Charge-Transfer Complexes of Tetracyanoethylene with Alkyl and Aryl Derivatives of the Halogens

Abstract

Spectral characteristics (λCT, Δν1/2, and e) and association constants (in dichloromethane) of charge-transfer (CT) complexes of tetracyanoethylene (T) with donors containing C−X linkages (X = F, Cl, Br, and I) are presented. The donor orbitals from which CT transitions originate are identified by correlation of λCT and Δν1/2 values of CT bands of the complexes with the ionization bands of the photoelectron spectra of the donor molecules. CT energies of the complexes are influenced by intramolecular conjugative and inductive effects between halogen atoms and alkyl and aryl groups. Haloalkanes form weak complexes with T through interaction of the px and py orbitals of the halogen with the π* LUMO of T. Monoiodoalkane−T complexes exhibit two spectral bands arising from the transfer of nonbonded electrons from the 5p orbitals of iodine which are split into 2E1/2 and 2E3/2 states through spin−orbit coupling. λ1 and λ2 values of monoiodoalkanes increase progressively with increasing bulk of the alkyl group. Ha...