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AIM analysis of electron density distribution based on B3LYP calculations, carried out for nido-5,6-C2B8H12 and its anion [nido-C2B8H11]−, and the data of IR spectroscopy lead to conclusion that the formally 6-member face is of greater size due to incorporation of adjacent triangular face and two extra-hydrogen atoms. In nido-5,6-C2B8H12 open face is characterized by complete absence of electron density. The Laplacian of electron density is used to predict the sites of electrophilic attack, which position was shown to depend on a number of extra-hydrogen atoms. The predictions are in agreement with known experimental data.

The presence of low-frequency large-amplitude modes in the vibrational spectrum, experimental and computed data on interboron distances and the results of the topological analysis of the electron density distribution in 2,3-C 2 B 9 H 11 , the molecule of a neutral 11-vertex dicarbaborane, lead to the conclusion that this polyhedron is not a deltahedron. This species lacks at least four two-center B–B bonds and thus it is formed not by triangular faces only. Hence, this dicarbaborane, as well as monocarbaborate [2-CB 10 H 11 ] − , another representative of 11-vertex polyhedra, do not have the closo -structure, traditionally ascribed to both by formal [2 n +2]-electron count.