Properties of atoms in molecules: structures and reactivities of boranes and carboranes

Abstract

This pelper-is deciicated to Professor Sigeru Hl~zir~ugn or1 the occasiotz of his 65th birthday R. F. W. BADER and D. A. LECARE. Can. J . Cheni. 70, 657 (1992). The energies, geometries, and charge distributions of the closo-, tlido-. and arachrro-boranes and closo-carboranes are determined in SCF calculations using a contracted (9s,5/2) basis set of Huzinaga, supplemented with polarization functions. Good agreement is obtained between the experimental and calculated geometries. Molecular structures are assigned on the basis of the bond paths defined by the topology of the charge density using the theory of atoms in molecules. This theory is used to characterize the atomic interactions and to account for the stabilities of these electron-deficient systems. It is shown that their stability is a consequence of the delocalization of charge over the surfaces of the three-and four-membered rings of atoms that result from the formation of bonds of reduced order, a delocalization that is itself essential to the fonnation of the ring bonds. The Laplacian of the charge density is used to predict the sites of nucleophilic and electrophilic attack in these molecules, predictions that are in agreement with known experimental findings.

Topological analysis of the experimental electron density

“…16. Analysis of more simple closo-carboranes on the basis of nonempirical calculations (58) has resulted in the same topological picture.…”

A practical and efficient method to calculate AIM localization and delocalization indices at post‐HF levels of theory

“…We also show selected internuclear distances that differ in the two studies because of their potential increases. It is interesting to note that B 2 H 6 , the archetypal molecule with significant delocalization, 33 also exhibits minor deviations.…”

Nature of weak inter- and intramolecular contacts in crystals 2. Character of electron delocalization and the nature of X—H...H—X (X = C, B) contacts in the crystal of 1-phenyl-o-carborane

“…For instance, the C(2)-C(1)-C(13)-C(14) (θ) torsion angle is 18.6 for α 1 and 22.3°f or β 1. This leads to formation of shortened contacts, H(2)...H (18) and H (5)...H (14), of length 2.041 and 2.148 Å, respectively (see Fig. 1).…”

“…As mentioned above, analysis of the critical points in the regions of the intramolecular H...H contacts allowed us to localize the (3,-1) critical points between the same pairs of atoms, H(2)...H (18) and H(5)...H (14), as in the calculations. The topological characteristics of these con tacts in the crystal are in good agreement with the results of calculations (Table 3).…”