Dense Dithiolene Units on Metal-Organic Frameworks for Mercury Removal and Superprotonic Conduction

With 2-COOH and 4-SH donors all packed onto the benzene ring, tetrasulfanyl terephthalic acid (TST) is a simple yet fully equipped ligand to move the field of metal-coordination materials-it is now accomplished. The hard-soft carboxyl-thiol synergy is leveraged here in selectively bonding the carboxyl units to Zr(IV) ions to form the same cubic net of UiO-66 (this being based on the terephthalic linker)-with the free-standing dithiolene units equipping the grid of ZrTST. The 3D network of ZrTST averages about 7.6 connections [as in Zr6O4(OH)(4)(C8H4O4S4)(3.8)], with the other 4.4 sealed by acetate ions. The ZrTST solid is stable in boiling water (it is formed in water/acetic acid/ethane dithiol) and remains ordered even above 300 degrees C. The thiol-enabled ZrTST (powder) takes up mercury from water with a high distribution coefficient K-d (e.g., 1.2 X 10(6) mL.g(-1)); it also shows proton conductivity (1.9 X 10(-3) S.cm(-1 )at 90 degrees C and 90% relative humidity), which, most notably, increases to a highest value of 3.7 X 10(-1) S.cm(-1) after oxidizing the -SH into the -SO3H groups.