Magnetic and Optical Properties of Ionic Electron-Donor-Acceptor Complexes

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The magnetic susceptibilities and optical absorption spectra of a number of ionic electron-donor-acceptor complexes have been studied in a solid state. The complexes of N,N,N′N′-tetra,-methyl-p-phenylenediamine with o-chloranil and o-bromanil were found to have a composition of 2 : 3 and their paramagnetic susceptibilities followed the Curie-Weiss law with the Weiss constant of 0±5°K in the temperature range between 77°K and room temperature. It was noted that in these complexes paramagnetism is dominated by the monopositive ion radical of the amine and not by the quinone part. In contrast to this, the complexes formed by combinations of p-phenylenediamine and tetramethyl-p-phenylenediamine with p-chloranil and p-bromanil had a composition of 1 : 1 and showed paramagnetic susceptibilities which varied with temperature according to the thermal equilibrium between magnetic and non-magnetic states. The thermal equilibrium is characterized by the activation energy determined by the interaction between the monopositive and the mononegative ion radicals of the components. The absorption spectra of 1 : 1 complexes showed a charge-transfer band in the near-infrared region, while those of 2 : 3 complexes did not. The activation energy obtained magnetically is discussed in relation to the appearance of the charge-transfer absorption band. The temperature dependence of the activation energy is also discussed.
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