Insights into the Synthesis of a Semiconducting Nickel Bis(dithiolene) Coordination Polymer

Nickel bis(dithiolene) complexes are promising candidates for novel n-type semiconductors, which are air-stable and highly conductive. A key issue for further development is that their synthesis often yields undesired products, greatly limiting the degree of polymerization as well as purity and adversely affecting their electronic properties. Crucially, there is 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 investigation also reveals that the ligand can form dimeric and trimeric species via disulfide bonds as byproducts. These insights are pivotal knowledge to develop metal bis(dithiolene)-based coordination polymers to achieve purity and quality required for electronic applications.