Site-specific metal and ligand substitutions in a microporous Mn²⁺-based metal–organic framework

Abstract

The precise tuning of the structural and chem. features of microporous metal-org. frameworks (MOFs) is a crucial endeavour for developing materials with properties that are suitable for specific applications. In recent times, techniques for prepg. frameworks consisting of mixed-metal or ligand compns. have emerged. However, controlled spatial organization of the components within these structures at the mol. scale is a difficult challenge, particularly when species possessing similar geometries or chem. properties are used. Here, we describe the synthesis of mixed-metal and ligand variants possessing the Mn3L3 (Mn-MOF-1; H2L = bis(4-(4'-carboxyphenyl)-3,5-dimethylpyrazolyl)methane) structure type. In the case of mixed-ligand synthesis using a mixt. of L and its trifluoromethyl-functionalised deriv. (H2L' = bis(4-(4'-carboxyphenyl)-3,5-di(trifluoromethyl)pyrazolyl)methane), a mixed-ligand product in which the L' species predominanantly occupies the pillar sites lining the pores is obtained. Meanwhile, post-synthetic metal exchange of the parent Mn3L3 compd. using Fe2+ or Fe3+ ions results in cation exchange at the carboxylate clusters and metalation at the pillar bispyrazolate sites. The results demonstrate the versatility of the Mn3L3 structure type toward both metal and ligand substitutions, and the potential utility of site-specific functionalisations in achieving even greater precision in the tuning of MOFs. [on SciFinder(R)]