Postsynthetic paddle-wheel cross-linking and functionalization of 1,3-phenylenebis(azanetriyl)tetrabenzoate-based MoFs
A new metal-organic framework, Cu2(mpbatb)(H2O)2 (DUT-71; DUT, Dresden University of Technology) (mpbatb, 4,4',4,4-(1,3-phenylenebis(azanetriyl)tetrabenzoate)), was prepared by a solvothermal reaction in a mixture of DMF and EtOH. Postsynthetic modification of DUT-71 using different neutral nitrogen-containing bridging molecules in a single-crystal to single-crystal transformation fashion results in a series of porous compounds (DUT-72, DUT-73a, DUT-73b, DUT-74, DUT-90, DUT-91, and DUT-95) with apparent BET surface area up to 2700 m2 g-1. Interestingly, the Cu-Cu distances between paddle wheels during the transformation are adapted to the bridging ligands, demonstrating the flexible character of DUT-71. After solvent removal and resolvation, a drastic color change from green to dark blue and vice versa was observed. This observation was studied in detail in situ by monitoring the adsorption of ethanol in the low-concentration region by UV/vis analysis. The correlation between the ethanol adsorption uptake and the intensity of the characteristic absorption peaks in the UV/vis spectra renders the new materials promising candidates for vapochromic sensing.