Iron(III) spin-crossover complexes [Fe(pap)2]ClO4. H2O (1), [Fe(pap)2]BF4. H2O (2), [Fe(pap)2]PF6. CH3OH (3), [Fe(CH3-pap)2]ClO4. H2O (4), [Fe0.5Al0.5(pap)2]ClO4. CH3OH (5) and [Fe0.25Al0.75(pap)2] ClO4. CH3OH (6)were prepared andthe spin transition behaviors of the complexes have been studied from magnetic susceptibility and Mössbauer
spectroscopy measurements. The magnetic properties of light-induced metastable state are measured using Hg-Xe light source.
T1/2is temperature at which the populations of the high-spin and low-spin species are fifty-fifty. Metastable HS is produced by
light irradiation at 5 K. T(LIESST) is the temperature at which the populations of the metastable high-spin species decrease to one half and cooperativity
factor Cis defined as the parameter which presents the strength of cooperativity. The value of T(LIESST) decreases as T1/2increases and the plots of T(LIESST) vs. Cshow linear correlation. The effect of cooperativity of the complexes on the relaxations in solid was confirmed for the iron(III)