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The magnetism of solvatomorphic copper(II)- intermediates in the synthesis of mixed-metal MOF- 74 materials

Mixed-metal MOF-74 materials (MM-MOF-74)1 based on the 2, 5-dihydroxyterephthalic acid (H4dhta) with controlled stoichiometry and distribution of metal nodes are much-sought materials due to their advanced properties for catalysis and magnetism2. Still, that level of control is hard to achieve in a solution. Recently, mechanochemistry provided a unique templated pathway toward bimetallic MOF-74 materials with 1:1 stoichiometry and ordered distribution of the metal nodes.1 This approach relies on solid 1:1 metal:H2dhta coordination compounds that react with the other metal by milling, resulting in the porous mixed-metal MOF- 74 framework. In the synthesis of CuM-MOF-74 from copper(II)-intermediate, we observed that the Cu- int changes color from blue to green when subjected to low pressure. Time-resolved low- temperature PXRD monitoring revealed the rapid transformation of the Cu-int to the new phase that slowly transforms into CU-int by standing on the bench. The two phases display interesting and different magnetic properties and electron-spin resonance (ESR) spectra stemming from the altered connectivity among the copper centers that rise upon the phase transformation.

Mechanochemistry, MOF-74, Magnetism, MOF intermediates

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