High-Pressure Behaviour of Prussian Blue Analogues: Interplay of Hydration, Jahn-Teller Distortions and Vacancies
H L B Boström, I E Collings, A B Cairns, C P Romao and A L Goodwin
Dalton Transactions (2018)

We report a high-pressure crystallographic study of four hydrated Prussian blue analogues: M[Pt(CN)6] and M[Co(CN)6]0.67 (M = Mn2+, Cu2+) in the range 0–3GPa. Mn[Co(CN)6]0.67 was studied by single-crystal X-ray diffraction, whereas the other systems were only available in poly-crystalline form. The Mn-containing compounds undergo pressure-induced phase transitions from Fm–3m to R–3 at ∼1.0–1.5 GPa driven by cooperative tilting of the octahedral units. No phase transition was found for the orbitally disordered Cu[Co(CN)6]0.67 up to 3 GPa. Mn[Co(CN)6]0.67 is significantly softer than the other samples, with a bulk modulus of ∼14 GPa compared to ∼35 GPa of the powdered samples. The discrepant pressure responses are discussed in terms of the presence of structural defects, Jahn-Teller distortions, and hydration. The implications for the development of polar systems are reviewed based upon our high-pressure study.