Construction of Chimeric Metal-Organic Frameworks with Symmetry-Mismatched Building Blocks

Chimeric metal-organic frameworks (CMOFs) composed of symmetry-mismatched inorganic and organic building blocks are rare because the interconnections between these blocks are topologically demanding. Herein, an MOF with symmetry-matched building blocks is used as a self-template for the template-assisted synthesis of CMOFs. Specifically, the post-synthetic transformation of the [Zn₄O(COO)₆] clusters in the self-templating MOF into the [Fe₃^IIIO(COO)₆]⁺ clusters with symmetry-mismatched trigonal prismatic site symmetry affords isoreticular CMOFs while maintaining the template morphology and crystallinity. The framework strain of CMOFs due to the symmetry-mismatched linkages between their building blocks is reduced by modulating the conformation of organic building blocks with torsional degrees of freedom. The further transformation of [Fe₃^IIIO(COO)₆]⁺-based CMOFs through redox-facilitated metal exchange using Cr²⁺ ions yields highly stable isostructural CMOFs containing [Cr₃^IIIO(COO)₆]⁺ clusters and exhibiting stabilities in strongly acidic and moderately basic media comparable to those of prototypical [Cr₃^IIIO(COO)₆]⁺-based MOFs with symmetry-matched building blocks. These results hold significant potential and highlight the vast opportunities for revisiting well-known yet fragile MOFs built upon the zinc acetate clusters.