Binary Sulfides

Abstract

A major interest of solid state chemists has been the development of novel synthetic methods for the low-temperature preparation of transition metal sulfides. The traditional method used to prepare these compounds involves the direct combination of the elements in evacuated silica tubes. Complete reaction requires the use of high temperatures for long periods of time. To ensure homogeneity, it is necessary to expose periodically fresh metal surface to the chalcogen. This is accomplished by one of two methods. The sample can be removed from the tube intermittently and ground under an inert atmosphere, or it can be mechanically shaken while it is still sealed in the evacuated tube. Direct combination of the elements can result in homogeneous, single-phase materials, but the products are highly crystalline and have low surface areas. These features are undesirable for certain applications, e.g., in catalytic processes. A number of ternary compounds in which anion substitution has been achieved [e.g., CoPxS2−x (1), CoAsxS2−x (2), and CoSexS2−x (3)] have also been prepared by direct combination of the elements.