Intercluster B-H and B-B aggregation in iso- and trans -[B 20 H 18 ] 2- . Spherical aromaticity in borane dimers.

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 -[B 10 H 10 ] 2- anions, an induced aggregation of two cluster units is achieved, retaining their parent B 10 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 -[B 10 H 10 ] 2- units in two isomers, namely, iso- and trans -[B 20 H 18 ] 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 -[B 10 H 10 ] 2- cluster are persistent in both iso- and trans -[B 20 H 18 ] 2- isomers as an interplay between the spherical aromatic properties from both B 10 motifs, leading to an overlap of the shielding regions from shielding cone properties, ascribed as a dual spherical-spherical aromatic cluster. From 11 B-NMR features, it came out that trans -[B 20 H 18 ] 2- involves larger differences in comparison to closo -[B 10 H 10 ] 2- , owing to the variation of the B 10 -B 10 backbone provided by the intercluster B-interaction, thus resulting in a more effective aggregation connecting such building units, towards boron-based cluster materials.