IR Studies of H/D Exchange of Water, Hydroxyl, and Carboxylic Groups Reveal Slowly Diffusing Lattice Defects in Sub-Nanometer Pores

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• 作者：Natalia Pe虂rez-Herna虂ndez ; Marti虂n Febles ; Cirilo Pe虂rez ; Johann Spandl ; Julio D. Marti虂n ; Hans-Heinrich Limbach
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：May 19, 2011
• 年：2011
• 卷：115
• 期：19
• 页码：9393-9402
• 全文大小：1049K
• 年卷期：v.115,no.19(May 19, 2011)
• ISSN：1932-7455

文摘

We have studied the properties of a series of solid hydrated organic porous networks with pore diameters ranging from approximately 0.4 to 0.9 nm using the attenuated total reflection infrared (ATR-IR) technique. These subnanometer organic pores are composed of water and of organic racemic bicyclic monomers containing carboxylic, alcoholic, ether functions and different appendices. In particular, the doubly hydrated hydroxyl acids 1 2H₂O and 2 2H₂O form cylindrical pores in which half of the water molecules are part of the walls and the other half are located inside the pores. In a first step, by a comparison of the spectra of a family of related compounds, the COOH, COH as well as the wall and pore water stretches were assigned. The COOH bands are broad and red-shifted as compared to carboxylic acid dimers, and exhibit a substructure assigned to Fermi resonances. The OH stretches fulfill well Novak鈥檚 correlation with the corresponding crystallographic O...O distances. In a second step, we have followed the deuteration of the different functional groups of solid 2 2H₂O by ATR-IR by heavy water vapor. Surprisingly, we observe that the rates of deuteration are the same for all functional groups although exhibiting biexponential time dependence, in contrast to the liquid state where COOH groups exchange protons with water much faster than with alcohols. This result is rationalized in terms of slowly diffusing lattice defects resembling a local liquid or glass in the subnano scale in which the different exchange reactions take place. The nonexponential deuteration is explained in terms of a faster deuteration of crystal surface layers.