Exploring Coinage Bonding Interactions in [Au(CN)₄]⁻ Assemblies with Silver and Zinc Complexes: A Structural and Theoretical Study

This study investigates the non-covalent interactions between [Au(CN)₄]⁻ anions and silver and zinc complexes, with a particular focus on coinage bonding interactions. Four new complexes, [Ag2(pyNP)2][Au(CN)4]2(1) [Zn(bipy)3][Au(CN)4]2 (2), [Zn(phen)3][Au(CN)4]2 (3) and [Zn(terpy)(H2O)3][Au(CN)4]2 (4), were synthesized and spectroscopically characterized, including their X-ray solid state structures, where pyNP is (2-(2-pyridyl)-1,8-naphthyridine, bipy is 2,2′ bipyridine, phen is 1,10’-phenantrolyne and terpy is terpyridine. The [Au(CN)₄]⁻ anion exhibits unique anion···anion interactions, despite the electrostatic repulsion, forming stable 1D supramolecular polymers in the solid state. Using a combination of X-ray crystallography and DFT calculations, this work characterizes the coordination and non-covalent bonding modes, including Au···N coinage bonds. Energy decomposition analysis (EDA), QTAIM, and NCIplot methods were applied to understand the energetics and bonding nature. The study reveals that electrostatic and dispersion forces play critical roles in stabilizing these assemblies, especially in the formation of π-stacking and T-shaped dimers. These findings offer insights into the design of new materials leveraging coinage bonding in molecular architectures.