Decomposition of CH2O by lanthanum: a theoretical study

Area of Science:

• Inorganic Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Lanthanum and yttrium are Group III elements with similar chemical properties.
• Formaldehyde is a simple organic molecule that can undergo various reactions with metal atoms.
• Understanding reaction mechanisms is crucial for predicting chemical behavior and designing new materials.

Purpose of the Study:

• To investigate the gas-phase reaction mechanism between lanthanum and formaldehyde.
• To compare the reaction pathways with those of yttrium and formaldehyde.
• To explore the influence of electronic states and computational methods on the reaction outcomes.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Coupled Cluster (CC) calculations, specifically CCSD(T).
• Estimation of potential energy surface (PES) crossing regions.

Main Results:

• The minimum energy pathway involves eta2-formaldehyde-metal complex formation followed by two C-H insertions, yielding metal dihydrides and carbon monoxide.
• A competing pathway produces a metal-carbonyl compound and hydrogen, requiring a spin conversion from doublet to quartet state.
• BP86 and CCSD(T) methods show qualitative agreement on the mechanism, though BP86 overestimates binding energies for d-rich compounds.

Conclusions:

• The reaction mechanism of La with formaldehyde is similar to Y with formaldehyde, proceeding through C-H insertions.
• Spin state plays a critical role in the formation of metal-carbonyl compounds.
• An electronic promotion effect ((n-1)d1ns2 to (n-1)d2ns1) is proposed to explain differences in metal-carbonyl formation across rare earth elements.