Highlighting the structure – directing capability of the functional groups of angular dicarboxylic ligands: New 2-dimensional Cu2+ MOFs from analogous synthetic routes

Abstract

The reaction of Cu(NO3)2·2.5H2O with the angular dicarboxylic ligands 4,4′-oxybis(benzoic acid) (H2OBA), or 4,4′-(hexafluoroisopropylidene)bis(benzoic acid)) (H2HFPBBA), or 4,4′-sulfonyldibenzoic acid (H2SDBA) in a ~1/2 molar ratio in the presence of 50 μL concentrated (69%) HNO3 in N,N-dimethylacetamide (DMA)/H2O (6 ml/2 ml) at elevated temperature (100 °C) in a closed vial afforded three new microporous 2D Cu2+ MOFs formulated as [Cu2(OBA)2(DMA)2]n·2nDMA·5nH2O (1)n·2nDMA·5nH2O, [Cu2(HFPBBA)2(DMA)1.42(H2O)0.58]n·5.5nDMA·11.5nH2O (2)n·5.5nDMA·11.5nH2O, and [Cu(HSDBA)(μ-OH)]n·nH2O·0.7nDMA (3)n·nH2O·0.7nDMA. Interestingly, although the three compounds were prepared from the same procedure and are based on similar angular dicarboxylic ligands, they display substantially different structural features. Thus, (1)n and (2)n contain a Cu2+ – paddle – wheel SBU but (1)n exhibits an interpenetrated network and (2)n a non – interpenetrated one, whereas compound (3)n is based on a 1D Cu2+ chain. This structural versatility could be attributed to the structure – directing capability of the functional groups connecting the two benzoic acid moieties of the three angular dicarboxylic ligands since all other reaction parameters involved in the synthesis of the three compounds were kept identical in the procedures afforded the three 2D MOFs. Compounds (1)n – (3)n also display significant thermal stability, up to 350 °C for (2)n and (3)n as shown from thermogravimetric analysis and variable temperature powder X – ray diffraction studies. Ar sorption studies for compounds (1)n and (2)n revealed that they exhibit moderate internal BET surface areas of 107 m2/g and 238 m2/g (Langmuir 121 and 260 m2/g), respectively.