Using Coordination Chemistry to Control “Click” Reactions: The Selective Formation of Asymmetrically Ligated Polyoxometalates

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction between (NBu₄)₂[V₆O₁₃((OCH₂)₃CCH₂N₃)₂] and 3-ethynylpyridine led to the formation of products capable of forming poorly soluble coordination compounds with transition metal ions such as Cu(I) and Zn(II). The formation of these poorly soluble phases is an important feature that was used to determine the course of reactions, allowing the selective preparation of symmetric bis-pyridyltriazolyl and asymmetric monopyridyltriazolyl derivatives with relatively high yields and high substrate conversions. The asymmetric compound (NBu₄)₂[V₆O₁₃((OCH₂)₃CCH₂-N₃C₂H-C₅H₄N)((OCH₂)₃CCH₂N₃)] (V₆^asym) was utilized in the subsequent "click" postfunctionalization reaction with 1,4-diethynylbenzene, resulting in a covalently bound V₆^asym-V₆^asym dimer. This dimeric compound was subjected to scanning probe microscopy studies on gold surfaces, which revealed no electronic coupling between the hexavanadate cores within the dimer upon potential-induced switching. This observation indicates that such dimers and higher-order oligomers composed of polyoxometalate-ligand-polyoxometalate bridges can be exploited as active capacitor/memristor units, relevant to increase the data storage capacity of standard memory devices with innovative molecular switching mechanisms.