Exploring the Potential Energy Surface of E2P4 Clusters (E=Group 13 Element): The Quest for Inverse Carbon‐Free Sandwiches

AbstractInverse carbon‐free sandwich structures with formula E2P4 (E=Al, Ga, In, Tl) have been proposed as a promising new target in main‐group chemistry. Our computational exploration of their corresponding potential‐energy surfaces at the S12h/TZ2P level shows that indeed stable carbon‐free inverse‐sandwiches can be obtained if one chooses an appropriate Group 13 element for E. The boron analogue B2P4 does not form the D4h‐symmetric inverse‐sandwich structure, but instead prefers a D2d structure of two perpendicular BP2 units with the formation of a double BB bond. For the other elements of Group 13, Al–Tl, the most favorable isomer is the D4h inverse‐sandwich structure. The preference for the D2d isomer for B2P4 and D4h for their heavier analogues has been rationalized in terms of an isomerization‐energy decomposition analysis, and further corroborated by determination of aromaticity of these species.