Octa-coordinated alkaline earth metal-dinitrogen complexes M(N₂)₈ (M=Ca, Sr, Ba).

Area of Science:

• Inorganic Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Alkaline earth metals (Ca, Sr, Ba) are typically electropositive and form ionic compounds.
• Dinitrogen (N2) is a stable molecule with a strong triple bond, making its coordination challenging.
• Understanding metal-ligand bonding is crucial for designing new materials and catalysts.

Purpose of the Study:

• To isolate and characterize novel alkaline earth metal-dinitrogen complexes.
• To investigate the electronic structure and bonding nature of these complexes.
• To explore the potential for these complexes to obey the 18-electron rule.

Main Methods:

• Isolation of complexes in a low-temperature neon matrix.
• Spectroscopic identification using vibrational and electronic spectroscopy.
• Computational analysis of electronic structure and bonding.

Main Results:

• Successful isolation and identification of eight-coordinated M(N2)8 (M=Ca, Sr, Ba) complexes with cubic symmetry.
• Electronic structure analysis revealed dominant [M(dπ)]→(N2)8 π backdonation.
• Observed large red-shift in N-N stretching frequencies and triplet electronic ground state (3A1g).
• Complexes exhibit bonding features consistent with the 18-electron rule.
• Isolation and bonding analysis of charged complexes [M(N2)8]+ (M=Ca, Sr) were also reported.

Conclusions:

• Alkaline earth metals can form stable, eight-coordinated dinitrogen complexes.
• The bonding is characterized by significant π backdonation, similar to transition metal complexes.
• These findings expand the known coordination chemistry of dinitrogen and alkaline earth metals.