Assembly of a series of Keggin-based multi- and mono-nuclear structures by tuning the bis(tetrazole)-functionalized thioether ligands

Four Keggin-based compounds, [CuI2(bmtm)3]2·[CuI2(bmtm)4]·(PW12O40)2 (1), (bmtm = 1,1′-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)methane), [CuI3(bmte)3(PW12O40)] (2) (bmte = 1,2-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)ethane), [CuII(bmtb)3(HPW12O40)] (3) and [CuII(bmtb)3(HPMo12O40)] (4) (bmtb = 1,4-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)butane), have been designed and synthesized under hydrothermal conditions. By tuning the bis(tetrazole)-functionalized thioether ligands, compounds 1–4 exhibit Keggin-based bi-, tri- and mono-nuclear structures respectively, in which copper ion is +I oxidation state in compounds 1–2, and +II oxidation state in compounds 3–4. Compound 1 is composed of three moieties, [PW12O40]3− anion and two kinds of bi-nuclear subunits [CuI2(bmtm)3]2+ and [CuI2(bmtm)4]2+. There exist abundant hydrogen-bonding and aryl stacking interactions inducing a two-dimensional (2D) supramolecular network of compound 1. Compound 2 exhibits a tri-nuclear cluster [CuI3(bmte)3]3+, which is connected by [PW12O40]3− anions to construct a 1D chain. Compounds 3 and 4 are isostructural, and show 2D layer structures, which are constructed from Keggin anions and mono-nuclear [CuII(bmtb)3]2+. In this 2D layer, the Keggin anions act as bidentate linkages to connect the CuII-btmb chains. The oxidation states of copper ions show great influence on the mono- and multi-nuclear structures of this series. In addition, the electrochemical properties of the title compounds have been investigated.

Four Keggin-based compounds, [CuI2(bmtm)3]2·[CuI2(bmtm)4]·(PW12O40)2 (1), (bmtm = 1,1′-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)methane), [CuI3(bmte)3(PW12O40)] (2) (bmte = 1,2-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)ethane), [CuII(bmtb)3(HPW12O40)] (3) and [CuII(bmtb)3(HPMo12O40)] (4) (bmtb = 1,4-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)butane), have been designed and synthesized under hydrothermal conditions. The oxidation states of copper ions play a key role in the structural control of assembling mono-/multi-nuclear subunits.Figure optionsDownload as PowerPoint slideHighlights
► The bis(tetrazole)-based thioethers are used to construct POM-based compounds.
► The oxidation state of Cu can be tuned by varying the amount and length of ligand.
► CuI and CuII play a key role in the assembly of multi- and mono-nuclear subunits.