Field dependence of nuclear magnetic relaxation of 119Sn in SnCl4, SnBr4, and SnI4

Longitudinal and transverse relaxation times of ¹¹⁹Sn have been measured as a function of temperature at several field strengths in SnCl₄, SnBr₄, and SnI₄. T₂ in all three liquids is field independent and is governed by scalar coupling to the halogen. T₁ is strongly field dependent in SnBr₄ and SnI₄ and exhibits a minimum with increasing temperature due to competing scalar and spin‐rotation interactions. Coupling constants and correlation times previously computed for SnCl₄ and SnI₄ have been confirmed by measurements at 3.3 kg. Analysis of the data for SnBr₄ yield J(¹¹⁹Sn–⁸¹Br)=920 Hz, T₂(⁸¹Br)=0.748×10⁻⁶ sec at 294°K, and ${\tau }_{\theta }^{\text{(2)}}$ =3.1×10⁻¹² sec at 294°K. Molecular reorientation in SnBr₄ is highly unusual in that the reduced angular correlation time τ_θ* reaches a minimum value owing to the onset of dynamically coherent reorientation at a temperature (80°C) that is not far above the melting point (30°C), and τ_θ* remains in the inertial rotation region over much of the liquid range. Various other indications of significant dissimilarity of microdynamical behavior in SnCl₄, SnBr₄, and SnI₄ are pointed out. Assuming the validity of the J‐diffusion model, we complete the spin‐rotation and magnetic shielding constants for SnBr₄, but these results are not consistent with the chemical shifts and shielding constants previously inferred for SnCl₄. The inconsistency is believed to be associated with the extremely small reduced frictional constant of SnBr₄ and with the possibly inappropriate use of extended diffusion theory to describe reorientation in this liquid.