Postsynthetic Paddle-Wheel Cross-Linking and Functionalization of 1,3-Phenylenebis(azanetriyl)tetrabenzoate-Based MOFs

A new metal–organic framework, Cu 2 ( m pbatb)(H 2 O) 2 (DUT-71; DUT, Dresden University of Technology) ( m pbatb, 4,4′,4″,4‴-(1,3- p henylene b is( a zanetriyl) t etra b enzoate)), 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 m 2 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.