A new class of halogen bonds that avoids the σ-hole

A new class of halogen bonds of the type X = Hal⋯Y has been investigated by using the density functional theory calculations. The strength of this new class of halogen bonds is in the range of 90–120 kcal/mol, which is greatly larger than that of the conventional halogen bond of the type X-Hal⋯Y. The geometry of this new class of halogen bonds is not determined by the halogen’s positive σ-hole. Natural bond orbital analysis shows it is the n → π∗ interaction that determines the geometry of this new class of halogen bonds. Experimental results are in good agreement with the theoretical predictions.