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From light to heavy alkali metal tetraphosphonates (M = Li, Na, K, Rb, Cs): cation size-induced structural diversity and water-facilitated proton conductivity

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Abstract

A family of alkali metal-based frameworks containing the tetraphosphonate ligand hexamethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid), HDTMP, is reported. A cation size-induced structural diversity, from monodimensional solids (Li+ and Na+) through layered (K+) to pillared-layered (Rb+ and Cs+) structures, was found. The proton conductivity properties of the Li compounds (hydrated and dehydrated) are reported and the influence of dehydration/rehydration processes in enhancing proton transfer processes is highlighted. Reversible changes in the dimensionality occurred upon full dehydration/rehydration with minor rearrangements in the framework, implying variations in the Li+–ligand connectivity but preserving the tetracoordination of the metal ion. The reversibly dehydrated–rehydrated sample displayed the highest proton conductivity (5 × 10−3 S cm−1 at 80 °C and 95% RH), a behavior attributed to reversible formation/reformation of P–O(H)–Li bonds that, in turn, provoked changes in the acidity of acid groups and water mobility in the temperature range of impedance measurements.

Graphical abstract: From light to heavy alkali metal tetraphosphonates (M = Li, Na, K, Rb, Cs): cation size-induced structural diversity and water-facilitated proton conductivity

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Publication details

The article was received on 11 Aug 2018, accepted on 16 Sep 2018 and first published on 17 Sep 2018


Article type: Paper
DOI: 10.1039/C8CE01351A
Citation: CrystEngComm, 2018, Advance Article
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    From light to heavy alkali metal tetraphosphonates (M = Li, Na, K, Rb, Cs): cation size-induced structural diversity and water-facilitated proton conductivity

    I. R. Salcedo, R. M. P. Colodrero, M. Bazaga-García, A. Vasileiou, M. Papadaki, P. Olivera-Pastor, A. Infantes-Molina, E. R. Losilla, G. Mezei, A. Cabeza and K. D. Demadis, CrystEngComm, 2018, Advance Article , DOI: 10.1039/C8CE01351A

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