Synthesis and spectroscopic studies of charge transfer complexes between chloranilic acid and some heterocyclic amines in ethanol

Charge transfer (CT) complexes formed between 2-amino-4-methoxy-6-methyl-pyrimidine (AMMP), 2-amino-4,6-dimethyl-pyrimidine (ADMP), 3-amino-pyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-methyl-1,3,4-thiadiazole (AMTD) and 3-amino-5,6-dimethyl-1,2,4-triazine (ADMT) as electron donors with the π-acceptor chloranilic acid (CHA) were investigated spectrophotometrically in ethanol. Minimum–maximum absorbances method has been used for estimating the formation constants of the charge transfer reactions (KCT). It has been found that KCT depends on the pKa of the studied donors. Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient (ε), oscillator strength (f), dipole moment (μ), charge transfer energy (ECT), ionization potential (IP) and the dissociation energy (W) of the formed complexes were estimated, they reached acceptable values suggesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and characterized by elemental analyses, 1HNMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.