Direct Synthesis and Mass Spectroscopic Observation of the {M 40 } Polyoxothiometalate Wheel

The nanosized, 2.2 nm, {Mo40} oxo(thio)metalate wheel was isolated in high yield using a direct synthetic procedure which involves acidification of a molybdate solution in the presence of the {Mo2O2S2}2+oxothio cation as the starting material. The [(Mo8O28)4(Mo2O2S2)4]24– wheel, 1a, was characterised by single-crystal X-ray diffraction analysis, IR, Raman, UV/Vis and flame atomic absorption spectroscopy (FAAS). Solid state and solution Raman spectroscopic studies allowed the unambiguous determination of the critical conditions by which compound 1 retains its integrity in solution. Electrospray ionisation mass spectrometry (ESI-MS) studies carried out on aqueous solutions of the crystalline material showed that the nanosized wheel retains its integrity in concentrated solutions. High resolution ESI-MS studies allowed the direct observation of the discrete wheel as well as the distinct self-assembly stages of its formation; from the fundamental building units through to the final formation of well resolved aggregations of 1D chains which is in agreement with the solid state studies.