Solvate-Induced Semiconductor to Metal Transition: Flat 1∞ [Bi1−] Zigzag Chains in Metallic KBi⋅NH3 versus 1∞ [Bi1−] Helices in Semiconducting KBi

Abstract

Polymeric (Formula presented.) [Bi]− in KBi⋅NH3 has planar zigzag chains with two-connected Bi atoms and metallic properties, whereas KBi, which has helical chains of Bi atoms, is semiconducting. The isomerization of the Bi chain is induced by solvate molecules. In the novel layered solvate structure uncharged (Formula presented.) [KBi] layers are separated by intercalated NH3 molecules. These layers are a structural excerpt of the iso(valence)electronic CaSi, whose metallic properties arise from the planarity of the zigzag chain of Si atoms. Computational studies support this view, they show an anisotropic metallic behavior along the Bi chain. Electron delocalization is also found in the new cyclic anion [Bi6]4− isolated in K2[K(18-crown-6)]2[Bi6]⋅9 NH3. Although [Bi6]4− should exhibit one localized double bond, electron delocalization is observed in analogy to the lighter homologues [P6]4− and [As6]4−. Both compounds were characterized by single-crystal X-ray structure determination.