On the Nature of the Bonding in Coinage Metal Halides.

Slađana Đorđević,Slavko Radenković,Benoît Braïda,Sason Shaik

doi:10.3390/molecules27020490

Abstract

This article analyzes the nature of the chemical bond in coinage metal halides using high-level ab initio Valence Bond (VB) theory. It is shown that these bonds display a large Charge-Shift Bonding character, which is traced back to the large Pauli pressure arising from the interaction between the bond pair with the filled semicore d shell of the metal. The gold-halide bonds turn out to be pure Charge-Shift Bonds (CSBs), while the copper halides are polar-covalent bonds and silver halides borderline cases. Among the different halogens, the largest CSB character is found for fluorine, which experiences the largest Pauli pressure from its σ lone pair. Additionally, all these bonds display a secondary but non-negligible π bonding character, which is also quantified in the VB calculations.

Highlights

Understanding the nature of bonds in transition metal-containing molecules is a more challenging task than for main group atoms [1,2,3,4,5,6,7]
The detailed nature of bonding in coinage metal halide dimers has been dissected based on the high-level ab initio classical Valence Bond Breathing Orbital VB (BOVB) method
This method has been shown to provide accurate estimates of bond dissociation energies for these dimers, as compared with CCSD(T) combined with the large aug-cc-pVQZ basis set, and the bonding analysis inferred from the BOVB wave function can be considered as fully reliable and quantitative

Summary

Introduction

Understanding the nature of bonds in transition metal-containing molecules is a more challenging task than for main group atoms [1,2,3,4,5,6,7]. A key reason is the presence of two different valence shells, the (n−1)d and ns shells, which have similar spatial extensions and energies These orbitals can be partially filled depending on the metal and its oxidation state and will usually involve a larger number of valence electrons than main group elements, which represent an additional complexity [8]. It is reasonable to expect that the presence of an electron-rich coinage metal M containing a filled (n−1)d semicore shell acting as lone pairs, together with a halogen X bearing lone pairs, can cause a significant CSB characteristics in the resulting MX dimers To tackle this bonding question, we apply, a high-level ab initio VB method. Two main issues are addressed in this article: quantifying the CSB character of MX, and dissecting the roles of the semicore fully filled (n−1)d shells in M atoms and of the lone pairs on X atoms in the bonding mechanism

Computational Details

Results and Discussion

Conclusions