Insights into the synthesis of a semiconducting nickel bis(dithiolene) coordination polymer

Nickel bis(dithiolene) complexes are promising candidates for developing coordination polymer n-type semiconductors with a 1D ladder-type structure which are air-stable and highly conductive. A key issue related to these materials is that their synthesis often yields undesired products that greatly limit the degree of polymerization and purity, which then have detrimental effects on their electronic properties. Furthermore, there is still a lack of in-depth identification of these species and understanding of the reaction mechanism. This study explores the mechanism of a reaction forming the coordination polymer nickel-thieno[3,2-b]thiophenetetrathiolate (Ni-TT). We find that the Unoxidized Ni-TT intermediate contains negatively charged polymer chains with Ni2+ counter cations. Oxidation in the final synthetic step occurs primarily at the ligand, resulting in a more neutral Ni-TT. Our study also reveals that the ligand can form dimeric and trimeric species via disulfide bonds as byproducts. These insights provide pivotal knowledge to improve and optimize the synthesis of nickel bis(dithiolene)-based coordination polymers to achieve purity and quality required for electronic applications.