Structure bifurcation in containerless low-temperature syntheses of solid state niobium chloride compounds from lanthanoid atoms: an X-ray absorption and ab initio EXAFS analysis

A new method of preparing solid state chlorometallates by reductive dechlorination of solvated niobium pentachloride with the vapour of nominally free atoms of erbium and samarium is described. Products were prepared in a model of a rotatable Pyrex cryostat by evaporating Sm or Er into a turbulently mixed solution of NbCl5 in toluene at 130 K. Since no single crystal had been isolated, local order around the Nb atom was probed by far-IR, XPS, and EXAFS spectroscopy. Depending on the vaporized rare earth, two structurally distinct products were found. Combining information gathered by EXAFS results and ab initio EXAFS calculations on clusters to model the growing solid state compound using the FEFF6 code, two different condensation patterns were proposed: chlorine edge-shared aggregation was preferred for Er vaporization, face-shared condensation patterns emerged from Sm vaporization. Resume : Ce travail dOcrit une nouvelle mOthode de synthse de composOs chloromOtalliques par abstraction rOductrice des atomes de chlore ‡ partir de pentachlorure de niobium solvatO et de vapeur diatomes libres dierbium et de samarium. Les produits ont OtO prOparOs dans un cryostat rotatif par Ovaporation de Sm et Er sur la solution de NbCl5 dans le tolune, agitOe et refroidie ‡ 130 K. Aucun monocristal niayant pu Œtre isolO, liordre local autour du Nb a OtO sondO par spectroscopie IR, XPS et EXAFS. Deux structures diffOrentes dOpendantes de la terre rare vaporisOe ont OtO identifiOes. Additionnant les informations EXAFS aux calculs ab initio diEXAFS par FEFF6 et simulant la croissance des clusters formOs, deux modes de condensation ont OtO proposOs : condensation via les chlores des arŒtes de lioctadre pour la vaporisation diEr et condensation via les chlores des faces de lioctadre pour la vaporisation de Sm. Mots clOs : spectroscopie diabsorption des rayons X, niobium, synthse ‡ liaide de mOtaux ‡ liOtat vapeur, spectroscopie photoOlectronique des rayons X, « XPS ».