Speaker	Roald Hoffmann, Nobel Laureate Department of Chemistry and Chemical Biology Cornell University Baker Laboratory Ithaca, NY 14853-1301
Topic	Electron-Rich Multicenter Bonding in  Molecules and Extended Structures
Date	December 12, 2002
Time	16:00 - 16:50 hrs.
Venue	MLS Hall Indian Association for the Cultivation of Science

Abstract of the Lecture :

From Rundle and Pimentel's fruitful early constructs we've known how to describe the bonding in hypervalent molecular systems such as PF5, SF4, BrF3, XeF2 or I3, XeF4. More recently linear, T-shaped, and square planar arrays of main group elements have cropped up in remarkable variety in extended phases, especially antimonides and tellurides. And the more crystal structures we know, the clearer it becomes that in the solid state there are many electron-rich contacts between a bond and a van der Waals approach. A qualitative molecular orbital account will be given of the continuum variously described as electron-rich three-center, hypervalent, or secondary bonding.