2D-Graph of intermolecular interactions predicts radical character of anion-π* type charge-transfer complexes.

The molecular orbital (MO) theory is one of the most useful methods to describe the formation of a new chemical bond between two molecules. However, it is less often employed for modelling non-bonded intermolecular interactions because of the small charge-transfer contribution. Here we introduce two simple descriptors, the energy difference () of the HOMO of an electron donor and the LUMO of an acceptor against such HOMO-LUMO overlap integral (), to show that the MO theory could give a unified charge-transfer picture of both bonding and non-bonding interactions for two molecules.