Concerted Ligand Exchange and the Roles of Counter Anions in the Reversible Structural Switching of Crystalline Peptide Metallo-Macrocycles

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• 作者：Ryosuke Miyake ; Mitsuhiko Shionoya
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 2, 2014
• 年：2014
• 卷：53
• 期：11
• 页码：5717-5723
• 全文大小：478K
• 年卷期：v.53,no.11(June 2, 2014)
• ISSN：1520-510X

文摘

To understand reversible structural switching in crystalline materials, we studied the mechanism of reversible crystal-to-crystal transformation of a tetranuclear Ni^II macrocycle consisting of artificial 尾-dipeptides. On the basis of detailed structural analyses and thermodynamic measurements made in a comparison of pseudo-isostructural crystals (NO₃ and BF₄ salts), we herein discuss how ligand-exchange reactions take place in the crystal due to changes in water content and temperature. Observations of the structural transformation of NO₃ salt indicated that a pseudo crystalline phase transformation takes place through concerted ligand-exchange reactions at the four Ni^II centers of the macrocycle with hydrogen bond switching. A mechanism for this ligand exchange was supported by IR spectroscopy. Thermodynamic measurements suggested that the favorable compensation relationship of the enthalpy changes due to water uptake and structural changes are keys to the reversible structural transformation. On the basis of a comparison with the pseudo-isostructural crystals, it is apparent that the crystal packing structure and the types of counter anions are important factors for facilitating reversible ligand exchange with single crystallinity.