Vapor-Induced Conversion of a Centrosymmetric Organic–Inorganic Hybrid Crystal into a Proton-Conducting Second-Harmonic-Generation-Active Material

Chemical responsivity in materials is essential to build systems with switchable functionalities. However, polarity-switchable materials are still rare because inducing a symmetry breaking of the crystal structure by adsorbing chemical species is difficult. In this study, we demonstrate that a molecular organic–inorganic hybrid crystal of (NEt4)2[MnN­(CN)4] (1) undergoes polarity switching induced by water vapor and transforms into a rare example of proton-conducting second-harmonic-generation-active material. Centrosymmetric 1 transforms into noncentrosymmetric polar 1·3H 2 O and 1·MeOH by accommodating water and methanol molecules, respectively. However, only water vapor causes a spontaneous single-crystal-to-single-crystal transition. Moreover, 1·3H 2 O shows proton conduction with 2.3 × 10–6 S/cm at 298 K and a relative humidity of 80%.