Fe‐2,5‐furandicarboxylate Metal Organic Frameworks with Rare Building Blocks and a Ligand that can be Biomass‐Derived as Effective Catalysts for Selective Nitroarene Reduction

We report two three-dimensional metal-organic frameworks constructed from Fe³⁺ and the ligand, 2,5-furandicarboxylate (FDC) that can be derived from biomass. One contains an unprecedented infinite-rod-shaped building unit, and the other is the first crystalline framework of FDC that contains solely iron in the metal nodes. The materials are formed as microcrystals and their structures are determined using 3D-electron diffraction with the bulk confirmed by powder XRD. UOW-7, NaFe₅O₃(FDC)₄(CH₃COO)₂(H₂O) is a bimetallic structure with acetate as co-ligand, constructed from infinite chains of iron octahedra, wherein tetramers comprising edge-sharing pairs linked by corner sharing octahedra are crosslinked by FDC ligands. In contrast, UOW-8, [Fe₂O(FDC)₂(H₂O)₂]⋅(H₂O)₄ contains a rare form of tetrameric building unit, cross-linked by FDC, and having Fe-bound water as well as occluded water. The materials crystallise under hydrothermal conditions and are water-stable coordination polymers with no measurable free pore space. The catalytic ability of UOW-7 and UOW-8 is, nevertheless, established in the reduction of 4-nitrophenol to 4-aminophenol by borohydride, where both act as recyclable, catalysts to give ~100 % yield of the product without use of precious metals. UOW-8 is found to have the more favourable reaction kinetics, likely due to the presence of surface Lewis acidic Fe³⁺ centres that enhance substrate binding.