Structural, Magnetic, and Gas Adsorption Study of a Series of Partially Fluorinated Metal−Organic Frameworks (HF-MOFs)

Four new partially fluorinated metal organic frameworks (HF-MOFs) have been synthesized under different solvothermal conditions (H2O or dimethylformamide (DMF)) from transition metal cations [Co2+ and Mn2+], 3-methyl pyridine (3-mepy) and 4,4′-(hexafluoroisopropylidene) bis(benzoic acid) (C17H10F6O4, H2hfbba), to determine the influence of reaction conditions on the formation of MOFs. This family of materials displays a striking degree of structural similarity depending on the solvent of synthesis. HF-MOFs synthesized from H2O [Co-HFMOF-W, Co(hfbba)(3-mepy)(H2O) and Mn-HFMOF-W, Mn(hfbba)(3-mepy)(H2O)] contain three-dimensional connectivity whereas HF-MOFs synthesized from DMF Co-HFMOF-D, [Co2(hfbba)2(3-mepy)2]·(DMF)3 and Mn-HFMOF-D, [Mn2(hfbba)2(3-mepy)]·(H2O) are two-dimensional in nature. Co-HFMOF-W and Mn-HFMOF-W are iso-structural polymeric materials. Thermal gravimetric analysis performed on as-synthesized HF-MOFs revealed that these compounds have high thermal stability (∼350 °C). The continuous decrease of the χT product with decreasing T for Co-HFMOF-D and Co-HFMOF-W respectively indicates the presence of antiferromagnetic exchange interaction between two Co2+ (S = 3/2) metal centers within a cluster.