Chemical bonding and aromaticity in trinuclear transition-metal halide clusters.

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Materials Science

Background:

• Trinuclear transition-metal halide clusters, exemplified by Re(3)X(9), possess unique structures that raise questions about multicenter electron delocalization.
• Previous studies on rhenium complexes have highlighted the complexity of electron distribution in such systems.

Purpose of the Study:

• To investigate the chemical bonding and aromaticity of technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I).
• To compare the electronic properties of technetium clusters with their known rhenium counterparts.
• To evaluate the accuracy of different theoretical methods in predicting cluster aromaticity.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to predict the structures and electronic properties of technetium halide clusters.
• The Adaptive Natural Density Partitioning (ANDP) method was utilized for detailed analysis of chemical bonding and electron delocalization.
• Comparison with the Nucleus-Independent Chemical Shift (NICS) concept was performed to assess prediction accuracy.

Main Results:

• The study identified [Tc(3)X(9)](2-) clusters as isomorphous to rhenium congeners.
• Adaptive Natural Density Partitioning revealed that only the dianionic [Tc(3)X(9)](2-) clusters exhibit aromatic character.
• Aromaticity in these dianionic clusters originates from a d-orbital-based π bond delocalized across the three technetium centers.

Conclusions:

• Technetium halide clusters display distinct electronic properties compared to rhenium analogs, particularly regarding aromaticity.
• The dianionic [Tc(3)X(9)](2-) species are predicted to be aromatic due to multicenter π bonding.
• Standard NICS calculations incorrectly predict aromaticity for neutral Tc(3)X(9) clusters, highlighting the importance of advanced methods like ANDP.