Two Metal-Organic Frameworks with a Tetratopic Linker: Solvent-Dependent Polymorphism and Postsynthetic Bromination

Synthesis of two polymorphous porous metal organic frameworks (MOFs), both based on a linear tetracarboxylate linker containing ethinyl functionalities and copper ions, is presented. The resulting structure of the MOF is highly dependent on the solvent used during the synthesis: use of N,N-dimethylacetamide as a solvent results in a three-dimensional structure with fof topology (UHM-8)-a widespread net regarding MOFs composed of linear tetracarboxylates and copper ions while a solvent mixture of N,N-dimethylformamide, dioxane, and water (2:1:1) gives rise to a three-dimensional structure based on the more rare stx net (UHM-9). Possible reasons why which topology is favored in each case is discussed in terms of the thermodynamic stability and solvent stabilizing effects. Furthermore, the first postsynthetic modification (PSM) of a nonterminal triple bond inside a MOF structure was accomplished by addition of bromine under mild conditions to UHM-8. Quantitative conversion rates and retention of the crystallinity of the brominated MOF could be confirmed by Raman and NMR spectroscopy and powder X-ray diffraction, respectively.