Two phase transition materials [iPrQ]₂MnBr₄ (1, iPrQ = N-isopropyl-quinuclidinium) and [iPrQ]₂MnCl₄ (2) were synthesized and characterized. Dielectric measurements and differential scanning calorimetry showed that the two compounds underwent reversible phase transitions at ca. –47 and –37 °C, respectively. Variable-temperature single-crystal X-ray diffraction suggested that the two compounds underwent the same phase transitions from space group C2/c to Cc but at different temperature. The variable crystal structures indicated that the structural phase transitions of the compound were ascribed to the torsional movement of quinuclidine ring and the disappearance of the c-slide plane. The second harmonic generation (SHG) response further proved this structural phase transition. Fluorescence tests showed that the two compounds have strong fluorescence. The strong variations in dielectric anomalies make compounds 1 and 2 suitable for promising switchable dielectric materials.