A new class of “all-metal” aromatic hydrido-bridged binary coinage metal heterocycles. A DFT study

Abstract

Electronic structure calculations (DFT) suggest that the series of hydrido-bridged binary coinage metal clusters with general formulae cyclo-Cu_nAg_3−n(μ₂-H)_n (n = 1–3), cyclo-Cu_nAg_4−n(μ₂-H)_n (n = 1–4) and cyclo-Cu_nAg_5−n(μ₂-H)_n (n = 1–5) are stable entities. The aromaticity of these bimetallic systems was explored by employing a number of established criteria such as the nucleus-independent chemical shift, the hardness, η, and the electrophilicity index, ω. Aromaticity decreases upon increasing the number of Cu atoms in the metallic ring core structure or increasing its size. The structural, energetic, spectroscopic (IR, NMR, UV-Vis) and electronic properties of these novel classes of inorganic compounds characterized by a common ring-shaped electron density are thoroughly analyzed. The hydrido-bridged binary coinage metal clusters exhibit a composite bonding mode involving both σ-, π- and δ-type components. Noteworthy is the presence of π-type MOs resulting from the bonding interaction of nd AOs of the metal atoms, delocalized over the entire metallic framework analogous to the π-type MOs of the aromatic hydrocarbons.