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 T-1/2 = 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 pi stacking between the aromatic rings of pap ligands, which appears to be responsible for the LIESST effect. (C) 2002 Elsevier Science B.V. All rights reserved.