Metallophilic interactions in silver(i) dicyanoaurate complexes

Abstract

This manuscript reports four new gold(I)–silver(I) complexes with 2-(2-pyridyl)-1,8-naphthyridine (pyNP) and terpyridine (terpy) as ancillary ligands, having formulae [Ag(pyNP)(Au(CN)₂)]₂ (1), [Ag₂Au₂(μ-CN)₂(CN)₂(pyNP)₂] (2), [Ag₂Au(μ-CN)₂(terpy)₂][Au(CN)₂] (3) and [Ag₄Au₄(μ-CN)₈(terpy)₂(py)] (4). Complexes 1 and 2 are structural isomers obtained from different solvents. The Au(CN)₂⁻ anion is not coordinated and establishes intramolecular Au⋯Ag,Ag interactions in 1. In contrast, it is monocoordinated to silver atoms via a CN fragment in compound 2 and no metallophilic interaction is observed. In compound 3, one Au(CN)₂ anion bridges two Ag(terpy) fragments. In this complex an infinite array of gold atoms is found, exhibiting aurophilic interactions of 3.415 Å. In complex 4 the 3D architecture observed in the crystal packing is driven by Au⋯Au and Au⋯Ag metallophilic interactions. All compounds have been structurally and vibrationally characterized to better understand the crystal forces. In addition, a solution chemistry study in different solvents by ESI-MS spectrometry was performed to comprehend the speciation and solvent effects. Finally, DFT calculations were carried out to analyze the Ag⋯Au interactions and also the π-stacking interactions that are relevant in the crystal packing of some structures. Special attention has been paid to the bifurcated nature of the Au⋯Ag,Ag interactions in compound 1 that has been analyzed theoretically using the quantum theory of atoms-in-molecules (QTAIM) and the Natural Bond Orbital (NBO) computational tools.