Relation between Exchange Interaction and Crystal Structure of Verdazyl Radicals. As Studied by Means of McConnell’s Spin Density Hamiltonian

Abstract

Abstract The exchange interactions in four kinds of verdazyl crystals, 2,4,6-triphenylverdazyl (TPV), 2,4,6-triphenyl-3-methylverdazyl (MeTPV), 2,4,6-tri-p-tolylverdazyl (TTV), and 2,6-di-p-tolyl-4-phenylverdazyl (DTPV), have been studied by means of McConnell’s spin density Hamiltonian. The calculated exchange parameters, J, have been compared with the experimental values derived from the magnetic susceptibilities. The observed order of J’s J⁄k=−5.4 (TPV), −9.1 (MeTPV), −11.1 (DTPV), and 0–−0.3 K (TTV), can be qualitatively explained by the following equation: J∝\undersetijΣ (−1⁄rij)ρilρjl+1, where ρil and ρjl+1 are π-spin densities on atoms i and j of the l-th and (l+1)-th molecules in the crystallographic column and rij is the interatomic distance between atoms i and j. The magnetic susceptibility data of MeTPV and TTV between 1.6 and 300 K are presented and interpreted with the Heisenberg linear chain model. The susceptibility of DTPV is re-interpreted in the same framework as above.