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

Abstract

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 μm, enabling atomicresolution 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•••Ni/S•••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 × 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.

2D metal–organic frameworks bearing butterfly-shaped metal-bis(dithiolene) linkers from dithiol-functionalized benzenedicarboxylic acid

“…Following this direction, the incorporation of metal-bis(dithiolene) in frameworks was first actualized by a series of metal-bis(dithiolene) bridged 2D conductive networks. 6 Shifting from separate molecular metal-bis(dithiolene) to a continuous network transforms discrete orbitals to band structures, which determine the observed electrical conductivity. Beyond electrical conduction, Zou et al invented tetratopic Ni-bis(dithiolene) linkers to construct stable 2D or 3D frameworks and demonstrated their functions in different applications such as sensing, 7 CO 2 reduction, 8 batteries, 9 and photothermal conversion 10 with flying colours.…”