Issue 33, 2023

Planar pentacoordinate s-block metals

Abstract

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
Submitted
27 10 2022
Accepted
14 7 2023
First published
14 7 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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