UC Davis

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(p-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 (Na-1; triclinic, P1̅, a = 25.8088(3) Å, b = 25.8336(3) Å, c = 27.1598(3) Å, α = 78.1282(11)°, β = 61.7276(14)°, γ = 60.6220(14)°, V = 13888.9(3) ų, Z = 2) and Na₂₅[Co₉(OH)₃(H₂O)₆(H₂NC₆H₄AsO₃)₂(P₂W₁₅O₅₆)₃]·86H₂O (Na-2; triclinic, P1̅, a = 14.2262(2) Å, b = 24.8597(4) Å, c = 37.9388(4) Å, α = 81.9672(10)°, β = 87.8161(10)°, γ = 76.5409(12)°, V = 12920.6(3) ų, Z = 2). The axially oriented para-aminophenyl groups in 2 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.