Molten alkali-metal polychalcogenides as reagents and solvents for the synthesis of new chalcogenide materials

An old molten salt technique is highlighted for its enormous potential for the synthesis of new materials. Transition- and main-group-metal chalcogenides with unusual structures can be synthesized and crystallized at relatively low temperatures (200-450°C) from alkali-metal polychalcogenide molten salts (fluxes). Often long polychalcogenide chains are stabilized. The materials that are stable in this temperature regime are unstable at higher temperatures. The abundance of the different structure types obtained underscores the structural and bonding diversities of chalcogenide and polychalcogenide ligands in the solid state. A survey of reactions in alkali-metal polychalcogenide molten salts, known to yield new materials (with Ti, Cu, Au, Hg, and Sn), is given.