Spin Switching Effect in Nickel Nitroprusside: Design of a Molecular Spin Device Based on Spin Exchange Interaction

A new approach for designing optically switchable molecular communication devices based on spin-exchange interactions is proposed in the present paper. The device is constituted from two parts, i.e., a paramagnetic block (PMB) and a coupling control block (CCB). As a prototype of this model, nickel nitroprusside, Ni[Fe(CN)₅NO]·5.3H₂O was synthesized, in which the nickel ion acts as the PMB and the nitroprusside molecule does as the CCB. In this compound, as there is no spin on Fe, the magnetic interaction between the neighboring Ni cations is very weak. No magnetic phase transition can be observed until 1.8 K. Photoirradiation at 475 nm causes a charge transfer from the metal, Fe, to the ligand, NO, which induces two antiferromagnetically coupled spins on Fe and NO. Furthermore, the new spin on Fe interacts ferromagnetically with those on neighboring nickels. As a result, the spins on the Ni ions, which surround the Fe with spin, form a magnetic cluster with S = 5.