Issue 33, 2023

Planar pentacoordinate s-block metals


The presence of a delocalized π-bond is often considered an essential criterion for achieving planar hypercoordination. Herein, we show that σ-delocalization could be sufficient to make the planar configuration the most stable isomer in a series of planar pentacoordinate s-block metals. High-level ab initio computations reveal that the global minimum of a series of interalkali and interalkali-alkaline earth clusters (LiNa5, Li5Mg+, Na5Mg+, K5Ca+, CaRb5+, Rb5Sr+, and SrCs5+) adopts a singlet D5h structure with a planar pentacoordinate lithium or alkaline earth metal (AE = Mg, Ca, Sr). These clusters are unusual combinations to stabilize a planar pentacoordinate atom, as all their constituents are electropositive. Despite the absence of π-electrons, Hückel's rule is fulfilled by the six σ-electrons. Furthermore, the systems exhibit a diatropic ring current in response to an external magnetic field and a strong magnetic shielding, so they might be classified as σ-aromatic. Therefore, multicenter σ-bonds and the resulting σ-delocalization stabilize these clusters, even though they lack π-aromaticity.

Graphical abstract: Planar pentacoordinate s-block metals

Supplementary files

Article information

Article type
Edge Article
27 Oct 2022
14 Jul 2023
First published
14 Jul 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2023,14, 8785-8791

Planar pentacoordinate s-block metals

M. Wang, A. J. Kalita, M. Orozco-Ic, G. Yan, C. Chen, B. Yan, G. Castillo-Toraya, W. Tiznado, A. K. Guha, S. Pan, G. Merino and Z. Cui, Chem. Sci., 2023, 14, 8785 DOI: 10.1039/D2SC05939H

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