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 Zr 6 O 4 (OH) 4 (C 8 H 4 O 4 S 4 ) 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 °C. The thiol-enabled ZrTST (powder) takes up mercury from water with a high distribution coefficient K d (e.g., 1.2 × 10 6 mL·g -1 ); it also shows proton conductivity (1.9 × 10 -3 S·cm -1 at 90 °C and 90% relative humidity), which, most notably, increases to a highest value of 3.7 × 10 -1 S·cm -1 after oxidizing the -SH into the -SO 3 H groups.