ELECTRONIC SPECTRAL STUDIES OF SOME CHARGE-TRANSFER COMPLEXES OF A PURINE ANALOG OF BIOLOGICAL INTEREST WITH IODINE

The reaction between 3,7-disubstituted-2-5-diamino-pyrazolo [1,5-a] py rimidine-6-carbonitriles (DPC) with iodine is studied photometrically in various chlorinated solvents. The results obtained from spectroscop ic measurements revealed that in each solvent the (DPC): I2 ratio is 1 :2 and the charge transfer (CT) iodine complex is assigned the formula (DPC) I+I3-. Values of the formation constant (k), molar absorptivity (epsilon) and oscillator strength (f) for the I2- (CT) complex were o btained. It was shown that the values of these constants depend entire ly on the polarity of the solvent. Where it was indicated that there i s a linear correlation between either the oscillator strength or the m olar absorptivity and the dielectric constant of the solvent, suggesti ng a type of interaction between the ionic (CT) complex with the solve nt.