Photoinduced magnetization has been recently evidenced by Hashimoto et al. in CoFe Prussian blue analogues. We synthesized three compounds with a variable cobalt environment to point out the conditions required to observe the photoinduced magnetization. Structure and electronic structure of the compounds have been investigated combining XANES, infrared spectroscopy, and powder X-ray diffraction experiments. Magnetization as a function of temperature before and after irradiation showed that diamagnetic pairs Co III -NC-Fe II are necessary for the existence of the photoinduced magnetization, but their presence is not a sufficient condition. The role of hexacyanoferrate vacancies in the phenomenon is pointed out.

We synthesized a series of CoFe Prussian blue analogues along which we tuned the amount of cesium cations inserted in the tetrahedral sites of the structure. Structure and electronic structure have been investigated, combining XANES, infrared spectroscopy, powder X-ray diffraction experiments, and magnetization measurements. The change of the magnetization induced by light along the series shows that the efficiency of the photoinduced magnetization, evidenced a few years ago in similar compounds by Hashimoto et al. (Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 272, 704-705; Sato, O.; Einaga, Y.; Iyoda, T.; Fujishima, A.; Hashimoto, K. J. Electrochem. Soc. 1997, 144, L11-L13; Sato, O.; Einaga, Y.; Iyoda, T.; Fujishima, A.; Hashimoto, K. J. Phys. Chem. B 1997, 101, 3903-3905; Einaga, Y.; Ohkoshi, S.-I.; Sato, O.; Fujishima, A.; Hashimoto, K. Chem. Lett. 1998, 585-586; and Sato, O.; Einaga, Y.; Fujishima, A.; Hashimoto, K. Inorg. Chem. 1999, 38, 4405-4412), depends on a compromise between the number of excitable diamagnetic pairs and the amount of [Fe(CN)6] vacancies giving the network flexibility. Besides the efficiency of the photoinduced process, the amount of [Fe(CN)6] vacancies also controls a thermally induced electron transfer.