Events & Seminars > Event Details

Where:

4:00 pm
Room 303, Chemistry Building

The Nature of the Halogen Bond and Other Single-Hole Interactions

Speaker:

Professor Kelling Donald
University of Richmond

Hosted by: Professor Lester Andrews

Abstract: The halogen bond is the best known incarnation of the set of so called sigma-hole interactions. The sensitivity of the size and strength of sigma holes (localized regions of positive potential) on terminal halides (X) bonded to sufficiently electron withdrawing groups has been investigated at the MP2(full) level of theory. We focus in particular on small Lewis Acids, including the MR4-nXn systems (M = C, Si, Ge, Sn, and Pb) interacting with simple Lewis bases. A dramatic substituent-directed reversal in the relative strengths of the (R3M-X—Base) halogen bond energies is identified and explained. We explore a complicated dependence of the relative halogen bond strengths on M and m for the mixed halide MH3-mFmI compounds. We assess the stability of halogen bonds formed by MF3I acids to a wide class of Lewis bases and the viability of competing interactions (such as hydrogen bonding). A few (experimental) observations by other groups on the roles halogen bonding by larger organic systems can and do play in biology and in materials science will be mentioned during the talk. The general class of weak so-called sigma-hole interactions is not a feature unique to terminal atoms. We examine in some detail the related interactions that occur via the central M centers instead, especially when X = Fluorine. The latter forms of sigma-hole interactions – supported by an increasing covalent contribution as M gets larger – help to stabilize species that span the spectrum from weak non-covalent to dative bonding in R3FM·R’ adducts.