Direct Synthesis and Mass Spectroscopic Observation of the {M₄₀} Polyoxothiometalate Wheel

The nanosized, 2.2 nm, {Mo 40 } 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 {Mo 2 O 2 S 2 } 2+ oxothio cation as the starting material. The [(Mo 8 O 28 ) 4 (Mo 2 O 2 S 2 ) 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.