Guest Molecule-Responsive Functional Calcium Phosphonate Frameworks for Tuned Proton Conductivity
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- 作者：Montse Bazaga-Garc铆a ; Rosario M. P. Colodrero ; Maria Papadaki ; Piotr Garczarek ; Jerzy Zo艅 ; Pascual Olivera-Pastor ; Enrique R. Losilla ; Laura Le贸n-Reina ; Miguel A. G. Aranda ; Duane Choquesillo-Lazarte ; Konstantinos D. Demadis ; Aurelio Cabeza
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：April 16, 2014
- 年：2014
- 卷：136
- 期：15
- 页码：5731-5739
- 全文大小：551K
- 年卷期：v.136,no.15(April 16, 2014)
- ISSN：1520-5126
文摘
We report the synthesis, structural characterization, and functionality (framework interconversions together with proton conductivity) of an open-framework hybrid that combines Ca2+ ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]路5H2O (Ca-PiPhtA-I) is obtained by slow crystallization at ambient conditions from acidic (pH 鈮?3) aqueous solutions. It possesses a high water content (both Ca coordinated and in the lattice), and importantly, it exhibits water-filled 1D channels. At 75 掳C, Ca-PiPhtA-I is partially dehydrated and exhibits a crystalline diffraction pattern that can be indexed in a monoclinic cell with parameters close to the pristine phase. Rietveld refinement was carried out for the sample heated at 75 掳C, Ca-PiPhtA-II, using synchrotron powder X-ray diffraction data, which revealed the molecular formula Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]. All connectivity modes of the 鈥減arent鈥?Ca-PiPhtA-I framework are retained in Ca-PiPhtA-II. Upon Ca-PiPhtA-I exposure to ammonia vapors (28% aqueous NH3) a new derivative is obtained (Ca-PiPhtA-NH3) containing 7 NH3 and 16 H2O molecules according to elemental and thermal analyses. Ca-PiPhtA-NH3 exhibits a complex X-ray diffraction pattern with peaks at 15.3 and 13.0 脜 that suggest partial breaking and transformation of the parent pillared structure. Although detailed structural identification of Ca-PiPhtA-NH3 was not possible, due in part to nonequilibrium adsorption conditions and the lack of crystallinity, FT-IR spectra and DTA-TG analysis indicate profound structural changes compared to the pristine Ca-PiPhtA-I. At 98% RH and T = 24 掳C, proton conductivity, 蟽, for Ca-PiPhtA-I is 5.7 脳 10鈥? S路cm鈥?. It increases to 1.3 脳 10鈥? S路cm鈥? upon activation by preheating the sample at 40 掳C for 2 h followed by water equilibration at room temperature under controlled conditions. Ca-PiPhtA-NH3 exhibits the highest proton conductivity, 6.6 脳 10鈥? S路cm鈥?, measured at 98% RH and T = 24 掳C. Activation energies (Ea) for proton transfer in the above-mentioned frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism of proton conduction. These results underline the importance of internal H-bonding networks that, in turn, determine conductivity properties of hybrid materials. It is highlighted that new proton transfer pathways may be created by means of cavity 鈥渄erivatization鈥?with selected guest molecules resulting in improved proton conductivity.