Si₆C₁₈: A bispentalene derivative with two planar tetracoordinate carbons

Here we show that substituting the ten protons in the dianion of a bispentalene derivative (C₁₈H₁₀²⁻) by six Si²⁺ dications produces a minimum energy structure with two planar tetracoordinate carbons (ptC). In Si₆C₁₈, the ptCs are embedded in the terminal C₅ pentagonal rings and participate in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Our exploration of the potential energy surface identifies a triphenylene derivative as the putative global minimum. Nevertheless, robustness to Born–Oppenheimer molecular dynamics (BOMD) simulations at 900 and 1500 K supports bispentalene derivative kinetic stability. Chemical bonding analysis reveals ten delocalized π-bonds, which, according to Hückel's 4n + 2 π-electron rule, would classify it as an aromatic system. Magnetically induced current density analysis reveals the presence of intense local paratropic currents and a weakly global diatropic current, the latter agreeing with the possible global aromatic character of this specie.