Revisiting stacking interactions in tetra­thia­fulvalene and selected derivatives using tight-binding quantum chemical calculations and local coupled-cluster method

The engineering of supramolecular architectures needs accurate descriptions of the intermolecular interactions in crystal structures. Tetra­thia­fulvalene (TTF) is an effective building block used in the construction of promising functional materials. The parallel packing of the neutral TTF–TTF system was studied previously using the high-level quantum chemical method, advancing it as a valuable model system. The recently developed tight-binding quantum chemical method GFN2-xTB and local coupled-cluster method DLPNO-CCSD(T) were used to investigate the stacking interactions of TTF and selected derivatives deposited in the Cambridge Structural Database. Using the interaction energy of the TTF–TTF dimer calculated at the CCSD(T)/CBS level as the reference, the accuracies of the two methods are investigated. The energy decom­position analysis within the DLPNO-CCSD(T) framework reveals the importance of dispersion interaction in the TTF-related stacking systems. The dispersion interaction density plot vividly shows the magnitude and distribution of the dispersion interaction, providing a revealing insight into the stacking interactions in crystal structures. The results show that the GFN2-xTB and DLPNO-CCSD(T) methods could achieve accuracy at an affordable com­putational cost, which would be valuable in understanding the nature of parallel stacking in supra­molecular systems.