Stacking interactions of borazine: important stacking at large horizontal displacements and dihydrogen bonding governed by electrostatic potentials of borazine

Abstract

A detailed scan of potential energy surfaces for borazine stacking revealed important interactions encountered in borazine crystal structures.

Electrostatics does not dictate the slip-stacked arrangement of aromatic π–π interactions

“…between electrostatics and dispersion has since emerged as the principle paradigm for interpreting conformational preferences in aromatic systems, [13][14][15][16][17][18][19][20][21] and in particular is used to explain the emergence of the slip-stacked conguration in (C 6 H 6 ) 2 . 11 Since the seminal paper by Hunter and Sanders, 11 additional analysis has begun to erode the simple electrostatic picture proffered by this model.…”

Reinterpreting π-stacking

“…Nevertheless, quadrupolar electrostatics is a recurring theme in discussion of π-π interactions, and has long been the principle paradigm through which paralleldisplaced π-stacking has been rationalized. [9][10][11][12][13][14][15][16][17][18][19][20][21] This conventional wisdom persists despite considerable evidence that charge penetration effects, which nullify or at least complicate classical electrostatic arguments, are significant at typical π-stacking dis- tances. [22][23][24][25][26][27][28][29] Benzene dimer is the archetypal π-stacked system and its conformational preferences are traditionally discussed in terms of several geometric isomers that are depicted in Fig.…”

“…While the Hunter-Sanders model correctly predicts a slip-stacked structure for (C 6 H 6 ) 2 , in agreement with ab initio calculations, it does not explain the fact that (C 6 H 6 )• • • (C 6 F 6 ) also exhibits a parallel-offset structure, [34][35][36] despite quadrupolar electrostatic interactions that are attractive in the cofacial arrangement. Various studies have since suggested that the Hunter-Sanders model exaggerates the role of electrostatics, 3,[22][23][24][25][26]32,[37][38][39][40][41] however this model remains a widelydiscussed paradigm for π-π interactions, [9][10][11][12][13][14][15][16][17][18][19][20][21] highlighted in contemporary textbooks. 14,15 We have recently provided a clear and concise demonstration that the importance of electrostatics in π-π interactions has been misconstrued, and that the Hunter-Sanders model does not simply "overemphasize" electrostatics, 1 but is in fact qualitatively wrong and represents a fundamentally flawed framework for understanding π-π interactions.…”

Reinterpreting π-Stacking

“…Nevertheless, quadrupolar electrostatics is a recurring theme in discussion of π-π interactions, and has long been the principle paradigm through which paralleldisplaced π-stacking has been rationalized. [9][10][11][12][13][14][15][16][17][18][19][20][21] This conventional wisdom persists despite considerable evidence that charge penetration effects, which nullify or at least complicate classical electrostatic arguments, are significant at typical π-stacking dis- tances. [22][23][24][25][26][27][28][29] Benzene dimer is the archetypal π-stacked system and its conformational preferences are traditionally discussed in terms of several geometric isomers that are depicted in Fig.…”

“…While the Hunter-Sanders model correctly predicts a slip-stacked structure for (C 6 H 6 ) 2 , in agreement with ab initio calculations, it does not explain the fact that (C 6 H 6 )• • • (C 6 F 6 ) also exhibits a parallel-offset structure, [34][35][36] despite quadrupolar electrostatic interactions that are attractive in the cofacial arrangement. Various studies have since suggested that the Hunter-Sanders model exaggerates the role of electrostatics, 3,[22][23][24][25][26]32,[37][38][39][40][41] however this model remains a widelydiscussed paradigm for π-π interactions, [9][10][11][12][13][14][15][16][17][18][19][20][21] highlighted in contemporary textbooks. 14,15 We have recently provided a clear and concise demonstration that the importance of electrostatics in π-π interactions has been misconstrued, and that the Hunter-Sanders model does not simply "overemphasize" electrostatics, 1 but is in fact qualitatively wrong and represents a fundamentally flawed framework for understanding π-π interactions.…”