Auxiliary Ligand-Coordinated Nanoconfined Hydrophobic Microenvironments in Nickel(II)-Acetylide Framework for...

Metal-acetylide frameworks (MAFs), featuring metal-bis(acetylide) linkages (─C≡C─M─C≡C─), are emerging as a new class of 2D nanomaterials with promise in catalysis. Here, we report a new 2D Ni^II-acetylide framework, TPA-Ni(PR₃)₂-GYs, that incorporates the Ni^II(PR₃)₂ moiety [R = CH₃ (Me), CH₂CH₃ (Et), and CH₂CH₂CH₂CH₃ (Bu)] into tris(4-ethynylphenyl)amine-based graphdiyne framework (TPA-GDY). As a result, TPA-Ni(PBu₃)₂-GY exhibits an exceptional photocatalytic CO₂ reduction activity of 3807 µmol g^-1 h^-1 and a high selectivity of 99.4% for CO production upon visible light irradiation. Mechanistic investigations reveal a strong orbital matching effect between the d orbitals of Ni^II and the p orbitals of the alkynyl C atoms in organic ligands, which not only accelerates the transfer and separation of photogenerated charge carriers but also reduces the reaction potential barrier for the formation of *COOH intermediates. Furthermore, the high hydrophobicity of the auxiliary coordinated ligands (trialkylphosphines) to Ni center, particularly tributylphosphine, creates a nanoconfined space that enhances both the accessibility of CO₂ and the utilization of Ni^II catalytic active sites while inhibiting hydrogen evolution. This study highlights the benefit of modulating the microenvironment around the coordinated metal center to enhance the performance of catalysts with direct metal-acetylide bonding.