Inorg. Chem. 2009, 48, 4811–4816 DOI:10.1021/ic802344b
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Building Alkali-Metal-Halide Layers within a Perovskite Host by Sequential Intercalation: (A2Cl)LaNb2O7 (A = Rb, Cs) Jonglak Choi, Xiao Zhang, and John B. Wiley* Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana 70148 Received December 8, 2008
Alkali-metal-halide layers were constructed within Dion-Jacobson (DJ) layered perovskites by a two-step sequential intercalation method. Reductive intercalation with an alkali metal, followed by oxidative intercalation with chlorine gas, leads to the formation of the compounds, (A2Cl)LaNb2O7 (A = Rb, Cs). Rietveld refinement of X-ray powder diffraction data shows that an alkali-metal-halide layer is formed between the perovskite blocks. The alkali-metal cation is eightcoordinate with four oxygens from the perovskite layer and four chlorides from the new halide layer; this environment is similar to cesium in the CsCl structure (B2). Thermal analysis indicates that these are low-temperature phases where decomposition begins by 400 °C. Details on the synthesis and characterization of this set of compounds are presented, and the general utility of this approach discussed.
Introduction Topochemical reactions, such as ion exchange and intercalation/deintercalation, are powerful tools for carrying out structural modifications on receptive host compounds at low temperatures. Strategies based on these methods can be effective in forming new materials with interesting new structural, magnetic, and electronic properties.1-6 One continuing goal in this work is to develop an extensive reaction library that can serve in the directed (premeditated) construction of new active structural features. This ability could allow researchers to more effectively design new technologically significant materials such as high temperature superconductors, magnetoresistive materials, and ferroelectrics. Recently researchers have been quite successful in the manipulation of a variety of perovskite systems by topo*To whom correspondence should be addressed. E-mail:
[email protected]. (1) Schaak, R. E.; Mallouk, T. E. Chem. Mater. 2002, 14, 1455. (2) Gopalakrishnan, J. Chem. Mater. 1995, 7, 1265. (3) Tsujimoto, Y.; Tassel, C.; Hayashi, N.; Watanabe, T.; Kageyama, H.; Yoshimura, K.; Takano, M.; Ceretti, M.; Ritter, C.; Paulus, W. Nature (London) 2007, 45, 7172. (4) Yoshida, M.; Ogata, N.; Takigawa, M.; Yamaura, J.; Ichihara, M.; Kitano, T.; Kageyama, H.; Ajiro, Y.; Yoshimura, K. J. Phys. Soc. Jpn. 2007, 76, 104703. (5) Kageyama, H.; Watanabe, T.; Tsujimoto, Y.; Kitada, A.; Sumida, Y.; Kanamori, K.; Yoshimura, K.; Hayashi, N.; Muranaka, S.; Takano, M.; Ceretti, M.; Paulus, W.; Ritter, C.; Andre, G. Angew. Chem., Int. Ed. 2008, 47, 5740. (6) Machida, M.; Yabunaka, J. i.; Kijima, T. Chem. Mater. 2000, 12 812. (7) Caignaert, V.; Millange, F.; Domenges, B.; Raveau, B.; Suard, E. Chem. Mater. 1999, 11(4), 930.
© 2009 American Chemical Society
chemical methods.7-9 Reactions with the layered perovskites Dion-Jacobson (DJ), A[A0 n-1BnO3n+1], and RuddlesdenPopper (RP), A2[A0 n-1BnO3n+1] (A is an alkali-metal cation, A0 is typically an alkaline-earth or rare-earth cation, and B a d0 transition metal cation), have been especially fruitful. These sets of compounds readily undergo ion exchange10-13 and the DJ series are also receptive to reductive intercalation.14-16 One goal among current researchers has been to use such layered hosts as templates for the interlayer growth of new metal-anion arrays; the formation of such layers can be viewed analogously to epitaxial thin film growth, though here the new layer forms within a crystal instead of on the surface. Some of the initial reports in this area have involved the formation of transition-metal-halide and metal-oxide layers. Metal-halide layers (MX; M = V, Cr, Mn, Fe, Co, Cu; X = Cl (and Br for M = Cu)) have been constructed within DJ hosts by ion exchange with simple metal halides :: (8) Gonen, Z. S.; Paluchowski, D.; Zavalij, P.; Eichhorn, B. W.; Gopalakrishnan, J. Inorg. Chem. 2006, 45, 8736. (9) Schottenfeld, J. A.; Kobayashi, Y.; Wang, J.; Macdonald, D. D.; Mallouk, T. E. Chem. Mater. 2008, 20, 213. (10) Gopalakrishnan, J.; Bhat, V.; Raveau, B. Mater. Res. Bull. 1987, 22, 413. (11) Sato, M.; Abo, J.; Jin, T.; Ohta, M. J. Alloys Comp. 1993, 192 81. (12) Sato, M.; Abo, J.; Jin, T. Solid State Ionics 1992, 57, 285. (13) Sato, M.; Jin, T.; Ueda, H. Chem. Lett. 1994, 1, 161. (14) Armstrong, A. R.; Anderson, P. A. Inorg. Chem. 1994, 33 4366. (15) Toda, K.; Takahashi, M.; Teranishi, T.; Ye, Z. G.; Sato, M.; Hinatsu, Y. J. Mater. Chem. 1999, 9, 799. (16) Bohnke, C.; Bohnke, O.; Fourquet, J. L. J. Electrochem. Soc. 1997, 144, 1151.
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(MX2) to produce compounds such as (MX)LaNb2O7. Metal-oxide layers have been inserted into layered perovskites by reactions with mixed-metal oxyhalides;23,24 Ca2La2CuTi2O10, for example, has been prepared from NaLaTiO4 and Ca2CuO2Cl2.24 Multistep topochemical reaction strategies have also been reported. Methods involving a combination of ion exchange and reductive intercalation were utilized to construct tetrahedrally coordinated lithium- and sodiumchloride layers within DJ hosts.25,26 Herein we report a new multistep reaction strategy for the fabrication of metal-halide arrays with large alkali-metal cations. A two-step sequential reductive-oxidative intercalation procedure is used to build alkali-metal-halide layers within a layered perovskite. The resulting new compounds, (A2Cl)LaNb2O7 (A = Rb, Cs), have alkali-halide layers with cesium-chloride-like structural features.27 Experimental Section Synthesis.
ALaNb2O7 (A = Li, Na, K, Rb, and Cs).
RbLaNb2O7 and CsLaNb2O7, were prepared by methods similar to those reported in the literature;10,28,29 well-ground stoichiometric mixtures of La2O3 (Alfa Aesar, 99.99%), Nb2O5 (Alfa Aesar, 99.9985%), and a 25% molar excess of Rb2CO3 (Alfa Aesar, 99.0%) or Cs2CO3 (Alfa Aesar, 99.9%), respectively, were heated for ∼12 h at 850 °C and for 24 h at 1050 °C with one intermediate grinding. The excess of carbonate was added to balance that lost because of volatilization. After the reaction, the products were washed thoroughly with distilled water and dried with acetone followed by overnight heating at 150 °C. The other members of the series, ALaNb2O7 (A = Li, Na, and K), were obtained by ion exchange of RbLaNb2O7 with a 10:1 molar ratio of the alkali metal nitrates, LiNO3 (Alfa Aesar, 99.0% anhydrous), NaNO3 (Alfa Aesar, 99.999%), and KNO3 (Alfa Aesar, 99.997%), for 4 days at 300, 310, and 350 °C, respectively.10-12 The resulting products, LiLaNb2O7 and KLaNb2O7, were washed with distilled water and dried with acetone followed by overnight heating at 150 °C. After washing, the hygroscopic NaLaNb2O7 was dried at 260 °C in air18 and quickly transferred to a drybox. The unit cells of the products, as determined by X-ray powder diffraction, were all in good agreement with published results.10-14 (17) Kodenkandath, T. A.; Lalena, J. N.; Zhou, W. L.; Carpenter, E. E.; Sangregorio, C.; Falster, A. U.; Simmons, W. B. Jr.; O’Connor, C. J.; Wiley, J. B. J. Am. Chem. Soc. 1999, 121, 10743. (18) Kodenkandath, T. A.; Kumbhar, A. S.; Zhou, W. L.; Wiley, J. B. Inorg. Chem. 2001, 40, 710. (19) Viciu, L.; Caruntu, G.; Royant, N.; Koenig, J.; Zhou, W. L.; Kodenkandath, T. A.; Wiley, J. B. Inorg. Chem. 2002, 41, 3385. (20) Viciu, L.; Koenig, J.; Spinu, L.; Zhou, W. L.; Wiley, J. B. Chem. Mater. 2003, 15, 1480. (21) Tsujimoto, Y.; Kageyama, H.; Baba, Y.; Kitada, A.; Yamamoto, T.; Narumi, Y.; Kindo, K.; Nishi, M.; Carlo, J. P.; Aczel, A. A.; Williams, T. J.; Goko, T.; Luke, G. M.; Uemura, Y. J.; Ueda, Y.; Ajiro, Y.; Yoshimura, K. Phys. Rev. B 2008, 78, 214410. (22) Tsujimoto, Y.; Baba, Y.; Oba, N.; Kageyama, H.; Fukui, T.; Narumi, Y.; Kindo, K.; Saito, T.; Takano, M.; Ajiro, Y.; Yoshimura, K J. Phys. Soc. Japan 2007, 76, 063711. (23) Gopalakrishnan, J.; Sivakumar, T.; Ramesha, K.; Thangadurai, V.; Subbanna, G. N. J. Am. Chem. Soc. 2000, 122, 6237. (24) Sivakumar, T.; Lofland, S. E.; Ramanujachary, K. V.; Ramesha, K.; Subbanna, G. N.; Gopalakrishnan, J. J. Solid State Chem. 2004, 177, 2635. (25) Viciu, L.; Kodenkandath, T. A.; Wiley, J. B. J. Solid State Chem. 2007, 180, 583. (26) Viciu, L.; Zhang, X.; Kodenkandath, T. A.; Golub, V.; Wiley, J. B. Mater. Res. Soc. Symp. Proc. 2007, 988, 0988-QQ08-04. (27) It should be noted that preliminary results for (Rb2Cl)LaNb2O7 were initially revealed in reference 26. (28) Dion, M.; Ganne, M.; Tournoux, M. Mater. Res. Bull. 1981, 16, 1429. (29) Viciu, L.; Liziard, N.; Golub, V.; Kodenkandath, T. A.; Wiley, J. B. Mater. Res. Bull. 2007, 42 (1), 196.
Reductive Intercalation. A2LaNb2O7 (A = Li, Na, K, Rb, and Cs) were prepared by reductive intercalation of the ALaNb2O7 series. Initially ALaNb2O7 pellets (typically 0.5 g, 7 mm dia.), prepared with a simple hand press (Aldrich Quick Press), were placed in a Pyrex tube, and thoroughly dried with a heat gun under dynamic vacuum. Cs2LaNb2O7 was obtained by intercalation of CsLaNb2O7 with Cs metal vapor (Alfa Aesar, 99.98%). A slight excess of alkali metal, molar ratio of about 1:
