Proton NMR in a hydrogen molybdenum bronze

Abstract

Solid state nuclear magnetic resonance (NMR) has been used to probe the nature of hydrogen in the hydrogen bronze H1.64MoO3. The line shape of the proton NMR at room temperature is found to be associated only with shielding anisotropy. Below 230 K, dipolar interactions become important in broadening the line. The response of the protons under a magic angle spinning experiment indicates that there is predominantly only one type of hydrogen in this sample. The shielding anisotropy indicates that at room temperature this species is not a hydroxyl proton. The longitudinal relaxation time of protons in this material exhibits a minimum between 190–320 K indicating that dipolar interactions modulated by motion are responsible for T1 relaxation. Comparison of longitudinal relaxation times of partially deuterated and nondeuterated samples indicates that there exists a contribution to T1 relaxation not dependent upon interproton distance. There does not appear to be a conduction electron contribution to the proton T1.