Use of vanadocene as an organometallic reducing agent for the preparation of ultrafine magnetic iron powder and organized iron particles from iron salts
Abstract
A THF suspension of FeCl2 reacts with the 15-electron complex, vanadocene [V(C5H5)2] to give ultrafine magnetic Fe powder. X-Ray diffraction and Mössbauer spectra confirm the presence of the α-iron phase. The average crystallite size was estimated to be 18 nm and the magnetic hyperfine field was found to be 341 kG at 100 K, as expected for fine iron particles. A typical ferromagnetic behaviour was observed for the powder in the 5–300 K range. Saturation magnetization at 5 K (223 emu gFe-1), very close to the value for bulk α-Fe, revealed the presence of small α-iron particles without iron oxide contaminant at the surface. The same reaction carried out in the presence of polyvinylpyrrolidone (PVP) yields PVP-protected zerovalent iron particles. Mössbauer analysis revealed the presence of 83% F and 17% unreduced FeCl2. The sample exhibits ferromagnetic behaviour with saturation magnetization (ca. 240 emu gFe-1) comparable to the bulk value, confirming the presence of small zerovalent nanoparticles. HREM experiments performed at high magnification display small Fe particles (diameter of about 8 nm) agglomerated into 50–200 nm superstructures. The particles show an astonishing common magnetic and crystallographic orientation.