Ionothermal Synthesis, Structure, and Bonding of theCatena‐Heteropolycation1∞[Sb2Se2]+

The reaction of antimony and selenium in the Lewis‐acidic ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrachloridoaluminate, [BMIm]Cl·4.7AlCl3, yielded dark‐red crystals of [Sb2Se2]AlCl4. The formation starts above 160 °C; at about 190 °C, irreversible decomposition takes place. The compound crystallizes in the triclinic space groupP1̄ witha= 919.39(2) pm,b= 1137.92(3) pm,c= 1152.30(3) pm,α= 68.047(1)°,β= 78.115(1)°,γ= 72.530(1)°, andZ= 4. The structure is similar to that of [Sb2Te2]AlCl4but has only half the number of crystallographically independent atoms. Polycationic chains1∞[Sb2Se2]+form a pseudo‐hexagonal arrangement along [011̄ ], which is interlaced by tetrahedral AlCl4–groups. Thecatena‐heteropolycation1∞[Sb2Se2]+is a sequence of three different four‐membered [Sb2Se2] rings. The chemical bonding scheme, established from the topological analysis of the real‐space bonding indicator ELI‐D, includes significantly polar covalent bonding in four‐member rings within the polycation. The rings are connected into an infinite chain by homonuclear non‐polar Sb–Sb bonds and highly polar Sb–Se bonds. Half of the selenium atoms are three‐bonded.