3]. Among these approaches, using chiral organic linkers to assembly with metal ions or metal clusters is the most effective method [4]. Although HMOFs can be obtained from achiral or racemic ligands, the spontaneous resolution phenomena is very rare and unpredictable for the crystallization process tends to centrosymmetry [5]. Therefore, how to select appropriate enantiopure ligands becomes the key factor for construction of HMOFs. Natural amino acids may be ideal enantiopure linkers for they are cheap and possess several functional groups in one molecule [6]. Nevertheless, the flexible nature and small size of pure amino acids with transition metals often results in zero or one dimensional complex formation instead of high-dimensiona HMOFs [7].

⇑ Corresponding author at: Department of Chemistry, Zunyi Normal College, Zunyi, Guizhou 563002, PR China. E-mail address: [email protected] (Z.-X. Xu). http://dx.doi.org/10.1016/j.poly.2016.08.005 0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

As a result, to date using amino acids to synthesize 3D HMOFs is still a great challenge. Recently, in order to overcome the aforementioned problem, we have synthesized a pair of enantiopure 5-(2-carboxypyrrolidine1-carbonyl) isophthalic acid (denoted: (S)-H3PIA and (R)-H3PIA) (Scheme 1) by modifying the functional NH2 group of proline via attaching one isophthalate unit [8]. Containing chiral proline unit and rigid aromatic part, the pair of proline derived links have be used in 3D homochiral MOFs formation in our previous work [9]. As a continuation of our effort on the constructions of HMOFs based on proline ligands (S)-H3PIA and (R)-H3PIA, a pair of HMOFs have been gained by using mixed N, N-diethylformamide (DEF), methanol and H2O solvents, namely [Cd3Na((S)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-L) and [Cd3Na((R)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-D). Complexes 1-L and 1-D exhibit 3D frameworks with unique helical chains and infinite hetrometallic chains. 2. Experimental 2.1. Materials and general methods The enantiopure ligands (S)-H3PIA and (R)-H3PIA were prepared from L-proline, D-proline and benzene-1,3,5-tricarboxylic acid (1,3,5-BTC) according to our previously reported procedure [8]. The other reagents and solvents were commercially available and used without further purification. Elemental analyses were carried out in the analysis center of Fujian Institute of Research on the Structure of Matte. The solid-state circular dichroism (CD) spectra

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were located by geometrical calculations. The water hydrogen atoms were found in difference Fourier maps, and then fixed at the corresponding O atoms. Relevant crystallographic data are listed in Table 1 and some selected bond lengths and angles are given in Table S1–2.

3. Results and discussion

Scheme 1. Synthesis of 1-D and 1-L.

were recorded on a MOS-450 spectropolarimeter using KCl pellets. The determination of photoluminescence was conducted in a powder form at room temperature on a FL920 fluorescence spectrometer equipped with an R928 PMT detector. ICP analyses were performed on an Ultima2 ICP-OES spectrometer. The FT-IR spectra were recorded from KBr pellets on a Nicolet Magna 750 FT-IR spectrometer in the range of 400–4000 cm 1. Thermal analyses were carried out on a NETSCHZ STA-449C thermoanalyzer, heated from 25 °C to 800 °C with a heating rate of 10 °C/min under nitrogen. Powder X-ray diffraction (PXRD) analyses were recorded on a Rigaku Dmax2500 diffractometer with Cu Ka radiation (k = 1.54056 Å). 2.2. Synthesis of [Cd3Na((S)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-L) As shown scheme 1, complex 1-L was synthesized under solvothermal reaction conditions. The mixture of Cd(CH3COO)2
2H2O (0.2 mmol, 0.053 g), NaCl (0.006 g, 0.1 mmol), (S)-H3PIA (31 mg, 0.1 mmol), DEF (1 mL), ethanol (0.5 mL) and H2O (0.5 mL was sealed in a 23 mL Parr Teflon-lined stainless steel vessel and heated to 90 °C for four days. After cooled to room temperature, white block crystals were separated from the mixture by filtration (Yield: 35%, based on (S)-H3PIA). Elemental analysis (%) calcd for 1-L (C30H29Cd3N2NaO24): C 31.01, H 2.52, N 2.41, Cd 29.03, Na 1.98; found: C 30.46, H 2.57, N 2.30, Cd 28.02, Na 2.12; IR (solid KBr pellet, cm 1): 3433.5m, 1612.3m, 1555.6m, 1438.2w, 1381.8s, 725.0w. 2.3. Synthesis of [Cd3Na((R)-PIA)2(CH3CO2) (H2O)6]
2H2O (1-D) The same procedure as 1-L, except (R)-H3PIA was used. White block crystals were separated from the mixture by filtration (Yield: 40%, based on (R)-H3PIA). Elemental analysis (%) calcd for 1-D (C30H29Cd3N2NaO24): C 31.01, H 2.52, N 2.41, Cd 29.03, Na 1.98; found: C 30.20, H 2.52, N 2.24, Cd 28.32, Na 2.07; IR (solid KBr pellet, cm 1): 3433.5m, 1612.0m, 1569.1m, 1431.5w, 1375.0s, 725.0w. 2.4. X-ray crystallography The diffraction data for the complexes 1-L and 1-D were collected on a Rigaku 007 CCD diffractometer and a SuperNova CCD diffractometer, respectively. Both the CCD diffractometers are equipped with a graphitemonochromated Mo Ka radiation (k = 0.71073 Å). The structures of the two complexes were solved by direct methods and refined on F2 full-matrix least-squares with the SHELXTL-97 program package. All non-hydrogen atoms were refined anisotropically and the hydrogen atoms bound to carbon

Crystal structure analyses have revealed that complexes 1-L and 1-D crystallize in the monoclinic space group P21 with Flack parameters 0.04(2) and 0.002(16), respectively. Since complexes 1-L and 1-D are enantiomers, only the structure of 1-L will be discussed in detail. The asymmetric unit of 1-L is comprised of three crystallographically independent Cd2+ cations (Cd1, Cd2 and Cd3), one Na+ ion, two (S)-PIA3 ligands, one CH3CO2 anion, six coordinated water molecules and two guest water molecules. As shown in Fig. 1, the first (S)-PIA3 ligand acts as j8-linker to connect four Cd2+ions and two Na+ ions, and the second (S)-PIA3 ligand act as j7-linker to connect five Cd2+ ions and one Na+ ion. For the above unique coordination modes of (S)-PIA3 ligands, an infinite hetrometallic chain [Cd3Na(CO2)6(CH3CO2)(H2O)6]n is formed, which is first outstanding structural feature of 1-L (Fig. 2a). In the hetrometallic chain, Cd1 adopts an distorted pentagonal bipyramid geometry, which is coordinated by five carboxylate O atoms from three (S)-PIA ligands, one carboxylate O atom from CH3COO- anion and a water molecule. Cd2 has an octahedral coordination geometry, which is coordinated by four carboxylate O atoms from three (S)-PIA ligands and two water molecules. Cd3 also has an octahedral coordination geometry, which is coordinated by three carboxylate O atoms from three (S)-PIA ligands, two carboxylate O atoms from a CH3COO- anion and one water molecule. Besides the three Cd2+ ions, Na+ ion shows pentahedral geometry, which is surrounded by three carboxylate O atoms from three (S)-PIA ligands and two water molecules. As stated previously, (S)-PIA3-and (R)-PIA3 ligands are comprised of chiral proline unit and rigid aromatic part, so it is easy to divide the whole structure into two parts to further simplify their complicated structures. If only the connectivity between rigid aromatic part of PIA3 ligands and Cd2+ centers is considered, an interesting 2D framework with helical channels is generated,

Table 1 Crystal data and structure refinement for complexes 1-L and 1-D. Compound reference

1-L

1-D

Chemical formula Formula mass Crystal system a (Å) b (Å) c (Å) a (°) b (°) c (°) Unit cell volume (Å3) T (K) Space group Z Radiation type l (mm 1) No. of reflections measured No. of independent reflections Rint Final R1 values (I > 2r(I)) Final wR (F2) values (I > 2r(I)) Final R1 values (all data) Final wR (F2) values (all data) Goodness of fit (GOF) on F2 Flack parameter

C30H29Cd3N2NaO24 1161.74 monoclinic 8.183(3) 25.845(9) 10.044(5) 90.00 112.724(6) 90.00 1959.2(15) 293(2) P2(1) 2 Mo Ka 1.719 11 807 6557 0.0188 0.0245 0.0662 0.0256 0.0669 1.085 0.04(2)

C30H29Cd3N2NaO24 1161.74 monoclinic 8.1897(3) 25.8282(7) 10.0294(4) 90.00 112.682(4) 90.00 1957.39(12) 293(2) P2(1) 2 Mo Ka 1.720 18 340 9784 0.0287 0.0307 0.0674 0.0355 0.0697 1.004 0.002(16)

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Fig. 1. The coordination environment in enantiomers 1-L and 1-D. Symmetry codes: (a) (f) x, y, 1 + x.

1 + x, y,

1 + z; (b)

x, 0.5 + y,

z; (c) 1 + x, y, 1 + z; (d) x, y, 1 + z; (e)

x,

0.5 + y,

z;

Fig. 2. (a) The hetrometallic chain in 1-L; (b) the left-handed helical chain in 1-L constructed by rigid isophthalate unit of (S)-PIA3 ligands, CH3CO2 anions and Cd2+ centers; (c) the right-handed helical chain in 1-D constructed by rigid isophthalate unit of (R)-PIA3 ligands, CH3CO2 anions and Cd2+ centers; (d) the 2D layer in 1-L comprised of the left-handed helical chains; (e) the 2D layer in 1-D comprised of the right-handed helical chains.

which is the second outstanding structural feature of 1-L and 1-D (Fig. 2b–e). The Cd(II) ions are linked by carboxylate groups from isophthalate unit of (R)-PIA3 ligands and CH3CO2 anions to form

an infinite left-handed helical chain running along the a-axis in 1-L (Fig. 2b), and it is the opposite phenomenon (homo righthanded helical chains) in 1-D (Fig. 2c). Moreover, the pitch lengths

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Fig. 3. The 3D framework of 1-L constructed by (S)-PIA3 ligands, CH3CO2 anions, Cd2+ centers and Na+ ions.

Fig. 4. The solid-state CD spectra of bulk samples 1-D and 1-L.

Fig. 5. Photoluminescences of complex 1-L and (S)-H3PIA.

of all the helical chains are identical to the length of a-axis. Finally, the above 2D layer is further filled and linked by proline units of PIA3 ligands and Na+ ions resulting in a 3D framework (Fig. 3). To check the purity of complexes 1-L and 1-D, their powder Xray diffraction (PXRD) was carried out at room temperature. As shown in Fig. S3, all the peaks displayed in the measured patterns match very well with the simulated ones, indicating the phase purity of the bulk materials. Furthermore, the thermal gravimetric analysis (TGA) of complexes 1-D and 1-L was also carried out from room temperature to 800 °C under a nitrogen atmosphere to characterize their thermal behaviors (Fig. S4). The TGA curves of 1-L and 1-D show that the first weight loss from room temperature

to 250 °C correspond to the guest water molecules and coordinated water molecules(observed, 10.8%; calculated, 12.4%). Above 360 °C, the frameworks of complexes 1-D and 1-L begin to collapse. To further determine their enantiomeric characteristic, circular dichroism spectra (CD) of bulks amples from 1-L and 1-D were measured in the solid state at room temperature (Fig. 4). The CD curve of 1-L shows obvious negative cotton effect (CE) peak at about 260 nm, confirming its homochiral nature. Moreover, a mirror image is also observed for 1-D, which reveals that complexes 1-L and 1-D are enantiomers. The solid-state photoluminescent spectra of complex 1-L was investigated at room temperature for d10 metal inorganic–organic

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hybrid coordination polymers with luminescent properties. Excitation of the microcrystalline samples of 1-L at 322 nm shows the intense luminescence with the peak maxima at 422 nm (Fig. 5). The luminescence property of the free (S)-H3PIA ligand was also measured to better understand the nature of above emission bands, which has a maximum emission peak at 481 nm under excitation at 387 nm. The emission peaks position of complex 1-L is blue-shifted about 59 nm, where these emission bands probably arise from either an n–p⁄ or p–p⁄ excitation and the decay should be assigned to p⁄ to n or p [10].

[3]

[4]

4. Conclusion We have used the proline derivative ligands pictured in Scheme 1 to construct a pair of HMOFs with interesting structural and physical properties. The above structures are built on infinite hetrometallic and homochiral helical chains, only a few of which have been reported previously. This work demonstrates selfassembly of proline derivative ligands and heterometal ions is also a feasible synthesis method to construct functional HMOFs. Acknowledgment

[5]

We thank the support of this work by the Natural Science Foundation of Guizhou Province (20122344 and LKZS201213) and the Doctoral Scientific Fund of Zunyi Normal College (Grant No. 2012BSJJ12). Appendix A. Supplementary data CCDC 1478604-1478605 contain the supplementary crystallographic data for 1-L and 1-D. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.poly.2016.08.005. References [1] (a) J. Crassous, Chem. Soc. Rev. 38 (2009) 830; (b) J.A. Kelly, M. Giese, K.E. Shopsowitz, M.J. Maclachlan, Acc. Chem. Res. 47 (2014) 1088; (c) J. Shen, Y. Okamoto, Chem. Rev. 116 (2016) 1094; (d) H.K. Bisoyi, Q. Li, Acc. Chem. Res. 47 (2014) 3184; (e) X. Zhang, J. Yin, J. Yoon, Chem. Rev. 114 (2014) 4918. [2] (a) W.B. Lin, J. Solid State Chem. 178 (2005) 2486; (b) L. Ma, C. Abney, W.B. Lin, Chem. Soc. Rev. 38 (2009) 1248; (c) L. Yan, W.M. Xuan, Y. Cui, Adv. Mater. 22 (2010) 4112; (d) W. Zhang, R.G. Xiong, Chem. Rev. 112 (2012) 1163; (e) M. Yoon, R. Srirambalaji, K. Kim, Chem. Rev. 112 (2012) 1196;

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