We report the synthesis of spin crossover 69 nm spherical nanoparticles of [Fe(NH2-trz)3](Br)2.3H2O.0.03(surfactant) (NH2trz = 4-amino-1,2,4-triazole, surfactant = Lauropal), prepared by the reverse micelle technique, which exhibit at room temperature a thermal hysteresis characterized by magnetic, diffuse reflectivity and Raman studies.

The first single crystal-based description of a spin transition compound from the patented [Fe(Rtrz)(3)]X(2)·nH(2)O family is reported, properly the compound with Rtrz = 4-amino-1,2,4-triazole, X = NO(3) and n = 2. This study definitively proves the 1-D polymeric nature of the crystal structure and allows a description of the [Fe(Rtrz)(3)] chains, as well as of the anions and water implementation within the crystal lattice opening the possibility of subsequent investigations of the structure-property correlation within this peculiar family of spin transition compounds.