2-formylpyridinethiosemicarbazone and methyl derivatives:: spectroscopic studies

The Z-E isomerization of 2-formylpyridinethiosemicarbazone (PATS2), 2-formylpyridine-2'-methyl thiosemicarbazone (2'MePATS2), 2-formylpyridine-4'-methyl thiosemicarbazone (4'MePATS2) and 2-formylpyridine-4',4'-dimethyl thiosemicarbazone (4',4'DMePATS2) was studied in various solvents by Raman and H-1 NMR spectroscopies. The interactions of alkali and alkaline earth perchlorates with these compounds were investigated in acetonitrile (ACN) solution. The results showed that the most favorable configuration in the solid state is E for PATS2, changing to Z configuration when methyl groups substitute the two hydrogen atoms of the N(4') atom in 4',4'DMePATS2. In solution, the E-Z equilibrium ratio depends on the compound and it is strongly affected by the solvent employed (H2O, DMSO, ACN and CH2Cl2). These results are rationalized considering the possibility of intra and intermolecular hydrogen bonding and the donor number of the solvents. The interaction of alkali and alkaline earth perchlorates with these compounds in ACN solutions results in the formation of complexes with E-4',4'DMePATS2 while for PATS2 these cations increase the rate of E-Z isomerization. (C) 2001 Elsevier Science Ltd. All rights reserved.