Theoretical Insights into Stabilities and Configuration Selectivity of Yttrium Cyanide Clusterfullerenes YNC@C₈₄

A series of monometallic cyanide clusterfullerenes (mono-CYCFs) have been obtained in experiment, but the structural characterization of them is still ambiguous since the carbon and nitrogen atoms of the CN group can hardly be distinguished experimentally. In this study, theoretical investigations for the stability and configuration preference for the C₈₄-based yttrium cyanide clusterfullerenes (YNC@C₈₄) have been performed. Based on density functional theory (DFT) calculations in conjunction with the statistical thermodynamic analyses, four YNC@C₈₄ structures, including the experimentally recognized YNC@C₂(51581)-C₈₄ and three newly disclosed ones, YNC@D_2d(51591)-C₈₄, YNC@C_s(51583)-C₈₄, and YNC@C₁(51580)-C₈₄, have been identified as thermodynamically stable isomers. It is revealed that the YNC@C₈₄ configuration is energetically favored over the YCN@C₈₄ configuration due to the inherent stability of the free YNC cluster. Energy decomposition analysis (EDA) shows that it is the stronger electrostatic and orbital interactions between the Y metal and NC species induce better stability of YNC@C₈₄ compared with YCN@C₈₄. Furthermore, the comparison between MNC and MCN species referring to various metal elements reveals that, for early transition metals (Y and Sc) and lanthanide metals (Tb and Dy), the preference of MNC configuration mainly stems from stronger M-NC orbital interaction. In contrast, for cases of Li and Cu, the MNC configuration becomes much less favorable or even less stable than the MCN configuration. In addition, explorations of the electronic properties, bonding features, and optical spectra of the important YNC@C₈₄ isomers have been provided to aid future research of mono-CYCFs. This work provides deep insights into the configuration selectivity of mono-CYCFs, which will assist future experimental characterization.