Covalently Bonded [Pt]^- Chains in BaPt: Extension of the Zintl−Klemm Concept to Anionic Transition Metals?

BaPt has been synthesized by reaction of a 1:1 mixture of Ba and Pt at 1223 K in argon and characterized by single-crystal X-ray structure determination and electrical resistivity and magnetic susceptibility measurements. The compound crystallizes in the NiAs structure type with an extremely low value for the c/a ratio (hexagonal space group P63/mmc with a = 5.057(2) Å, c = 5.420(3) Å, c/a = 1.072, R1 = 0.0297, Nhkl = 93). This c/a ratio reflects structural features that are unusual for the NiAs type: Pt is coordinated linearly by two other Pt atoms at a distance as short as 2.71 Å, thus forming a chain along [001] of homonuclearly bonded platinum. Band structure calculations and electron localization function analyses reveal a covalent character of Pt−Pt interactions along the c axis and two-dimensional metallic conductivity parallel to the ab plane. In terms of the Zintl−Klemm concept, in its most general sense, BaPt can be formulated as (Ba2+) , and it can be considered a new example of platinide anions in the solid state.