Schiff base ligands play a pivotal role in tuning the electronic and steric properties of metal complexes, thereby significantly influencing their catalytic activity in HER . For Ni (II) bidentate complexes, the Schiff base ligand typically coordinates through two donor atoms, such as nitrogen and oxygen, providing a constrained environment around the nickel center. This bidentate coordination helps stabilize intermediate states during the HER process, facilitating electron transfer and proton reduction. However, the limited denticity may lead to lower structural rigidity, which can slightly reduce catalytic efficiency compared to higher-denticity complexes. Nonetheless, the inherent electronic properties of nickel, combined with the ligand's modulation, often make these complexes effective HER catalysts under mild conditions.