Light actuated single-chain magnet with magnetic coercivity

In this study, a pair of cyanide-bridged {Fe2Co}-based coordination polymers, {[((Pz)Tp)Fe(CN)(3)](2)Co(L)(2)}(.)4H(2)O (1) and {[(Tp)Fe(CN)(3)](2)Co(L)(2)}(.)3H(2)O(.)CH(3)OH (2), was synthesized by assembling Co-II with [((Pz)Tp)Fe-III(CN)(3)](-) ((Pz)Tp: tetrakis(pyrazolyl)borate) and the less hindered [(Tp)Fe-III(CN)(3)](-) (Tp: tris(pyrazolyl)borate) in the presence of the asymmetric ditopic ligand L (4-(1H-imidazol-5-ylmethylene-amino)-4H-1,2,4-triazole). Both compounds exhibited thermally induced metal-to-metal electron transfer (MMET) accompanied by the dielectric anomaly, resulting in the transformation between a high-temperature (HT) phase of {Fe-LS(III)-Co-HS(II)-Fe-LS(III)} and a low-temperature (LT) phase of {Fe-LS(II)-Co-LS(III)-Fe-LS(III)}. Contributed by the light-actuated electron transfer from Fe-II to Co-III ions, the LT phase can be converted into the HT phase by 946 nm light irradiation. Interestingly, compound 1 exhibited the stepwise transition of the dielectric constant with the electron transfer process, presenting a rare example showing the synergetic switching of dielectric and magnetic properties. Moreover, compound 1 showed the photo-induced slow relaxation of magnetization and a coercive field of 400 Oe, being a single-chain magnet. In contrast, compound 2 exhibited metamagnetization behavior after light irradiation.