Pentagonal Bismuth Antiprisms with Endohedral Palladium or Platinum Atoms by Low-Temperature Syntheses

We present the syntheses, crystal structures, and properties of five metal-rich salts containing the Bi-10(4+) pentagonal antiprism with an endohedral palladium or, for the first time, platinum atom. Tetragonal [Pt@Bi-10](AlBr4)(4) [P4(2)/n at 296(1) K; Pstyled-content style text-decoration:overline4/styled-content at 150(2) K] was obtained by reacting platinum, bismuth, and bismuth tribromide in [BMIm]Br4.1AlBr(3) at 140 degrees C (BMIm = 1-butyl-3-methylimidazolium). Monoclinic [Pt@Bi-10](AlBr4)(2)(Al2Br7)(2) [P2(1)/n] occurs as by-product. The two corresponding palladium compounds result from the dissolution of Bi16PdCl22 in [BMIm]Br4.1AlBr(3). [Pd@Bi-10](AlBr4)(4) [P4(2)/n] adopts a disordered structure homeotypic to its platinum analog. [Pd@Bi-10](AlBr4)(2)(Al2Br7)(2) [P2(1)/n] is isostructural to [Pt@Bi-10](AlBr4)(2)(Al2Br7)(2). In all structures, the [M@Bi-10](4+) cations are well separated by the bromido-aluminate anions with inter-cluster BiBi distances longer than 520 pm. This is not the case in [Pd@Bi-10][Bi2Sn6Cl22], which crystallized from a tin-containing melt of the metals and BiCl3. In its monoclinic structure [P2(1)/c], the cluster cations are arranged in chains along [001] with an inter-cluster distance of only 357 pm. Despite further structural evidence, DFT-based quantum chemical analysis gave no hint on inter-cluster bonding. According to the calculated band structure as well as resistivity and magnetic susceptibility measurements, the black compound is a diamagnetic semiconductor.