Spin-Crossover and Coherent Transport Behaviors of a Six-Coordinate Iron(II) Complex with a N4O2 Donor Set

Single-molecule spin-crossover (SCO) complexes have been considered to be the promising candidates to design molecular spintronic devices due to their magnetic bistability between the high-spin (HS) and low-spin (LS) states. By performing extensive density functional theory calculations in combination with the nonequilibrium Green function method, we explore the SCO and coherent transport behaviors of a six-coordinate Fe(II) complex with a N4O2 donor set. The calculated relative total electronic energies imply that the spin transition between the HS and LS states can be achieved by external stimuli in experiments via changing the metal–ligand bond lengths. Based on the calculated transport results, we find that the current through the six-coordinate Fe(II) complex with the LS state sandwiched between gold electrodes is significantly less than that of the HS state due to their significantly different electronic structures. Moreover, the molecular junction with the HS state displays a robust spin-filtering effect, and the current under the small bias voltage is dominated by the spin-down electrons. Interestingly, we observe that the transport properties of this examined Fe(II) complex with the HS and LS states are not sensitive to the detailed anchoring configuration, which is highly desirable in molecular spintronics. These theoretical findings suggest this Fe(II) SCO complex holds great potential in molecular spintronic devices.