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 g_Fe^-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 g_Fe^-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.