Two-Dimensional Coordination Polymers Comprising Mixed Tripodal Ligands for Selective Colorimetric Detection of Water and Iodine Capture

Two ternary coordination polymers (CPs) {[Co3(BTC)2­(TIB)2­(H2O)4]­·(H2O)4}n (1) and {[Cu3(BTC)2­(TIB)2­(H2O)2]­·(H2O)6}n (2) comprising tripodal linkers 1,3,5-benzenetricarboxylate (BTC) and 1,3,5-tris­(imidazol-1-ylmethyl)­benzene (TIB) are synthesized and characterized by single crystal X-ray diffraction and other physicochemical techniques. Adsorption experiments show that the materials can uptake molecular iodine in the vapor phase and can endure the adsorbed guest at ambient conditions. 27.92 and 28.62 wt % iodine uptake was observed for 1 and 2 respectively, which corresponds to the 1.88 and 1.96 molecules of iodine per formula units of 1 and 2 respectively. The adsorbed iodine can be slowly released in organic solvents. An interesting chromism phenomenon was also observed in the case of 1 which shows intense pink color in its pristine (hydrated) form and dark blue color in dehydrated forms which also may be attributed to the change in coordination environment around Co­(II) centers. Interestingly, reversible blue to pink color transition can only be accomplished in the presence of water. Dehydrated framework retained its blue color in a range of organic solvents, advocating the ability of material to selectively sense water in liquid as well as vapor forms. Comprehensive structural description, thermal stability and luminescence behavior for both the CPs has also been presented.