Formation of air stable carbon-skinned iron nanocrystals from FeC2

Charge neutralization reaction in ionic salt of Fe2+C22− is found to produce carbon-skinned Fe nanocrystals. FeC2 is formed as an intermediate product in the reaction of FeCl2 solved in acetonitrile with CaC2 fine powder and also able to be isolated as black nanocrystals. Heating of FeC2 at temperature higher than 250 °C induces segregation of metallic iron. The segregated carbons grow as graphitic sheets parallel to the growing Fe lattice plane. This direct bonding is due to an accidental matching of the Fe–Fe distance (2.866 Å) with that of the C1–C4 distance (2.842 Å) of the hexagonal rings in graphite. The x-ray diffraction pattern indicates that the particles are composed of α-Fe and graphitic carbon. The thickness of the skin is almost constant as thick as 3.5 nm independent of the body size. The particles with an average size of 30 nm exhibit temperature dependence of the magnetic cohesive force as function of T−0.275.