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

A nanoscale FeIII-substituted polyoxotungstate [KFe12(OH)18-(alpha-1,2,3-P2W15O56)4]29- is synthesized starting from the trilacunary {P2W15} Dawson cluster and [Fe3(mu3-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.