Metallylene complexes as precursors of nano-alloys

In the race towards miniaturization of integrated circuits, microelectronics is now reaching technological limits which make the use of nano-objects an extremely promising alternative. Indeed, in addition to the original optical and electrical properties, nanostructured materials based on germanium and iron occupy a special position due to their compatibility for direct integration into existing integrated circuits. Most of the routes for the synthesis of Ge nanoparticles involve the oxidation of germanides or the reduction of tetravalent Ge derivatives. However, the drastic conditions necessary for the synthesis (aggressive reducing agents, high temperature) and the formation of potentially polluting by-products constitute major drawbacks. The thermolysis of thermo-labile precursors, such as germylene-iron complexes with amidinato-, NHC- or pincer-type ligands in solution seemed to be a method of choice to overcome these problems. In addition, this allows us to easily study the influence of precursors (type of germylene, Ge/Fe stoichiometry) in the final composition of materials.

In this context, different carbonyl iron complexes of germylenes (1 and 2) have been synthesized (Organometallics, 2015, 34, 571). In particular, in order to study the influence of the substituent on the preparation of nano-alloys, we synthesized iron-germylene complexes 2 with various substituents on the germanium atom by substitution of the chloride of complex 1 using different anionic nucleophiles (MeOLi or LiHMDS). In addition, in order to modulate the Ge/Fe (2:1) stoichiometry, we have developed a new method for the preparation of  the iron complexe 3 with two germylene ligands, the second being introduced under irradiation.

Thermolysis of the Ge-Fe precursor substituted with HMDS group, with a the Ge-N bond significantly weaker than the corresponding Ge-Cl bond, allowed the preparation of iron germanide nano-alloys in solution at 200 °C in mesitylene in the presence of 0.5 equivalent of hexadecylamine HDA. The crystalline iron germanide Nps Fe3Ge2 nanoparticles show a hexagonal phase, with a quasi-spherical shape and an average diameter of 6.3 nm (Dalton Trans. 2018, 47, 15114 and Chem. Commun. 2019, 55, 9539-9542). This thermolysis method appears particularly efficient for the controlled preparation of nano-alloys under milder conditions than those hitherto used, while allowing modulation of the shape and size of the nanoparticles by modifying the substituents on the precursor.

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