2, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
3, IR Dynamics, Albuquerque, New Mexico, United States
Iron Oleate has long been one of the most popular precursors for the synthesis of high-quality iron oxide nanoparticles. This is true despite the fact that it is not commercially available and must be custom synthesized. There are a handful of related syntheses that are in common use, but reproducibility of the synthesis is a significant concern. Iron oleate does not readily form a simple complex with one iron atom bonded to three oleate ligands as one might imagine. Instead, iron oleate often exists as a complex mixture of species that includes a series of oligomeric species with iron atoms bonded to each other through oxo bridges as well as other structure. This non-stoichiometric mixture is not easily purified as iron oleate resists the most common purification approaches. Iron oleate can not be recrystallized, as it does not crystallize and instead forms an oil or glass depending upon its temperature. Washing approaches are difficult to reproduce as the oleate ligands can be very labile, and repeated washes will continue to remove oleate ligands until it finally forms an insoluble solid. This lability of the oleates also make it difficult to purify the compound through chromatography as the compound can decompose on the column. Unfortunately, differences in the precursor synthesis can lead to difficulty in reproducing nanoparticles syntheses. We will discuss two approaches that have been demonstrated to yield highly reproducible iron oleate precursors. In the first approach, we produce iron oleate through the decomposition of another organometallic species in an excess of oleic acid yielding a solution of known stoichiometry that can be used without purification. In the second approach, judicious selection of reagents, solvents, and reaction conditions can yield an isolated compound of pure iron oleate with an iron:oleate ratio of exactly 1:3. These compounds can then be used to enhance the reproducibility of iron oxide nanoparticle syntheses. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the DOE’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States government.