Electrical control over the Fe(II) spin crossover in a single molecule: Theory and experiment

We report on theoretical and experimental work involving a particular molecular switch, an [Fe-II(L)(2)](2+) complex, that utilizes a spin transition ("crossover"). The hallmark of this transition is a change of the spin of the metal ion, S-Fe = 0 to S-Fe = 2, at fixed oxidation state of the Fe ion. Combining density functional theory and first principles calculations, we demonstrate that within a single molecule this transition can be triggered by charging the ligands. In this process the total spin of the molecule, combining metal ion and ligands, crosses over from S = 0 to S = 1. Three-terminal transport through a single molecule shows indications of this transition induced by electric gating. Such an electric field control of the spin transition allows for a local, fast, and direct manipulation of molecular spins, an important prerequisite for molecular spintronics.