Ionothermal Syntheses, Crystal Structures, and Chemical Bonding of the Rhodium-Centered Clusters [RhBi9]4+ and [(RhBi7)I8].

The first filled Bi₉⁵⁺ polycation was isolated in the form of [RhBi₉](AlCl₄)₄ crystals by dissolution of the solid precursor Bi_{12- x}Rh X_{13- x} in the Lewis-acidic ionic liquid [BMIm]Cl·3.6AlCl₃ (BMIm = 1-butyl-3-methylimidazolium) at 140 °C. In the monoclinic crystal structure [ P2₁/ n, a = 1217.5(2) pm, b = 1741.6(3) pm, c = 5085.7(7) pm, β = 90.117(8)°], the almost spherical [RhBi₉]⁴⁺ polycations (approximate D_{3 h} symmetry; Rh-Bi 276 ± 3 pm) show pronounced orientational disorder. Shiny black needles of Bi₇RhI₈ were obtained from the reaction of rhodium, bismuth, and BiI₃ in the ionic liquid [BMIm]Cl ·1.3AlCl₃ at 200 °C. Bi₇RhI₈ [ P2₁/ n, a = 943.10(1) pm, b = 1582.40(1) pm, c = 1645.40(1) pm, β = 95.48(1)°] is isostructural to Bi₇RhBr₈ and consists of molecular clusters [(RhBi₇)I₈]. The rhodium atom centers a pentagonal bipyramid of bismuth atoms, and the two apical bismuth atoms are in square-planar coordination of iodide ions. DFT-based calculations indicate strong bismuth-rhodium bonding with predominantly covalent character for both clusters. The electronic structure of the Bi₉⁵⁺ cage is notably modified by this interaction, but the characteristic bonding features of the host cluster with the D_{3 h} configuration are still maintained. In Bi₇RhI₈, on the other hand, bonding is dictated by the spatial distribution of mutually repelling iodine atoms, and the Bi-Rh bonding is highly polar. [ABSTRACT FROM AUTHOR]