The ESR Study of the Ion Pair Complexes of m-Iodonitrobenzene with Alkali and Alkaline Earth Metals

The ESR spectra of the ion-pair complexes of the m-iodonitrobenzene anion with alkali and alkaline earth cations were measured. Cation-induced variations in the nitrogen and proton splitting constants were found. When the observed alkali metal splittings were related to the back-transferred charge, ρ, on the ns-shell of each metal, ρ increased in the sequence: Li<Na<K<Rb<Cs at 20°C. The solvent and the temperature effects on alkali-metal splitting varied with the alkali metal. The Cs and Rb splitting constants increased in the sequence: DME<THF<THP solutions, and were independent of the temperature. The Na and Li splitting constants decreased in the above sequence of solvents. With a lowering of the temperature, the Na splitting constant decreased while the Li splitting constant increased. The K splitting constant was independent of both the temperature and the solvent. These results were found in the ion pairs of other halogeno-nitrobenzenes, also.