On the Isomer Problem of Mixed−Addenda and Heterogroup−Substituted Polyoxometalates
- Polyoxometalates (POMs) represent nanoscale metal−oxide clusters, conventionally constructed of early transition metals in high oxidation states (mainly V, Mo and W). POMs exhibit tunable physicochemical properties, which make them suitable for applications in catalysis, magnetism and preparation of nanostructured materials. The properties of POMs are predominantly tuned by the number, the type and by the arrangement of the involved building blocks in unique structural architectures. The stabilities and the properties rising from the arrangement of the building blocks define the problem of POM isomerism. In this thesis, density functional theory (DFT) and its time-dependent implementation (TD-DFT) are applied to shed light into the isomer problem of mixed−addenda and heterogroup−substituted POMs. The following problems were addressed: (i) Elucidation of the solution structure of the two reported polyoxoaurates [Au4Se4O16]4− and [Au4As4O16]8−. (ii) Understanding of the positional isomerism problem and structure-stability relationship in the mixed-addenda [NaAuxPd12–xAs8O40](x−15) and [NaAuxPd12–xSe8O32](x−7) polyoxoanions. (iii) Structure-stability relationship of the isomeric α–/γ–/β–[V14E8O50]12− and α–/γ–/β–[V14E8O42X8]12− (E = Si, Ge and Sn; X = S, Se and Te) heteropolyoxovanadates. (iv) Comparative study of the arsenate capped polyoxopalladates [Na2Pd22As16O76]26– and [Pd13As8O40]14–. (v) Study of anti–/syn–[Pt2(PW11O39)2]10− and their two electron oxidized species anti–/syn– [Pt2(H2O)2(PW11O39)2]8−.
