Anomalous Magnetic Behavior in Three Kinds of 3-(Aryl-substituted)-1,5-diphenylverdazyl Radical Crystals (p-FPDV, p-PyDV and m-PyDV) Induced by Frustrated Spin Interaction

摘要

Magnetic susceptibilities (χ_M) of three kinds of 3-(aryl-substituted)-1,5-diphenyl-verdazyl radical crystals (aryl: 4-fluorophenyl (p-FPDV), 4-pyridyl (p-PyDV), and 3-pyridyl (m-PyDV)) have been measured between 1.8 and 300 K, showing a broad maximum T_(max) at 200, 272, and 157 K, respectively. The values of T_(max) observed are 1 or 2 orders of magnitude larger than those for usual organic neutral radical crystals, suggesting strong intermolecular antiferromagnetic (AFM) exchange interactions (J) in the crystals. The temperature dependence of the susceptibilities cannot be explained by a simple model, such as the one-dimensional (1D) Heisenberg AFM linear- and alternating-chain model. The values of χ_M observed for the p-FPDV, p-PyDV and m-PyDV radicals are about 42, 76, and 35% larger than the corresponding values calculated by a 1D Heisenberg AFM linear-chain model at each temperature. The result of the crystal structure analysis of p-FPDV inicates the existence of butterfly-type spin frustration in the system. The origin of the anomalous magnetic behavior observed for these verdazyl radical crystals has been discussed based on the results of the crystal structure analysis and unpaired spin density calculation.