Deltahedra with holes: Structural preferences of supraicosahedral boranes

A systematic quantum chemical inquiry on supraicosahedral boranes (BnHn2−, n > 12) reveals that larger polyhedral boranes no longer prefer pure deltahedral structures. In an attempt to avoid vertices that has six polyhedral neighbors (hex-caps), inevitable for larger deltahedra; they resort to faces other than triangles (squares and pentagons). These larger faces behave like holes rather than open faces as they obey the Wade’s n + 1 rule for closo boranes. Further, these holes prefer to be isolated, similar to the pentagons in carbon fullerenes. The convex polyhedron, snub dodecahedron (B60H602−, I symmetry) derived from these structural preferences, is a promising candidate for experimental characterization. The larger size of borane snub balls allows the hosting of counter ions endohedrally and this increases the rigidity of the cluster. The structural principles deduced in this paper successfully explain the mystery behind the observation of square faces in some of the known supraicosahedral carboranes, and helps in understanding the complex MB66 type borides which are characterized to have a O symmetric snub frameworks. They also provide the fundamental information towards the design of borane based nanostructures.

A systematic computational enquiry reveals that larger supraicosahedral boranes prefer squares and pentagonal holes in their deltahedral structures and still obey Wade’s n + 1 rule for closo boranes. These faces when isolated, increase the stability of the resulting structure, similar to isolated pentagons rule in fullerenes. The borane analog of C60 fullerene, is B60H602−, containing triangular and pentagonal faces.Figure optionsDownload as PowerPoint slide