Factors contributing to halogen bond strength and stretch or contraction of internal covalent bond

Abstract

The halogen bond formed by a series of Lewis acids TF3X (T=C, Si, Ge, Sn, Pb; X=Cl, Br, I) with NH3 are studied by quantum chemical calculations. The interaction energy...

Enhancement of Halogen Bond Strength by Intramolecular H-Bonds

“…However, this effect can be counteracted if a shortening of the bond might intensify the X σ-hole, and thereby raise the electrostatic component of the interaction. Indeed, the effects of this competition were demonstrated in a recent study of the halogen bond involving a series of TF 3 X Lewis acids.…”

“…This binary behavior can be explained as a balance between two competing factors. 72 On the one hand, the addition of density into the σ*(CX) antibonding orbital would tend to weaken and lengthen this bond. However, this effect can be counteracted if a shortening of the bond might intensify the X σ-hole, and thereby raise the electrostatic component of the interaction.…”

“…The C–Cl bonds are contracted, while elongation is observed for C–I; the Br analogues are intermediate, with some in either direction. This binary behavior can be explained as a balance between two competing factors . On the one hand, the addition of density into the σ*­(CX) antibonding orbital would tend to weaken and lengthen this bond.…”

Does a halogen bond require positive potential on the acid and negative potential on the base?

“…As study of the XB has ramped up over recent years it has come to be understood that very similar factors contribute to its stability. [8][9][10][11][12][13][14][15][16][17] The primary difference is that the overall positive charge of the bridging H is replaced by a narrower positive region that lies along the extension of the RX covalent bond, known generally as a s-hole. This polar hole is surrounded by a negative equator that leaves the X atom with an overall negative charge, which tends to make the XB somewhat more directional than a standard HB.…”

Halogen bonds with carbenes acting as Lewis base units: complexes of imidazol-2-ylidene: theoretical analysis and experimental evidence

“…29,30 These factors have been analyzed in detail recently. 30 Hence one can see that there are only a few studies on halogen bonds in complexes of carbenes, and often they do not concern the halogen bond directly. That is why the aim of this study is to analyse the halogen bonds that link the imidazol-2-ylidene moiety with XCCH, XCN and X 2 Lewis acid units (X = F, Cl, Br and I).…”