Structural architecture and physical properties of some inorganic fluoride series: a review

Many structural networks of transition metal fluorides and oxide fluorides may be derived from simple units of octahedral MF6 units, connected by common corners, generally in a 3D way: e.g., perovskite, ReO3, elpasolite, HTB, TTB, pyrochlore, etc. The accurate knowledge of these structures, together with the stabilities of these phases vs. temperature, allows deeper interpretation and fitting of many of their physical properties. Among the numerous fluoro-compounds which derive from these structural arrangements, several fluorinated and oxyfluorinated series have been chosen to illustrate the great range of outstanding physical properties, including ferromagnetism, piezoconductivity, ferroelasticity, high TC superconductivity, surface functionalization, that can be better understood with the help of structural considerations. The concept of nanometric particles in materials science has also drastically changed the investigations in solid state fluorine chemistry, not only for finding original synthetic routes, but also new characterization tools. As an example, in nanostructured M(OH,F)3 metal hydroxyfluorides that can be used as acidic heterogeneous catalysts, the morphological nature and specific area of the materials can be tuned by changing the experimental parameters of synthesis. In particular, the number and strength of Brønsted/Lewis acidic sites and the thermal stability can be correlated to the structural arrangements.

Graphical abstractThe great variety of outstanding physical properties displayed by inorganic fluorides, including ferromagnetism, piezoconductivity, ferroelasticity, surface functionalization, can be better understood with the help of accurate structural considerations. These relationships will be illustrated using several examples relating to ReO3, perovskite, elpasolite and related networks.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Structural networks of metal fluorides may be described from simple arrangements of MF6 octahedra. ► Knowledge of the stability of these phases vs. temperature allows fitting their physical properties. ► Varied nano-fluoride materials can be obtained by tuning experimental synthetic parameters. ► Peculiar physical behaviour can be better understood thanks to accurate structural considerations.