A SPIN TRANSITION MOLECULAR MATERIAL WITH AN EXCEPTIONALLY LARGE THERMAL HYSTERESIS LOOP AT ROOM-TEMPERATURE

The compound [Fe(NH(2)trz)(3)](tos)(2) . 2H(2)O, with NH(2)trz=4-amino -1,2,4-triazole and tos=tosylate, exhibits an abrupt low-spin-->high-s pin transition in the warming regime at T-c up arrow=361 K accompanied by the removal of the two noncoordinated water molecules. When [Fe(NH (2)trz)(3)](tos)(2) is cooled down, the high-spin --> low-spin transit ion occurs at T-c down arrow = 279 K. The synergy between spin transit ion and dehydration process provides a material for which the room tem perature falls within the thermal hysteresis loop. This system seems t o be presently the most promising spin transition material for low-cos t display application.