“Mechanochemical synthesis and spectroscopic analysis of Cu2+ loading in ZIF-62”

Metal organic frameworks (MOFs) provide customisable structures for gas separation, catalysis, and glass production. Among them, zeolitic imidazolate frameworks (ZIFs) stand out for their thermal stability and ability to yield melt-quenched glasses. ZIF-62, a well-studied glass-forming MOF, exhibits limited compositional flexibility, particularly when attempts are made to introduce transition metals. This study explores copper incorporation into ZIF-62 via mechanochemical and solvothermal synthesis. X-ray diffraction indicated ZIF-62 framework formation when acetate was used as a copper source by mechanochemical synthesis; however, complementary spectroscopic techniques (XAS, solid-state NMR, FTIR, Raman, DR UV-VIS, ICP-OES) showed that copper was not integrated into the framework. Instead, Cu species preferentially adopted coordination environments incompatible with the Zn-imidazolate framework structure and were more likely associated with surface or pore environments. Thermal analysis revealed reduced melting and glass transition temperatures in Cu-containing samples, demonstrating that even non-framework Cu species can influence the thermal behaviour of ZIF-62. Additional solvothermal synthesis attempts involving several Cu-containing precursors yielded crystalline or amorphous phases distinct from ZIF-62, further highlighting the strong influence of Cu coordination chemistry on framework formation. These findings demonstrate that Cu incorporation into ZIF-62 is strongly limited under the mechanochemical and solvothermal conditions explored in this work, emphasizing the importance of precursor selection and metal–ligand coordination preferences in the design of mixed-metal MOFs.