Two New Members of the Covalent Organic Frameworks Family: Crystalline 2D-Oxocarbon and 3D-Borocarbon Structures

Abstract

While graphene oxide (GO) is representative of a disordered phase of oxocarbons with lackluster electronic properties, the coexistence of ordered, stoichiometric solid-state carbon oxides with graphene brings renewed momentum to the exploration of two-dimensional crystalline oxocarbons. This enduring subject, spanning decades, has recently witnessed significant advancements. In this context, our study delves into a novel material class, COF-66, notable for its meticulously ordered two-dimensional crystalline structure and intrinsic porosity. Employing a global optimization algorithm alongside density-functional calculations, our investigation highlights a standout member within the COF-66 family exceptional quasi-flat oxocarbon (C6O6)exhibiting an unconventional oxygen-decorated pore configuration. This pioneering study introduces C6O6 as an innovative entrant into the crystalline carbon oxide arena, augmenting the established understanding alongside the well-recognized graphene oxide and two graphene monoxide, i.e. α-GMO and \b{eta}-GMO. Expanding the exploration, the COF-66 series encompasses 2D-porous carbon nitride (C6N6) and the recently synthesized 2D-porous boroxine (B6O6), adhering to a generalized stoichiometry of X6Y6, where X = B, C, and Y = B, N, O, with X 6= Y. Remarkably, the entire COF-66 ensemble adopts a 2D-crystalline framework, with the exception of C6B6, which assumes a distinct 3D-crystalline arrangement. Employing the PBE (HSE06) level of theory, our electronic structure calculations yield band gap values of 0.01 (0.05) eV, 3.68 (5.29) eV, 0.00 (0.23) eV, and 1.53 (3.09) eV for B6N6, B6O6, C6B6, and C6N6, respectively, reinforcing and aligning with prior investigations.