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Fluorescent selectivity for small molecules of two coordination polymers based on a tetracarboxylate ligand
Inorganic Chemistry Communications 73 (2016) 21–25
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Fluorescent selectivity for small molecules of two coordination polymers based on a tetracarboxylate ligand Xiao Zhang, Xiao-Qing Wang, Xiao-Xiao Wang, Zhi-jia Xue, Tuo-Ping Hu ⁎ Department of Chemistry, College of Science, North University of China, Taiyuan 030051, China
a r t i c l e
i n f o
Article history: Received 12 July 2016 Received in revised form 27 August 2016 Accepted 5 September 2016 Available online 06 September 2016 Keywords: Terphenyl-3,3″,5,5″-tetracarboxylic acid Transition-metal coordination polymer Luminescent sensing
a b s t r a c t Two coordination polymers [Cd(tptc)0.5(4,4′–bibp)]n (1) and {[Zn3(Htptc)2(phen)2]·1.5H2O}n (2) (H4tptc = terphenyl-3,3″,5,5″-tetracarboxylic acid, 4,4′-bibp = 4,4′-bis(imidazolyl)biphenyl, and phen = 1,10phenanthroline) were synthesized under solvothermal conditions. Complex 1 displays a 3D structure with a Schläfli symbol of {44.62}{48.620}. Complex 2 possesses a 2D layer network, incorporating [Zn3(COO)6] second building units (SBUs), which is packed into a 3D supramolecular architecture by π ⋯ π interactions. Both of them exhibit strong luminescence characteristics. It is worth to note that complexes 1 and 2 show potential application to detect small organic molecules. © 2016 Elsevier B.V. All rights reserved.
Over the past few decades, coordination polymers (CPs) have become a rapidly growing research project. In general, the complicated topological structure of coordination polymers can be achieved by selecting appropriate ligands, pH values, solvents, metal ions, reaction temperature, and so on [1–3]. With the prominent development, functional coordination polymers have attracted widespread attention because of the enormous potential applications in catalysis, gas adsorption and storage, drug delivery, magnetism, luminescence and so on [4–8]. Especially, luminescent coordination polymers could be applied to many kinds of fields, such as ratiometric temperature sensing, luminescence sensing, warm-white LED and fluorescent indicator [9–12]. With the tremendous improvements of economy, environmental issues, for instance, industrial pollution, exhaust emission and pesticide residue, turn into the hot topics which are drawn lots of attention [13]. These organic compounds are toxic compounds that have significant effects for the environment. Thus, the emission of anthropogenic organic compounds must be monitored, and as such, detection of organic compounds is vital. So developing chemical sensors for fast detecting harmful compounds, especially those with toxic contaminant are exceedingly pressing issues from the perspective of the ecological protection, security and human health. The traditional selective recognition of small molecules requires expensive instruments and multiple spectrometry as well as intricate characterization approaches [14]. Therefore, luminescent coordination polymers detection becomes a promising method due to the high selectivity, simple technological process, low cost, high efficiency and other advantages. Luminescent complexes are considered to be a sort of material for detecting
⁎ Corresponding author. E-mail address: [email protected] (T.-P. Hu).
http://dx.doi.org/10.1016/j.inoche.2016.09.005 1387-7003/© 2016 Elsevier B.V. All rights reserved.
small molecules. Hence, it is urgent to synthesize the luminescent coordination polymers for recognizing the toxic substances in environment. Under above background, two new luminescent coordination polymers, namely, [Cd(tptc)0.5(4,4′–bibp)]n (1) and {[Zn3(Htptc)2(phen)2]· 1.5H2O}n (2), were synthesized by solvothermal method. Compared with other compounds based on H4tptc, complexes 1 and 2 are constructed by H4tptc and auxiliary ligands, 4,4′–bibp and phen, which exhibit different structures [15]. Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the triclinic crystal system with a space group of Pī, which possesses a 3D framework with 4,8-connecting topology. The asymmetric unit contains one independent Cd1 ion, half a tptc4−, one 4,4′-bibp ligand. As shown in Fig. 1a, Cd1 is hexa-coordinated by two N atoms from two 4,4′-bibp ligands [Cd1–N1 = 2.255(6) Å and Cd–N3 = 2.365(7) Å] and four O atoms from three tptc4 − ligands [Cd1–O1 = 2.162(5) Å, Cd1–O3i = 2.363 (5) Å, Cd1–O4i = 2.520(5) Å and Cd1– O3ii = 2.501(6) Å]. The carboxyl groups of tptc4− assume different coordinating modes, which connect two neighbouring Cd(II) ions to generate the dinuclear [Cd2(COO)2] SBUs with a Cd┄Cd distance of 3.872 Å. During the reaction, four carboxylate groups of H4tptc are all deprotonated and adopt bridging (μ2-η2:η1) and monodentate (μ1-η1:η0) coordination modes. Each tptc4 − links four [Cd2(COO)2] units to give a lattice-shaped 2D layer structure along the a-axis (Fig. 1b), which are further pillared by 4,4′-bibp to form a 3D structure (Fig. 1c). To further understand the complicated architecture, the dinuclear unit is regarded as a 8-connected node, and tptc4− is served as a 4-connected node, thus the structure of complex 1 is simplified topologically a 4,8-connected two nodes with the Schläfli symbol of (44·62)(48·620) (Fig. 1d).
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Fig. 1. (a) Coordination environment of the Cd(II) ion. (b) 2D layer constructed from tptc4− and dinuclear units. (c) 3D complicated framework of 1. (d) Overall topological network for compound 1. Symmetry codes: (i) + x, 1 + y, + z; (ii) −x, 1 − y, 1 − z; (iii) −x, 2 − y, 1 − z.
Single crystal X-ray diffraction analysis reveals that complex 2 belongs to the monoclinic crystal system with the C2/c space group. The repeating unit of 2 consists of one and a half independent Zn(II) ions, one Htptc3− and one phen. As shown in Fig. 2a, Zn1 and Zn2 ions are in two different coordination environments. Each Zn1 is five-coordinated by three O atoms (O2, O3, O5) from three carboxyl groups and two nitrogen atoms (N1, N2) from one phen. Each Zn2 is six-coordinated by six O atoms (O1, O3, O4, O1i, O3i and O4i) provided by six carboxyl groups. The bond lengths of Zn1–O vary from 2.0206(18) to 2.184(2) Å, the Zn1–N1/N2 bond distances are 2.129(2) Å and 2.122(2) Å, respectively. The bond lengths of Zn2–O are in the range of 1.9869(17)–2.347(2) Å. The three carboxyl groups from Htptc3 − adopt syn-syn μ2-η1:η1, syn-anti μ2-η1:η1 and μ2-η2:η0 coordination modes, respectively. Interestingly, three Zn(II) cations are connected by six carboxyl groups to form a [Zn3(COO)6] unit, which are further organized by Htptc3− to generate a complicated 2D network (Fig. 2b). The adjacent 2D layers of 2 interact further to form a 3D supramolecular architecture through the π⋯π interactions (Fig. 2c and Table S3). The distances of Cg7iii–Cg10vi and Cg10–Cg7ii are 3.922 Å, the distances of Cg10–Cg6vi and Cg6–Cg10i are 3.917 Å and the distance of Cg6–Cg6vi is 3.540 Å (Cg6 is the centroid of ring N2, C22, C23, C24, C25, C26, Cg7 is the centroid of benzene ring C2, C3, C4, C5, C6, C7, Cg10 is the centroid of benzene ring C25, C26, C27, C28, C29, C30). The solid state luminescent spectra for complexes 1–2 were performed at room temperature. As shown in Fig. 3, the main characteristic peak of free H4tptc ligand is observed at 408 nm (λex = 280 nm). The emission band of free H4tptc ligand is attributed to the π*–n transition. Under the same experimental onditions, free phen ligand shows two shoulder emission peaks at 371 nm and 390 nm, respectively, excited at 280 nm, and 4,4′-bibp ligand has an main emission at 374 nm (λex = 280 nm) (Fig. S4). As previously reported, fluorescent emission of carboxyl ligands resulting from the π*–n transition is very weak
compared with that of the π*–π transition of the N-donor ligands, so solid-state carboxyl ligands almost have no obvious contribution to the coordination polymers based on mixed ligands [16]. Therefore, the emission bands of 1–2 would be assigned to π*–π transition of corresponding bis(pyridyl) ancillary ligands. In comparison with the emission peak of free H4tptc, the blue shift of the luminescence emissions in 1 and 2 perhaps mainly contributes to the coordination of the H4tptc ligand to the metal ions, which effectively increases the rigidity of the coordination polymers and reduces the loss of energy by radiationless decay [17]. Besides, the quantum yields φf of 1 and 2 are 2.90% and 1.10%, respectively. To further explore the sensing sensitivity of 1–2 for solvent molecules, six kinds of solvent molecules, that is, DMF, CH3OH, CH3CN, Nbutyl alcohol, acetone and DMSO, are selected for the luminescent sensing studies. Here, finely ground samples of complexes 1 and 2 (2 mg) were dispersed in various organic solvents (2 mL). As shown in Fig. 4a, complex 1 dispersed in DMSO displays the strongest luminescent intensity, which exhibits the weakest emission in acetone. 2 exhibits the strong luminescence intensity in DMF (Fig. 4b), and the emission is very weak in acetone. This phenomenon shows that complex 1 can detect acetone. A similar quenching behavior of acetone has been reported previously [18]. In order to research the recognition of complexes 1 and 2 for nitro aromatic compounds, a series of nitrobenzene derivatives, such as nitrobenzene (NB), 4-nitrotoluene (NT) 4-nitrobenzenamine (NA) and p-nitrophenol (NP), are opted as the analytes. Complex 1 presents obvious quenching effect of fluorescence intensity with increasing addition of NP, and Quenching rate of the emission reaches as much as 68% when the concentration of NP in the suspension solution is 0.15 mM (Fig. 5a). The quenching effect can be rationalized by the Stern–Volmer equation: (I0/I) = 1 + Ksv[Q], where I0 and I are the luminescence intensities of DMSO suspensions before and after addition of NP, respectively; Ksv is
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Fig. 2. (a) Coordination environment of the Zn(II) ion. (b) 2D layer constructed from Htptc3− and trinuclear units. (c) 3D supramolecular network of 2 formed by π⋯π interaction. The inset shows the details of the weak interactions. Symmetry codes: (i) 2 − x, y, 1.5 − z; (ii) x, −y, −0.5 + z; (iii) 1.5 − x, 0.5 + y, 1.5 − z; (iv) 0.5 + x, −0.5 + y, z; (vi) 1.5 − x, 0.5 − y, 1 − z.
the quenching constant (M−1); [Q] is the molar concentration of NP. The Stern–Volmer plots are nearly linear at low concentrations [19]. The Ksv value with NP is 1.37 × 104 M−1, and the limit of detection is down to 0.005 mM−1 (Fig. 6a). Compared with 1, the quenching percentage of 2 for the NA is much higher, the quenching effect is 67% (Fig. 5b). The Ksv value with NA is 1.54 × 104 M−1, and the limit of detection is down to 0.005 mM−1 (Fig. 6b). Moreover, complexes 1 and 2 exhibit higher NB sensing to compare with some Zn/Cd-MOFs [20]. The presence of an electron donating NH2 or OH group on the aromatic ring makes them possess electron donating/withdrawing ability. Thus, the long-range energy transfer plays a key role in the mechanism of
fluorescence based sensing, and the NH2 or OH group may form hydrogen-bonding interaction with the host framework, which leads that complexes 1 and 2 have higher sensing for NP and NA [21]. So far, few sensors have been reported for sensing p-nitroaniline [22]. In conclusion, two novel luminescent Cd(II)/Zn(II) coordination polymers have been successfully synthesized by solovothermal method. Complex 1 exhibits efficient fluorescence quenching behavior upon addition of NP, and the complex 2 shows better fluorescence quenching behavior in NA than 1. The study on constructing new luminescent coordination polymers based on tetracarboxylate ligand and d10 metal ions provides a promising method to detect nitro explosives. Acknowledgements The authors gratefully acknowledge the financial support of this work by the International Science & Technology Cooperation Program of China (No: 2011DFA51980), the International Scientific and Technological Cooperation Projects of Shanxi Province (No: 2015081043), “131” Leading Talents Project in Colleges and Universities, Science and Technology Innovation Project of Shanxi Province (No: 2014101002), Graduate Student Education Innovation Project of North University of China (No: 20151255). Appendix A. Supplementary data
Fig. 3. Room-temperature emission spectra for free H4tptc ligand and complexes 1–2.
The Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-1477923 and 1477922 (Fax:+44-1223-336-033; E-Mail: [email protected], http://www.ccdc.cam. ac.uk).
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Fig. 4. The photoluminescence intensities spectra of complexes 1 (a) and 2 (b) dispersed in different organic solvents.
Fig. 5. Percentage of fluorescence quenching obtained for introducing different nitro aromatic compounds into the DMSO-emulsion of complexes 1(a) and 2 (b).
Fig. 6. (a) The emission quenching linearity relationship at low concentration of NP for 1. (b) The emission quenching linearity relationship at low concentration of NA for 2.
Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.inoche.2016.09.005. References [1] (a) D.S. Li, Y.P. Wu, J. Zhao, J. Zhang, J.Y. Lu, Coord. Chem. Rev. 261 (2014) 1; (b) S.R. Zhang, S.Y. Yin, M. Pan, L. Chen, B.B. Du, Y.J. Hou, K. Wu, Y.X. Zhou, J.J. Jiang, Inorg. Chem. Commun. 55 (2015) 116; (c) W. Xu, J.J. Jiang, M. Pan, C.Y. Su, Inorg. Chem. Commun. 31 (2013) 83. [2] Q.Y. Yue, Y.M. Lu, F.X. Chuan, D. Yuan, D.Y. Chen, G.W. Yang, Q.Y. Li, Inorg. Chem. Commun. 68 (2016) 68. [3] F.T. Xie, H.Y. Bie, L.M. Duan, G.H. Li, X. Zhang, J.Q. Xu, J. Solid State Chem. 178 (2005) 2858. [4] Z.Y. Guo, S.Q. Su, R.P. Deng, H.J. Zhang, Inorg. Chem. Commun. 51 (2015) 9. [5] A. Proust, B. Matt, R. Villanneau, G. Guillemot, P. Gouzerh, G. Izzet, Chem. Soc. Rev. 41 (2012) 7605. [6] P. Horcajada, R. Gref, T. Baati, P.K. Allan, G. Maurin, P. Couvreur, G. Férey, R.E. Morris, C. Serre, Chem. Rev. 112 (2012) 673. [7] X.T. Zhang, D. Sun, B. Li, L.M. Fan, B. Li, P.H. Wei, Cryst. Growth Des. 12 (2012) 3845.
[8] D. Yan, Q. Duan, Inorg. Chem. Commun. 36 (2013) 188. [9] Y. Cui, R. Song, J. Yu, M. Liu, Z. Wang, C. Wu, Y. Yang, Z. Wang, B. Chen, G. Qian, Adv. Mater. 27 (2015) 1420. [10] A. Douvali, A.C.T.S.V. Eliseeva, S. Petoud, Angew. Chem. Int. Ed. 54 (2015) 1651. [11] Y. Cui, R. Song, J. Yu, M. Liu, Z. Wang, C. Wu, Y. Yang, Z. Wang, B. Chen, G. Qian, Adv. Funct. Mater. 25 (2015) 4796. [12] (a) S.Y. Zhang, W. Shi, P. Cheng, M.J. Zaworotko, J. Am. Chem. Soc. 137 (2015) 12203; (b) C. Yan, Y.Z. Fan, L. Chen, M. Pan, L.Y. Zhang, J.J. Jiang, C.Y. Su, CrystEngComm 17 (2015) 546. [13] (a) Y.J. Cui, Y.F. Yue, G.D. Qian, B.L. Chen, Chem. Rev. 112 (2012) 1126; (b) X.F. Zheng, L. Zhou, Y.M. Huang, C.G. Wang, J.G. Duan, L.L. Wen, Z.F. Tian, D.F. Li, J. Mater. Chem. A 2 (2014) 12413. [14] (a) K. Sumida, D.L. Rogow, J.A. Mason, T.M. McDonald, E.D. Bloch, Z.R. Herm, T.H. Bae, J.R. Long, Chem. Rev. 112 (2012) 724; (b) J.M. Zhou, W. Shi, N. Xu, P. Cheng, Inorg. Chem. 52 (2013) 8082. [15] (a) L.M. Fan, W.L. Fan, B. Li, X. Zhao, X.T. Zhang, Cryst. Eng. Comm. 17 (2015) 9413; (b) J. Yang, L.L. Zhang, X.Q. Wang, R.M. Wang, F.N. Dai, D.F. Sun, RSC Adv. 5 (2015) 62982. [16] (a) T. Cao, Y.Q. Peng, T. Liu, S.N. Wang, J.M. Dou, Y.W. Li, C.H. Zhou, D.C. Lia, J.F. Bai, Cryst. Eng. Comm. 16 (2014) 10658;
X. Zhang et al. / Inorganic Chemistry Communications 73 (2016) 21–25
[17]
[18] [19] [20]
(b) D. Sun, N. Zhang, R.B. Huang, L.S. Zheng, Cryst. Growth Des. 10 (2010) 3699; (c) W. Chen, J.Y. Wang, C. Chen, Q. Yue, H.M. Yuan, J.S. Chen, S.N. Wang, Inorg. Chem. 42 (2003) 944. (a) Z.H. Li, L.P. Xue, S.H. Li, J.G. Wang, B.T. Zhao, J. Kan, W.P. Su, CrystEngComm. 15 (2013) 2745; (b) J. Zhao, L.Q. Xie, Y.M. Ma, A.J. Zhou, W. Dong, J. Wang, Y.C. Chen, M.L. Tong, CrystEngComm 16 (2014) 10006; (c) Y.R. Liu, X. Zhang, G.R. Liang, Inorg. Chem. Commun. 37 (2013) 1. H.H. Li, W. Shi, K. Zhao, Z. Niu, H. Li, P. Cheng, Chem. Eur. J. 19 (2013) 3358. H. Xu, H.G. Zheng, Inorg. Chem. Commun. 66 (2016) 51. (a) Z.F. Wu, B. Tan, M.L. Feng, A.J. Lan, X.Y. Huang, J. Mater. Chem. A 2 (2014) 6426;
25
(b) Y.P. Wang, F. Wang, D.F. Luo, L. Zhou, L.L. Wen, Inorg. Chem. Commun. 19 (2012) 43; (c) J. Yang, L.L. Zhang, X.Q. Wang, R.M. Wang, F.N. Dai, D.F. Sun, RSC Adv. 5 (2015) 62982. [21] (a) N. Kumar, S. Khullar, S.K. Mandal, RSC Adv. 4 (2014) 47249; (b) Z.C. Hu, B. B. J. D., J. L, Chem. Soc. Rev. 43 (2014) 5815; (c) D. B, Z.C. Hu, J. Li, Dalton Trans. 43 (2014) 10668. [22] (a) C.M. Teixeira, A.I. Costa, J.V. Prata, Tetrahedron Lett. 54 (2013) 6602; (b) Q. Gao, F. Liu, Y. Jiang, H. Dai, T. Fu, X. Kou, Anal. Sci. 27 (2011) 851.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Fluorescent selectivity for small molecules of two coordination polymers based on a tetracarboxylate ligand Xiao Zhang, Xiao-Qing Wang, Xiao-Xiao Wang, Zhi-jia Xue, Tuo-Ping Hu ⁎ Department of Chemistry, College of Science, North University of China, Taiyuan 030051, China
a r t i c l e
i n f o
Article history: Received 12 July 2016 Received in revised form 27 August 2016 Accepted 5 September 2016 Available online 06 September 2016 Keywords: Terphenyl-3,3″,5,5″-tetracarboxylic acid Transition-metal coordination polymer Luminescent sensing
a b s t r a c t Two coordination polymers [Cd(tptc)0.5(4,4′–bibp)]n (1) and {[Zn3(Htptc)2(phen)2]·1.5H2O}n (2) (H4tptc = terphenyl-3,3″,5,5″-tetracarboxylic acid, 4,4′-bibp = 4,4′-bis(imidazolyl)biphenyl, and phen = 1,10phenanthroline) were synthesized under solvothermal conditions. Complex 1 displays a 3D structure with a Schläfli symbol of {44.62}{48.620}. Complex 2 possesses a 2D layer network, incorporating [Zn3(COO)6] second building units (SBUs), which is packed into a 3D supramolecular architecture by π ⋯ π interactions. Both of them exhibit strong luminescence characteristics. It is worth to note that complexes 1 and 2 show potential application to detect small organic molecules. © 2016 Elsevier B.V. All rights reserved.
Over the past few decades, coordination polymers (CPs) have become a rapidly growing research project. In general, the complicated topological structure of coordination polymers can be achieved by selecting appropriate ligands, pH values, solvents, metal ions, reaction temperature, and so on [1–3]. With the prominent development, functional coordination polymers have attracted widespread attention because of the enormous potential applications in catalysis, gas adsorption and storage, drug delivery, magnetism, luminescence and so on [4–8]. Especially, luminescent coordination polymers could be applied to many kinds of fields, such as ratiometric temperature sensing, luminescence sensing, warm-white LED and fluorescent indicator [9–12]. With the tremendous improvements of economy, environmental issues, for instance, industrial pollution, exhaust emission and pesticide residue, turn into the hot topics which are drawn lots of attention [13]. These organic compounds are toxic compounds that have significant effects for the environment. Thus, the emission of anthropogenic organic compounds must be monitored, and as such, detection of organic compounds is vital. So developing chemical sensors for fast detecting harmful compounds, especially those with toxic contaminant are exceedingly pressing issues from the perspective of the ecological protection, security and human health. The traditional selective recognition of small molecules requires expensive instruments and multiple spectrometry as well as intricate characterization approaches [14]. Therefore, luminescent coordination polymers detection becomes a promising method due to the high selectivity, simple technological process, low cost, high efficiency and other advantages. Luminescent complexes are considered to be a sort of material for detecting
⁎ Corresponding author. E-mail address: [email protected] (T.-P. Hu).
http://dx.doi.org/10.1016/j.inoche.2016.09.005 1387-7003/© 2016 Elsevier B.V. All rights reserved.
small molecules. Hence, it is urgent to synthesize the luminescent coordination polymers for recognizing the toxic substances in environment. Under above background, two new luminescent coordination polymers, namely, [Cd(tptc)0.5(4,4′–bibp)]n (1) and {[Zn3(Htptc)2(phen)2]· 1.5H2O}n (2), were synthesized by solvothermal method. Compared with other compounds based on H4tptc, complexes 1 and 2 are constructed by H4tptc and auxiliary ligands, 4,4′–bibp and phen, which exhibit different structures [15]. Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the triclinic crystal system with a space group of Pī, which possesses a 3D framework with 4,8-connecting topology. The asymmetric unit contains one independent Cd1 ion, half a tptc4−, one 4,4′-bibp ligand. As shown in Fig. 1a, Cd1 is hexa-coordinated by two N atoms from two 4,4′-bibp ligands [Cd1–N1 = 2.255(6) Å and Cd–N3 = 2.365(7) Å] and four O atoms from three tptc4 − ligands [Cd1–O1 = 2.162(5) Å, Cd1–O3i = 2.363 (5) Å, Cd1–O4i = 2.520(5) Å and Cd1– O3ii = 2.501(6) Å]. The carboxyl groups of tptc4− assume different coordinating modes, which connect two neighbouring Cd(II) ions to generate the dinuclear [Cd2(COO)2] SBUs with a Cd┄Cd distance of 3.872 Å. During the reaction, four carboxylate groups of H4tptc are all deprotonated and adopt bridging (μ2-η2:η1) and monodentate (μ1-η1:η0) coordination modes. Each tptc4 − links four [Cd2(COO)2] units to give a lattice-shaped 2D layer structure along the a-axis (Fig. 1b), which are further pillared by 4,4′-bibp to form a 3D structure (Fig. 1c). To further understand the complicated architecture, the dinuclear unit is regarded as a 8-connected node, and tptc4− is served as a 4-connected node, thus the structure of complex 1 is simplified topologically a 4,8-connected two nodes with the Schläfli symbol of (44·62)(48·620) (Fig. 1d).
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Fig. 1. (a) Coordination environment of the Cd(II) ion. (b) 2D layer constructed from tptc4− and dinuclear units. (c) 3D complicated framework of 1. (d) Overall topological network for compound 1. Symmetry codes: (i) + x, 1 + y, + z; (ii) −x, 1 − y, 1 − z; (iii) −x, 2 − y, 1 − z.
Single crystal X-ray diffraction analysis reveals that complex 2 belongs to the monoclinic crystal system with the C2/c space group. The repeating unit of 2 consists of one and a half independent Zn(II) ions, one Htptc3− and one phen. As shown in Fig. 2a, Zn1 and Zn2 ions are in two different coordination environments. Each Zn1 is five-coordinated by three O atoms (O2, O3, O5) from three carboxyl groups and two nitrogen atoms (N1, N2) from one phen. Each Zn2 is six-coordinated by six O atoms (O1, O3, O4, O1i, O3i and O4i) provided by six carboxyl groups. The bond lengths of Zn1–O vary from 2.0206(18) to 2.184(2) Å, the Zn1–N1/N2 bond distances are 2.129(2) Å and 2.122(2) Å, respectively. The bond lengths of Zn2–O are in the range of 1.9869(17)–2.347(2) Å. The three carboxyl groups from Htptc3 − adopt syn-syn μ2-η1:η1, syn-anti μ2-η1:η1 and μ2-η2:η0 coordination modes, respectively. Interestingly, three Zn(II) cations are connected by six carboxyl groups to form a [Zn3(COO)6] unit, which are further organized by Htptc3− to generate a complicated 2D network (Fig. 2b). The adjacent 2D layers of 2 interact further to form a 3D supramolecular architecture through the π⋯π interactions (Fig. 2c and Table S3). The distances of Cg7iii–Cg10vi and Cg10–Cg7ii are 3.922 Å, the distances of Cg10–Cg6vi and Cg6–Cg10i are 3.917 Å and the distance of Cg6–Cg6vi is 3.540 Å (Cg6 is the centroid of ring N2, C22, C23, C24, C25, C26, Cg7 is the centroid of benzene ring C2, C3, C4, C5, C6, C7, Cg10 is the centroid of benzene ring C25, C26, C27, C28, C29, C30). The solid state luminescent spectra for complexes 1–2 were performed at room temperature. As shown in Fig. 3, the main characteristic peak of free H4tptc ligand is observed at 408 nm (λex = 280 nm). The emission band of free H4tptc ligand is attributed to the π*–n transition. Under the same experimental onditions, free phen ligand shows two shoulder emission peaks at 371 nm and 390 nm, respectively, excited at 280 nm, and 4,4′-bibp ligand has an main emission at 374 nm (λex = 280 nm) (Fig. S4). As previously reported, fluorescent emission of carboxyl ligands resulting from the π*–n transition is very weak
compared with that of the π*–π transition of the N-donor ligands, so solid-state carboxyl ligands almost have no obvious contribution to the coordination polymers based on mixed ligands [16]. Therefore, the emission bands of 1–2 would be assigned to π*–π transition of corresponding bis(pyridyl) ancillary ligands. In comparison with the emission peak of free H4tptc, the blue shift of the luminescence emissions in 1 and 2 perhaps mainly contributes to the coordination of the H4tptc ligand to the metal ions, which effectively increases the rigidity of the coordination polymers and reduces the loss of energy by radiationless decay [17]. Besides, the quantum yields φf of 1 and 2 are 2.90% and 1.10%, respectively. To further explore the sensing sensitivity of 1–2 for solvent molecules, six kinds of solvent molecules, that is, DMF, CH3OH, CH3CN, Nbutyl alcohol, acetone and DMSO, are selected for the luminescent sensing studies. Here, finely ground samples of complexes 1 and 2 (2 mg) were dispersed in various organic solvents (2 mL). As shown in Fig. 4a, complex 1 dispersed in DMSO displays the strongest luminescent intensity, which exhibits the weakest emission in acetone. 2 exhibits the strong luminescence intensity in DMF (Fig. 4b), and the emission is very weak in acetone. This phenomenon shows that complex 1 can detect acetone. A similar quenching behavior of acetone has been reported previously [18]. In order to research the recognition of complexes 1 and 2 for nitro aromatic compounds, a series of nitrobenzene derivatives, such as nitrobenzene (NB), 4-nitrotoluene (NT) 4-nitrobenzenamine (NA) and p-nitrophenol (NP), are opted as the analytes. Complex 1 presents obvious quenching effect of fluorescence intensity with increasing addition of NP, and Quenching rate of the emission reaches as much as 68% when the concentration of NP in the suspension solution is 0.15 mM (Fig. 5a). The quenching effect can be rationalized by the Stern–Volmer equation: (I0/I) = 1 + Ksv[Q], where I0 and I are the luminescence intensities of DMSO suspensions before and after addition of NP, respectively; Ksv is
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Fig. 2. (a) Coordination environment of the Zn(II) ion. (b) 2D layer constructed from Htptc3− and trinuclear units. (c) 3D supramolecular network of 2 formed by π⋯π interaction. The inset shows the details of the weak interactions. Symmetry codes: (i) 2 − x, y, 1.5 − z; (ii) x, −y, −0.5 + z; (iii) 1.5 − x, 0.5 + y, 1.5 − z; (iv) 0.5 + x, −0.5 + y, z; (vi) 1.5 − x, 0.5 − y, 1 − z.
the quenching constant (M−1); [Q] is the molar concentration of NP. The Stern–Volmer plots are nearly linear at low concentrations [19]. The Ksv value with NP is 1.37 × 104 M−1, and the limit of detection is down to 0.005 mM−1 (Fig. 6a). Compared with 1, the quenching percentage of 2 for the NA is much higher, the quenching effect is 67% (Fig. 5b). The Ksv value with NA is 1.54 × 104 M−1, and the limit of detection is down to 0.005 mM−1 (Fig. 6b). Moreover, complexes 1 and 2 exhibit higher NB sensing to compare with some Zn/Cd-MOFs [20]. The presence of an electron donating NH2 or OH group on the aromatic ring makes them possess electron donating/withdrawing ability. Thus, the long-range energy transfer plays a key role in the mechanism of
fluorescence based sensing, and the NH2 or OH group may form hydrogen-bonding interaction with the host framework, which leads that complexes 1 and 2 have higher sensing for NP and NA [21]. So far, few sensors have been reported for sensing p-nitroaniline [22]. In conclusion, two novel luminescent Cd(II)/Zn(II) coordination polymers have been successfully synthesized by solovothermal method. Complex 1 exhibits efficient fluorescence quenching behavior upon addition of NP, and the complex 2 shows better fluorescence quenching behavior in NA than 1. The study on constructing new luminescent coordination polymers based on tetracarboxylate ligand and d10 metal ions provides a promising method to detect nitro explosives. Acknowledgements The authors gratefully acknowledge the financial support of this work by the International Science & Technology Cooperation Program of China (No: 2011DFA51980), the International Scientific and Technological Cooperation Projects of Shanxi Province (No: 2015081043), “131” Leading Talents Project in Colleges and Universities, Science and Technology Innovation Project of Shanxi Province (No: 2014101002), Graduate Student Education Innovation Project of North University of China (No: 20151255). Appendix A. Supplementary data
Fig. 3. Room-temperature emission spectra for free H4tptc ligand and complexes 1–2.
The Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-1477923 and 1477922 (Fax:+44-1223-336-033; E-Mail: [email protected], http://www.ccdc.cam. ac.uk).
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Fig. 4. The photoluminescence intensities spectra of complexes 1 (a) and 2 (b) dispersed in different organic solvents.
Fig. 5. Percentage of fluorescence quenching obtained for introducing different nitro aromatic compounds into the DMSO-emulsion of complexes 1(a) and 2 (b).
Fig. 6. (a) The emission quenching linearity relationship at low concentration of NP for 1. (b) The emission quenching linearity relationship at low concentration of NA for 2.
Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.inoche.2016.09.005. References [1] (a) D.S. Li, Y.P. Wu, J. Zhao, J. Zhang, J.Y. Lu, Coord. Chem. Rev. 261 (2014) 1; (b) S.R. Zhang, S.Y. Yin, M. Pan, L. Chen, B.B. Du, Y.J. Hou, K. Wu, Y.X. Zhou, J.J. Jiang, Inorg. Chem. Commun. 55 (2015) 116; (c) W. Xu, J.J. Jiang, M. Pan, C.Y. Su, Inorg. Chem. Commun. 31 (2013) 83. [2] Q.Y. Yue, Y.M. Lu, F.X. Chuan, D. Yuan, D.Y. Chen, G.W. Yang, Q.Y. Li, Inorg. Chem. Commun. 68 (2016) 68. [3] F.T. Xie, H.Y. Bie, L.M. Duan, G.H. Li, X. Zhang, J.Q. Xu, J. Solid State Chem. 178 (2005) 2858. [4] Z.Y. Guo, S.Q. Su, R.P. Deng, H.J. Zhang, Inorg. Chem. Commun. 51 (2015) 9. [5] A. Proust, B. Matt, R. Villanneau, G. Guillemot, P. Gouzerh, G. Izzet, Chem. Soc. Rev. 41 (2012) 7605. [6] P. Horcajada, R. Gref, T. Baati, P.K. Allan, G. Maurin, P. Couvreur, G. Férey, R.E. Morris, C. Serre, Chem. Rev. 112 (2012) 673. [7] X.T. Zhang, D. Sun, B. Li, L.M. Fan, B. Li, P.H. Wei, Cryst. Growth Des. 12 (2012) 3845.
[8] D. Yan, Q. Duan, Inorg. Chem. Commun. 36 (2013) 188. [9] Y. Cui, R. Song, J. Yu, M. Liu, Z. Wang, C. Wu, Y. Yang, Z. Wang, B. Chen, G. Qian, Adv. Mater. 27 (2015) 1420. [10] A. Douvali, A.C.T.S.V. Eliseeva, S. Petoud, Angew. Chem. Int. Ed. 54 (2015) 1651. [11] Y. Cui, R. Song, J. Yu, M. Liu, Z. Wang, C. Wu, Y. Yang, Z. Wang, B. Chen, G. Qian, Adv. Funct. Mater. 25 (2015) 4796. [12] (a) S.Y. Zhang, W. Shi, P. Cheng, M.J. Zaworotko, J. Am. Chem. Soc. 137 (2015) 12203; (b) C. Yan, Y.Z. Fan, L. Chen, M. Pan, L.Y. Zhang, J.J. Jiang, C.Y. Su, CrystEngComm 17 (2015) 546. [13] (a) Y.J. Cui, Y.F. Yue, G.D. Qian, B.L. Chen, Chem. Rev. 112 (2012) 1126; (b) X.F. Zheng, L. Zhou, Y.M. Huang, C.G. Wang, J.G. Duan, L.L. Wen, Z.F. Tian, D.F. Li, J. Mater. Chem. A 2 (2014) 12413. [14] (a) K. Sumida, D.L. Rogow, J.A. Mason, T.M. McDonald, E.D. Bloch, Z.R. Herm, T.H. Bae, J.R. Long, Chem. Rev. 112 (2012) 724; (b) J.M. Zhou, W. Shi, N. Xu, P. Cheng, Inorg. Chem. 52 (2013) 8082. [15] (a) L.M. Fan, W.L. Fan, B. Li, X. Zhao, X.T. Zhang, Cryst. Eng. Comm. 17 (2015) 9413; (b) J. Yang, L.L. Zhang, X.Q. Wang, R.M. Wang, F.N. Dai, D.F. Sun, RSC Adv. 5 (2015) 62982. [16] (a) T. Cao, Y.Q. Peng, T. Liu, S.N. Wang, J.M. Dou, Y.W. Li, C.H. Zhou, D.C. Lia, J.F. Bai, Cryst. Eng. Comm. 16 (2014) 10658;
X. Zhang et al. / Inorganic Chemistry Communications 73 (2016) 21–25
[17]
[18] [19] [20]
(b) D. Sun, N. Zhang, R.B. Huang, L.S. Zheng, Cryst. Growth Des. 10 (2010) 3699; (c) W. Chen, J.Y. Wang, C. Chen, Q. Yue, H.M. Yuan, J.S. Chen, S.N. Wang, Inorg. Chem. 42 (2003) 944. (a) Z.H. Li, L.P. Xue, S.H. Li, J.G. Wang, B.T. Zhao, J. Kan, W.P. Su, CrystEngComm. 15 (2013) 2745; (b) J. Zhao, L.Q. Xie, Y.M. Ma, A.J. Zhou, W. Dong, J. Wang, Y.C. Chen, M.L. Tong, CrystEngComm 16 (2014) 10006; (c) Y.R. Liu, X. Zhang, G.R. Liang, Inorg. Chem. Commun. 37 (2013) 1. H.H. Li, W. Shi, K. Zhao, Z. Niu, H. Li, P. Cheng, Chem. Eur. J. 19 (2013) 3358. H. Xu, H.G. Zheng, Inorg. Chem. Commun. 66 (2016) 51. (a) Z.F. Wu, B. Tan, M.L. Feng, A.J. Lan, X.Y. Huang, J. Mater. Chem. A 2 (2014) 6426;
25
(b) Y.P. Wang, F. Wang, D.F. Luo, L. Zhou, L.L. Wen, Inorg. Chem. Commun. 19 (2012) 43; (c) J. Yang, L.L. Zhang, X.Q. Wang, R.M. Wang, F.N. Dai, D.F. Sun, RSC Adv. 5 (2015) 62982. [21] (a) N. Kumar, S. Khullar, S.K. Mandal, RSC Adv. 4 (2014) 47249; (b) Z.C. Hu, B. B. J. D., J. L, Chem. Soc. Rev. 43 (2014) 5815; (c) D. B, Z.C. Hu, J. Li, Dalton Trans. 43 (2014) 10668. [22] (a) C.M. Teixeira, A.I. Costa, J.V. Prata, Tetrahedron Lett. 54 (2013) 6602; (b) Q. Gao, F. Liu, Y. Jiang, H. Dai, T. Fu, X. Kou, Anal. Sci. 27 (2011) 851.