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.

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