Interligand Charge-Transfer Interactions in Electroactive Coordination Frameworks Based on N,N′‑Dicyanoquinonediimine (DCNQI)

Coordination frameworks containing DCNQI^2– (DCNQI = N,N′-dicyanoquinonediimine ligand) are produced by deprotonation of DCNQIH₂ in the presence of a metal center and a co-ligand. This approach has yielded two-dimensional (2D) sheet compounds [Cd­(DCNQI)­(L)₂] (where L = pyridine (py) or isoquinoline (isoquin)) that can be partially oxidized via solid-state electrochemical and in situ spectroelectrochemical methods to materials that contain DCNQI as its radical monoanion. The new frameworks display charge-transfer bands that are indicative of interligand charge-transfer interactions as supported by TD-DFT computational calculations. The redox-state dependent spectral properties of the frameworks have been probed using a newly developed solid-state spectroelectrochemical cell. Coupled with computational calculations, the experimental data provide an understanding of the fundamental charge-transfer processes that may underpin long-range functional properties such as conductivity in framework materials.