Photo-induced spin transition for iron(III) compounds with π–π interactions

The magnetic susceptibilities of the spin-crossover compound [Fe(pap)2]PF6·MeOH (1) have been measured and compared with that of the previously reported compound [Fe(pap)2]ClO4·H2O (2). Compound 1 is a spin-crossover compound with spin transition temperature T1/2=288 K, and does not show a hysteresis loop around the spin transition temperature, in contrast with compound 2. Magnetic susceptibilities measured after illumination prove that 1 exhibits the LIESST effect, so does compound 2. The crystallographic data on the molecular packing show the presence of π stacking between the aromatic rings of pap ligands, which appears to be responsible for the LIESST effect.