Theoretical investigation on the structure of mixed-metal zeolitic imidazolate framework and its interaction with CO2

Determining the effect of mixed-metal in metal-organic frameworks (MOFs) provides insight into how the distribution of various metal types affects their chemical bonding, electronic properties, particularly net atomic charge distribution and their interaction with guest molecules. In this report, the structural characteristic of the mixed-metal zeolitic imidazolate framework ZIF-8(Cd/Zn) has been thoroughly investigated, employing a periodic density functional theory approach to identify the effect of various locations of different metals. Increasing the fraction of Zn2+ in the mixed-metal ZIFs induces the reduction of lattice parameters and affects the bond distance between metal and linker. Moreover, identification of the chemical bonding present in the mixed-metal ZIFs provides an insight regarding the bond character of the metal to organic linker where Zn-N has a higher bond character than Cd-N, implying a different bond strength. Further confirmation was done by calculating the relative energy of the defective mixed-metal ZIF-8(Cd/Zn) by comparing when either Cd2+ or Zn2+ ions were removed from the structure. Furthermore, the interaction between CO2 and mixed-metal ZIF-8(Cd/Zn) in various positions yielded an overview where different CO2 location affects the binding energy. This study showed how the structure of mixed-metal ZIF-8(Cd/Zn) affects their electronic properties and its consequences on CO2 adsorption.