Salts of octabismuth(2+) polycations crystallized from Lewis-acidic ionic liquids

Abstract

Abstract The reaction of Bi and BiCl3 with RbCl or CsCl in the Lewis-acidic ionic liquid (IL) [BMIm]Cl·4AlCl3 at T = 200 °C yielded air-sensitive, shiny black crystals. X-ray diffraction on single crystals revealed the hexagonal structures of two new salts (Bi8)M[AlCl4]3 (M = Rb, Cs), which are isostructural to the high-temperature form of (Bi8)Tl[AlCl4]3. The known (Bi8)2+ polycation is a square antiprism and can be interpreted as an arachno cluster following modified Wade rules. The crystal structure is a complex variant of the hexagonal perovskite structure type ABX 3 with A = (Bi8)2+, B = M + and X = [AlCl4]–. Chiral strands ∞ { M [ AlCl 4 ] 3 } 2 − ∞ 1 $\infty {}_{\infty }{}^{1}{\left\{M{\left[{\text{AlCl}}_{4}\right]}_{3}\right\}}^{2-}$ (M = Rb, Cs) run along [001]. The (Bi8)2+ polycations are only weakly coordinated inside a cage of 24 chloride ions and show dynamic rotational disorder at room temperature. Upon slow cooling to 170 K, the reorientation of the clusters was frozen, yet no long-range order was established.