Phase-controlled synthesis of transition-metal phosphide nanowires by Ullmann-type reactions.

Transition-metal phosphide nanowires were facilely synthesized by Ullmann-type reactions between transition metals and triphenylphosphine in vacuum-sealed tubes at 350-400 degrees C. The phase (stoichiometry) of the phosphide products is controllable by tuning the metal/PPh(3) molar ratio and concentration, reaction temperature and time, and heating rate. Six classes of iron, cobalt, and nickel phosphide (Fe(2)P, FeP, Co(2)P, CoP, Ni(2)P, and NiP(2)) nanostructures were prepared to demonstrate the general applicability of this new method. The resulting phosphide nanostructures exhibit interesting phase- and composition-dependent magnetic properties, and magnetic measurements suggested that the Co(2)P nanowires with anti-PbCl(2) structure show a ferromagnetic-paramagnetic transition at 6 K, while the MnP-structured CoP nanowires are paramagnetic with Curie-Weiss behavior. Moreover, GC-MS analyses of organic byproducts of the reaction revealed that thermally generated phenyl radicals promoted the formation of transition-metal phosphides under synthetic conditions. Our work offers a general method for preparing one-dimensional nanoscale transition-metal phosphides that are promising for magnetic and electronic applications.