Non-Covalent Interactions of the Lewis Acids Cu–X, Ag–X, and Au–X (X = F and Cl) with Nine Simple Lewis Bases B: A Systematic Investigation of Coinage–Metal Bonds by Ab Initio Calculations

Ibon Alkorta,Anthony C Legon,Nicholas R Walker

doi:10.3390/inorganics9020013

Abstract

The equilibrium geometry and two measures (the equilibrium dissociation energy in the complete basis set limit, De(CBS) and the intermolecular stretching force constant kσ) of the strength of the non-covalent interaction of each of six Lewis acids M–X (M = Cu, Ag, Au) with each of nine simple Lewis bases B (B = N2, CO, HCCH, CH2CH2, H2S, PH3, HCN, H2O, and NH3) have been calculated at the CCSD(T)/aug-cc-pVTZ level of theory in a systematic investigation of the coinage–metal bond. Unlike the corresponding series of hydrogen-bonded B⋯HX and halogen-bonded B⋯XY complexes (and other series involving non-covalent interactions), De is not directly proportional to kσ. Nevertheless, as for the other series, it has been possible to express De in terms of the equation De = cNB.EMX, where NB and EMX are the nucleophilicities of the Lewis bases B and the electrophilicities of the Lewis acids M–X, respectively. The order of the EMX is determined to be EAuF > EAuCl > ECuF > ECuCl > EAgF ≈ EAgCl. A reduced electrophilicity defined as (EMX/σmax) is introduced, where σmax is the maximum positive value of the molecular electrostatic surface potential on the 0.001 e/bohr3 iso-surface. This quantity is, in good approximation, independent of whether F or Cl is attached to M.

Highlights

Isolated complexes of the general type B· · · M–X, where B is a simple Lewis base,M is a coinage–metal atom (Cu, Ag, or Au), and X is a halogen atom, have been investigated extensively in the gas phase via rotational spectroscopy [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Molecular electrostatic surface potentials (MESP) of the various M–X monomers were calculated at the 0.001 e/bohr3 electron density iso-surface using the MP2/aug-cc-pVTZ
For the B···LiX and B···NaX series [26], the order of the NB values is as for the hydrogenand halogen-bonded analogues but the magnitudes are significantly different. These observations probably indicate that the nature of the interaction and the relative contributions of electrostatics, polarisation, and exchange repulsion affect the numerical nucleophilicity that is generated by this particular approach

Summary

Introduction

M is a coinage–metal atom (Cu, Ag, or Au), and X is a halogen atom, have been investigated extensively in the gas phase via rotational spectroscopy [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] Properties, such as geometry, intermolecular stretching force constant kσ , and the change in ionicity of. In view of the closed-shell nature of the molecules M–X, their interaction with Lewis bases in the B· · · M–X complexes can be classified as of the non-covalent type and, following recent practice in the naming and definition of halogen and chalcogen bonds [17,18], can be called coinage–metal or Group 11 bonds [16,19]. Does this indicate whether the electrophilicity per unit positive potential along the molecular axis near to the atom M changes from F to Cl?

Computational Methods

Results

Electrophilicities

Conclusions