Comparative study of water reactivity with Mo2Oy− and W2Oy− clusters: A combined experimental and theoretical investigation

Abstract

A computational investigation of the Mo2O(y)(-) + H2O (y = 4, 5) reactions as well as a photoelectron spectroscopic probe of the deuterated Mo2O6D2(-) product have been carried out to understand a puzzling question from a previous study: Why is the rate constant determined for the Mo2O5(-) + H2O/D2O reaction, the terminal reaction in the sequential oxidation of Mo2O(y)(-) by water, higher than the W2O5(-) + H2O/D2O reaction? This disparity was intriguing because W3O(y)(-) clusters were found to be more reactive toward water than their Mo3O(y)(-) analogs. A comparison of molecular structures reveals that the lowest energy structure of Mo2O5(-) provides a less hindered water addition site than the W2O5(-) ground state structure. Several modes of water addition to the most stable molecular and electronic structures of Mo2O4(-) and Mo2O5(-) were explored computationally. The various modes are discussed and compared with previous computational studies on W2O(y)(-) + H2O reactions. Calculated free energy reaction profiles show lower barriers for the initial Mo2O(y)(-) + H2O addition, consistent with the higher observed rate constant. The terminal Mo2O(y)(-) sequential oxidation product predicted computationally was verified by the anion photoelectron spectrum of Mo2O6D2(-). Based on the computational results, this anion is a trapped dihydroxide intermediate in the Mo2O5(-) + H2O/D2O → Mo2O6(-) + H2/D2 reaction.

Fragmentation of [Ni(NO3)3]−: A Study of Nickel–Oxygen Bonding and Oxidation States in Nickel Oxide Fragments

“…The orbital occupancies for smaller oxide complexes are more difficult to interpret, and 3d spin density becomes a more useful parameter. The electron configuration for [Ni(NO 3 ) 3 ] − shows excess 3d α spin (total α − total β): +1.66α for nickel, close to the expected value of +2α for a pure 3d 8 Figure 6, are nearly degenerate with the unpaired metal electrons. The net spin densities in Table 2, ca.…”

CexOy– (x = 2–3) + D2O Reactions: Stoichiometric Cluster Formation from Deuteroxide Decomposition and Anti-Arrhenius Behavior

“…While the entropies, heat capacities, and energies of species along the actual Ce x O y − + H 2 O reaction coordinate are not expected to be identical to values determined in our previous computational studies on transition metal oxides, 13,14,16 the plots serve to show the range of negative barriers expected and how they relate to features in the reaction free-energy path. We conclude that the range of negative barriers determined from the Arrhenius plots is in line with what is expected based on the energy and entropy of complex formation and subsequent covalently bound complex formation.…”

“…While we have not yet done a computational treatment of possible pathways for Ce x O y − + water reactions, previous studies suggest that the dipole−dipole interaction between an O−H bond of water and a local M−O bond is stronger than charge−dipole interactions in the electrostatic complex in the optimized structure, 16 35,36 In our current study, deuteroxide formation is preceded by suboxide formation in reactions between metallic or highly reduced clusters with water, after which −OD groups add sequentially. However, the emergence of Ce 2 O 4 − and Ce 3 O 6 − from deuteroxide (or deuteride) precursors is evocative of the bulk properties, whether the −OD groups remain as deuteroxyls or rearrange to form deuteride groups.…”

“…13,14,16 The reaction paths generally involve (1) formation of an electrostatic complex governed by local dipole−dipole interactions followed by (2) low-barrier formation of covalently bound intermediates featuring dihydroxide groups or hydride hydroxide groups, depending on the initial cluster−water complex formed: …”

Photoinduced conversion of carbon dioxide and water molecules to methanol on the surface of molybdenum oxide MoO x (x < 2)

“…The known mechanisms of adsorption of CO 2 and H 2 O molecules on the surface of oxides can be invoked as a possible explanation of the observed effect [4,5]. For example, it has been well established that the CO 2 molecule is adsorbed on the stoichiometric metal oxide surface to yield carbonate-like compounds via formation of bonds between an oxygen atom of the molecule and an oxygen atom of the substrate and between the carbon and the substrate metal.…”