Photomagnetic properties in a series of spin crossover compounds [Fe(PM-L)(2)(NCX)(2)] (X = S, Se) with substituted 2 '-pyridylmethylene-4-amino ligands

The spin crossover (SC) compounds [Fe(PM-AzA)(2)(NCX)(2)] and [Fe(PM-FlA)(2 )(NCX)(2)] (with PM-AzA = N-2'-pyridylmethylene-4-(phenylazo)aniline, PM-Fl A = N-2'-pyridylmethylene-4-(2-amino)fluorene, and X = S, Se) have been pre pared. The SC regimes have been deduced from variable-temperature magnetic susceptibility data. The enthalpy and entropy changes associated with the S C have been evaluated from DSC measurements. A cooperativity factor, C, has been defined, and its values for the different com-pounds have been deduce d from the spin crossover curves. At 10 K. the light-induced excited spin s tate trapping (LIESST) effect has been observed within the cavity of the SQ UID magnetometer. The critical temperatures T-c(LIESST) have been determine d for [Fe(PM-AzA)(2)(NCS)(2)] and [Fe(PM-FlA)(2)(NCX)(2)], and the role of cooperativity has been analyzed. A linear correlation has been found betwee n the T-c(LIESST) and C values The kinetics of HS --> LS relaxation have be en investigated: a thermally activated mechanism at elevated temperatures a nd a nearly temperature independent relaxation behavior at low temperatures have been found. Finally, the magnetic behavior recorded under light irrad iation in the warming and cooling modes has revealed the occurrence of the light-induced thermal hysteresis (LITH) effect.