SPECTRAL PROPERTIES OF SOME WEAK ELECTRON-DONOR-ACCEPTOR (EDA)-COMPLEXES IN THE FAR INFRARED (FIR) REGION (40-400 CM-1)

The absorption spectra of 11 solid‐state EDA‐complexes of unsaturated hydrocarbon donors with TCNE as acceptor have been studied in the FIR. region (40–400 cm−1). The dominant feature in the spectra is the appearance of a new intense absorption in the region 80–100 cm−1 which is assigned to the intra charge‐transfer lattice mode. The (idealized) force constant for this lattice mode is found to be roughly constant for most of the EDA‐complexes and is thus believed to be a measure of the total interaction of donor and acceptor within the crystal site. Force constants differing in magnitude from those of the majority of complexes are traced back to a particular structure of the donor component and/or the EDA‐crystal as a whole. A recently proposed reassignment of the Raman active fundamentals of pure TCNE is questioned in view of the present findings. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim