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.

Chemical exchange in NH4HSeO4single crystals studied by two-dimensional2H nuclear magnetic resonance

“…They are in agreement with the expected range of values for deuteron jumps in crystals with hydrogen bonds, e.g. like in betaine compounds such as betaine phosphate (83 kJ mol −1 ) and others [15]. For the pre-exponential factors p 0 , we find values of 1.6 × 10 13 s −1 and 1.9 × 10 14 s −1 .…”

“…The order of magnitude of these data is potentially of interest for the comparison of these results with conductivity measurements, which are still in progress. It has been shown recently for the mixed crystal system of deuterated betaine phosphate/phosphite [15,16] that by means of establishing a relationship between chemical exchange and conductivity processes new findings on the charge carriers in systems with ionic conductivity can be obtained.…”

NMR relaxation study of disorder in condensed matter: solid solutions of betaine phosphate and phosphite

“…The crystal structure diagrams of DBP and DBPI (deuterated BP and BPI) were reported by Braeter et al [30], Freude et al [31] and Dvorak [32].…”

2H nuclear magnetic resonance studies on the deuteron dynamics in betaine phosphate/phosphite mixed crystals

“…In order to study the dynamics of this exchange process and to find explanations for the different exchange rates in pure DBP and DBPI, similar considerations to those for the pure substances in [19] on the calculation of an absorption spectrum are necessary [20]. For the system DBP 1−x DBPI x we find a total of seven (four of DBP and three of DBPI) deuterium sites taking part in the exchange processes.…”

“…The second significant phenomenon which can be inferred from the temperature dependence of the 2 H NMR spectra (figure 5) is a broadening and overlapping of the 2 H NMR lines originating from the bridging deuterons (except the H 14 line of DBPI) if the temperature is increased above ≈330 K. These changes of line shape can be clearly attributed to chemical exchange processes which can be expected from having in mind the exchange phenomena observed in the pure compounds [19]. However, even at the highest temperatures measured (≈400 K) no averaged line pair belonging to the bridging deuterons can be observed.…”