Pressure-induced Jahn-Teller switch in the homoleptic hybrid perovskite [(CH3)2NH2]Cu(HCOO)3: orbital reordering by unconventional degrees of freedom

Through in situ, high-pressure X-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH3)(2)NH2]Cu(HCOO)(3) undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct from previously reported Jahn-Teller switching in coordination polymers, which required at least two different ligands that crystallize in a reverse spectrochemical series. We show that the orbital reordering phase transition in [(CH3)(2)NH2]Cu(HCOO)(3) is instead primarily driven by unconventional octahedral tilts and shifts in the framework, and/or a reconfiguration of A-site cation ordering. These structural instabilities are unique to the coordination polymer perovskites, and may form the basis for undiscovered orbital reorientation phenomena in this broad family of materials.

Automated summary

The study demonstrates a pressure-induced orbital reordering phase transition in [(CH3)(2)NH2]Cu(HCOO)(3) above 5.20 GPa, driven primarily by unconventional octahedral tilts and shifts in the framework. This transition differs from previously reported Jahn-Teller switching in coordination polymers, and may lead to undiscovered orbital reorientation phenomena in this family of materials.