Magnetic Behavior of Organic Free Radicals with Localized and Delocalized Electrons

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Abstract
Magnetic and thermal properties have been studied on two kinds of organic free radicals, TANOL(2,2,6,6-tetramethyl-4-piperidinol-1-oxyl) and TPV(1,3,5-triphenylverdazyl), where the unpaired electrons are localized on the NO bond in the former compound but delocalized on the larger molecular orbitals in the latter. TANOL has been confirmed magnetically as a typical one-dimensional Heisenberg system with localized quantum spins coupled with the exchange constant J / k B =-5.2 K. On the other hand, the experimental results on TPV can not reasonably be understood on the basis of a localized model with the possible paths of magnetic interactions such as a railroad trestle lattice. It is suggested that organic free radicals offer promising real systems for getting essential physical phenomena which can check model Hamiltonians for a delocalized and frustrated quantum system.