Tuning the oxidation states of copper ions (+I/+II) to construct different Keggin-based topology structures

Through tuning the oxidation states of Cu-I/II, two Keggin-based compounds with different topologies, [Cu-5(I)(btx)(4)((PW10W2O40)-W-VI-O-V)] (1) and [Cu-2(II)(btx)(4)(SiW12O40)] (2) (btx = 1,6-bis(1,2,4-triazol-1-yl)hexane), were synthesized and structurally characterized. In 1, there exist decanuclear Cu-I circuits, which are linked through N1-containing btx ligands to construct a grid-like 2-D layer. Three sets of these layers interpenetrate to build a three-fold interpenetrating framework. The Keggin polyanions connect the adjacent three-fold interpenetrating frameworks to construct a 3-D structure. In 2, the Cu-II-btx moiety shows a (6(6)) 3-D hexagonal channel-style framework. The Keggin polyanion offering four terminal oxygen atoms incorporates with this metal-organic framework imbedding the channels. The different oxidation states of copper ions (+I/+II) induces distinct coordination modes of btx and Keggin polyanions and affects the whole structural topologies. Tuning the oxidation states of copper ions is an effective strategy for obtaining POM-based topologies. In addition, the electrochemical properties of 1 and 2 bulk-modified carbon-paste electrodes are reported.