Investigations of the Phase Transition and Proton Dynamics in Rubidium Methane Phosphonate Studied by Solid-State NMR
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- 作者：M. Vijayakumar ; Jason W. Traer ; James F. Britten ; Gillian R. Goward
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：April 3, 2008
- 年：2008
- 卷：112
- 期：13
- 页码：5221 - 5231
- 全文大小：206K
- 年卷期：v.112,no.13(April 3, 2008)
- ISSN：1932-7455
文摘
In search of new solid acid proton conductors, we prepared the solid acid rubidium methane phosphonate(RMP). These crystals have a monoclinic structure (P2/c; a = 9.3452, b = 9.3142, and c = 7.5021 Å; 
=101.12). The salt incorporates a hydrated lamellar structure. The 1H MAS NMR reveals two different typesof acidic protons as well as the water protons in the lamella. The 1H VT MAS NMR of RMP·2H2O singlecrystal shows a structural phase transition around 320 K, and the high-temperature phase exhibits significantproton dynamics. The proton proximities are established by solid state 1H DQF NMR. The dehydration ofRMP crystal leads to structural collapse, and the resultant RMP powder is extremely hygroscopic. The protonenvironment and dynamics are examined using 1H DQF NMR, which reveals that the dehydrated RMP powderhas rigid lattice, in contrast with the hydrated form. Further the 1H VT MAS NMR shows that dehydratedRMP powder has no phase transition, and no significant proton dynamics are observed in the temperaturerange of 250-350 K. The new hydrated crystal, RMP·2H2O, shows high proton mobility at relatively lowtemperature (~330 K) and a proton transport mechanism that uniquely relies on crystalline water.
=101.12). The salt incorporates a hydrated lamellar structure. The 1H MAS NMR reveals two different typesof acidic protons as well as the water protons in the lamella. The 1H VT MAS NMR of RMP·2H2O singlecrystal shows a structural phase transition around 320 K, and the high-temperature phase exhibits significantproton dynamics. The proton proximities are established by solid state 1H DQF NMR. The dehydration ofRMP crystal leads to structural collapse, and the resultant RMP powder is extremely hygroscopic. The protonenvironment and dynamics are examined using 1H DQF NMR, which reveals that the dehydrated RMP powderhas rigid lattice, in contrast with the hydrated form. Further the 1H VT MAS NMR shows that dehydratedRMP powder has no phase transition, and no significant proton dynamics are observed in the temperaturerange of 250-350 K. The new hydrated crystal, RMP·2H2O, shows high proton mobility at relatively lowtemperature (~330 K) and a proton transport mechanism that uniquely relies on crystalline water.