Photoinduced single-molecule magnet properties in a four-coordinate iron(II) spin crossover complex.

The four-coordinate Fe(II) complex, PhB(MesIm)3Fe-N═PPh3 (1) has been previously reported to undergo a thermal spin-crossover (SCO) between high-spin (HS, S = 2) and low-spin (LS, S = 0) states. This complex is photoactive below 20 K, undergoing a photoinduced LS to HS spin state change, as determined by optical reflectivity and photomagnetic measurements. With continuous white light irradiation, 1 displays slow relaxation of the magnetization, i.e. single-molecule magnet (SMM) properties, at temperatures below 5 K. This complex provides a structural template for the design of new photoinduced mononuclear SMMs based on the SCO phenomenon.