Novel phosphanegold(I) cluster cations combined with polyoxometalate (POM) anions, i.e., intercluster compounds, [(Au{P(m-FPh)₃})₄(μ₄-O)]₂[{(Au{P(m-FPh)₃})₂ (μ-OH)}₂][α-PMo₁₂O₄₀]₂·EtOH (1), [(Au{P(m-FPh)₃})₄(μ₄-O)]₂[α-SiMo₁₂O₄₀]·4H₂O (2), [(Au{P(m-MePh)₃})₄(μ₄-O)]₂[α-SiM₁₂O₄₀] (M = W (3), Mo (4)) and [{(Au {P(p-MePh)₃})₄(μ₄-O)}{(Au{P(p-MePh)₃})₃(μ₃-O)}][α-PW₁₂O₄₀] (5) were synthesized by POM-mediated clusterization, and unequivocally characterized by elemental analysis, TG/DTA, FT-IR, X-ray crystallography, solid-state CPMAS ³¹P NMR and solution (¹H, ³¹P{¹H}) NMR. Formation of the these gold(I) cluster cations was strongly dependent upon the charge density and acidity of the POMs, and the substituents and substituted positions on the aryl group of triarylphosphane ligands. These gold(I) cluster cations contained various bridged-oxygen atoms such as μ₄-O, μ₃-O and μ-OH groups.

We have successfully synthesized K₁₇{[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}·35H₂O (potassium salt of In₁₀-open), an open-Wells–Dawson polyoxometalate (POM) containing ten indium metal atoms. This novel compound was characterized by X-ray crystallography, ²⁹Si NMR, FTIR, complete elemental analysis, and TG/DTA. X-ray crystallography results for {[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}¹⁷⁻ (In₁₀-open) revealed two open-Wells–Dawson units containing two In³⁺ ions and a K⁺ ion, [{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]¹¹⁻, connected by an In₆-hydroxide cluster moiety, [In₆(μ-OH)₁₃(H₂O)₈]⁵⁺. In₁₀-open is the first example of an open-Wells–Dawson POM containing a fifth-period element. Moreover, to the best of our knowledge, it exhibits the highest nuclearity among the indium-containing POMs reported to date.

The β,β-isomer of open-Wells–Dawson polyoxometalate (POM) containing a tetra-iron(III) cluster, K₉[{Fe₄(H₂O)(OH)₅}(β,β-Si₂W₁₈O₆₆)]·17H₂O (potassium salt of β,β-Fe₄-open), was synthesized by reacting Na₉H[A-β-SiW₉O₃₄]·23H₂O with FeCl₃·6H₂O at pH 3, and characterized by X-ray crystallography, FTIR, elemental analysis, TG/DTA, UV–Vis, and cyclic voltammetry. X-ray crystallography revealed that the {Fe³⁺₄(H₂O)(OH)₅}⁷⁺ cluster was included in the open pocket of the β,β-type open-Wells–Dawson polyanion [β,β-Si₂W₁₈O₆₆]¹⁶⁻ formed by the fusion of two trilacunary β-Keggin POMs, [A-β-SiW₉O₃₄]¹⁰⁻, via two W–O–W bonds. The β,β-open-Wells–Dawson polyanion corresponds to an open structure of the standard γ-Wells–Dawson POM. β,β-Fe₄-open is the first example of the compound containing a geometrical isomer of α,α-open-Wells–Dawson structural POM.