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Density functional theory calculation is used to investigate the oxidation of cyclo-olefin (cyclobutene, cyclopentene, cyclohexene, cycloheptene, and cyclo-octene) by the complex [FeIV(O)(TQA)(NCMe)]2+, which has S = 2 ground state, and the effect of electronic factors and steric hindrance on reaction barriers. Our results suggest that the oxo–iron(IV) complex can oxidise C–H and C = C bonds via a single-state mechanism, and two different ways of electron transport exist. The energy barriers initially decrease with increasing substrate size, and the trend then reverses. Comparison of the energy barrier in different systems reveals that except for the reaction between [FeIV(O)(TQA)(NCMe)]2+ and cycloheptene, oxo–iron(IV) complexes prefer epoxidation to hydroxylation. However, the hydroxylated product is more stable than the corresponding epoxidated product. This result indicates that the products of epoxidation tend to decompose first. The energy barrier of hydroxylation and epoxidation originates from the balance of orbital interaction and Pauli repulsion from the equatorial ligand and protons on the approaching substrate. In this regard, we calculate the weak interaction between two fragments (oxo–iron complex and substrates) using the independent gradient model and drawn the corresponding 3D isosurface representations of reactants. [ABSTRACT FROM AUTHOR]

• The multi-metallic LDHs provide exciting electronic property than traditional binary LDHs. • The transformation from binary LDH to LMMH (layered multi-metallic hydroxides) is accompanied by changes in electronic or morphological structure. • The prepared LDHs exhibit enhanced photo/electrocatalytic performance. The development of efficient photo/electrocatalysis using sustainable renewable resources to prepare high value-added products is now a major goal to achieve new environmentally friendly technologies. However, existing solutions still offer unsatisfied catalytic efficiency and low energy utilization. Therefore, it is paramount to develop new strategies to control the morphology and structure of functional materials to improve their photo/electrocatalytic activity. Layered double hydroxides (LDHs), as a kind of two-dimensional (2D) materials, have been largely explored in photo/electrocatalytic reactions due to their extensive tenability of elemental composition and interlayered anions. Furthermore, the intrinsic feature of atomic dispersion has been utilized to introduce more active sites to further improve the reaction performance. Herein, we review strategies that have been developed for introducing more active sites into or onto the LDH layer for the construction of multi-metallic LDHs based photo/electrocatalytic material. The accompanied structure and electronic changes that are pivotal for modulation for catalytic activity are proposed, such as, improving carrier transportation, and optimizing molecular activation energy. We review the catalytic performance of multi-metallic LDHs for photo/electrocatalytic water splitting, CO 2 photoreduction, CO hydrogenation, heavy metal mineralization/reutilization and beyond. We highlight future challenges and opportunities to design multi-metallic LDHs to address future photo/electrocatalysis research challenges. [ABSTRACT FROM AUTHOR]