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<p><b>Through in-situ, high-pressure x-ray diffraction experiments
we have shown that the homoleptic perovskite-like coordination polymer [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub>
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 [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub>
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</b><b> in this
broad family of materials.</b><b></b></p>
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Pressure-Induced Jahn-Teller Switch in the Homoleptic Hybrid Perovskite [(CH3)2NH2]Cu(HCOO)3: Orbital Reordering by Unconventional Degrees of Freedom
