CLOSO-BORANES, CLOSO-CARBORANES, AND CLOSO-SILABORANES - A TOPOGRAPHICAL STUDY USING ELECTRON-DENSITY AND MOLECULAR ELECTROSTATIC POTENTIAL

A topographical study on a series of n-vertex (n = 5-7) closo-boranes, closo-carboranes, and closo-silaboranes using electron density (ED) a nd molecular electrostatic potential (MESP) reveals many interesting f eatures on the molecular structure and reactivity. No B-B bond critica l points exist in the equatorial plane for the five vertex cages. The charge density is found to be more on the exterior of the molecule tha n on the interior. However, all borane anions exhibit localization of ED in the centroid of the cage. The bond polarities are reversed while going from closo-carboranes to closo-silaboranes. But, the reactivity pattern toward electrophiles essentially parallels in both cases. Amo ng borane anions, B5H52- is more prone toward electrophilic attack. Us ing MESP as a tool, the positional isomer stabilities of various closo -heteroboranes are predicted and found to agree well with experimental results and other theoretical models.