Carbide\nClusterfullerene Gd₂C₂@C₉₂ vs Dimetallofullerene\nGd₂@C₉₄: A Quantum Chemical Survey

Abstract

The geometric, electronic structure,\nand thermodynamic stability\nof Gd₂C₉₄ species, including dimetallofullerenes\nGd₂@­C₉₄ and carbide clusterfullerenes\nGd₂C₂@­C₉₂, have been systematically\ninvestigated by a density functional theory approach combined with\nstatistical mechanics calculations. Although the Gd₂@<i>C</i>_<i>2</i>(153480)-C₉₄ is\ndetermined to possess the lowest energy, its molar fraction at the\ntemperature region of fullerene formation is extremely low if the\ntemperature effect is taken into consideration. Meanwhile, three C₉₂-based carbide clusterfullerene species, Gd₂C₂@­<i>D</i>_<i>3</i>(126408)-C₉₂, Gd₂C₂@­<i>C</i>_<i>1</i>(126390)-C₉₂, and Gd₂C₂@­<i>C</i>_<i>2</i>(126387)-C₉₂, with some higher energy are exposed to possess\nconsiderable thermodynamic stabilities within a related temperature\ninterval, suggesting that carbide clusterfullerenes rather than dimetallofullerenes\ncould be isolated experimentally. Although one isomer, Gd₂C₂@­<i>D</i>_<i>3</i>(126408)-C₉₂, has been indeed obtained experimentally,\na novel structure, Gd₂C₂@­<i>C</i>_<i>1</i>(126390)-C₉₂, behaving as\nthe most abundant isomer at more elevated temperatures with the largest\nSOMO–LUMO gap, is predicted for the first time to be another\nproper isomer isolated in the experiment. Moreover, in order to further\nanalyze the interaction between gadolinium atoms and carbon atoms\nin either a carbide cluster or a fullerene cage, frontier molecular\norbital, natural bond orbital, and Mayer bond order analyses have\nbeen employed, and the results show that the covalent interaction\ncannot be neglected. The IR spectra of Gd₂C₂@­C₉₂ have been simulated to provide some valuable\nguidance for future experiments.