Coordination Chemistry of the Magic Inorganic Building Block {FeII[Mo6P4O31]2}: Hydrothermal Synthesis and Crystal Structure of a New Reduced Ferrous Molybdophosphate

Crystal structures of hybrid completely reduced phosphomolybdates and catalytic performance applied as molecular catalysts for the reduction of chromium(VI)

The exploration of highly efficient and low-cost catalysts for the treatment of hexavalent chromium Cr^VI in environmental remediation is currently one of the most challenging topics. Here, three phosphomolybdate hybrid compounds have been successfully isolated by the hydrothermal method and been applied as supramolecular catalysts for the reduction of Cr^VI. Single-crystal X-ray diffraction revealed their formulae as (H₂bpp)₂[Fe(H₂O)][Sr(H₂O)₄]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·5H₂O (1), (H₂bpp)₂[Na(H₂O)(OC₂H₅)][Fe(H₂O)₂][Ca(H₂O)₂]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·4H₂O (2) and (H₂bpe)₃{Fe[Mo₆O₁₂(OH)₃(HPO₄)₃(H₂PO₄)]₂}·8H₂O (3) [bpp is 1,3-bis(pyridin-4-yl)propane (C₁₃H₁₄N₂) and bpe is trans-1,2-bis(pyridin-4-yl)ethylene (C₁₂H₁₀N₂)]. The three hybrids consist of supramolecular networks built up by noncovalent interactions between {Fe[P₄Mo₆^VO₃₁]₂}^22- polyanions and protonated organic cations. This kind of hybrid polyoxometalate could be applied as heterogeneous molecular catalysts for the reduction of Cr^VI. It was found that the organic moiety plays a vital role in influencing the catalytic activity of the polyanions. Organic bpp-containing hybrids 1 and 2 are highly active in the catalytic reduction of heavy metal Cr^VI ions using HCOOH as reductant, while bpe-containing hybrid 3 is inactive to this reaction. This work is significant for the design of new catalysts, as well as the exploration of reaction mechanisms at a molecular level.

The highest connected pure inorganic 3D framework assembled by {P4Mo6} cluster and alkali metal potassium

Potassium cation is introduced into the {(P₄Mo₆} systems, leading to 18-connected assemblies, which represents the highest connection of the POMs and shows bifunctional electrocatalytic activities and excellent photocatalytic activities.