Thermodynamic Stability of Clusters of Molybdenum Oxide

Abstract

We show that a single geometrical rule underlies the stability of "polyoxomolybdates", the variety of clusters of molybdenum(VI) oxide in (acidified) aqueous solution that are found experimentally. We predict that upon increasing the proton or total molybdenum oxide concentration, the average size of the clusters increases. We compare our predictions with results from ultracentrifugation experiments and with data in the literature. Finally, it is shown that the formation of metal oxide clusters is thermodynamically equivalent to the formation of surfactant micelles.

Charge Regulation as a Stabilization Mechanism for Shell-Like Assemblies of Polyoxometalates

“…The values of the cohesive bond energy for the two POMs in Table I are consistent with hydrogen bonds [18] and also with the weak metal-oxygen bonds in simple complexes of Molybdenum(VI) oxide [19]. These values also are typical for those found in other self-assembling systems such as surfactant micelles [18] and virus capsids [20].…”

Novel morphology of needle-Like nanoparticles of Na2Mo2O7 synthesized by using Ultrasonic spray pyrolysis

“…The average diameter was found to be around 100 nm and length up to 10 µm. It should be mentioned that as far as we are aware this is the first synthesis of needle-like nanoparticles of Na 2 16,17 . Complexes processed by the spray pyrolysis process are self-organized in non-polar toluene in a way that spherical nanoparticles probably through oriented-attachment of individual nanoparticles form needles.…”

“…Aqueous complexes of molybdenum (VI) are formed in a number of overlapping and simultaneously existing protonation -deprotonation and aggregation -disaggregation equilibria 16,18,19 . Depending on the total molybdate concentration and the degree of acidification of the solution, different molybdenum (VI) complexes appeared.…”

“…Aqueous solutions of thermodynamically stable molybdenum (VI) oxide clusters were prepared as described in literature 16,17 . Briefly, molybdenum (VI) oxide solutions were prepared at pH = 3.9 (adjusted by HClO 4 ) and at constant ionic strength of 3 M (adjusted by NaClO 4 ).…”

“…We repeat the procedure under above mentioned condition several times, in order to verify the results obtained. The system chosen for this study (total molybdate concentration of 0.1 M and pH = 3.9) is well characterized in literature 16 Absorption spectra of the precursor solution were measured using UV-Vis spectrophotometer (Perkin Elmer Lambda 5, Waltham, Massachusetts, USA). Reflection spectra of Na 2 Mo 2 O 7 powder were recorded using Avantes S2000 (Eerbeek, Netherlands) instrument with Deuterium-Halogen light source.…”