Field dependence of nuclear magnetic relaxation of 207Pb in aqueous Pb(ClO4)2

Nuclear magnetic relaxation times of the 207Pb resonance have been measured as a function of temperature and concentration at field strengths of 16.9, 11.7, and 6.56 kG in aqueous Pb(ClO4)2. Longitudinal relaxation is composed of spin-rotation, chemical shift anisotropy, and dipolar contributions in a 3.5M solution, while spin-rotation strongly dominates the relaxation at all temperatures between the melting and boiling points in a 1.15M solution. T2 accurately equals T1 at 1.15M, as is expected for a dominant spin-rotation interaction, but is 20–30% shorter in the 3.5M solution, possibly due to a minor relaxation component arising from scalar coupling to naturally abundant H217O. Chemical shifts of 207Pb have also been measured in aqueous Pb(ClO4)2 and Pb(NO3)2. The chemical shift and relaxation data show that ClO4− penetrates the Pb+2 hydration sphere at concentrations above about 2M, but no effects of such penetration are seen at lower concentration.