Scandium chalcogenides

Quaternary chalcogenides of the type A Ln M X, containing three metal elements from different blocks of the Periodic Table (A is an alkali or alkaline earth metal, Ln is an /-block lanthanide or scandium, M is a p-block main group or a r/-block transition metal, and X is S or Se) are also known [65]. 

It is noteworthy that the two structures of the scandium derivatives, SC2X3, are both related to close packed structures of the general MX types, in which vacancies appear on the metal sites. It is a consequence of the affinity of scandium (also Yb(III) and Lu) for regular octahedral sites. This behavior is observed in the lower chalcogenides as well. 

The 3d elements, from which we exclude scandium studied in the section 3 with the rare earths, exhibit primarily the two oxidation states +2 and +3 in their ternary chalcogenides. The +2 oxidation state is the more frequent from Cr to Ni and is the only one in the case of Mn and Ni. The +2 state is observed as tabulated below. 

The following chemical symbols are used in this chapter R designates the rare earth elements, including the lanthanides, yttrium and scandium M stands for the elements of group I (lithium, sodium, calcium, rubidium, cesium, copper, silver), X is used to designate chalcogenides (sulphur, selenium, tellurium). 

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