Regulated Second-sphere Coordination in Amorphous Metal-organic Framework for Efficient CO₂ Fixation

The endeavor toward photocatalytic CO₂ fixation is largely hampered by the rigid spatial configurations and inadequate orbital overlap between the catalytic site and CO₂. Herein, we propose a second-sphere coordination regulation strategy by atomically tailoring the metal-metal coordination of the secondary building unit (SBU). Amorphous metal-organic framework (a-MOF) is constructed as proof-of-concept to achieve creative control over the second coordination sphere. Such architecture transforms rigid trinuclear nodes into flexible dinuclear motifs. This shift can open spatial proximity to access the guest molecules and optimize s-π* overlap by enabling orbital reorientation. Both in situ experiments and theoretical calculations verify second-sphere engineering endows the Lewis base sites with high electron donating capacity and promotes the electron injection into the π^* anti-bonding orbitals of the CO₂ molecule effectively. Hence, the a-MOF displays approximately double the yield in various photocatalytic CO₂ reactions compared with its crystalline counterpart. Moreover, its photo-assisted Li-CO₂ battery delivers higher discharging voltage and a fourfold increment of discharge capacity at 200 µA cm^-2. The unique ability to tailor the secondary coordination sphere performs attractive merits governing the small molecule binding affinity, aiming to manipulate the local microenvironment of open metal sites for efficient CO₂ fixation.