Complexation of tetravalent uranium cations by the As4W40O140 cryptand

The polyanionic cryptand {As₄W₄₀O₁₄₀} was successfully used to bind up to four tetravalent uranium cations leading to the formation of three new cryptates. The obtained species appears to be stable in solution and the cryptand was used for U^IV/Nd^III separation studies.

Bottom-up synthesis of functionalized {Ce4(SiW9O34)2(l)2} polyoxometalates

Bottom-up synthesis allows the formation of four organic-functionalized Ce^IV containing polyoxometalates and one unprecedented polyanion stabilizing two different Ce^IV clusters.

Investigating the Transformations of Polyoxoanions Using Mass Spectrometry and Molecular Dynamics

The reactions of [γ-SiW10O36](8-) represent one of the most important synthetic gateways into a vast array of polyoxotungstate chemistry. Herein, we set about exploring the transformation of the lacunary polyoxoanion [β2-SiW11O39](8-) into [γ-SiW10O36](8-) using high-resolution electrospray mass spectrometry, density functional theory, and molecular dynamics. We show that the reaction proceeds through an unexpected {SiW9} precursor capable of undertaking a direct β → γ isomerization via a rotational transformation. The remarkably low-energy transition state of this transformation could be identified through theoretical calculations. Moreover, we explore the significant role of the countercations for the first time in such studies. This combination of experimental and the theoretical studies can now be used to understand the complex chemical transformations of oxoanions, leading to the design of reactivity by structural control.

The transformation of polyoxometalates in the formation of intercluster compound [Ag41(α-SiW(10)O37)((t)BuC≡C)27(CH3CN)3][β-SiW(12)O40]

We report a unique intercluster compound comprising a Ag41 cage encapsulating a divacant [α-SiW(10)O37](10-) anion and a complete [β-SiW(12)O40](4-) anion as a counteranion. Two electro-redox centers associated with the inner and outer POM anions show interesting electrochemical behaviours, because the stable Ag41 cage acts as an electron transfer mediator.

B-α-[AsW9O33](9-) polyoxometalates incorporating hexanuclear uranium {U6O8}-like clusters bearing the U(IV) form or unprecedented mixed valence U(IV)/U(VI) involving direct U(VI)=O-U(IV) bonding

The use of B-α-[AsW9O33](9-) anionic moieties in association with the tetravalent 5f uranium UCl4 precursor affords three new hexanuclear uranium {U6O8}-like clusters embedded in a polyoxometalate architecture. Two of them are constituted by an unprecedented uranium mixed valence U(IV)/U(VI) cluster.

Exploiting the equilibrium dynamics in the self-assembly of inorganic macrocycles based upon polyoxothiometalate building blocks

Manipulation of the equilibrium dynamics allowed access to new thermodynamic minima and formation of two new inorganic macrocycles, {Mo₁₆} = {(Mo₂O₂S₂)₈(OH)₁₆(C₄O₄)₂}⁴⁻ and {Mo₁₂} = {(Mo₂O₂S₂)₆(OH)₁₂(CH₃COO)₂}²⁻.

Stabilization of Tetravalent 4f (Ce), 5d (Hf), or 5f (Th, U) Clusters by the [α-SiW9O34](10-) Polyoxometalate

The reaction of Na10[α-SiW9O34] with tetravalent metallic cations such as 4f ((NH4)2Ce(NO3)6), 5d (HfCl4), or 5f (UCl4 and Th(NO3)4) in a pH 4.7 sodium acetate buffer solution leads to the formation of four sandwich-type polyoxometalates [Ce4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (1), [U4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (2), [Th3(μ(3)-O)(μ(2)-OH)3(SiW9O34)2](13-) (3), and [Hf3(μ(2)-OH)3(SiW9O34)2](11-) (4). All four compounds consist of a polynuclear cluster fragment stabilized by two [α-SiW9O34](10-) polyanions. Compounds 1 and 2 are isostructural with a tetranuclear core (Ce4, U4), while compound 3 presents a trinuclear Th3 core bearing a μ(3)-O-centered bridge. It is an unprecedented configuration in the case of the thorium(IV) cluster. Compound 4 also possesses a trinuclear Hf3 core but with the absence of the μ(3)-O bridge. The molecules have been characterized by single-crystal X-ray diffraction, (183)W and (29)Si nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis.

Divacant polyoxotungstates: reactivity of the gamma-decatungstates [γ-XW10O36]8-(X = Si, Ge)

The dilacunary, Keggin-based gamma-decatungstate ions [γ-XW(10)O(36)](8-) (X = Si, Ge) {XW(10)} exhibit an exciting and versatile solution chemistry, which is probably unmatched by any other lacunary polytungstate. The reactivity of {XW(10)} in the presence, and even absence, of electrophiles, includes loss/gain of tungsten, isomerization, and dimerization. Ever since the syntheses and structures of {XW(10)} were reported, many research groups around the world have investigated the reactivity of these polyanions towards nucleophiles (mostly d-block metal ions) and different products with various shape, size and composition were obtained. Here we provide an overview of the state-of-the-art in this subarea of polyoxometalate chemistry, with a focus on synthetic and structural aspects.