Tm was determined by fitting Hahn echo decays to a stretched exponential function (see Supporting Information Eqn 1; Figures ). The maximum Tm relaxation times observed are 0.7, 1.0 and 1.7 μs for 1-Nd, 1-Ce and 1-Sm, respectively (Tables ), in each case measured at the highest field g-value. Tm measured at the EDFS maxima are 0.5, 0.6 and 1.6 μs, respectively.