A Review on Jahn–Teller Distortions in Prussian Blue Analogs Molecular Magnets

Prussian blue analogs (PBAs) represent a versatile class of molecule-based magnetic materials in which subtle changes or distortion in local coordination geometry can strongly influence their macroscopic properties. In general, many types of distortions could exist in PBAs, such as octahedral tilts, A-site slides, Jahn-Teller (JT), vacancy, hydration-driven distortions, and so on. Among all types of distortions, JT distortions play a pivotal role by coupling electronic degeneracy with lattice deformation, thereby governing structural symmetry, magnetic exchange pathways, and ion-transport behavior. In addition, JT distortions play a pivotal role in governing the structural phase transitions of PBAs. This review critically surveys the latest advances in understanding how JT distortions, particularly those induced by the spin configuration of JT-active transition-metal ions, drive symmetry-breaking phase transitions within PBA frameworks. The interplay between electronic structure and lattice deformation is discussed, highlighting the mechanisms by which distortion leads to new crystallographic phases, influences ion diffusion, and modulates the electrochemical properties. Special attention is given to understanding the evolution of the JT effect in relation to structural phase transitions. It also summarizes effective strategies to suppress unwanted phase changes and improve overall structural stability. Ultimately, this review elucidates how control over JT effects can tailor electrochemical properties such as specific capacity, cycling stability, and voltage profile, offering design principles for the next generation of high-performance PBA-based energy materials.