Electrical conductivity and phase transition studies of some selected Congo Red-metal complexes

The electrical properties of Congo Red dye (L) and its metal (M) complexes of M:L molar ratios of 1:1 and 2:1, where M=Cr(III), Fe(III), Cu(II), Zn(II), Zr(IV), Th(IV) and UO2(II), indicated semiconducting behaviour. The activation energies and electrical conductivities depend on the ionic charge of the metal chelates. The activation energies of 1:1 metal complexes are greater than those of 2:1 metal complexes. The conductivity data obtained are interpreted on the basis of the molecular structure of the Congo Red complexes. One phase transition was obtained during DTA study of Congo Red dye at 212 degrees C. This phase transition may be due to the rotation of the two naphthalene rings and the N=N groups around the diphenyl group centre.