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 s table organic free radicals some of which in solid form exhibit ferrom agnetism and spin-Peierls transitions. Molecular mechanisms responsibl e for these properties remain somewhat unclear. This study reports on the growth of single crystals of several substituted verdazyls and mul tifrequency (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 ang ular, temperature, and magnetic field dependence of the EPR line width and the temperature dependence of the g-factor anisotropy provide dir ect evidence of a pseudo-low-dimensional spin diffusion in the crystal lattice. Analysis of the EPR line width for the crystal, oriented wit h the c-axis at the magic angle, theta approximate to 54.7 degrees vii ith respect to the external magnetic field, indicates a weak logarithm ic dependence upon the frequency of the EPR experiment typical for a q uasi-two-dimensional spin system.