New materials from high temperature synthesis
Over 40 new and remarkable types of metal-rich compounds have been synthesized since about 1970 by high temperature reactions. These are found in binary and ternary systems of the early (group Ill-VI) transition and lanthanide elements with the nonmetals Cl, Br, I, 0, 5, Se or Te. Metal—metal bonding is characteristic of all the structures. These are conveniently organized in terms of the presence of discrete clusters of four to six metal atoms or their condensation products in the form of extended clusters, infinite chains of clusters sharing faces or edges, or double-metal-layered sheets. All the metal structures are well bound by nonmetals in relatively specific ways. Several recent discoveries also involve small nonmetal atoms interstitially bound within the metal units. A range of examples is discussed and illustrated. Some developing concepts and principles involving structural, bonding and electronic regularities and effects and some of the experimental aspects are also considered.