Room temperature spin crossover properties in a series of mixed-anion Fe(NH 2 trz) 3 (BF 4 ) 2- x (SiF 6 ) x /2 complexes.

A series of mixed-anion Fe(NH 2 trz) 3 (BF 4 ) 2- x (SiF 6 ) x /2 spin crossover complexes is obtained modifying the reaction time but also using an increase amount of tetraethyl orthosilicate as the source for the production and the incorporation of SiF 6 2- competing with the BF 4 2- anions present in the mother solution. The increase of the SiF 6 2- anion inclusion to the detriment of the BF 4 - counterpart induces a shift of the temperature transition toward high temperatures leading to interesting bistability properties around room temperature with T 1/2 spanning from 300 K to 325 K. Moreover, the implementation of a solid-liquid post synthetic modification approach from the Fe(NH 2 trz) 3 (BF 4 ) 2 parent complex with identical TEOS proportions and under certain experimental conditions lead systematically to the same Fe(NH 2 trz) 3 (BF 4 ) 1.2 (SiF 6 ) 0.4 composition. This compound presents an abrupt spin crossover behaviour with a narrow hysteresis loop just above room temperature (320 K), which is stable under thermal cycling and along time with no specific storage conditions. Such crystalline powder sample incorporates homogeneous rod-shaped particles whose formation and physical properties can be followed simultaneously using infra-red spectroscopy, dynamic light scattering (DLS), transmission electronic microscopy (TEM) and optical reflectance. The observation of a stabilized single ca. 800 nm population of mixed-anion particles starting from insoluble various sizes (from nano- to microscale) Fe(NH 2 trz) 3 (BF 4 ) 2 particles supports the key role of the solvent (water molecules) on the separation, the reactivity and the reorganization of the 1D iron-triazole chains forming the packing of the structure.