Two-Dimensional Mercury(II)–Acetylide Framework with Built-in Dipole Field for Efficient Photocatalytic CO₂-to-CO Conversion

Abstract

The development of efficient photocatalysts for CO2 reduction remains a critical challenge in artificial photosynthesis. While two-dimensional (2D) coordination frameworks provide structural versatility, the catalytic potential of main-group metal-containing frameworks is still largely underexplored. Herein, we report a semicrystalline 2D HgII-acetylide framework featuring linear –C≡C–Hg–C≡C– motifs, which exhibits exceptional photocatalytic activity and selectivity for CO2-to-CO conversion. Density functional theory (DFT) analysis reveals anisotropic orbital hybridization within these motifs, wherein Hg 5dπ orbitals engage in backbonding with alkynyl π* systems, creating an electron-deficient catalytic interface precisely tailored for CO2 activation. Importantly, the asymmetric electron distribution across each −C≡C−Hg− unit generates a strong local dipole moment that aligns coherently throughout the framework, establishing a macroscopic built-in electric field. This field functions as an internal charge pump under vibration, dramatically enhancing photogenerated carrier separation and directing electrons toward the metal-acetylide active sites. The synergy between orbital hybridization and dipole-driven charge transfer enables efficient CO2 adsorption/activation and rapid *CO desorption, achieving a CO evolution rate of 338.57 μmol g–1 h–1 with 65% selectivity, along with 30.15 μmol g–1 h–1 of CH4 in the presence of triethanolamine (TEOA) and sacrificial agents in photocatalytic performance under ultrasonic vibration, highlighting the kinetic advantages conferred by the field-driven mechanism. This work demonstrates dipole engineering in main-group metal-acetylide frameworks as a generalizable strategy for designing high-performance photocatalytic materials.