Stacking Interactions: A Supramolecular Approach to Upgrade Weak Halogen Bond Donors

Abstract

The co‐crystallization of tetracyanobenzene (TCB) with haloarenes ArX provided six new co‐crystals TCB ⋅ ArX (ArX=PhCl, PhBr, 4‐MeC6H4Cl, 4‐MeC6H4Br, 4‐MeOC6H4Cl, 1,2‐Br2C6H4) which were studied by X‐ray diffraction. In these systems, the strong collective effect of π⋅⋅⋅π stacking interactions and lone pair‐(X)⋅⋅⋅π‐hole‐(C) bondings between TCB and ArX promote the strength of X⋅⋅⋅Ncyano halogen bonding (HaB). Theoretical studies showed that the stacking interactions affect the σ‐hole depth of the haloarenes, thus significantly boosting their ability to function as HaB donors. According to the molecular electrostatic potential calculations, the σ‐ hole‐(Cl) value (1.5 kcal/mol) in the haloarene 4‐MeOC6H4Cl (featuring an electron‐rich arene moiety and exhibiting very poor σ‐hole‐(Cl) ability) increases significantly in the stacked trimer (TCB)2 ⋅ 4‐MeOC6H4Cl (12.5 kcal/mol). Theoretical DFT calculations demonstrate the dramatic increase of X⋅⋅⋅Ncyano HaB strength for stacked trimers in comparison with parent unstacked haloarenes.

Noncovalent Chelation by Halogen Bonding in the Design of Metal-Containing Arrays: Assembly of Double σ-Hole Donating Halolium with CuI-Containing O,O-Donors

“…This level of theory has been used before to evaluate noncovalent interactions in the solid state. 64,65 The QTAIM/NCIplot results were represented using the VMD program. 66 ■ ASSOCIATED CONTENT * sı Supporting Information…”

“…The calculations were carried out using the Turbomole 7.2 program at the PBE0-D3/def2-TZVP level of theory. − The MEP surface plots, QTAIM and NCIplot analyses, were calculated at the same level of theory. This level of theory has been used before to evaluate noncovalent interactions in the solid state. , The QTAIM/NCIplot results were represented using the VMD program …”

Competition Between the Two σ‐Holes in the Formation of a Chalcogen Bond

“…[1][2][3][4][5][6] The halogen bond (XB) is a prime example where the bridging H of the HB is replaced by any of the halogen group of the periodic table. [7][8][9][10][11][12][13][14][15][16] Like the HB, there is an attractive charge transfer component that shifts density from a lone pair of the nucleophile to the σ*(RX) antibonding orbital, where X refers to a halogen rather than a H atom. One distinction between the two sorts of bonds arises within the context of the electrostatic component.…”

“…Noncovalent bonding has gained a great deal of attention of late as research has shifted to a family of interactions that share many facets with the well studied H‐bond (HB) [1–6] . The halogen bond (XB) is a prime example where the bridging H of the HB is replaced by any of the halogen group of the periodic table [7–16] . Like the HB, there is an attractive charge transfer component that shifts density from a lone pair of the nucleophile to the σ*(RX) antibonding orbital, where X refers to a halogen rather than a H atom.…”

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.…”