Structure and packing arrangement of molecular compounds - VI. Molecular orbitals and charge-transfer interactions in TCNQ-containing π-π* complexes

The calculation of electronic structures of TCNQ and several electron-donor molecules has been performed by the Iterative Extended Hückel Method, taking into account all valence electrons of various atoms and retaining the overlap integrals. Calculations of intermolecular overlaps involving the lowest vacant molecular orbital of TCNQ and one or more highest occupied orbitals of each of the donors have been correlated with the observed donor-TCNQ geometrical configurations. The results of this simple approach, which is based on Mulliken's "Overlap and Orientation Principle", suggest that the charge-transfer interaction plays an important role in the particular observed packing arrangement in the solid state.