New niobium and rhenium halides synthesis routes by atomic vaporization. X-ray absorption spectroscopy characterization

New synthetic route as the so called 'chimie douce' or MVS (Metal Vapor Synthesis) has been an increasing field lately to synthesize new kind of solid state structures. Our interest is the assembly of small molecular building blocks of early transition metal halides. We illustrate the use of vaporized rare earth metals to condense NbCls units. We probed the local order around the Nb atom with X-Ray Absorption Spectroscopy, far Infra-Red and XPS in order to better understand the mechanisms involved. A first EXAFS, IR and XPS study on solid state products has shown the evolution of the NbCl₅ dimer towards a chain like structure. However, the condensation patterns depends on the rare earth atoms vaporized. These results have been confirmed by X-ray Absorption ab initio calculations. Because our compounds are extremely air sensitive we have developed in situ MVS reactor to take 'snapshots' of the structural intermediates by EXAFS. This study showed the condensation of the initial NbCl₅ building blocks by reduction of the Nb oxidation state by rare earth vaporization. This method is a new way of looking at condensation mechanisms via structural evolution observed by EXAFS. (author)