Coordination networks from Cu cations and tetrakis(methylthio) benzenedicarboxylic acid : Tunable bonding patterns and selective sensing for NH3 gas

This paper aims to illustrate the rich potential of the thioether-carboxyl combination in generating coordination networks with tunable and interesting structural features. By simply varying the ratio between Cu(NO₃) ₂ and the bifunctional ligand tetrakis(methylthio)benzenedicarboxylic acid (TMBD) as the reactants, three coordination networks can be hydrothermally synthesized in substantial yields, which present a distinct evolution with regard to metal-ligand interactions. Specifically, Cu(TMBD)_0.5(H ₂TMBD)_0.5•H₂TMBD (1) was obtained with a relatively small (1:1) Cu(NO₃)₂/TMBD ratio, and crystallizes as an one-dimensional (1D) coordination assembly based on Cu(I)-thioether interactions, which is integrated by hydrogen-bonding to additional H₂TMBD molecules to form a three-dimensional (3D) composite network with all the carboxylic acid and carboxylate groups remaining uncoordinated to the metal ions. A medium (1.25:1) Cu(NO₃) ₂/TMBD ratio leads to compound Cu₂TMBD, in which Cu(I) ions simultaneously bond to the carboxylate and thioether groups, while an even higher (2.4:1) Cu(NO₃)₂/TMBD ratio produced a mixed-cation compound Cu^II ₂OHCu^I(TMBD)₂• 2H₂O (2), in which the carboxylic groups are bonded to (cupric) Cu^II ions, and the thioether groups to Cu^I. Despite the lack of open channels in 2, crystallites of this compound exhibit a distinct and selective absorption of NH₃, with a concomitant color change from green to blue, indicating substantial network flexibility and dynamics with regards to gas transport. © 2010 American Chemical Society.