| Summary: | The reaction of Bi, BiCl<sub>3</sub>, and TlCl in the ionic liquid [BMIm]Cl·4AlCl<sub>3</sub> (BMIm = 1-<i>n</i>-butyl-3-methylimidazolium) at 180 °C yielded air-sensitive black crystals of (Bi<sub>8</sub>)Tl[AlCl<sub>4</sub>]<sub>3</sub>. X-ray diffraction on single crystals at room temperature revealed a structure containing <inline-formula> <math display="inline"> <semantics> <mrow> <mmultiscripts> <mrow> <msub> <mrow> <mrow> <mo>[</mo> <mi>Tl</mi> <mo>(</mo> <mi>AlCl</mi> </mrow> </mrow> <mn>4</mn> </msub> <msub> <mo stretchy="false">)</mo> <mn>3</mn> </msub> <mo>]</mo> </mrow> <mo>∞</mo> <mn>1</mn> </mmultiscripts> <msup> <mrow></mrow> <mrow> <mrow> <mn>2</mn> <mo>−</mo> </mrow> </mrow> </msup> </mrow> </semantics> </math> </inline-formula> strands separated by isolated Bi<sub>8</sub><sup>2+</sup> square antiprisms. The thallium(I) ion is coordinated by twelve Cl<sup>−</sup> ions of six [AlCl<sub>4</sub>]<sup>−</sup> groups, resulting in a chain of face-sharing [TlCl<sub>12</sub>]<sup>11−</sup> icosahedra. The Bi<sub>8</sub><sup>2+</sup> polycation is disordered, simulating a threefold axis through its center and overall hexagonal symmetry (space group <i>P</i>6<sub>3</sub>/<i>m</i>). Slowly cooling the crystals to 170 K resulted in increased order in the Bi<sub>8</sub> cluster orientations. An ordered structure model in a supercell with <i>a</i>’ = 2<i>a</i>, <i>b</i>’ = 2<i>b</i>, <i>c</i>’ = 3<i>c</i> and the space group <i>P</i>6<sub>5</sub> was refined. The structure resembles a hexagonal perovskite, with complex groups in place of simple ions.
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