Insights into Formation and Relationship of Multimetallic Clusters: On the Way toward Bi-Rich Nanostructures

Bismuth-rich polyanions show a unique potential in constructing nanostructured bismuth-based materials, but they are still poorly investigated. We use a ternary precursor of the nominal composition "K₅Ga₂Bi₄" for the formation of [K(crypt-222)]⁺ salts of novel Bi-rich polyanions [Bi@Ga₈(Bi₂)₆] (q = 3, 5; in 1), (Ga₂Bi₁₆)^4- (in 2), and [{Ru(cod)}₄Bi₁₈]^4- (in 3). Their bismuth contents exceed that of the largest homoatomic polyanion, Bi₁₁^3-. The numbers of bismuth atoms in the anions in 2 and 3 furthermore surmount that of the Bi-richest binary main-group anion, (Ge₄Bi₁₄)^4-, and they equal (2) or surmount (3) that reported for the anion and the cations with the largest number of Bi atoms so far, [K₂Zn₂₀Bi₁₆]^6-, [(Bi₈)Ru(Bi₈)]⁶⁺, and [(Bi₈)Au(Bi₈)]⁵⁺. Compounds 1 and 2 were obtained from reaction mixtures that contain [La(C₅Me₄H)₃], apparently assisting in the network formation without being included in the products. In the presence of [Ru(cod)(H₂CC(Me)CH₂)₂], yet another reaction pathway leads to the formation of the anions in 3 (conformers 3a and 3b), which are Bi-Bi linked dimers of two "[{Ru(cod)}₂Bi₉]^2-" subunits. They comprise the largest connected assemblies of Bi atoms within one molecule and may be viewed as snapshots on the way toward even larger polybismuthide units and, ultimately, new bismuth modifications. Mass spectrometry allowed insight into the processes in solution that precede the cluster formation. In-depth quantum chemical studies were applied to explain structural peculiarities, stabilities of the observed isomers, and bonding characteristics of these bismuth-rich nanoarchitectures. The work demonstrates the high potential of the method for the access of new Bi-based materials.