Project content

Question 1

How are the HAT enthalpies calculated?

Answer 1

• For that, the electronic reaction energy is obtained, which is defined as the energy difference calculated from the electronic structures of the reactants and products, which can be represented mathematically as: ∆E_reaction = E_products – E_reactants
• The choice of basis set is critical, as larger basis sets (e.g., triple-zeta or quadruple-zeta) generally yield more accurate results. The acceptable error for reaction energy calculations is typically around 1-2 kcal/mol.

Question 2

What is the correlation between the energy position of the σ* transition, and the assignement of a superoxide vs. peroxide for the O2 unit.

Answer 2

• The energy of the σ* transition is inversily proportional to the O-O bond length → as we add electrons to the π* HOMO of O2, we weaken the bond(decrease the bond order), i.e., increase bond length, i.e., decrease the E(σ), therefore
  E(σ, O₂) > E(σ, O₂^-) > E(σ, O₂^2-)
• Typical values pf bond lengths are:
  1.21 Å for molecular O₂ → E(σ) ⁓540.5 eV
  1.34 Å for O₂^-
  1.49 Å for O₂^2- → E(σ) ⁓533 eV
• Dependence of E(σ*) on bond length, R, is better described by a linear (∝R) or inversely quadratic (∝1/R²) relationship (respectively solid and dashed lines in figure b).

Question 3

What are the enthalpies of hydrogen atom transfer from methane calculated for your oxygen-centered radical systems? How do they compare to symilar systems in literature?

Answer 3

Our calculated HAT from CH4 in - kJ/mol:
[RuO4]+: 73
[ReO4]+: 110 (literature: 115.5)
[ReO4H]+: 100 (literature: 157.5)

Other similar systems from literature:
[OsO4]+: 85
[TiO2]+: > 62.8
[ZrO2]+: > 62.8
[CuO]+: 30
[TaO3]+: 163.3
[AuO]+: 5.8
[FeO]+: 9.6
[MnO]+: 50
[CaO]+: 111

Further
[Al8O12]+: 91
[MgO]+: 120.4
[P4O11]+: 127
La2O3[001]: 205

Question 4

What is the average M-O bond length for oxo, oxyl, peroxo and superoxo ligands? What about hydroxo ligands?

Answer 4

M–O^2-: 1.66 Å
M–O^*-: 1.75 Å
M–(O₂): 1.87 Å
M–OH: 1.80 Å

Question 5

Why there is a significan blue shift at the absorption energy of the rhenium N3 edge between [ReO3]+, [ReO4]+, [ReO4H]+ and [ReO4H2]+, if the oxidation state of rhenium stays constant?

Answer 5

Possible explanations:
* Addition of one further oxygen ligand from [ReO3]+ to [ReO4]+ causes more delocalization of the electrons torwards the ligands, and we are increasing the number of highly electronegative ligands.
* The M–OH bond (1.80 Å) is slightly longer than the M–O* bond (1.75 Å), which might also cause the atraction of electrons torwards the ligands.
* The absorption energy is also affected by other effects (such as final states effects) and the dependence with the oxidation state is not necessarily linear.

Question 6

Give examples of applications of rhodium oxides.

Answer 6

• The very first industrial application of rhodium was in a heterogeneous catalyst of a Pt—Rh net for the production of nitric acid by catalytic oxidation of ammonia
• The current primary use of rhodium is in catalytic converters for vehicles, where it helps reduce harmful nitrogen oxides in exhaust gases, a crucial application for controlling air pollution
• Its oxides, such as sesquioxidorhodium(III), Rh2O3, and dioxidorhodium(IV), RhO2, are stable and have applications in catalysis and in chemical synthesis
• Our predicted vertical electron affinity of [RhO3]+, which is **10.6 eV ** and 11.1 eV at the CCSD(T) and B3LYP levels, respectively, is higher than 9.59 eV for [NO2]+ but significantly lower than 12.07 eV for [O2]+. Since [O2]+ is stabilized by weakly coordinating anions like [PtF6]−, [BF4]−, or [AsF6]−, it might be possible to also stabilize [RhO3]+, based on its electron affinity

Question 7

Give examples of applications of ruthenium oxides.

Answer 7

• Ruthenium acts as a versatile catalyst in various industrial processes, including in Fischer-Tropsch synthesis, which converts carbon monoxide and hydrogen into liquid fuels

Question 8

Give examples of applications of rhenium oxides.

Answer 8

• Rhenium is widely used in, petrochemistry, organic synthesis and polymerization, mainly in metathesis reactions
• its highest possible oxidation state is the most stable, and the rhenium(VII) oxide Re2O7 finds many appplications, e.g., in Friedel-Crafts alkylation and in catalytic oxidations