Electrical properties of Cu(II)-N,N′-dimethyldithiooxamide polymers

Cu(II)-dithiooxamide polymers were prepared by a direct deprotonation of the ligand with a Cu(II) salt. The polymers had a chain length of about 13 units. The undoped polymers showed low electrical conductivity with an Arrhenius-type temperature dependence. Doping of Cu(II)-N,N′-dimethyldithiooxamide was performed by iodine in the vapour phase and by FeCl3 in solution. In both cases, the oxidative doping resulted in highly increased conductivities. A thermopower measurement indicated p-type conduction. The infrared spectra of the undoped material and the one doped with FeCl3 were completely identical, indicating that charge transfer from the ligand to the dopant is small. The conductivity curves of the doped polymer did not show an Arrhenius-type behaviour. In order to find an explanation for the conduction mechanism different models were tested. The best fit of the experimental conductivity data of the FeCl3-doped polymers was obtained with the theoretical prediction of a variable-range hopping model.