Solution-Phase Monitoring of the Structural Evolution of a Molybdenum Blue Nanoring

The inorganic host–guest complex Na₂₂{[Mo^VI₃₆O₁₁₂(H₂O)₁₆]⊂[Mo^VI₁₃₀Mo^V₂₀O₄₄₂(OH)₁₀(H₂O)₆₁]}·180H₂O ≡ {Mo₃₆}⊂{Mo₁₅₀}, compound <b>1</b>, has been isolated in its solid crystalline state via unconventional synthesis in a custom flow reactor. Carrying out the reaction under controlled flow conditions selected for the generation of {Mo₃₆}⊂{Mo₁₅₀} as the major product, allowing it to be reproducibly isolated in a moderate yield, as opposed to traditional “one-pot” batch syntheses that typically lead to crystallization of the {Mo₃₆} and {Mo₁₅₀} species separately. Structural and spectroscopic studies of compound <b>1</b> and the archetypal Molybdenum Blue (MB) wheel, {Mo₁₅₀}, identified compound <b>1</b> as a likely intermediate in the {Mo₃₆} templated synthesis of MB wheels. Further evidence illustrating the template effect of {Mo₃₆} to MB wheel synthesis was indicated by an increase in the yield and rate of production of {Mo₁₅₀} as a direct result of the addition of preformed {Mo₃₆} to the reaction mixture. Dynamic light scattering (DLS) techniques were also used to corroborate the mechanism of formation of the MB wheels through observation of the individual cluster species in solution. DLS measurement of the reaction solutions from which {Mo₃₆} and {Mo₁₅₀} crystallized gave particle size distribution curves averaging 1.9 and 3.9 nm, consistent with the dimensions of the discrete clusters, which allowed the use of size as a possible distinguishing feature of these key species in the reduced acidified molybdate solutions and to observe the templation of the MB wheel by {Mo₃₆} directly