Tuning Proton Conductivity in Alkali Metal Phosphonocarboxylates by Cation Size-Induced and Water-Facilitated Proton Transfer Pathways
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- 作者：Montse Bazaga-Garc铆a ; Maria Papadaki ; Rosario M. P. Colodrero ; Pascual Olivera-Pastor ; Enrique R. Losilla ; Bel茅n Nieto-Ortega ; Miguel 脕ngel G. Aranda ; Duane Choquesillo-Lazarte ; Aurelio Cabeza ; Konstantinos D. Demadis
- 刊名：Chemistry of Materials
- 出版年：2015
- 出版时间：January 27, 2015
- 年：2015
- 卷：27
- 期：2
- 页码：424-435
- 全文大小：730K
- ISSN：1520-5002
文摘
The structural and functional chemistry of a family of alkali-metal ions with racemic R,S-hydroxyphosphonoacetate (M-HPAA; M = Li, Na, K, Cs) are reported. Crystal structures were determined by X-ray data (Li+, powder diffraction following an ab initio methodology; Na+, K+, Cs+, single crystal). A gradual increase in dimensionality directly proportional to the alkali ionic radius was observed. [Li3(OOCCH(OH)PO3)(H2O)4]路H2O (Li-HPAA) shows a 1D framework built up by Li-ligand 鈥渟labs鈥?with Li+ in three different coordination environments (4-, 5-, and 6-coordinated). Na-HPAA, Na2(OOCCH(OH)PO3H)(H2O)4, exhibits a pillared layered 鈥渉ouse of cards鈥?structure, while K-HPAA, K2(OOCCH(OH)PO3H)(H2O)2, and Cs-HPAA, Cs(HOOCCH(OH)PO3H), typically present intricate 3D frameworks. Strong hydrogen-bonded networks are created even if no water is present, as is the case in Cs-HPAA. As a result, all compounds show proton conductivity in the range 3.5 脳 10鈥? S cm鈥? (Cs-HPAA) to 5.6 脳 10鈥? S cm鈥? (Na-HPAA) at 98% RH and T = 24 掳C. Differences in proton conduction mechanisms, Grothuss (Na+ and Cs+) or vehicular (Li+ and K+), are attributed to the different roles played by water molecules and/or proton transfer pathways between phosphonate and carboxylate groups of the ligand HPAA. Upon slow crystallization, partial enrichment in the S enantiomer of the ligand is observed for Na-HPAA, while the Cs-HPAA is a chiral compound containing only the S enantiomer.