Coordination networks from Cu cations and tetrakis(methylthio) benzenedicarboxylic acid: Tunable bonding patterns and selective sensing for NH 3 gas

Abstract

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(NO 3) 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•H 2TMBD (1) was obtained with a relatively small (1:1) Cu(NO 3) 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 H 2TMBD 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(NO 3) 2/TMBD ratio leads to compound Cu 2TMBD, in which Cu(I) ions simultaneously bond to the carboxylate and thioether groups, while an even higher (2.4:1) Cu(NO 3) 2/TMBD ratio produced a mixed-cation compound Cu II 2OHCu I(TMBD) 2• 2H 2O (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 NH 3, with a concomitant color change from green to blue, indicating substantial network flexibility and dynamics with regards to gas transport. © 2010 American Chemical Society.