Quasi-aromatic Möbius Metal Chelates.

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Polydentate ligands are crucial in designing coordination compounds with specific structures and properties.
• Understanding the electronic and structural characteristics of metal-organic complexes is key to developing new materials.

Purpose of the Study:

• To synthesize and characterize two new cadmium coordination compounds using novel polydentate ligands.
• To investigate the electronic structure and bonding nature of the chelate rings, classifying them as quasi-aromatic Möbius motifs.
• To explore the influence of ligand structure on coordination modes and intermolecular interactions.

Main Methods:

• Synthesis of cadmium coordination compounds using Cd(NO3)2·4H2O and benzilbis(pyridin-2-yl)methylidenehydrazone (L^I) or benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L^II) ligands with NH4NCS.
• Structural and spectroscopic characterizations.
• Application of computational methods including EDDB, HOMA index, and ETS-NOCV for electronic structure analysis.
• Investigation of optical properties using diffused reflectance spectroscopy and DFT/TD-DFT calculations.

Main Results:

• Two new cadmium coordination compounds, [Cd(SCN)(NCS)(L^I)(MeOH)] (1) and [Cd(NCS)₂(L^II)(MeOH)] (2), were successfully synthesized and characterized.
• The chelate rings containing Cd^II were identified as quasi-aromatic Möbius motifs using multiple computational methods.
• Ligand structure dictated the coordination of NCS^- and SCN^- ligands, with L^II leading to exclusive NCS^- coordination.
• The compounds are stabilized by hydrogen bonding, π-π stacking, and C-H···H-C interactions.
• Strong covalent bonding between monomers and significant stabilization by van der Waals dispersion forces were observed.

Conclusions:

• The study successfully designed and characterized novel cadmium coordination compounds with unique quasi-aromatic Möbius motifs.
• Ligand design offers control over coordination geometry and intermolecular interactions.
• The findings contribute to the understanding of aromaticity in coordination complexes and provide insights into their stabilization mechanisms and optical properties.