Tuning Molecular Electron Affinities against Atomic Electronegativities by Spatial Expansion of a π-System.

2,1,3-Benzochalcogenadiazoles C R N E (E/R; E=S, Se, Te; R=H, F, Cl, Br, I) and C H R N E (E/R'; E=S, Se, Te; R=Br, I) are 10π-electron hetarenes. By CV/EPR measurements, DFT calculations, and QTAIM and ELI-D analyses, it is shown that their molecular electron affinities (EAs) increase with decreasing Allen electronegativities and electron affinities of the E and non-hydrogen R (except Cl) atoms. DFT calculations for E/R+e⋅ →[E/R]⋅ electron capture reveal negative ΔG values numerically increasing with increasing atomic numbers of the E and R atoms; positive ΔS has a minor influence. It is suggested that the EA increase is caused by more effective charge/spin delocalization in the radical anions of heavier derivatives due to contributions from diffuse (a real-space expanded) p-AOs of the heavier E and R atoms; and that this counterintuitive effect might be of the general character.