Controlled assembly and solution observation of a 2.6 nm polyoxometalate 'super' tetrahedron cluster: [KFe12(OH)(18)(alpha-1,2,3-P2W15O56)(4)](29-)

A nanoscale Fe-III-substituted polyoxotungstate [KFe12(OH) (-)(18) (alpha-1,2,3-P2W15O56)(4)](29-) is synthesized starting from the trilacunary {P2W15} Dawson cluster and [Fe-3(mu(3)-O)( CH2 =CHCOO)(6)(H2O)(3)](1+) to give a 2.6 nm tetrahedral cluster species and the 16 kDa cluster can be directly observed in solution as revealed by mass spectrometry studies.