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Hierarchically ordered oxides are of critical importance in material science and catalysis. Unfortunately, the design and synthesis of such systems remains a key challenge to realizing their potential. In this study, we demonstrate how the deposition of small oligomeric (MoO 3 ) 1-6 clusters-formed by the facile sublimation of MoO 3 powders-leads to the self-assembly of locally ordered arrays of immobilized mono-oxo (MoO 3 ) 1 species on anatase TiO 2 (101). Using both high-resolution imaging and theoretical calculations, we reveal the dynamic behavior of the oligomers as they spontaneously decompose at room temperature, with the TiO 2 surface acting as a template for the growth of this hierarchically structured oxide. Transient mobility of the oligomers on both bare and (MoO 3 ) 1 -covered TiO 2 (101) areas is identified as key to the formation of a complete (MoO 3 ) 1 overlayer with a saturation coverage of one (MoO 3 ) 1 per two undercoordinated surface Ti sites. Simulations reveal a dynamic coupling of the reaction steps to the TiO 2 lattice fluctuations, the absence of which kinetically prevents decomposition. Further experimental and theoretical characterizations demonstrate that (MoO 3 ) 1 within this material are thermally stable up to 500 K and remain chemically identical with a single empty gap state produced within the TiO 2 band structure. Finally, we see that the constituent (MoO 3 ) 1 of this material show no proclivity for step and defect sites, suggesting they can reliably be grown on the (101) facet of TiO 2 nanoparticles without compromising their chemistry., Competing Interests: The authors declare no competing interest.

Understanding adsorbed water and its dissociation to surface hydroxyls on oxide surfaces is key to unraveling many physical and chemical processes, yet the barrier for its deprotonation has never been measured. In this study, we present direct evidence for water dissociation equilibrium on rutile-TiO 2 (110) by combining supersonic molecular beam, scanning tunneling microscopy (STM), and ab initio molecular dynamics. We measure the deprotonation/protonation barriers of 0.36 eV and find that molecularly bound water is preferred over the surface-bound hydroxyls by only 0.035 eV. We demonstrate that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O-H bonds and inducing deprotonation. The developed methodology for studying metastable reaction intermediates prepared with a high-energy molecular beam in the STM can be readily extended to other systems to clarify a wide range of important bond activation processes.