Construction of a ‘Russian doll’ ptC@Al₄@C₆₀(<i>Cs</i>) based on the planar tetracoordinate carbon

Since the concept of the planar tetracoordinate carbon (ptC) was proposed, the search for new ptC has never stopped. Here, we try to keep it stableusing the confinement effect of fullerene. First, the restricted space C₆₀(<i>Cs</i>) with four pairs of isolated pentagons can be obtained from traditional C₆₀(<i>Ih</i>) by two Stone–Wales transformations. Further, the famous ptC@Al₄ skeleton was then encapsulated into C₆₀(<i>Cs</i>): the stable ‘Russian doll' planar tetracoordinate carbons ptC@Al₄@C₆₀(<i>Cs</i>) (<b>1</b>) and its charged species, namely <b>1</b>⁻ and <b>1²</b>⁻ are constructed. Furthermore, their charge distribution, Wiberg bond indices (WBIs) and the interaction energy (Δ<i>E</i>_int) are analysed. Finally, their infrared spectroscopy (IR) and its other electronic properties are explored that might be used by the experimentalists to identify this novel kind of complex. We hope the present research results are expected to enrich the research results in the fields of planar carbon chemistry and molecular electronics.