[Ru2Bi14Br4](AlCl4)4 by mobilization and reorganization of complex clusters in ionic liquids.

Two polymorphs of the new cluster compound [Ru(2)Bi(14)Br(4)](AlCl(4))(4) have been synthesized from Bi(24)Ru(3)Br(20) in the Lewis acidic ionic liquid [BMIM]Cl/AlCl(3) ([BMIM](+) : 1-n-butyl-3-methylimidazolium) at 140 °C. A large fragment of the precursor's structure, namely the [(Bi(8))Ru(Bi(4)Br(4))Ru(Bi(5))](5+) cluster, dissolved as a whole and transformed into a closely related symmetrical [(Bi(5))Ru(Bi(4)Br(4))Ru(Bi(5))](4+) cluster through structural conversion of a coordinating Bi(8)(2+) to a Bi(5)(+) polycation, while the remainder was left intact. Both modifications have monoclinic unit cells that comprise two formula units (α form: P2(1)/n, a=982.8(2), b=1793.2(4), c=1472.0(3) pm, β=109.05(3)°; β form: P2(1)/n, a=1163.8(2), b=1442.7(3), c=1500.7(3), β=97.73(3)°). The [Ru(2)Bi(14)Br(4)](4+) cluster can be regarded as a binuclear inorganic complex of two ruthenium(I) cations that are coordinated by terminal Bi(5)(+) square pyramids and a central Bi(4)Br(4) ring. The presence of a covalent Ru-Ru bond was established by molecular quantum chemical calculations utilizing real-space bonding indicator ELI-D. Structural similarity of the new and parent cluster suggests a structural reorganization or an exchange of the bismuth polycations as mechanisms of cluster formation. In this top-down approach a complex-structured unit formed at high temperature was made available for low-temperature use.