Crystal Packing-Driven Selective Hg(II) Ion Sensing Using Thiazolothiazole-Based Water-Stable Zinc Metal-Organic Framework.

A soft acid-soft base interaction is highly predictable. However, we demonstrate how the crystal packing of the newly synthesized zinc framework [Zn 2 (5-AIA) 2 (DPTTZ)]·DMF (where 5-AIA = 5-aminoisophthalic acid, DPTTZ = N,N' -di(4-pyridyl)thiazolo-[5,4- d ]thiazole, DMF = N,N' -dimethylformamide) directs an unexpected interaction between the soft acid Hg(II) and the hard base oxygen instead of having a soft center like nitrogen and sulfur in the system attributed to a strong solvent interaction and a favorable ionic radius of Hg(II) ion for oxygen chelation. This engenders selective Hg(II) ion sensing through a "turn-off" emission quenching in water (limit of detection = (2.174 ± 0.06) × 10 -9 M) along with natural water resources and in a broad pH range. A quantum-chemical calculation elucidates the turn-off quenching mechanism and favorable Hg(II) interaction with encompassed oxygen atoms inside the framework.