Origin of structure and stability of M@C18 (M = Cu, Ag, and Au) complexes with D9h point group

Theoretical predictions and recent experimental studies lead to the discovery of an exciting new member of the carbon allotrope family polyynic cyclo[18]carbon (C-18). Present investigation aims to probe the structure, stability, and properties of coinage metal (M)@C-18 complexes using density functional theory (DFT) calculations. The DFT results unequivocally show that even Cu@C-18, Ag@C-18, and Au@C-18 complexes substantially preserve the ground state polyynic structure of C-18. It is also worth to mention that only Au@C-18 is a stable D-9h structure, however the symmetry is distorted in the case of Cu@C-18 and Ag@C-18. Due to computational limitations, in this investigation the M@C-18 complexes were scrutinized using the C-2v sub abelian group of D-9h. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of D-9h conformers are a singlet a(1) and two same value singlets a(1) ? b(1) generated from doublet e, respectively. The non-covalent interaction index (NCI), quantum theory of atoms in molecule (QTAIM), and energy decomposition analysis (EDA) vividly explains the interaction between a coinage metal atom and C-18 ring. It is found from the results that the stability of Cu@C-18 Ag@C-18, and Au@C-18 is governed by the attractive electrostatic, orbital and dispersion interaction.