Abstract
Jahn-Teller (JT) distorted Cu(II)-containing compounds often display interesting structural and functional behaviour upon compression. We use high-pressure X-ray and neutron diffraction to investigate four JT-distorted Prussian blue analogues: Cu[Co(CN)(6)](0.67), CuPt(CN)(6), and ACuCo(CN)(6) (A = Rb, Cs), where the first two were studied in both their hydrated and dehydrated forms. All compounds are less compressible than the JT-inactive Mn(II)-based counterparts, indicating a coupling between the electronic and mechanical properties. The effect is particularly strong for Cu[Co(CN)(6)](0.67), where the local JT distortions are uncorrelated (so-called orbital disorder). This sample amorphises at 0.5 GPa when dehydrated. CuPt(CN)(6) behaves similarly to the Mn(II)-analogues, with phase transitions at around 1 GPa and low sensitivity to water. For ACuCo(CN)(6), the JT distortions reduce the propensity for phase transitions, although RbCuCo(CN)(6) transitions to a new phase (P2/m) around 3 GPa. Our results have a bearing on both the topical Prussian blue analogues and the wider field of flexible frameworks.