Solution-Phase Monitoring
of the Structural Evolution
of a Molybdenum Blue Nanoring
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Abstract
The inorganic host–guest complex Na<sub>22</sub>{[Mo<sup>VI</sup><sub>36</sub>O<sub>112</sub>(H<sub>2</sub>O)<sub>16</sub>]⊂[Mo<sup>VI</sup><sub>130</sub>Mo<sup>V</sup><sub>20</sub>O<sub>442</sub>(OH)<sub>10</sub>(H<sub>2</sub>O)<sub>61</sub>]}·180H<sub>2</sub>O ≡ {Mo<sub>36</sub>}⊂{Mo<sub>150</sub>}, 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 {Mo<sub>36</sub>}⊂{Mo<sub>150</sub>} 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 {Mo<sub>36</sub>} and {Mo<sub>150</sub>} species separately. Structural and spectroscopic studies of compound <b>1</b> and the archetypal Molybdenum Blue (MB) wheel, {Mo<sub>150</sub>}, identified compound <b>1</b> as a likely intermediate in
the {Mo<sub>36</sub>} templated synthesis of MB wheels. Further evidence
illustrating the template effect of {Mo<sub>36</sub>} to MB wheel
synthesis was indicated by an increase in the yield and rate of production
of {Mo<sub>150</sub>} as a direct result of the addition of preformed
{Mo<sub>36</sub>} 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
{Mo<sub>36</sub>} and {Mo<sub>150</sub>} 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 {Mo<sub>36</sub>} directly
