Heat capacity of potassium p-chloranil anion radical salt between 13 and 330 K.

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概要

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• The heat capacity measurement for an organic free-radical salt, potassium <I>p</I>-chloranil, revealed a first-order phase transition at <I>T</I><SUB>c</SUB>=260.01 K. In spite of a first-order nature, the pre- and the post-transitional effects are remarkable. The enthalpy and the entropy of transition were determined to be <I>ΔH</I>=2796 J mol<SUP>−1</SUP> and <I>ΔS</I>=11.06 JK<SUP>−1</SUP> mol<SUP>−1</SUP>, respectively. The magnetic contribution to <I>ΔS</I> is only 2.23 JK<SUP>−1</SUP> mol<SUP>−1</SUP> when a dimeric configuration with a singlet-triplet spin equilibrium is assumed in the low temperature phase and a monomeric behavior of radicals with spin doublet is assumed above <I>T</I><SUB>c</SUB>. The present phase transition bears a close resemblance to a spin-Peierls transition in a linear chain system. The infrared spectrum at 120 K indicates a possible formation of dimers in the low temperature phase of this salt. A phenomenological model for the present phase transition is presented.

• 公益社団法人 日本化学会の論文

著者

• Seki Syuzo

  Department Of Chemistry Faculity Of Science Osaka University

• SORAI Michio

  Department of Chemistry, Faculty of Science, Osaka University

• Sorai Michio

  Department Of Chemistry Faculty Of Science Osaka University

• Suga Hiroshi

  Department Of Chemistry Faculty Of Science Osaka University

• Kosaki Akio

  Department of Chemistry, Faculty of Science, Osaka University

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