Synthesis of nickel nanoparticles. Influence of aggregation induced by modification of poly(vinylpyrrolidone) chain length on their magnetic properties

The reaction of Ni(COD)(2) with Hz (3 bar) in CH2-Cl-2 in the presence of p oly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of approx imate to 30 nm, composed of individual 3-4 nm fee Ni particles and displayi ng a ferromagnetic behavior whereas the same reaction in the presence of PV P K 90 leads to 4 nm, well-dispersed fee Ni particles displaying a superpar amagnetic behavior. In both cases the magnetic moment per atom is similar t o the value found for bulk nickel, hence demonstrating the absence of oxida tion of the surface of the particles.