Photoinduced Magnetization in a Spin Crossover Iron(II)-Octacyanidoniobate(IV) Complex with Bridging Ligands between Iron(II) Centers

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We report a double-linked Fe(II) spin crossover complex, [Fe II (dpp) 2 ] 2 [Nb IV (CN) 8 ]·6H 2 O, in which 1,3-di(4-pyridyl)propane (dpp) ligands link Fe sites, while cyanide ligands bridge Fe and Nb sites. This complex exhibits spin crossover between the high-spin Fe II ( S = 2) and low-spin Fe II ( S = 0) states at 120 K. Analysis of the temperature dependence of magnetic susceptibility revealed that the low-temperature phase consists of high-spin and low-spin Fe II sites in a 36:64 ratio. Photoirradiation of the low-temperature phase at 3 K induces light-induced excited spin-state trapping (LIESST), in which the low-spin Fe II sites transition to the high-spin state. Following this transition, magnetic interactions between the high-spin Fe II ( S = 2) sites and the Nb IV ( S = 1/2) sites in the photoinduced phase lead to spontaneous magnetization with a Curie temperature of 15 K.