Structure and chemical bonding in K₁₄Cd₉Tl₂₁, a compound containing both isolated Tl₁₁/^7- clusters and (∞)/²([Cd₉Tl₁₀/^7-] metallic layers

The compound K₁₄Cd₉Tl₂₁ has been prepared by fusion of the elements in a tantalum reactor followed by slow cooling at the rate of 6 per hour to enable crystal growth. The X-ray crystal structure (hexagonal, P62m; a = 9.884(3),c= 17.173(5) Å; Z= 2) was refined to reliability factors of R1 = 5.09, wR2 = 11.64%. The anionic substructure contains both isolated clusters of Tl₁₁/^7- and a layered network based on Cd₅Tl₂ pentagonal bipyramids. The structure electron count relationship for the Tl₁₁/^7- cluster was analyzed in detail. The Cd₉Tl₁₀/^7- layers are found to confer metallic properties to the material, and the bonding within such layers is found to be highly delocalized.