Magnetic properties of 1,5-dimethyl-6-oxoverdazyl radical crystals. Observation of a spin-Peierls transition in 3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl radical, p-CyDOV

Magnetic susceptibilities of 5 kinds of 3-(4-R-phenyl)-1,5-dimethyl-6-oxoverdazyl radicals (PDOV (R  H), p-MDOV (R  CH3O), p-MeDOV (R  CH3), p-CyDOV (R  CN), and p-NDOV (R  NO2)) have been measured in the temperature range of 4.2–300 K. The susceptibilities of PDOV, p-MDOV, and p-MeDOV can be explained by an antiferromagnetic Heisenberg alternating chain model. The susceptibility of p-CyDOV shows a broad maximum at 54 K, and decreases abruptly at 15 K, suggesting a spin-Peierls transition. High-field magnetization data (H = 0−35 T) which provide a clear evidence for a spin-Peierls transition were reported.