The Intermetalloid Clusters [Ni2Bi12]4+ and [Rh2Bi12]4+ - Ionothermal Synthesis, Crystal Structures, and Chemical Bonding

The intermetalloid clusters [M2Bi12](4+) (M = Ni, Rh) were synthesized as halogenido-aluminates in Lewis-acidic ionic liquids. The reaction of bismuth and NiCl2 in [BMIm]Cl5AlCl(3) (BMIm = 1-butyl-3-methylimidazolium) at 180 degrees C yielded black, triclinic crystals of [Ni2Bi12][AlCl4](3)[Al2Cl7]. Black, monoclinic (P2(1)/m) crystals of [Rh2Bi12][AlBr4](4) precipitated after dissolving the cluster salt Bi12-xRhX13-x (X = Cl, Br; 0 < x < 1) in [BMIm]Br4.1AlBr(3) at 140 degrees C. In the cationic cluster [Ni2Bi12](4+), the nickel atoms center two base-sharing square antiprisms of bismuth atoms (symmetry close to D-4h). The valence-electron-poorer rhodium-containing cluster is a distorted variant of this motif: the terminating Bi-4 rings are folded to bicyclic butterflies and the central square splits into two dumbbells (symmetry close to D-2h). DFT-based calculations and real-space bonding analyses place the intermetalloid units between a triple-decker complex and a conjoined Wade-Mingos cluster.