Theoretical investigation of CB5H6(Hfac) and CB5H5(H2) carboranes: Combined MO and QTAIM analysis

Anion [CB5H6]– is suitable object for molecular modeling of carborane properties. Its protonated form CB5H6(Hfac) has been of special interest to researchers for several decades. One of the reasons of such interest is the nature of chemical bonding between additional Hfac and cluster cage. In present research, the nature of given interaction was investigated with the analysis of molecular orbitals and topology of electron density. This combined analysis allows to rigorous and clear representation of bonding nature between Hfac and cluster cage. CB5H6(Hfac) can be isomerized to systems in which boron atom attached to two hydrogen atoms CB5H5(H2). The electronic structure of CB5H5(H2) was also investigated in detail in present study. CB5H6(Hfac) and CB5H5(H2) are the key intermediates in EINS (electrophile induced nucleophilic substitution) process. Extensive investigation of structure of these systems gives an insight on EINS substitution process not only in the [CB5H6]– anion, but also for the whole family of carborane systems.