Introducing a Structural Phase Transition in a 1D Perovskite via Cation’s Terminal Group Lengthening

Structural phase transitions in organic–inorganic hybrid perovskites offer the potential for controlling a wide range of physical properties. However, the rational design of phase-transition materials remains challenging in the relevant fields. In this study, we synthesized and characterized two one-dimensional (1D) perovskites: (4ATHP)PbI3 (1; 4ATHP = 4-aminotetrahydropyran), featuring face-shared inorganic chains and (4AMTHP)6Pb5I16(H2O)2 (2; 4AMTHP = 4-aminomethyltetrahydropyran), which contains rare mixed face-shared and edge-shared inorganic chains. Interestingly, despite the minor difference in the cation between 1 and 2, solely defined by the length of the terminal group, 2 shows phase-transition properties while 1 does not. Crystal structure analysis and Hirshfeld surface analysis indicate that the phase transition arises from the ordered–disordered change of the cation’s terminal group and the weakening of the interactions between the cation and inorganic skeleton. In addition, compound 2 exhibits rare biaxial negative thermal expansion behavior. These findings provide valuable insights into the expansion of functional phase-transition materials, offering a promising avenue for further design and development.