Synthesis and structural comparisons of five new fluorinated metal organic frameworks (F-MOFs)

Abstract

A series of fluorinated metal–organic frameworks (F-MOFs) have been successfully synthesized under hydrothermal condition using 4,4′-(hexafluoroisopropylidene) bis(benzoic acid) (C₁₇H₁₀F₆O₄, H₂hfbba) as a flexible dicarboxylate building block, Cu⁺² and various heterocyclic co-ligands. These F-MOFs formulated as [Cu(hfbba)(phen)₂]·2(H₂hfbba)(H₂O)(HCO₂) (F-MOF-1), [Cu(hfbba)₂(2,2′-bipy)₂(H₂O)] (F-MOF-2), [Cu(hfbba)(4,4′dime-2,2′-bipy)(HCO₂)]·(hfbba)(H₂O) (F-MOF-3), [Cu₂(hfbba)₂(3-mepy)₂]·(DMF)₂(3-mepy) (F-MOF-4), and [Cu(hfbba)₂(phen)₂]·0.5(DMF) (F-MOF-5) (hfbba = 4,4′-(Hexafluoroisopropylidene) bis(benzoate), phen = 1,10-phenanthroline; 2,2′-bipy = 2,2′-bipyridine; 4,4′dime-2,2′-bipy = 4,4′dimethyl 2,2′-bipyridine; 3-mepy = 3-methyl-pyridine and DMF = dimethyl formamide) display interesting H-bonded, 1D and 2D structural features. All these F-MOFs were structurally determined by single-crystal X-ray diffraction. F-MOF-1 and 5 form a distorted octahedral Cu⁺² secondary building unit (SBU). F-MOF-5 forms a one-dimensional architecture constructed from Cu²⁺ ions bridged by phen anions and two types of 4 hfbba ligands while in F-MOF-1, two among the three acid co-ligands are not coordinated with Cu²⁺ ions. F-MOF-2 displays dinuclear SBUs within the three-dimensional frameworks whereas F-MOF-3 displays mononuclear SBUs and forms a one-dimensional chain. F-MOF-4 display a interesting 2D framework with conventional Cu₂(CO₂)₄ paddle wheel SBU. In the crystal structures four hfbba ligands, each coordinated to a dicopper paddlewheel unit via one of their carboxylate groups. Solid-state properties such as UV-vis and thermal stability of F-MOF-1–5 have also been studied.