Exploring a new kind of aromatic hydrogen bond: hydrogen bonding to all-metal aromatic species

Abstract

Based on the recent advance of the aromaticity concept into all-metal species, we put forward a new kind of hydrogen bond: hydrogen bonding to all-metal aromatic species. The similarities and differences between the hydrogen bonds in all-metal aromatic systems and those in traditional organic aromatic systems are systematically explored: we investigated the interactions between all-metal aromatic complexes Al₄²⁻/Al₄M (M = Mg²⁺, Ca²⁺, 2Na⁺) and H–Y (Y = CH₃, NH₂, OH, F, Cl, Br) as well as those between benzene and H–Y. Geometric configuration calculations, molecular orbital (MO) analysis, nuclear independent chemical shift (NICS) and frequency shift (FS) as well as binding energy calculations were employed for the investigation of the Al₄²⁻⋯H–Y, Al₄M⋯H–Y and C₆H₆⋯H–Y complexes. The calculated results revealed that there exist distinct differences between the hydrogen bonds in all-metal aromatic systems and those in traditional organic aromatic systems in many aspects such as binding energy and interaction distance as well as frequency shift of H–Y. Furthermore, because the aromaticity of all-metal aromatic systems can be changed by interaction with different metal ions, the intensity of hydrogen bonding can also be adjusted and controlled by changing the ions. The natures of hydrogen bonds in all-metal aromatic systems are summarized.