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 CxCo4[Fe(CN)(6)]((8+x)/3)square((4-x)3) (x amount of alkali cation inserted per conventional cell, C = Na, K, Rb, Cs; square = [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, Na1Co4[Fe(CN)(6)](3)square(1) is predicted to be the most efficient one.