Orientations of polyoxometalate anions on gold nanoparticles

Cryogenic transmission electron microscopy of polyoxometalate-protected gold nanoparticles reveals that the Preyssler ion, [NaP5W30O110](14-), lies face down with its C-5 axis perpendicular to the gold surface, while the Finke-Droege ion, [P4W30Zn4(H2O)(2)O-112](16-), is tilted, with its long axis close to 60 degrees from the normal to the surface.