Host–Guest Inclusion Self-Assembly of Zero-Dimensional Metal Halides for Enhanced Photocatalytic Amine Coupling

Abstract

The practical application of zero-dimensional (0D) organic–inorganic hybrid metal halides in photocatalysis is hindered by their poor stability, rapid charge-carrier recombination, and low surface reactivity. Herein, we report a host–guest self-assembly strategy for constructing two 0D anionic metal halides with enhanced photocatalytic activity, [(L1)2⊂(ZnCl4)2–3] (C1) and [(L1)2⊂(MnCl4)2–3] (C2), by one-pot reaction of an anthracene-pyridine-based cationic cavity ligand (L13+·3Br–) with ZnCl2 and MnCl2·4H2O, respectively. Single-crystal X-ray diffraction reveals that both compounds feature discrete tetrahedral [MX4]2– cores yet exhibit distinct lattice packing modes; notably, in C1, the anionic cluster is anchored via C–H···Cl hydrogen bonds rather than direct encapsulation. The host–guest inclusion systems of discrete metal halides exhibit optical band gaps of 2.19–2.27 eV, with observable charge separation. Under 455 nm blue-light irradiation, C2 demonstrates exceptional photocatalytic performance in benzylamine coupling (TOF of 492.66 h–1), achieving 71–99% conversion across 10 substrates and about 90% activity retention after five cycles, while C1 shows lower activity (TOF of 463.58 h–1). EPR spectroscopy and quenching experiments uncover a radical-based synergistic mechanism. These results show that host–guest self-assembly affords stable 0D metal halide photocatalysts and that metal-center exchange significantly affects catalytic activity.