Intermolecular interactions between hypervalent molecules: Ph2IX and XF3 (X=Cl, Br, I) dimers

Abstract

The intermolecular bonding in dimers of the T-shaped hypervalent title compounds is analyzed using a combination of density functional calculations and qualitative arguments. Fragment molecular orbital interaction diagrams lead us to the conclusion that the bonding in these species can be understood using the language of donor-acceptor interactions: mixing between occupied states on one fragment and unoccupied states on the other. There is also a strong electrostatic contribution to the bonding. The calculated strengths of these halogen–halogen secondary interactions are all less than 10 kcal mol^-1. There is a very soft potential energy surface for the deformation that makes the bridge in the dimers asymmetrical.