DESCRIPTION OF ELECTRON DONOR-ACCEPTOR COMPLEXES BY A SIMPLE MO METHOD - COMPARISON OF SPECTRAL PROPERTIES OF SYMMETRICAL DAD AND ASYMMETRIC ADD COMPLEXES

The spectral properties of the 1:1 and symmetric and asymmetric 2:1 el ectron donor-acceptor complexes are considered in the framework of the Huckel MO LCAO method. It is shown that on formation of the 2:1 compl ex a red shift of the charge-transfer band with respect to that of the 1:1 analogue can be expected, which is particularly noticeable for th e asymmetric complex. An increase of the band intensity can be also ex pected, this being more marked for the symmetric 2:1 complex. The resu lts obtained are in qualitative agreement with calculations using the INDO/S formalism but do not correlate in part with the extended Mullik en approach.