Synthesis, structures and DFT calculations on alkaline-Earth metal azide-crown ether complexes

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Crown ethers are cyclic polyethers known for their ability to selectively bind metal cations.
• Azide ligands (N3-) are versatile anions with diverse coordination behaviors in metal complexes.
• Alkaline-earth metal azides are less explored compared to alkali metal counterparts.

Purpose of the Study:

• To synthesize and characterize novel azide complexes of calcium, strontium, and barium featuring crown ether ligands.
• To investigate the coordination modes of azide groups and the structural features of these complexes.
• To explore the nature of the metal-azide bond and compare experimental findings with theoretical calculations.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Density Functional Theory (DFT) calculations for molecular structure comparison and electronic analysis.
• Spectroscopic characterization (implied, though not explicitly stated).

Main Results:

• Successful synthesis and characterization of four new alkaline-earth metal azide-crown ether complexes.
• Identification of various azide coordination modes (kappa 1-, mu-1,3-, H-bonded linkages).
• Discovery of a dinuclear barium complex with three mu-1,3-NNN bridges, a first in main group chemistry.
• Analysis of metal-azide bond lengths and charge densities, suggesting predominantly ionic or ion-dipole bonding.

Conclusions:

• The study expands the known chemistry of alkaline-earth metal azides by incorporating crown ether ligands.
• The structural diversity and bonding characteristics provide insights into the coordination preferences of these metal ions.
• DFT calculations aid in understanding the interplay between crystal lattice effects and intrinsic bonding properties.