The first binuclear sandwich-like complexes based on the aromatic tetraatomic species

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Materials Science

Background:

• Binuclear sandwich-like complexes offer unique structural and electronic properties.
• Aromatic tetraatomic species (E4) present opportunities for novel ligand design.
• Understanding metal-metal bonding and metal-ligand interactions is crucial for predicting stability and reactivity.

Purpose of the Study:

• To investigate the structural, electronic, and bonding properties of novel M(2)(η(4)-E(4))(2) complexes (M = Al, Ga; E = N, P, As).
• To assess the stability and potential synthetic feasibility of these complexes.
• To explore their potential applications, particularly as high energy density materials (HEDMs).

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study the complexes.
• Natural Bonding Orbital (NBO) analysis was used to investigate bonding characteristics.
• Molecular Orbital (MO) analysis elucidated the nature of metal-metal bonds.
• Nucleus-Independent Chemical Shift (NICS) calculations assessed aromaticity.

Main Results:

• Stable staggered conformers were identified for most complexes, with a C(2v) exception for Ga(2)(η(2)-N(4))(2).
• Strong sigma (σ) single bonds were found between metal atoms (Al-Al, Ga-Ga), primarily from s and pz orbitals.
• Metal-ligand interactions were predominantly covalent for M(2)(η(4)-E(4))(2) (E = P, As), and ionic for Al(2)(η(4)-N(4))(2).
• The E(4)(2-) ligands exhibited conflicting aromaticity (σ antiaromaticity, π aromaticity), with greater aromaticity in Ga complexes compared to Al.

Conclusions:

• The calculated strong metal-metal bonds suggest that these novel Al(2)(η(4)-E(4))(2) and Ga(2)(η(4)-E(4))(2) complexes are potentially synthesizable.
• Nitrogen-rich compounds like Al(2)(η(4)-N(4))(2) and Ga(2)(η(2)-N(4))(2) show promise as high energy density materials (HEDMs).
• The study provides fundamental insights into the bonding and aromaticity of these unique binuclear sandwich complexes.