Triangular prismatic coordination in ternary chalcogenides*

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Abstract
The crystal structures of sixteen ternary chalcogenide compounds, BaxMyXz, M = first row transition metal, with stoichiometries x:y:z of 2:1:3, 1:1:2, 1:4:3, 1:2:2 and 1:2:3, are distributed over nine different structure types. The structures are based on columns of face-sharing BaS6 triangular prisms. Isolated columns are present in the 1:2:3 and 1:4:3 stoichiometries, while the columns articulate by edge sharing to neighboring columns to form sheets in the 1:1:2 and 1:2:2 compounds. The 1:1:2 and 1:2:2 structures are stuffed derivatives of the PbCl2 type in which the transition metal fills one third of the available tetrahedral holes in the former and two thirds of the sites in the latter. The 1:4:3 structure is a stuffed derivative of the BRe3 type and the 1:2:3 is a stuffed derivative of SnNi3. Shoemaker previously pointed out that the 2:1:3 structures are stuffed derivatives of either Cr3C or Sb2S3.