So-called sigma holes are localized regions of positive electrostatic potential that have been induced on (often electron rich) atomic centers by electron withdrawing substituents. The presence of these ‘holes’, which allow even electron donors to behave like acceptors as well, favor the formation of halogen bonds and other weak bonding interactions. Halogen bonding in organic chemistry and biochemistry has received a substantial amount of attention in the literature. We reflect in this talk on the nature of sigma hole interactions to atoms elsewhere in the periodic table. We summarize our observations on halogen bonding and analogous interactions to the central M atoms, including MX<sub>4</sub>---Base complexes, where M = C, Si, Ge, Sn, and Pb, and X = H, F, Cl, Br, and I. As M gets larger, it becomes obvious that sigma hole interactions alone cannot account completely for the extent of the bonding or structural modifications observed in the resulting complexes. The bonding is a partnership among interactions, including sigma-holes, and fall in line with and reinforce expectations based on common molecular orbital and valence bond theory. Experimental evidence of the influence of sigma-hole interactions in chemistry is highlighted. We identify, as well, a role for weak sigma hole interactions in quantifying rigorously and in a straightforward way certain basic physico-chemical concepts.

Sigma-hole supported interactions across the periodic table

254th National Meeting (2017)

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