Intercluster B–H and B–B aggregation in iso- and trans-[B20H18]2−. Spherical aromaticity in borane dimers

Abstract

The formation of molecular-based functional materials is a key step towards the development of technologies at the nanoscale. Recently, it has been shown that after oxidation of closo-[B₁₀H₁₀]²⁻ anions, an induced aggregation of two cluster units is achieved, retaining their parent B₁₀ backbones as persistent building blocks. Such characterization provides an interesting scenario to further understand relevant factors leading to aggregation in a minimal structure involving two units. Here, we explore the interaction between closo-[B₁₀H₁₀]²⁻ units in two isomers, namely, iso- and trans-[B₂₀H₁₈]²⁻, involving different intercluster contacts based on B–B and B–H interactions, respectively. Our results show that the inherent spherical aromatic characteristics of the parent closo-[B₁₀H₁₀]²⁻ cluster are persistent in both iso- and trans-[B₂₀H₁₈]²⁻ isomers as an interplay between the spherical aromatic properties from both B₁₀ motifs, leading to an overlap of the shielding regions from shielding cone properties, ascribed as a dual spherical–spherical aromatic cluster. From ¹¹B-NMR features, it came out that trans-[B₂₀H₁₈]²⁻ involves larger differences in comparison to closo-[B₁₀H₁₀]²⁻, owing to the variation of the B₁₀–B₁₀ backbone provided by the intercluster B-interaction, thus resulting in a more effective aggregation connecting such building units, towards boron-based cluster materials.