Variable-Temperature EPR Studies of Illinois No. 6 Coal Treated with Donor and Acceptor Molecules

Variable-temperature EPR studies of Illinois No. 6 coal, its pyridine extract, and samples of each after treatment with known donor and acceptor molecules are reported. The purpose of the study was to explore the origin of the EPR signals near g = 2 and to elucidate the nature of noncovalently bonded interactions in coal. Curie Law behavior is exhibited for each sample, indicating that the EPR signals are dominated by doublet state species. No evidence for thermally accessible, low-lying triplet states, such as those found in some charge-transfer complexes, was found. Infrared spectroscopy suggests, however, that electron transfer from the coal does occur after treatment with electron acceptors such as TCNQ and TCNE. EPR studies of the Illinois No. 6 coal samples after treatment with the known electron donor TTF revealed the formation of the TTF radical cation.