Mesophases and Ionic Conductivities of Simple Organic Salts of M(<i>m</i>‑Iodobenzoate) (M = Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺)

Simple organic salts such as (Li+)­(m-IBA) (1), (Na+)­(m-IBA) (2), (K+)­(m-IBA) (3), (Rb+)­(m-IBA) (4), and (Cs+)­(m-IBA) (5) (m-IBA = m-iodobenzoate) were shown to form a mesophase before crystal melting or decomposition. The crystals were obtained in the hydrated form, e.g., 1·(H2O), 2·(H2O), 3·0.5­(H2O), 4·(H2O), and 5·(H2O); they were then converted into dehydrated forms by increasing the temperature to ∼450 K. Optically anisotropic-layered mesophases were observed in unhydrated crystals 2, 3, 4, and 5, whereas an optically isotropic mesophase (e.g., rotator phase) was found for crystal 1. The single-crystal X-ray structural analysis of the hydrated crystals revealed an inorganic–organic alternate layer structure, which is consistent with the average molecular orientation in the layered mesophase. The m-IBA anions formed a π-stacking columnar structure in the hydrated crystals, while one- or two-dimensional M+∼O networks were observed in the inorganic layers. Our results showed that the M+∼O interactions and their connectivity are strongly influenced by the size of the cations. The reconstruction of the M+∼O networks by removing H2O molecules was crucial for the formation of the mesophases. A strong response of both the real and imaginary parts of the dielectric constant was observed around the solid-mesophase phase-transition temperatures of crystals 1–5, with the ionic conductions playing a critical role.