Organoarsonate Functionalization of Heteropolyoxotungstates

Functionalization of the {P₈W₄₈} polyoxotungstate (POT) archetype with aromatic organoarsonates results in the first homometallic {P₈W₄₈} derivatives, with the general formula [(RAs^VO)₄P^V₈W^VI₄₈O₁₈₄]³²⁻ [R = C₆H₅ (<b>1</b>) or <i>p</i>-(H₂N)­C₆H₄ (<b>2</b>)]. Short As−O bonds here induce unusual bending of the otherwise rigid {P₈W₄₈} macrocycle, breaking its <i>D</i>_4<i>h</i> symmetry. The obtained species also represent the first lacunary POTs functionalized with organoarsonates and can potentially act as polyoxometalate precursors themselves. We elaborate solution stability in different aqueous media using ¹H and ³¹P NMR spectroscopy and possible pathways for subsequent transformations in aqueous solutions of the functionalized polyanions. Recrystallization of the K⁺/Li⁺/dimethylammonium salt of <b>2</b> from 4 M LiCl solution yielded a further functionalized POT, [(H₃NC₆H₄AsO)₃P₈W₄₈O₁₈₄H_<i>x</i>{WO₂(H₂O)₂}_0.4]^{(30.2−<i>x</i>)−} (<b>3</b>), revealing dissociation of the organoarsonate fragments in slightly acidic aqueous solutions followed by their rearrangement within the inner POT cavity

Probing Frontier Orbital Energies of {Co₉(P₂W₁₅)₃} Polyoxometalate Clusters at Molecule–Metal and Molecule–Water Interfaces

Functionalization of polyoxotungstates with organoarsonate coligands enabling surface decoration was explored for the triangular cluster architectures of the composition [Co^II₉(H₂O)₆(OH)₃(<i>p</i>-RC₆H₄As^VO₃)₂­(α-P^V₂W^VI₁₅O₅₆)₃]^25– ({Co₉(P₂W₁₅)₃}, R = H or NH₂), isolated as Na₂₅[Co₉(OH)₃(H₂O)₆­(C₆H₅AsO₃)₂­(P₂W₁₅O₅₆)₃]·86H₂O (<b>Na-1</b>; triclinic, <i>P</i>1̅, <i>a</i> = 25.8088(3) Å, <i>b</i> = 25.8336(3) Å, <i>c</i> = 27.1598(3) Å, α = 78.1282(11)°, β = 61.7276(14)°, γ = 60.6220(14)°, <i>V</i> = 13888.9(3) ų, <i>Z</i> = 2) and Na₂₅[Co₉(OH)₃­(H₂O)₆­(H₂NC₆H₄AsO₃)₂­(P₂W₁₅O₅₆)₃]·86H₂O (<b>Na-2</b>; triclinic, <i>P</i>1̅, <i>a</i> = 14.2262(2) Å, <i>b</i> = 24.8597(4) Å, <i>c</i> = 37.9388(4) Å, α = 81.9672(10)°, β = 87.8161(10)°, γ = 76.5409(12)°, <i>V</i> = 12920.6(3) ų, <i>Z</i> = 2). The axially oriented <i>para</i>-aminophenyl groups in <b>2</b> facilitate the formation of self-assembled monolayers on gold surfaces and thus provide a viable molecular platform for charge transport studies of magnetically functionalized polyoxometalates. The title systems were isolated and characterized in the solid state, in aqueous solutions, and on metal surfaces. Using conducting tip atomic force microscopy, the energies of {Co₉(P₂W₁₅)₃} frontier molecular orbitals in the surface-bound state were found to directly correlate with cyclic voltammetry data in aqueous solution