Dalton Transactions COMMUNICATION
Cite this: Dalton Trans., 2015, 44, 2970 Received 3rd March 2014, Accepted 8th January 2015 DOI: 10.1039/c4dt00640b
Second-sphere coordination-induced morphology transformation from phosphorescent nanowires to microcubes† Fengfeng Xue,a Yunsheng Ma,b Zhiguo Zhou,*a Lijie Qin,a Yang Lu,a Hong Yanga and Shiping Yang*a
www.rsc.org/dalton
Nanowires of a pyridyl-functionalized iridium complex are transformed into microcubes as a result of hydrogen-bond-assisted second-sphere coordination between pyridyl groups and monovalent anions of 1,3,5-benzenetricarboxylic acid (H2BTC−). This is accompanied by a blue-shift of the phosphorescence from 662 to 638 nm.
Phosphorescent iridium complexes, which exhibit a strong metal-to-ligand charge-transfer transition (MLCT) process, have several advantageous features, such as efficient phosphorescence, long excited-state lifetimes, and tunable phosphorescence wavelengths from the visible to the near-infrared region. Therefore, they have attracted much attention in the field of organic phosphorescent materials,1 chemosensors/ biosensors,2–4 phosphorescent probes,5–8 therapeutic agents,9 and so on. Recently, owing to their favorable properties, nanomaterials of iridium complexes have attracted much attention for their potential application in organic waveguides,10,11 upconverted luminescence emission, 12 light-emitting diodes,13–15 and photodynamic therapy.16–18 For example, Yao et al. have reported iridium complex nanowires10 and metal/ iridium complex nanowire heterostructures11 for use as waveguides and in optical signal manipulation, respectively. Lee et al.13 and Fréchet et al.14 have presented phosphorescent polymer nanoparticles and silica nanoparticles doped with iridium complexes for use in organic light-emitting diodes, respectively. Chou et al.16–18 have demonstrated the applicability of silica nanoparticles containing iridium complexes for
a The Education Ministry Key Lab of Resource Chemistry and Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, China. E-mail: [email protected], [email protected]; Fax: +86-21-64322343 b School of Chemistry and Materials Engineering, Jiangsu Key Laboratory of Advanced Functional Materials, Changshu Insititute of Technology, Changsu, Jiangsu 215500, P. R. China † Electronic supplementary information (ESI) available. CCDC 999600 and 999601. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00640b
2970 | Dalton Trans., 2015, 44, 2970–2972
photodynamic therapy. Recently, our group had reported a d–f heteronuclear complex19 and coordination polymer nanoparticles for phosphorescence imaging and magnetic resonance imaging,20 respectively. Second-sphere coordination, which refers to non-covalent bonding interaction between coordinatively saturated metal complexes (first-sphere metal complexes) and external ligands, such as hydrogen bonding, charge interaction, π–π interaction, etc., has attracted much interest because changes in the environment of first-sphere metal complexes can substantially alter their electrochemical, magnetic, and optical properties, as well as their reactivity and geometry.21 Although a number of second-sphere coordination complexes have been reported,22–24 there have been few investigations on modifying nano-systems through second-sphere coordination.25 Herein, we report the preparation of phosphorescent nanowires from a pyridyl-functionalized iridium complex by a facile solvent-evaporation route. SEM, X-ray diffraction, and laser confocal fluorescence microscopy analyses have revealed that nanowire 1 was transformed into microcubes as a result of hydrogen-bond-assisted second-sphere coordination between the pyridyl groups and monovalent anions of 1,3,5-benzenetricarboxylic acid (H2BTC−). The change in morphology was accompanied by a change in the phosphorescence properties. Nanowire 1 was prepared by solvent evaporation on a horizontal glass slide. In a typical procedure, a drop of a solution of the iridium complex (3.3 mM in CH3CN–CH3OH, 2 : 1, v/v) was placed on a glass slide at room temperature. After complete evaporation of the solvent, a uniform nanowire 1 was formed on the substrate. A typical SEM image of the product is shown in Fig. 1a. The smooth nanowire 1 had a diameter of ca. 100 nm and a length of several μm. Interestingly, in the presence of 1,3,5-benzenetricarboxylic acid (BTC) under otherwise similar conditions, nanowire 1 was transformed into regular microcubes of dimensions ∼0.6 × 0.8 × 1.2 µm3, as shown in Fig. 1b. X-ray diffraction analysis (Fig. S1†) indicated that whereas nanowire 1 was clearly amorphous, microcube 2 formed a crystalline state with three distinct (011), (020),
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Dalton Transactions
Communication
Fig. 1 (a) Typical SEM images of nanowire 1 (a) and microcube 2 (b). The inset images show a typical single nanowire 1 and microcube 2, respectively.
and (110) diffraction peaks. Energy-dispersive X-ray (EDX) spectra further confirmed that the chloride anion had been completely replaced by BTC (Fig. S2†). To investigate the morphological transformation from nanowire 1 to microcube 2 in the presence of BTC, SEM analysis was conducted on the products obtained with different BTC : 1 ratios in the CH3CN–CH3OH mixed solvent system. As shown in Fig. 2a, well-distributed nanowires with smooth surfaces were formed without BTC. In the presence of 0.1 equivalent of BTC, small irregular nanoparticles were observed in the network of nanowires (Fig. 2b). On increasing the amount of BTC, these small irregular nanoparticles gradually assembled into microcubes. The aggregation of small nanoparticles was clearly seen on the surface of the microcubes. Furthermore, the amount of aggregation of the small nanoparticles on the microcubes decreased with increasing the BTC : 1 ratio (Fig. 2c and d). When the BTC : 1 ratio was increased to 0.5, the nanowires were completely transformed into irregular smooth microcubes (Fig. 2e). Fine microcubes were obtained when the BTC : 1 ratio was higher than 0.5, as shown in Fig. 2f. To elaborate the mechanism of the morphological transformation, single-crystal X-ray structures of the iridium complexes with a chloride anion (crystal 1) and a monovalent anion of 1,3,5-benzenetricarboxylic acid (H2BTC−, crystal 2) as counter anions were determined. Both crystals 1 and 2 were
Fig. 2 SEM images of products obtained with different stoichiometries of BTC : 1. (a) 0, (b) 0.1 equivalent, (c) 0.3 equivalent, (d) 0.4 equivalent, (e) 0.5 equivalent and (f ) 0.7 equivalent.
This journal is © The Royal Society of Chemistry 2015
Fig. 3 π–π Stacking and hydrogen-bonding interactions in crystal 1 (a) and crystal 2 (b). Hydrogen atoms and chloride anions have been omitted for clarity. Ir: light purple, N: dark blue, O: red.
obtained from a solvent mixture of CH3CN and CH3OH (1/1 v/v). The crystal data of 1 were not good enough due to the residual electron on the iridium center. Compared to 1, the iridium center in the first sphere of 2 exhibits a distorted octahedral coordination geometry with similar bond lengths and angles, indicating that the second-sphere coordination has a weak effect on the iridium center (Table S2†). However, the stacking structure was obviously affected by the second-sphere coordination. As shown in Fig. 3, though significant π–π interactions were observed in both cases, the distance between the pyridyl group and the phenanthroline ligand was elongated from 3.668 Å in crystal 1 to 3.749 Å in crystal 2. More importantly, O–H⋯N hydrogen bonds were established between one carboxylic acid group of H2BTC− and a pyridyl unit with a distance of 2.628 Å. Therefore, we can infer that the assembly of nanowire 1 was mainly induced by strong π–π stacking interactions, but that a synergistic effect of π–π and hydrogen-bond interactions resulted in the formation of microcube 2. In view of the distinct 3-D structures induced by the different counter anions, we were prompted to investigate the emission properties of nanowire 1 and microcube 2. As shown in Fig. 4c, nanowire 1 and microcube 2 both exhibited broad and featureless red phosphorescence upon excitation at 405 nm, as a result of the triplet metal-to-ligand charge-transfer state (3MLCT).26 The peak of nanowire 1 was located at 662 nm, whereas the phosphorescence of microcube 2 was blue-shifted to 638 nm. This might be attributed to the hydrogen-bond-assisted second-sphere coordination between the
Dalton Trans., 2015, 44, 2970–2972 | 2971
Communication
Fig. 4 (a) Laser confocal fluorescence (a1 and b1) and bright-field (a2 and b2) images of nanowire 1 and microcube 2, respectively. (c) The emission spectra of nanowire 1 and microcube 2. The excitation wavelength was 405 nm.
carboxylic acid groups of BTC and the pyridyl units of the N^N ligand, resulting in a decrease of π–π packing interactions between the pyridyl group and the phenanthroline ligand, which can be confirmed by the crystal structures of 1 and 2.27 By virtue of their phosphorescent properties, nanowire 1 and microcube 2 could be clearly observed on a glass slide by laser confocal fluorescence microscopy upon excitation with a 405 nm laser (Fig. 4a1 and b1).
Conclusions In summary, we have employed a pyridyl-functionalized iridium complex and a monovalent anion of BTC as the donor and acceptor, respectively, of a hydrogen bond to construct a hydrogen-bond-assisted second-sphere coordination system. Through this second-sphere coordination interaction, nanowires can be transformed into microcubes. Accordingly, the phosphorescence emission peak is blue-shifted from 662 to 638 nm. This strategy should be widely applicable for modulating the morphologies and the corresponding properties of organic nanostructures.
Acknowledgements This work was partially supported by the National Natural Science Foundation of China (no. 21271130 and 21371122), Program for Changjiang Scholars and Innovative Research Team in University (no. IRT1269), Shanghai Science and Technology Fund Program (no. 12ZR1421800 and 13520502800), Shanghai Pujiang Program (13PJ1406600), Shanghai Municipal Education Commission (no. 13ZZ110) and Shanghai Normal University (no. SK201339).
Notes and references 1 C. H. Chang, M. C. Kuo, W. C. Lin, Y. T. Chen, K. T. Wong, S. H. Chou, E. Mondal, R. C. Kwong, S. Xia, T. Nakagawa and C. Adachi, J. Mater. Chem., 2012, 22, 3832.
2972 | Dalton Trans., 2015, 44, 2970–2972
Dalton Transactions
2 Q. Zhao, F. Li and C. Huang, Chem. Soc. Rev., 2010, 39, 3007. 3 H. Yang, Y. C. Zhu, L. T. Li, Z. G. Zhou and S. P. Yang, Inorg. Chem. Commun., 2012, 16, 1. 4 H. Yang, J. J. Qian, L. T. Li, Z. G. Zhou, D. R. Li, H. X. Wu and S. P. Yang, Inorg. Chim. Acta, 2010, 363, 1755. 5 Q. Zhao, C. Huang and F. Li, Chem. Soc. Rev., 2011, 40, 2508. 6 H. Yang, L. T. Li, L. Q. Wan, Z. G. Zhou and S. P. Yang, Inorg. Chem. Commun., 2010, 13, 1387. 7 Y. Chen, L. P. Qiao, L. N. Ji and H. Cao, Biomaterials, 2014, 35, 2014. 8 K. K. W. Lo, M. W. Louie and K. Y. Zhang, Coorg. Chem. Rev., 2010, 254, 2603. 9 C. H. Leung, H. J. Zhong, D. S. H. Chan and D. L. Ma, Coorg. Chem. Rev., 2013, 257, 1764. 10 H. Wang, Q. Liao, H. Fu, Y. Zeng, Z. Jiang, J. Ma and J. Yao, J. Mater. Chem., 2009, 19, 89. 11 Y. J. Li, Y. Yan, C. Zhang, Y. S. Zhao and J. Yao, Adv. Mater., 2013, 25, 2784. 12 C. Zhang, J. Y. Zheng, Y. S. Zhao and J. Yao, Chem. Commun., 2010, 46, 4959. 13 O. H. Kim, S. W. Ha, J. I. Kim and J. K. Lee, ACS Nano, 2010, 4, 3397. 14 H. Gao, D. A. Poulsen, B. Ma, D. A. Unruh, X. Zhao, J. E. Millstone and J. M. J. Fréchet, Nano Lett., 2010, 10, 1440. 15 L. J. Qin, Y. C. Zhu, H. Yang, L. Ding, F. Sun, M. Shi and S. P. Yang, Mater. Chem. Phys., 2013, 139, 345. 16 C. W. Lai, Y. H. Wang, C. H. Lai, M. J. Yang, C. Y. Chen, P. T. Chou, C. S. Chan, Y. Chi, Y. C. Chen and J. K. Hsiao, Small, 2008, 4, 218. 17 J. M. Hsieh, M. L. Ho, P. W. Wu, P. T. Chou, T. T. Tsai and Y. Chi, Chem. Commun., 2006, 615. 18 Y. K. Peng, C. W. Lai, C. L. Liu, H. C. Chen, Y. H. Hsiao, W. L. Liu, K. C. Tang, Y. Chi, J. K. Hsiao, K. E. Lim, H. E. Liao, J. J. Shyue and P. T. Chou, ACS Nano, 2011, 5, 4177. 19 H. Yang, L. Ding, L. An, Z. Xiang, M. Chen, J. Zhou, F. Li, D. Wu and S. Yang, Biomaterials, 2012, 33, 8591. 20 Z. Zhou, D. Li, H. Yang, Y. Zhu and S. Yang, Dalton Trans., 2011, 40, 11941. 21 F. M. Raymo and J. F. Stoddart, Chem. Ber., 1996, 129, 981. 22 X. J. Yang, B. Wu, W. H. Sun and C. Janiak, Inorg. Chim. Acta, 2003, 343, 366. 23 B. Wu, X. J. Yang, C. Janiak and P. Gerhard Lassahn, Chem. Commun., 2003, 902. 24 D. J. Mercer and S. J. Loeb, Chem. Soc. Rev., 2010, 39, 3612. 25 F. Zhuge, B. Wu, J. Yang, C. Janiak, N. Tang and X. J. Yang, Chem. Commun., 2010, 46, 1121. 26 W. L. Jiang, Y. Cao, Y. Sun, F. Ding, Y. Xu, Z. Q. Bian, F. Y. Li, J. Bian and C. H. Huang, Inorg. Chem., 2010, 49, 3252. 27 L. J. Qin, H. Yang, C. Y. Qin, Z. Y. Xiang, M. M. Zhang, L. Ding, T. Yi and S. P. Yang, Dalton Trans., 2013, 42, 4790.
This journal is © The Royal Society of Chemistry 2015
Copyright of Dalton Transactions: An International Journal of Inorganic Chemistry is the property of Royal Society of Chemistry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Cite this: Dalton Trans., 2015, 44, 2970 Received 3rd March 2014, Accepted 8th January 2015 DOI: 10.1039/c4dt00640b
Second-sphere coordination-induced morphology transformation from phosphorescent nanowires to microcubes† Fengfeng Xue,a Yunsheng Ma,b Zhiguo Zhou,*a Lijie Qin,a Yang Lu,a Hong Yanga and Shiping Yang*a
www.rsc.org/dalton
Nanowires of a pyridyl-functionalized iridium complex are transformed into microcubes as a result of hydrogen-bond-assisted second-sphere coordination between pyridyl groups and monovalent anions of 1,3,5-benzenetricarboxylic acid (H2BTC−). This is accompanied by a blue-shift of the phosphorescence from 662 to 638 nm.
Phosphorescent iridium complexes, which exhibit a strong metal-to-ligand charge-transfer transition (MLCT) process, have several advantageous features, such as efficient phosphorescence, long excited-state lifetimes, and tunable phosphorescence wavelengths from the visible to the near-infrared region. Therefore, they have attracted much attention in the field of organic phosphorescent materials,1 chemosensors/ biosensors,2–4 phosphorescent probes,5–8 therapeutic agents,9 and so on. Recently, owing to their favorable properties, nanomaterials of iridium complexes have attracted much attention for their potential application in organic waveguides,10,11 upconverted luminescence emission, 12 light-emitting diodes,13–15 and photodynamic therapy.16–18 For example, Yao et al. have reported iridium complex nanowires10 and metal/ iridium complex nanowire heterostructures11 for use as waveguides and in optical signal manipulation, respectively. Lee et al.13 and Fréchet et al.14 have presented phosphorescent polymer nanoparticles and silica nanoparticles doped with iridium complexes for use in organic light-emitting diodes, respectively. Chou et al.16–18 have demonstrated the applicability of silica nanoparticles containing iridium complexes for
a The Education Ministry Key Lab of Resource Chemistry and Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, China. E-mail: [email protected], [email protected]; Fax: +86-21-64322343 b School of Chemistry and Materials Engineering, Jiangsu Key Laboratory of Advanced Functional Materials, Changshu Insititute of Technology, Changsu, Jiangsu 215500, P. R. China † Electronic supplementary information (ESI) available. CCDC 999600 and 999601. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00640b
2970 | Dalton Trans., 2015, 44, 2970–2972
photodynamic therapy. Recently, our group had reported a d–f heteronuclear complex19 and coordination polymer nanoparticles for phosphorescence imaging and magnetic resonance imaging,20 respectively. Second-sphere coordination, which refers to non-covalent bonding interaction between coordinatively saturated metal complexes (first-sphere metal complexes) and external ligands, such as hydrogen bonding, charge interaction, π–π interaction, etc., has attracted much interest because changes in the environment of first-sphere metal complexes can substantially alter their electrochemical, magnetic, and optical properties, as well as their reactivity and geometry.21 Although a number of second-sphere coordination complexes have been reported,22–24 there have been few investigations on modifying nano-systems through second-sphere coordination.25 Herein, we report the preparation of phosphorescent nanowires from a pyridyl-functionalized iridium complex by a facile solvent-evaporation route. SEM, X-ray diffraction, and laser confocal fluorescence microscopy analyses have revealed that nanowire 1 was transformed into microcubes as a result of hydrogen-bond-assisted second-sphere coordination between the pyridyl groups and monovalent anions of 1,3,5-benzenetricarboxylic acid (H2BTC−). The change in morphology was accompanied by a change in the phosphorescence properties. Nanowire 1 was prepared by solvent evaporation on a horizontal glass slide. In a typical procedure, a drop of a solution of the iridium complex (3.3 mM in CH3CN–CH3OH, 2 : 1, v/v) was placed on a glass slide at room temperature. After complete evaporation of the solvent, a uniform nanowire 1 was formed on the substrate. A typical SEM image of the product is shown in Fig. 1a. The smooth nanowire 1 had a diameter of ca. 100 nm and a length of several μm. Interestingly, in the presence of 1,3,5-benzenetricarboxylic acid (BTC) under otherwise similar conditions, nanowire 1 was transformed into regular microcubes of dimensions ∼0.6 × 0.8 × 1.2 µm3, as shown in Fig. 1b. X-ray diffraction analysis (Fig. S1†) indicated that whereas nanowire 1 was clearly amorphous, microcube 2 formed a crystalline state with three distinct (011), (020),
This journal is © The Royal Society of Chemistry 2015
Dalton Transactions
Communication
Fig. 1 (a) Typical SEM images of nanowire 1 (a) and microcube 2 (b). The inset images show a typical single nanowire 1 and microcube 2, respectively.
and (110) diffraction peaks. Energy-dispersive X-ray (EDX) spectra further confirmed that the chloride anion had been completely replaced by BTC (Fig. S2†). To investigate the morphological transformation from nanowire 1 to microcube 2 in the presence of BTC, SEM analysis was conducted on the products obtained with different BTC : 1 ratios in the CH3CN–CH3OH mixed solvent system. As shown in Fig. 2a, well-distributed nanowires with smooth surfaces were formed without BTC. In the presence of 0.1 equivalent of BTC, small irregular nanoparticles were observed in the network of nanowires (Fig. 2b). On increasing the amount of BTC, these small irregular nanoparticles gradually assembled into microcubes. The aggregation of small nanoparticles was clearly seen on the surface of the microcubes. Furthermore, the amount of aggregation of the small nanoparticles on the microcubes decreased with increasing the BTC : 1 ratio (Fig. 2c and d). When the BTC : 1 ratio was increased to 0.5, the nanowires were completely transformed into irregular smooth microcubes (Fig. 2e). Fine microcubes were obtained when the BTC : 1 ratio was higher than 0.5, as shown in Fig. 2f. To elaborate the mechanism of the morphological transformation, single-crystal X-ray structures of the iridium complexes with a chloride anion (crystal 1) and a monovalent anion of 1,3,5-benzenetricarboxylic acid (H2BTC−, crystal 2) as counter anions were determined. Both crystals 1 and 2 were
Fig. 2 SEM images of products obtained with different stoichiometries of BTC : 1. (a) 0, (b) 0.1 equivalent, (c) 0.3 equivalent, (d) 0.4 equivalent, (e) 0.5 equivalent and (f ) 0.7 equivalent.
This journal is © The Royal Society of Chemistry 2015
Fig. 3 π–π Stacking and hydrogen-bonding interactions in crystal 1 (a) and crystal 2 (b). Hydrogen atoms and chloride anions have been omitted for clarity. Ir: light purple, N: dark blue, O: red.
obtained from a solvent mixture of CH3CN and CH3OH (1/1 v/v). The crystal data of 1 were not good enough due to the residual electron on the iridium center. Compared to 1, the iridium center in the first sphere of 2 exhibits a distorted octahedral coordination geometry with similar bond lengths and angles, indicating that the second-sphere coordination has a weak effect on the iridium center (Table S2†). However, the stacking structure was obviously affected by the second-sphere coordination. As shown in Fig. 3, though significant π–π interactions were observed in both cases, the distance between the pyridyl group and the phenanthroline ligand was elongated from 3.668 Å in crystal 1 to 3.749 Å in crystal 2. More importantly, O–H⋯N hydrogen bonds were established between one carboxylic acid group of H2BTC− and a pyridyl unit with a distance of 2.628 Å. Therefore, we can infer that the assembly of nanowire 1 was mainly induced by strong π–π stacking interactions, but that a synergistic effect of π–π and hydrogen-bond interactions resulted in the formation of microcube 2. In view of the distinct 3-D structures induced by the different counter anions, we were prompted to investigate the emission properties of nanowire 1 and microcube 2. As shown in Fig. 4c, nanowire 1 and microcube 2 both exhibited broad and featureless red phosphorescence upon excitation at 405 nm, as a result of the triplet metal-to-ligand charge-transfer state (3MLCT).26 The peak of nanowire 1 was located at 662 nm, whereas the phosphorescence of microcube 2 was blue-shifted to 638 nm. This might be attributed to the hydrogen-bond-assisted second-sphere coordination between the
Dalton Trans., 2015, 44, 2970–2972 | 2971
Communication
Fig. 4 (a) Laser confocal fluorescence (a1 and b1) and bright-field (a2 and b2) images of nanowire 1 and microcube 2, respectively. (c) The emission spectra of nanowire 1 and microcube 2. The excitation wavelength was 405 nm.
carboxylic acid groups of BTC and the pyridyl units of the N^N ligand, resulting in a decrease of π–π packing interactions between the pyridyl group and the phenanthroline ligand, which can be confirmed by the crystal structures of 1 and 2.27 By virtue of their phosphorescent properties, nanowire 1 and microcube 2 could be clearly observed on a glass slide by laser confocal fluorescence microscopy upon excitation with a 405 nm laser (Fig. 4a1 and b1).
Conclusions In summary, we have employed a pyridyl-functionalized iridium complex and a monovalent anion of BTC as the donor and acceptor, respectively, of a hydrogen bond to construct a hydrogen-bond-assisted second-sphere coordination system. Through this second-sphere coordination interaction, nanowires can be transformed into microcubes. Accordingly, the phosphorescence emission peak is blue-shifted from 662 to 638 nm. This strategy should be widely applicable for modulating the morphologies and the corresponding properties of organic nanostructures.
Acknowledgements This work was partially supported by the National Natural Science Foundation of China (no. 21271130 and 21371122), Program for Changjiang Scholars and Innovative Research Team in University (no. IRT1269), Shanghai Science and Technology Fund Program (no. 12ZR1421800 and 13520502800), Shanghai Pujiang Program (13PJ1406600), Shanghai Municipal Education Commission (no. 13ZZ110) and Shanghai Normal University (no. SK201339).
Notes and references 1 C. H. Chang, M. C. Kuo, W. C. Lin, Y. T. Chen, K. T. Wong, S. H. Chou, E. Mondal, R. C. Kwong, S. Xia, T. Nakagawa and C. Adachi, J. Mater. Chem., 2012, 22, 3832.
2972 | Dalton Trans., 2015, 44, 2970–2972
Dalton Transactions
2 Q. Zhao, F. Li and C. Huang, Chem. Soc. Rev., 2010, 39, 3007. 3 H. Yang, Y. C. Zhu, L. T. Li, Z. G. Zhou and S. P. Yang, Inorg. Chem. Commun., 2012, 16, 1. 4 H. Yang, J. J. Qian, L. T. Li, Z. G. Zhou, D. R. Li, H. X. Wu and S. P. Yang, Inorg. Chim. Acta, 2010, 363, 1755. 5 Q. Zhao, C. Huang and F. Li, Chem. Soc. Rev., 2011, 40, 2508. 6 H. Yang, L. T. Li, L. Q. Wan, Z. G. Zhou and S. P. Yang, Inorg. Chem. Commun., 2010, 13, 1387. 7 Y. Chen, L. P. Qiao, L. N. Ji and H. Cao, Biomaterials, 2014, 35, 2014. 8 K. K. W. Lo, M. W. Louie and K. Y. Zhang, Coorg. Chem. Rev., 2010, 254, 2603. 9 C. H. Leung, H. J. Zhong, D. S. H. Chan and D. L. Ma, Coorg. Chem. Rev., 2013, 257, 1764. 10 H. Wang, Q. Liao, H. Fu, Y. Zeng, Z. Jiang, J. Ma and J. Yao, J. Mater. Chem., 2009, 19, 89. 11 Y. J. Li, Y. Yan, C. Zhang, Y. S. Zhao and J. Yao, Adv. Mater., 2013, 25, 2784. 12 C. Zhang, J. Y. Zheng, Y. S. Zhao and J. Yao, Chem. Commun., 2010, 46, 4959. 13 O. H. Kim, S. W. Ha, J. I. Kim and J. K. Lee, ACS Nano, 2010, 4, 3397. 14 H. Gao, D. A. Poulsen, B. Ma, D. A. Unruh, X. Zhao, J. E. Millstone and J. M. J. Fréchet, Nano Lett., 2010, 10, 1440. 15 L. J. Qin, Y. C. Zhu, H. Yang, L. Ding, F. Sun, M. Shi and S. P. Yang, Mater. Chem. Phys., 2013, 139, 345. 16 C. W. Lai, Y. H. Wang, C. H. Lai, M. J. Yang, C. Y. Chen, P. T. Chou, C. S. Chan, Y. Chi, Y. C. Chen and J. K. Hsiao, Small, 2008, 4, 218. 17 J. M. Hsieh, M. L. Ho, P. W. Wu, P. T. Chou, T. T. Tsai and Y. Chi, Chem. Commun., 2006, 615. 18 Y. K. Peng, C. W. Lai, C. L. Liu, H. C. Chen, Y. H. Hsiao, W. L. Liu, K. C. Tang, Y. Chi, J. K. Hsiao, K. E. Lim, H. E. Liao, J. J. Shyue and P. T. Chou, ACS Nano, 2011, 5, 4177. 19 H. Yang, L. Ding, L. An, Z. Xiang, M. Chen, J. Zhou, F. Li, D. Wu and S. Yang, Biomaterials, 2012, 33, 8591. 20 Z. Zhou, D. Li, H. Yang, Y. Zhu and S. Yang, Dalton Trans., 2011, 40, 11941. 21 F. M. Raymo and J. F. Stoddart, Chem. Ber., 1996, 129, 981. 22 X. J. Yang, B. Wu, W. H. Sun and C. Janiak, Inorg. Chim. Acta, 2003, 343, 366. 23 B. Wu, X. J. Yang, C. Janiak and P. Gerhard Lassahn, Chem. Commun., 2003, 902. 24 D. J. Mercer and S. J. Loeb, Chem. Soc. Rev., 2010, 39, 3612. 25 F. Zhuge, B. Wu, J. Yang, C. Janiak, N. Tang and X. J. Yang, Chem. Commun., 2010, 46, 1121. 26 W. L. Jiang, Y. Cao, Y. Sun, F. Ding, Y. Xu, Z. Q. Bian, F. Y. Li, J. Bian and C. H. Huang, Inorg. Chem., 2010, 49, 3252. 27 L. J. Qin, H. Yang, C. Y. Qin, Z. Y. Xiang, M. M. Zhang, L. Ding, T. Yi and S. P. Yang, Dalton Trans., 2013, 42, 4790.
This journal is © The Royal Society of Chemistry 2015
Copyright of Dalton Transactions: An International Journal of Inorganic Chemistry is the property of Royal Society of Chemistry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
