The pnictogen bond: a quantitative molecular orbital picture.

F. Matthias Bickelhaupt,Trevor A. Hamlin,Teodorico C. Ramalho,Lucas de Azevedo Santos

doi:10.1039/d1cp01571k

Abstract

We have analyzed the structure and stability of archetypal pnictogen-bonded model complexes D3Pn⋯A− (Pn = N, P, As, Sb; D, A = F, Cl, Br) using state-of-the-art relativistic density functional calculations at the ZORA-M06/QZ4P level. We have accomplished two tasks: (i) to compute accurate trends in pnictogen-bond strength based on a set of consistent data; and (ii) to rationalize these trends in terms of detailed analyses of the bonding mechanism based on quantitative Kohn–Sham molecular orbital (KS-MO) theory in combination with a canonical energy decomposition analysis (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. We have found that pnictogen bonds have a significant covalent character stemming from strong HOMO–LUMO interactions between the lone pair of A− and σ* of D3Pn. As such, the underlying mechanism of the pnictogen bond is similar to that of hydrogen, halogen, and chalcogen bonds.

Highlights

In this study, we have computationally analyzed a range of pnictogen-bonded D3PnÁ Á ÁAÀ complexes (Pn = N, P, As, Sb; D, A = F, Cl, Br; see Scheme 1), using relativistic density functional theory (DFT) at the zerothorder regular approximation (ZORA)-M06/QZ4P level
These model reactions go with a single-well potential energy surface (PES), that is, there is no energy barrier separating the reactants from their resulting product
Our analyses reveal that the pnictogen bonding mechanism is not purely electrostatic but, instead, has a relatively large covalent component (DEoi), stemming mainly from the HOMO– LUMO interaction between the occupied halide npy atomic orbital (AO) and the s* D–pnictogen atom (Pn) antibonding 5a0 acceptor orbital

Summary

Introduction

One purpose of our work is to provide a set of consistent structural and energy data from which reliable trends can be inferred for a wide range of model systems From these data, we have constructed a unified framework to rationalize the nature of pnictogen bonds, chalcogen bonds, halogen bonds, and hydrogen bonds, by studying the associated electronic structure and bonding mechanism.[8]. The context of Kohn–Sham molecular orbital (MO) theory in combination with a matching energy decomposition analysis (EDA) as implemented in the Amsterdam Density Functional (ADF) program.[10,11] Our analyses along the entire reaction profile for each of the pnictogen-bond complexation reactions demonstrate that pnictogen bonds are not at all purely electrostatic phenomena Instead, they are, to a substantial extent, covalent in nature, very similar to chalcogen bonds, halogen bonds, and hydrogen bonds. Using a quantitative energy decomposition analysis (EDA) as implemented in ADF.[10,11]

Theoretical methods

Results and discussion

D Estrain

D EPauli

Conclusions