Photomagnetism in CxCo4[Fe(CN)6](8+x)/3·n H2O Prussian blue analogues: looking for the maximum photo-efficiency

A family of CoFe Prussian blue analogues C x Co 4 [Fe(CN) 6 ] (8+ x /3) □ (4– x )3 ( x = amount of alkali cation inserted per conventional cell, C = Na, K, Rb, Cs; □ = [Fe(CN) 6 ] vacancy) have been synthesized and characterized. Their photomagnetic properties have been investigated by magnetic measurements before and after irradiation and X-ray diffraction under continuous irradiation. We show that the photo-induced magnetism depends on several parameters: ( i ) the amount of Co III –Fe II diamagnetic excitable pairs per cell; ( ii ) the amount of [Fe(CN) 6 ] vacancies, and ( iii ) the amount and nature of the alkali cations per cell. We evidence a discontinuity in the properties' change when the amount of alkali cation x varies, around x = 1. For x < 1, there is an excitation of diluted Co III –Fe II diamagnetic pairs in a phase mainly composed of magnetic Co II –Fe III entities within the same structural phase through a second-order continuous transformation. For x ≥ 1, the formation of domains mainly composed of Co II –Fe III * metastable magnetic pairs in a phase mainly composed of Co III –Fe II diamagnetic ones through a first-order discontinuous transition is observed. The study points out that sodium derivatives are more efficient than the others. Among them, Na 1 Co 4 [Fe(CN) 6 ] 3 □ 1 is predicted to be the most efficient one. .