Synthesis of a 6-nm-Long Transition-Metal-Rare-Earth-Containing Polyoxometalate.

An extremely long ribbon-shaped polyoxometalate (POM) octamer, {Eu16Co7Se16W128O448(CIT)10(HCIT)2(NO3)4(OH)4(H2O)52} (H4CIT = citric acid), with a maximum length of ca. 6 nm has been obtained, which is the longest molecular POM reported to date and the first Dawson-based 3d-4f-containing selenotungstate(IV). The nanoscale octamer is built from 8 new Dawson-type Eu2W2-substituted selenotungstates {(Eu2W2O4)Se2W14O52} bridged by 12 H4CIT ligands and 3 Co2+ ions, giving rise to a rare giant inorganic-organic hybrid molecular POM with more than 150 metal centers (7 CoII, 16 EuIII, 16 SeIV, and 128 WVI). Especially, with 128 W centers and more than 800 non-H atoms, the POM octamer also represents the largest known 3d-4f-containing polyoxotungstate.