Temperature dependence of X-band spin–lattice spin relaxation rates for the perpendicular lines in the spectra of 1 (+), 8 (◊), Cu(dtc)2 (▼), CuTTP (✰), ZnTTPbipy-Cu(hfac)2 (✚), and Cu(hfac)2−(Me2−bipy) (◆) in 2:1 toluene/chloroform solution; CuEDTA (✶), and Cu(aq)2+ (●) in water/glycerol (1:1); Cu(OH)42− in 3 M NaOH solution (■); CuIm4 (▲) in 1:1 water/ethylene glycol. T1 values were calculated using a single exponent fit to the data. The solid lines through the data are fits obtained using Eq. (2).