Direct synthesis and mechanism of the formation of mixed metal Fe2Ni-MIL-88B

Abstract

The direct synthesis of Fe₃-MIL-88B and Fe₂Ni-MIL-88B was analyzed using different characterization techniques including UV-vis, IR, and Raman spectroscopies and XRD. It was found that single metal Fe₃-MOF-235 seeds which were formed from the first stage of synthesis are precursors for the formation of MIL-88B. Fe₃-MOF-235 seeds formed in the first stage of synthesis were then transformed to Fe₃-MIL-88B in the case of single metal, and to mixed Fe₂Ni-MIL88B in the case of mixed metal synthesis. In the both cases of Fe₃-MIL-88B and Fe₂Ni-MIL-88B, the FeCl₄⁻ anion is a key feature for the formation of MOF-235. An anion-mediated mechanism for the formation of the MOF-235 structure is also suggested.