| Summary: | Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H<sup>+</sup>) from the cyclopentadienyl anion (C<sub>5</sub>H<sub>5</sub><sup>−</sup>) or the pentalene dianion (C<sub>8</sub>H<sub>6</sub><sup>2−</sup>) by three or four E<sup>2+</sup> dications (E = Si–Pb), respectively. The silicon derivatives of these series are the Si<sub>3</sub>C<sub>5</sub> and Si<sub>4</sub>C<sub>8</sub> clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si<sub>5</sub>C<sub>5</sub>, Si<sub>8</sub>C<sub>8</sub>, and Si<sub>9</sub>C<sub>9</sub>. In all these species, the ptC is embedded in a pentagonal C<sub>5</sub> ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria.
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