Photoinduced Magnetization with a High Curie Temperature and a Large Coercive Field in a Co‐W Bimetallic Assembly

The crystal structure, magnetic properties, and temperature- and photoinduced phase transition of [{CoII(4-methylpyridine)(pyrimidine)}2{CoII(H2O)2}{WV(CN)8}2]·4H2O are described. In this compound, a temperature-induced phase transition from the CoII (S = 3/2)-NC-WV(S = 1/2) [high-temperature (HT)] phase to the CoIII(S = 0)-NC-WIV(S = 0) [low temperature (LT)] phase is observed due to a charge-transfer-induced spin transition. When the LT phase is irradiated with 785 nm light, ferromagnetism with a high Curie temperature (TC) of 48 K and a gigantic magnetic coercive field (Hc) of 27 000 Oe are observed. These TC and Hc values are the highest in photoinduced magnetization systems. The LT phase is optically converted to the photoinduced phase, which has a similar valence state as the HT phase due to the optically induced charge-transfer-induced spin transition.