Chemical exchange and conductivity processes in betaine phosphate and betaine phosphite

Abstract

Chemical exchange processes of deuterons in partially deuterated betaine phosphate (DBP) and betaine phosphite (DBPI) crystals are investigated by means of NMR experiments over a wide temperature range. The lineshape analysis of one-dimensional (1D) NMR experiments on DBP reveals a behaviour which is characteristic for exchange processes between all deuterons in the hydrogen bonds. In the temperature range between 230 and 310 K two-dimensional (2D) NMR exchange spectroscopy has been applied, revealing a uniform rate of exchange between all sites. The exchange rates for both crystals are found to show an Arrhenius-like behaviour with activation energies of 83 and , respectively, where for temperatures above 360 K the rates are obtained from the lineshape analysis of 1D NMR spectra. In addition, conductivity measurements for DBP and DBPI are reported. The dc conductivity in the direction of the quasi-one-dimensional chains, formed essentially by the phosphate and phosphite groups in DBP and DBPI, is characterized by activation energies of 115 and , respectively. For DBPI this value is close to that obtained for the exchange processes by means of NMR, whereas a difference of about is found in the case of DBP. Quantitative relations between the exchange and conductivity processes are established and, on the basis of simplifying assumptions, an estimation of effective charge-carrier densities is discussed.