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 ${\mathrm{H}}_2^{17}\mathrm{O}$ . 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.