Pancake Bonding in Thiazyls From the Insights of EDA‐NOCV

Radical π ‐stacked assemblies are key building blocks in organic conductors and other open‐shell materials, where through‐space electronic coupling shapes magnetic and transport properties. In this study, a series of experimentally characterized neutral radical dimers ( 1a–4 ) was examined using various DFT techniques, such as NBO, QTAIM, and EDA‐NOCV analyses, to study the nature of pancake bonding, which displays short stacking contacts (2.53–3.31 Å), indicative of close π – π association. NBO and QTAIM analyses indicate weak yet finite intermolecular electron sharing, reflected in small Wiberg bond indices (0.05–0.34) and low electron densities at the bond critical points ( ρ (r c ) = 0.013–0.062 a.u.). Energy decomposition analysis indicates that stabilization arises from both orbital and dispersion interactions: the orbital term (43%–62%) provides the dominant contribution, while dispersion (5%–33%) remains significant. The NOCV analysis proves that even though the bond lengths are larger than the actual covalent bonds, the stabilizing factor is still held via the orbital interaction energy, governed primarily by a single interaction channel, Δ E orb(1) , which accounts for the major fraction of the orbital term (∼ 78%–86%) and corresponds to SOMO–SOMO overlap between the radical fragments. Furthermore, dispersion interactions contribute significantly higher amounts to the overall stabilization factor (5%–33%).