Wideline NMR studies of ammonia intercalation complexes. I. TaS2 (NH3) and TiS2 (NH3)

Abstract

Wideline NMR observations of the ¹H and ¹⁵N nuclei in the intercalation complexes TaS₂(NH₃) and TiS₂(NH₃) have been made at temperatures from 5 to 300 K. Changes in the dynamics of the intercalated NH₃ molecules have been traced by determining the temperature dependence of the linewidths and second moments of the ¹H resonance. Above 160 K, molecular motions average the proton dipolar interactions to zero, which requires that molecular diffusion and reorientation occur at rates in excess of 10⁵ s⁻¹. The residual proton shifts reflect the magnetic properties of the complexes. Around 125 K, a strong line broadening indicates that translation and reorientation have slowed to this rate. Although translation and reorientation are correlated, the data suggests that they are not tightly coupled to one another. The molecules continus to spin about their threefold (C₃) symmetry axes at 5 K, and saturation studies of the resonance line suggest that the rate for this spinning is still ∼10⁸ s⁻¹ at this temperature. In contrast to solid NH₃, the NH₃ molecules in these intercalation complexes are much more mobile in spite of comparable molecular densities. Apparently the two dimensional character of the NH₃ array precludes the establishment of the directed hydrogen bonds that inhibit motion in solid ammonia.