Theoretical insights into CO2 reduction over ZIF-inspired metal-imidazole models: the role of active site nucleophilicity.

The electrochemical carbon dioxide reduction reaction (CO2RR) is a critical strategy for mitigating anthropogenic carbon emissions, yet the design of catalysts that unite high activity with optimal thermodynamic selectivity remains a formidable challenge. Herein, we present a systematic density functional theory (DFT) investigation of the CO2-to-CO conversion mechanism over a matrix of twelve ZIF-inspired finite metal-imidazole cluster models. By varying the central metal ion (Zn, Ni, Co) and the electronic character of the imidazole linkers bearing (-CH3, -NH2, -CHO, -NO2) group, we elucidate the profound role of ligand nucleophilicity in governing catalytic performance. Within the unconstrained cluster series, kinetic profiling unequivocally identifies the amino-functionalized zinc imidazole complex (Zn-aIm) as an efficient catalyst, exhibiting an exceptionally low initial CO2 activation barrier of E a = 0.21 eV, significantly outperforming its Ni and Co analogues. A boundary-constrained sensitivity analysis of the Zn series shows that Zn-aIm remains the most favorable model. Comprehensive topological (QTAIM, NCI) and electron population (NBO, EDD) analyses reveal that this ultra-low barrier is driven by massive charge transfer from the nucleophilic linker directly into the CO2 π* antibonding orbital, physically forcing the molecule into a highly bent geometry. Furthermore, we demonstrate that this critical transition state is uniquely stabilized by a cooperative mechanism: primary Lewis acid-base activation at the Zn center paired with robust secondary-sphere hydrogen bonding from the -NH2 group. However, calculated hydrogen-adsorption thermodynamics do not exclude competitive HER. Ultimately, these findings establish that tuning ligand nucleophilicity and exploiting secondary-sphere stabilization are highly effective, rational design principles for developing next-generation metal-organic electrocatalysts.