The Intermetalloid Cluster Cation (CuBi₈)³⁺

Abstract

Abstract The reaction of Bi, BiCl 3 , and CuCl in the ionic liquid [BMIm]Cl ⋅ 4 AlCl 3 (BMIm=1‐ n ‐butyl‐3‐methylimidazolium) at 180 °C yielded air‐sensitive shiny black crystals of (CuBi 8 )[AlCl 4 ] 2 [Al 2 Cl 7 ] and (CuBi 8 )[AlCl 4 ] 3 . For both compounds X‐ray diffraction on single crystals revealed monoclinic structures that contain the intermetalloid cluster (CuBi 8 ) 3+ . It is the first pure bismuth cluster with a 3d metal and the first with a metal that does not form binary intermetallics with bismuth under ambient pressure. The cluster can be interpreted either as a copper(I) cation, η 4 ‐coordinated by a square‐antiprismatic Bi 8 2+ polycation (Bi−Cu 267 pm), or as a nine‐atomic intermetalloid nido‐cluster with 22 skeletal electrons and the C 4 v symmetry. One of the chloride ions of a tetrahedral [AlCl 4 ] − group coordinates the copper atom (Cu−Cl 228 pm) and thereby completes its 18 electron count. DFT‐based calculations, followed by real‐space bonding analysis, revealed a multicenter bonding situation between copper and bismuth atoms with about seven shared electrons.