Atomic-Resolution Crystal Structure of a Redox-Active Covalent Organic Framework with Ni-bis(dithiolene) Units

Two-dimensional redox-active covalent organic frameworks (COFs) hold promise for diverse applications in catalysis, energy storage, sensing, and optoelectronics. However, precisely determining their structures poses a significant challenge, because of their small particle sizes and low crystal quality, which limit the fundamental understanding of their intrinsic properties. In this study, we present the crystal structure analysis of a 2D COF based on Ni-bis(dithiolene) units and imine bonds, namely, Ni-PDA-COF. Crystals of Ni-PDA-COF were successfully synthesized with an average size of 10 mu m, enabling atomic-resolution structural characterization by continuous rotation electron diffraction (cRED). The determined crystal structure of Ni-PDA-COF contains a 2D square lattice network and exhibits close interlayer S<middle dot><middle dot><middle dot>Ni/S<middle dot><middle dot><middle dot>S interactions, resulting in a large surface area of 618 m(2) g(-1), high chemical stability within a pH range of 1-14, and fairly good electrical conductivity up to 1.37 x 10(-3) S m(-1). The precise crystal structure of Ni-PDA-COF not only facilitates the mechanistic understanding of their optical and electrical properties by density functional theory (DFT) computations but also enhances our broader understanding of similar COF systems.