Dedicated to Professor Josef Breu on the Occasion of his 60 th Birthday.The reaction of Bi and Bi 2 S 3 in the Lewis-acidic ionic liquid [BMIm]Cl • 4.3AlCl 3 (BMIm = 1-n-butyl-3-methylimidazolium) at 200 °C yielded air-sensitive black crystals of (Bi 2 S 2 )[AlCl 4 ]. X-ray diffraction on single-crystals revealed a monoclinic structure containing infinite chains 1 1 ðBi 2 S 2 Þ þ . These polycations contain bismuth(II,III) and sulfur(-II) atoms, connected by polar covalent BiÀ S and BiÀ Bi bonds. The assignment of bonds is ambiguous as a distinction between primary and secondary interactions is arbitrary based on interatomic distances. A real-space quantum chemical bonding analysis, including delocalization indices, helped to quantify the interactions and charge distribution, confirming that a simple Lewis formula is inappropriate to describe the polycation. 1 1 ðSb 2 Ch 2 Þ þ polycations are periodic sequences of four fouratomic rings (Sb 2 Ch 2 ) + , which are connected by SbÀ Sb as well[a
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