All-Metal Aromaticity: Revisiting the Ring Current Model among Transition Metal Clusters

Abstract

We present new insight into the nature of aromaticity in metal clusters. We give computational arguments in favor of using the ring-current model over local indices, such as nucleus independent chemical shifts, for the determination of the magnetic aromaticity. Two approaches for estimating magnetically induced ring currents are employed for this purpose, one based on the quantum theory of atoms in molecules (QTAIM) and the other where magnetically induced current densities (MICD) are explicitly calculated. We show that the two-zone aromaticity/antiaromaticity of a number of 3d metallic clusters (Sc3(-), Cu3(+), and Cu4(2-)) can be explained using the QTAIM-based magnetizabilities. The reliability of the calculated atomic and bond magnetizabilities of the metallic clusters are verified by comparison with MICD computed at the multiconfiguration self-consistent field (MCSCF) and density functional levels of theory. Integrated MCSCF current strength susceptibilities as well as a visual analysis of the calculated current densities confirm the interpretations based on the QTAIM magnetizabilities. In view of the new findings, we suggest a simple explanation based on classical electromagnetic theory to explain the anomalous magnetic shielding in different transition metal clusters. Our results suggest that the nature of magnetic aromaticity/antiaromaticity in transition-metal clusters should be assessed more carefully based on global indices.

Information on Gas‐Phase Diatomic Molecules from Magnetically Induced Current Densities

“…[50] Similarly, Badri et al have reviewed the ring current model in all-metal clusters and they found that in the Sc 2 3 cluster a multireference study is necessary. [51] Conversely, the MICD module in DIRAC is not programmed to treat multireference ground states and, therefore, the present study utilized the same approach as for the other molecules. This may be responsible for some of the complications of the current patterns.…”

“…Thus, it is expected that the "natural" direction of the current flow around atomic centers in molecules be diatropic. In the study by Badri et al, the Sc 2 3 and Cu 1 3 clusters were analyzed [51] and they found that the Sc 2 3 cluster presents strong local paratropic currents around the Sc nuclei, whereas the currents around the Cu nuclei in Cu 1 3 are diatropic. In another study, the aromaticity of the series of square clusters M 22 4 ðM5B; Al; Ga; In; TlÞ was calculated by Alvarez-Thon and Caimanque.…”

Recent developments and future prospects of all-metal aromatic compounds

“…Although it should be taken with caution (see ref. 101 and 102), ) clusters are very reactive towards H 2 , HX (X = F, Cl, Br, and I), O 2 and N 2 . However, both clusters retain their structural integrity upon reaction.…”

El lado químico de los cúmulos moleculares

“…cúmulos de Cu (Badri & Pathak, 2013), o de Au con alta nuclearidad (Au 309 ), que permitan tener propiedades de superconducción (Wuelfin & Green, 2000) y que podrían ser muy útiles para el desarrollo tecnológico actual.…”