Dielectric and electric conductivity studies of some pyrimidine compounds and their complexes

The values of the dielectric constant (ε), the loss tangent (tan ) and the electrical conductivity (σ) for solutions of ligands barbituric acid(BA),5-nitrobarbituric acid(NBA) in 50%(v/v) MeOH-water also the ligands phenobarbital(PB) and thiouracil(TU) in 50%(v/v) dioxane –water, all at 25°C, in most cases, are decreased by decreasing the concentration. The ln ε-T relationship for solutions of ligands and their complexes pointed to an increase of dielectric constant values with temperature. The presence of hydrogen bonding referred to cooperative reinforcement of dipole fields. NBA has a higher dielectric constant value than BA due to the presence of the electron withdrawing nitro group with large orientational polarization. PB has a lower dielectric constant value than TU since ε decreases as the steric hindrance effect increases. For the complexes, the dielectric constant (ε) values, are higher than that for the ligands. As the atomic number of the metal increases, the dielectric constant (ε) and the loss tangent (tan δ) are mostly decreased to block the charge distribution. The derived values of electrical conductivity that derived from ὲ and tan δ data are regularly decreased and the activation energy (∆E) of the complexes decreased in an irregular trend. The loss tangent (tan δ) increases by increasing the temperature due to a decrease in viscosity, which exerts an increase of the dipole rotation and the polarization of the material. The molar conductance Λm for the electrolytic solutions of BA, NBA, PB and TU at 25°C are increased by decreasing the concentration. The BA, PB and TU ligands are of weak electrolytic nature, while NBA is of strong electrolytic behavior. However, the Λm values for solutions of ligands and their complexes are increased by increasing both temperature and dielectric constant due to the increase of the ionic mobility. Correspondence to: MS Masoud, Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt, E-mail: drmsmasoud@yahoo.com