Synthesis and Characterization of a Series of [M2(β-SiW8O31)2]n− Clusters and Mechanistic Insight into the Reorganization of {β-SiW8O31} into {α-SiW9O34}

A new octa-Mn-substituted poly(polyoxotungstate)

A novel octa-Mn-substituted silicotungstate (ST) tetramer [H₂N(CH₃)₂]₈H₁₉Na₄{[K(H₂O)₄WO₄] [SiMnII2W₁₀O₃₈]₃}[SiMnIII2W₁₀O₃₈]·27H₂O (1) was prepared, and its electrochemistry, thermal stability and magnetic properties were investigated.

Soluble Hetero-Polyoxovanadates and Their Solution Chemistry Analyzed by Electrospray Ionization Mass Spectrometry

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self-assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water-soluble antimonato polyoxovanadates (Sb-POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI-MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb-POVs and how the knowledge of their reactivity obtained by ESI-MS has fostered the syntheses of numerous novel Sb-POV compounds.

An unprecedented Zr-containing polyoxometalate tetramer with mixed trilacunary/dilacunary Keggin-type polyoxotungstate units

A novel zirconium(IV)-substituted tetramer polyoxotungstate, H₆K₄Na₁₆[Zr₄(β-GeW₁₀O₃₈)₂(A-α-PW₉O₃₄)₂]·37H₂O, was synthesized hydrothermally and characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, energy-dispersive X-ray spectroscopy and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic P2/n space group. The most remarkable feature is that the centrosymmetric Zr-based polyoxotungstate tetramer consists of dilacunary Keggin-type germanotungstate and trilacunary Keggin-type phosphotungstate units that are linked by Zr^IV ions.

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.

Catalysis of "outer-phase" oxygen atom exchange reactions by encapsulated "inner-phase" water in {V15Sb6}-type polyoxovanadates

A water molecule encapsulated inside water-soluble {V₁₅Sb₆} antimonato polyoxovanadate cages accelerates oxygen-exchange reactions in the cluster periphery.

Antimonato polyoxovanadate (POV) cluster compounds {M(en)₃}₃[V₁₅Sb₆O₄₂(H₂O)_x]·nH₂O (M = Fe^II, Co^II, Ni^II and x = 0 or 1) obtained under solvothermal conditions exhibit unusual high water solubility making these compounds promising synthons for generation of new POV structure types. Electrospray ionization mass spectrometry provides evidence (i) for a water molecule encapsulated inside the cavity of a fraction of the spherical cluster shells, (ii) for a post-functionalization in water, namely a slow exchange of VO against Sb₂O, (iii) for the inner-phase reactivity of the encapsulated water that is capable of opening an oxo-bridge, and (iv) for a significant acceleration of the ¹⁶O/¹⁸O exchange reactions of oxygen atoms in the cluster periphery with surrounding H₂¹⁸O, when encapsulated water is present. To the best of our knowledge, this is the first example in polyoxovanadate chemistry for the transduction of inner-phase reactivity of an encapsulated guest molecule into changes in the outer-phase reactivity of the cluster. Magnetic susceptibility measurements reflect the individual contributions of the frustrated {V₁₅} spin polytope and the {M(en)₃}²⁺ complexes, with very weak coupling between these groups.