Versatile Post-functionalisation Strategy for the Formation of Modular Organic-Inorganic Polyoxometalate Hybrids

Rational synthesis of elusive organic-inorganic hybrid metal-oxo clusters: formation and post-functionalization of hexavanadates

Paving the way towards new functional materials relies increasingly on the challenging task of forming organic-inorganic hybrid compounds. In that regard, discrete atomically-precise metal-oxo nanoclusters have received increasing attention due to the wide range of organic moieties that can be grafted onto them through functionalization reactions. The Lindqvist hexavanadate family of clusters, such as [V₆O₁₃{(OCH₂)₃C-R}₂]^2- (V₆-R), is particularly interesting due to the magnetic, redox, and catalytic properties of these clusters. However, compared to other metal-oxo cluster types, V₆-R clusters have been less extensively explored, which is mainly due to poorly understood synthetic challenges and the limited number of viable post-functionalization strategies. In this work, we present an in-depth investigation of the factors that influence the formation of hybrid hexavanadates (V₆-R HPOMs) and leverage this knowledge to develop [V₆O₁₃{(OCH₂)₃CNHCOCH₂Cl}₂]^2- (V₆-Cl) as a new and tunable platform for the facile formation of discrete hybrid structures based on metal-oxo clusters in relatively high yields. Moreover, we showcase the versatility of the V₆-Cl platform through its post-functionalization via nucleophilic substitution with various carboxylic acids of differing complexity and with functionalities that are relevant in multiple disciplines, such as supramolecular chemistry and biochemistry. Hence, V₆-Cl was shown to be a straightforward and versatile starting point for the formation of functional supramolecular structures or other hybrid materials, thereby enabling their exploration in various fields.

Tris-decorated multi-iron polyoxotungstates

Solution-stable tris(hydroxymethyl)aminomethane-functionalized Fe^III-containing polyoxotungstates exhibit an unusual anchoring mode of triol moieties, with one -NH₂ and one -CH₂OH group remaining accessible for post-functionalization or chemisorption. The redox-active title compounds have been isolated under unusually mild reaction conditions and characterized in the solid state and in aqueous solutions.

Organic/Inorganic Species Synergistically Supported Unprecedented Vanadomolybdates

Vanadomolybdates (VMos), comprised of Mo and V in high valences with O bridges, are one of the most important types of polyoxometalates (POMs), which have high activity due to their strong capabilities of gaining/losing electrons. Compared with other POMs, the preparation of VMos is difficult due to their relatively low structural stability, especially those with unclassical architectures. To overcome this shortcoming, in this study, triol ligands were applied to synthesize VMos through a beaker reaction in the presence of V₂O₅, Na₂MoO₄, and organic species in the aqueous solution. The single-crystal X-ray diffraction results indicate that two VMo clusters, Na₄{V₅Mo₂O₁₉[CH₃C(CH₂O)₃]}∙13H₂O and Na₄{V₅Mo₂O₁₉[CH₃CH₂C(CH₂O)₃]}∙13H₂O, with a similar architecture, were synthesized, which were both stabilized by triol ligand and {MoO₆} polyhedron. Both clusters are composed of five V ions and one Mo ion in a classical Lindqvist arrangement with an additional Mo ion, showing an unprecedented hepta-nuclear VMo structure. The counter Na⁺ cations assemble into one-dimensional channels, which facilitates the transport of protons and was further confirmed by proton conductivity experiments. The present results provide a new strategy to prepare and stabilize VMos, which is applicable for developing other compounds, especially those with untraditional architectures.