Nanocrystalline iron oxide and sulfide by the thermal decomposition of cyclohexylammonium hexaisothiocyanatoferrate(III) 2.5H₂O

We reported for the first time the establishment of a simple, room-temperature synthesis protocol for the new organic-inorganic hybrid salt of cyclohexylammonium hexaisothiocyanatoferrate(III) 2.5H₂O, which was found a convenient single-source precursor for the synthesis of nanocrystalline iron oxide or sulfide. The formation of this salt was spectrophotometrically confirmed by FT-IR and UV-Vis. In addition, SCXRD revealed that this salt had the trigonal space group R-3 with disorder of some isothiocyanate sulfur atoms. The thermal stability and the thermal decomposition products of this salt were atmosphere-dependent (air: 169 °C; α-Fe₂O₃ at 550 °C; helium: 154 °C; FeS at 800 °C). The thermal decomposition impacted the textural properties of α-Fe₂O₃ (an average crystallite size of ~ 41 nm and S_BET = ~ 4.0 m²/g) and FeS (~ 14 nm and ~ 80 m²/g, respectively). The nanoparticulate nature affected the magnetic behavior of α-Fe₂O₃ and FeS, as revealed by ac-susceptibility. They showed widen maximum at ~ 55 K due to increasing disorder effect by particle sizes. However, below 40 K, the susceptibility increased sharply, indicating a ferromagnetic ordering. In comparison, the ac-susceptibility of the salt exhibited a broad maximum at ~ 130 K with an inflection point at ~ 180 K. No transition to spin-flip was detected for all three materials.