Semiconducting Polymers Containing Coordinated Metal Ions

Abstract

Ligands of the bis-(8-hydroxyquinoline) type were selected for the preparation of semiconducting coordination polymers. After some preliminary investigations in solvents, melt techniques with reaction temperatures of at least 250°C were found to be necessary for the formation of a conducting product from chloranil, o-phenylene- diamine, and a metal salt, which is postulated to involve polycoordination of a quinoxalo- phenazine derivative. Of 13 different metals studied, the FeCl₂ polymer was found to be the best conductor, having a resistivity of 38 kΩ cm with a preparation temperature of 350°C, the resistivity remaining at this level for preparation temperatures up to 450°C.

Studies of the reactions of the FeCl₂ and FeCl₃ polymers suggest intermolecular linking other than through the metal, a t least two types of organic cross-linking being evident. The presence of phenazinium salt structures in both polymers is postulated to account for the large amounts of chloride ion liberated by alkali.

The conducting properties are attributed to interaction between donor nitrogens and acceptor groups such as the metal ion, quinones, and quaternary nitrogens linked within a fully conjugated polycyclic system. The existence of the metal in more than one oxidation state, which might occur with the FeCl₂ polymer, may be of further benefit.