Synthesis of Fe_2–xMn_xP Nanoparticles from Single-Source Molecular Precursors

The feasibility of preparing Fe 2– x Mn x P nanoparticles using the single-source precursors FeMn(CO) 8 (μ-PR 2 ) (R = Ph or R = H) has been investigated. The solution-based thermal decomposition of FeMn(CO) 8 (μ-PPh 2 ) in the presence of hexadecylamine and oleic acid resulted in the formation of FeO nanoparticles, while decomposition of FeMn(CO) 8 (μ-PH 2 ) under similar conditions yielded iron-rich Fe 2– x Mn x P nanoparticles. Solventless decomposition of FeMn(CO) 8 (μ-PH 2 ) at 573 K resulted in the formation of hexagonal FeMnP, a structure generally observed only at temperatures above 1473 K. The role of surface stabilizing agents in the production of iron-rich Fe 2– x Mn x P nanoparticles was examined through a series of experiments in which the type and quantity of stabilizers were varied, and evidence that oleic acid was responsible for the leaching or sequestration of manganese atoms was obtained. X-ray photoelectron spectroscopy (XPS) data acquired from the Fe 2– x Mn x P nanoparticles and powder X-ray diffraction (PXRD) data from air-oxidized hexagonal FeMnP show that manganese is preferentially oxidized in these materials. The relatively high oxophilicity of manganese is believed to be a major contributor to the formation of iron-rich Fe 2– x Mn x P nanoparticles prepared in solution. Alternative stabilizers to oleic acid were screened to identify a stabilizer that would promote nanoparticle growth without depletion of manganese. Of the various stabilizers studied, only oleic acid and tetrakis(decyl)ammonium bromide were able to promote substantial nanoparticle growth, but the use of these additives invariably resulted in the formation of iron-rich Fe 2– x Mn x P nanoparticles.