Theoretical prediction of topological states in two-dimensional halogen-bonded organic frameworks (XOFs)

Abstract

The rapid development of two-dimensional (2D) crystalline porous frameworks, such as covalent organic frameworks (COFs), metal–organic frameworks (MOFs), and hydrogen-bonded organic frameworks (HOFs), have opened avenues for exploring exotic topological quantum states. However, experimental validation of these theoretical predictions remains rare. Here, we investigate the topological and magnetic properties of newly synthesized halogen-bonded organic frameworks (XOFs) (X. G. Bai, et al., Angew. Chem., Int. Ed., 2024, 63, e202408428), X-TPyB and X-TPEB (X = I, Br), through systematic first-principles calculations. Our results reveal that these frameworks exhibit half-metallic Kagome band structures near the Fermi level, with nontrivial edge states within spin–orbit coupling (SOC)-induced gaps confirming their topological nature. Notably, Br-substituted frameworks (Br-TPEB) demonstrate enhanced ferromagnetic exchange interactions and higher Curie temperatures (∼100 K) compared to I-based analogs, as validated by Monte Carlo simulations. This work opens up a new pathway for investigating topological states in XOFs and introduces a novel class of candidate materials for developing topological quantum devices.