Description: TCNQ Charge Transfer Complexes with Coals. TCNQ can be readily deposited in coals from pyridine solution. IR spectra of TCNQ and TCNQ in Illinois No. 6 coal are shown in Fig. 1. It is clear that the stretching frequency has been shifted by the full 44 cm[sup [minus]1] caused by the transfer of a single electron. Similar behavior has been observed with a variety of coals, including lignites, subbituminous and a range of bituminous coals. There are two possible explanations for the observed shift. The simplest explanation is that there exist in coals structures which are excellent single electron donors capable of transferring an electron to TCNQ in the ground state. All of the TCNQ dissolved in the coal is shifted. No uncomplexed TCNQ remains in the sample, as demonstrated by the absence of the unaltered CN stretch at 2227 cm[sup [minus]1]. The spectrum shown is for TCNQ in coal in a molar concentration equivalent to approximately 20% of the PNA systems in this coal as deduced from the NMR studies of Solum et al. (1989). It is highly unlikely that 20% of the PNA systems in coal are such good electron donors that the charge transfer complex would have an electron transferred in the ground state. The second explanation is that cooperative interactions between the TCNQ and the aromatic systems in coal have led to the formation of an extended valance band structure, that the TCNQ LUMO is part of this band structure, and that the band is half filled.
Date: July 24, 1990
Creator: Larsen, John W. & Flowers, Robert A., II.
Partner: UNT Libraries Government Documents Department