Microwave-Assisted Synthesis of Monodisperse Nickel Nanoparticles Using a Complex of Nickel Formate with Long-Chain Amine Ligands

We have successfully prepared face-centered cubic (fcc) Ni nanoparticles by the intramolecular reduction of Ni 2+ ion contained in a formate complex having long-chain amine ligands within an extremely short time under microwave irradiation. Formate ion coordinated to Ni 2+ ion acted as a reducing agent for Ni 2+ in this reaction and finally decomposed to hydrogen and carbon dioxide. Ligation of the long-chain amine lowered the reaction temperatures by decreasing the energy barrier required for the reduction of the nickel formate complex. Monodisperse Ni nanoparticles with average sizes of 43, 71, and 106 nm were prepared using the complex of nickel formate with several chain lengths of alkylamines such as oleylamine (=(Z)-9-octadecenylamine), myristylamine (=tetradecylamine), and laurylamine (=dodecylamine), respectively. The relationship between the magnetic properties and the particle sizes of Ni nanoparticles is discussed.