Single-Crystal Multifrequency EPR Evidence for a Quasi-Low-Dimensional Spin Exchange in 3-n-Butyl-2,4,6-Triphenylverdazyl

Verdazyls, 1,2,3,4-tetrahydro-s-tetrazin-1-(2H-yls), are a series of stable organic free radicals some of which in solid form exhibit ferromagnetism and spin-Peierls transitions. Molecular mechanisms responsible for these properties remain somewhat unclear. This study reports on the growth of single crystals of several substituted verdazyls and multifrequency (1.4−94.3 GHz) EPR measurements on single crystals of 3-n-butyl-2,4,6-triphenylverdazyl, a model compound in the series. The angular, temperature, and magnetic field dependence of the EPR line width and the temperature dependence of the g-factor anisotropy provide direct evidence of a pseudo-low-dimensional spin diffusion in the crystal lattice. Analysis of the EPR line width for the crystal, oriented with the c-axis at the magic angle, θ ≈ 54.7° with respect to the external magnetic field, indicates a weak logarithmic dependence upon the frequency of the EPR experiment typical for a quasi-two-dimensional spin system.