An Organometallic Approach for Very Small Maghemite Nanoparticles: Synthesis, Characterization, and Magnetic Properties

Abstract

Maghemite (gamma-Fe(2)O(3)) nanoparticles stabilized by long-alkyl-chain amines are synthesized by using an organometallic approach. This method consists of the hydrolysis and oxidation of an organometallic precursor, Fe[N(SiMe(3))(2)](2), in the presence of amine ligands as stabilizing agent in an organic solvent, namely tetrahydrofuran or toluene. Whatever the experimental conditions, particles with a diameter of 2.8 nm are obtained. The use of high-resolution transmission electron microscopy and wide-angle X-ray scattering, together with Mössbauer spectroscopy and SQuId magnetometry, allows a complete characterization of these particles. Herein, we show that their structure is composed of a well-ordered core surrounded by a more disordered shell. The size of the latter varies from 0.65 to 0.50 nm depending on the experimental conditions and is of prime importance for the understanding of the magnetic properties. We demonstrate that the shorter the alkyl chain length of the amine 1) the better the crystallinity of the particle's core and 2) the stronger the interparticle interactions.

Exploring the No‐Man’s Land between Molecular Nanomagnets and Magnetic Nanoparticles

“…Several different procedures have been proposed, including the use of thermal decomposition,46 precipitation in constrained media,14, 45, 49, 50 co‐precipitation,43 polymer‐based methods51 and sol‐gel 52. Chaudret and co‐workers reported a method in which, starting from the organometallic precursor [Fe{N(SiMe 3 ) 2 } 2 ] and using amines for keeping the particles well separated, reasonably monodisperse maghemite particles of approximately 2.8 nm diameter were obtained, although the average size was estimated only by magnetic measurements 46a. Mössbauer and HRTEM were in agreement with cubic maghemite.…”

Controlling the Sulfidation Process of Iron Nanoparticles: Accessing Iron−Iron Sulfide Core‐Shell Structures

“…The amido complex bis[bis(trimethylsilyl)amido]iron(II) (1) (Figure a) is known to be an excellent precursor for various iron based nanostructures. Controlled decomposition reactions of this compound at elevated temperature in an organic solvent in the presence of suitable surfactants previously gave clean access to zerovalent iron, iron oxide and iron carbide NPs . Inspired by these findings, the present work describes synthetic approaches to iron sulfide nanomaterials building either on the reaction of 1 with H 2 S gas or alternatively on controlled surface sulfidation of preshaped zerovalent iron nanoparticles with H 2 S or benzylthiol.…”

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ‐Fe2O3 Phase

“…[59] These results are in agreement with previous work in which we confirmed, using Mçssbauer spectroscopy,t hat g-Fe 2 O 3 was the only iron oxide phase obtained when hydrolysis ando xidation of the organometallic precursor were performed at room temperatureu nder experimental conditions similar to those used in this study. [53] Analysis of the HRTEM images by meanso f Fouriert ransformation reveals the presence of different sets of lattice planesi nside the particles (Figure 1). The corresponding spacings are d = 0.29, 0.21, and 0.15 nm for sample 3 and d = 0.30 and 0.15 nm for sample 4,w ithin the accuracy of the measurements.…”

“…[46][47][48][49][50][51][52] We previously reported an organometallic approach that produced ultrasmall iron oxide NCs of 2-3 nm with an arrow size distribution anda llowedu st os elect the iron oxide phase by controlling the reaction conditions. [53][54][55][56][57] In particular,w üstite NCs can be selectively obtained.…”