Counterintuitive noncovalent interactions of ammonia with the all metal ring of cyclic trinuclear Ag(i) clusters: a DFT study

Abstract

Density functional theory electronic structure calculations were employed to study a proposed novel type of interaction between NH₃ and the metallic ring of cyclic trinuclear Ag(I) clusters of the general formula cyclo-Ag₃(μ₂-L)₃ bearing 15 different bridging organic ligands L. Scan single point energy calculations revealed that the most stable orientation of NH₃ is that with a N atom facing the center of the silver metallic ring and bridging the three metal centers. Starting with this orientation we performed geometry optimizations of the cyclo-Ag₃(μ₂-L)₃(μ₃-NH₃) complexes. The optimized geometries retain the initial orientation of NH₃. The zero point energy corrected interaction energies, D₀, of NH₃ with the metallic ring are found in the range 4.2–12.4 kcal mol⁻¹ while the distance of NH₃ from the center of the ring is in the range 2.317–2.519 Å, both indicative of a relatively strong interaction. A multitude of theoretical methods employed revealed that the interaction of NH₃ with the silver metallic ring is mainly of ionic nature with a contribution of van der Waals forces. Molecular structure–property relationships indicate that the magnitude of D₀ increases upon increasing the charge of the silver metal centers and decreasing the LUMO energy of the cyclo-Ag₃(μ₂-L)₃ clusters.