Planar pentacoordinate s-block metals
Menghui Wang, Amlan J. Kalita, Mesías Orozco‐Ic, Gai-ru Yan, Chen Chen, Bing Yan, Gabriela Castillo-Toraya, William Tiznado, Ankur K. Guha, Sudip Pan, Gabriel Merino, Zhong‐hua Cui
Abstract
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.