Polar Molecule-Based Material with Optic–Electric Switching Constructed by Polar Anions

Polar crystal structures have attracted more and more attention, due to their unique characteristics, such as ferroelectricity, piezoelectricity, and nonlinear optical property, etc. However, the construction of polar materials is always accidental, and finding an effective synthesis strategy to construct polar materials remains a challenge. Herein, inorganic–organic hybrid compounds of [C₇H₁₄N]­[FeCl₄] (1) ([C₇H₁₄N] = quinuclidinium cation) and [C₇H₁₄N]­[GeCl₃] (2) were prepared, respectively, to verify the beneficial effect of polar anions on the construction of polar crystals. Compound 1 crystallized in the Pbca space group, while 2 belongs to the P4₃ space group at room temperature. Investigation into the structure of 2 reveals that the polarity of 2 derives from the triangular pyramid structure of [GeX₃]⁻ with lone pair electrons. Meanwhile, 2 undergoes a phase transition from the P4₃ space group to the center Pm3m at 385 K, leading to the optic–electric switching property. Thus, the present work exhibits the advantage of [GeX₃]⁻ as the inorganic constituent component in the hybrid polar materials and provides an effective approach for the construction of a polar molecule-based crystal with a switchable property.