Magnetic properties of 1,3,5,6-tetraphenyl- and related verdazyls

Abstract

The magnetic properties of 1,3,5,6-tetraphenyl-verdazyl and related verdazyls were characterized by static magnetic susceptibility measurements (1.8K ≤ T ≤ 300K, H ≤ 55 kOe), ESR (10 GHz, solid and solution) and proton NMR (360 MHz, dilute solution). Concentration of radical spins, asymptotic Curie temperature, 1d-exchange integral, ESR linewidth (and thus the strength of exchange narrowing) and spin densities (from proton paramagnetic shifts) were derived. The onedimensional antiferromagnetic exchange interaction is increased by a factor larger than 3 if one additional phenyl unit is added to 1,3,5–6-triphenyl-verdazyl (TPV). The unsymmetrical substitution of TPV by 3-trifluoromethylphenyl reduces the 1d antiferromagnetic exchange drastically, in contrast to the symmetrical substitution by 4-trifluoromethylphenyl.