Origin of structure and stability of M@C 18 (M = Cu, Ag, and Au) complexes with D 9h 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.