Structural phase transitions induced by molecular motions within an (anilinium)(l-tartrate) ionic molecular crystal

Yuya Yoshii, Norihisa Hoshino, Takayoshi Nakamura, Tomoyuki Akutagawa

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    14 Citations (Scopus)


    Ionic molecular crystals of (anilinium+)(l-tartrate-) were prepared in C2H5OH-H2O via Bronsted acid-base reaction between aniline and l-tartaric acid. Strong intermolecular O-H⋯O- hydrogen-bonding interactions between the terminal -COOH and -COO- groups of the l-tartrate- monoanion (l-HTart-) are essential in forming the one-dimensional hydrogen-bonding (l-HTart-) chains. Furthermore, N-H+⋯O- hydrogen-bonding interactions between l-HTart- and the ammonium moiety of anilinium (Ani+) form a π-stacking arrangement of the Ani+ cations that are orthogonal to the (l-HTart-) chains. DSC analysis revealed a two-step behavior with reversible phase transitions at ∼220 and ∼270 K, in which three types of crystal phases (I, T < 220 K; II, 220 < T < 270 K; III, 270 K < T) were identified. Phase I possesses the same acentric space group (P1), while its unit cell volume is half of that of phases II and III, in which the π-stacking periodicity of the Ani+ cations of phases II and III are double that of phase I. Although the conformation of the hydroxy (-OH) groups of l-HTart- of phase II (T = 250 K) was identical to that of phase I (T = 100 K), the rotation of the C-OH bond (activation energy of ∼70 kJ mol-1) was observed for phase III. The thermal fluctuation of the polar -OH group in phase III was dominated by a single minimum-type potential energy curve, as evaluated from the calculations. The temperature- and frequency-dependent dielectric constants suggested a low-frequency thermal fluctuation at temperatures above ∼250 K.

    Original languageEnglish
    Pages (from-to)7458-7465
    Number of pages8
    Issue number21
    Publication statusPublished - 2012 Nov 7

    ASJC Scopus subject areas

    • Chemistry(all)
    • Materials Science(all)
    • Condensed Matter Physics


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