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When (4n +2) π-electrons are located in single planar ring, it conventionally qualifies as aromatic. According Hückel's rule, systems possessing ten π-electrons should be aromatic. Herein we report a series of D 5h  Li 6 E 5 Li 6 sandwich structures, representing the first global minima featuring ten π-electrons E 5 10- ring (E=Si-Pb). However, these π-electrons localize as five π-lone-pairs rather than delocalized orbitals. The high symmetry structure achieved is a direct consequence of σ-aromaticity, particularly favored in elements from Si to Pb, resulting in a pronounced diatropic ring current flow that contributes to the enhanced stability of these systems., (© 2023 Wiley-VCH GmbH.)

After exploring the potential energy surfaces of M m CE 2 p (E=S-Te, M=Li-Cs, m=2, 3 and p=m-2) and M n CE 3 q (E=S-Te, M=Li-Cs, n=1, 2, q=n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE 2 2- and Y-shaped CE 3 2- dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals., (© 2021 Wiley-VCH GmbH.)

Herein, the first global minima containing a planar hexacoordinate carbon (phC) atom are reported. The fifteen structures belong to the CE 3 M 3 + (E=S-Te and M=Li-Cs) series and satisfy both geometric and electronic criteria to be considered as a true phC. The design strategy consisted of replacing oxygen in the D 3h  CO 3 Li 3 + structure with heavy and less electronegative chalcogens, inducing a negative charge on the C atom and an attractive electrostatic interaction between C and the alkali-metal cations. The chemical bonding analyses indicate that carbon is covalently bonded to three chalcogens and ionically connected to the three alkali metals., (© 2021 Wiley-VCH GmbH.)

Extensive explorations of their potential energy surfaces, combined with high-level quantum chemical computations, strikingly show that the lowest energy structures of the (Li 6 Si 5 ) 2-5 systems consist of 2-5 Si 5 6- aromatic units, surrounded by Li + counterions, respectively. These viable gas-phase compounds are the pioneering reported cases of oligomers made by planar aromatic silicon rings. Based on the key evidence that these oligomers are energetically favored, and that their silicon rings aromaticity is thoroughly preserved, the Li 6 Si 5 cluster is proposed as a potential assembly unit to build silicon-lithium nanostructures, thus opening new paths to design Zintl compounds at the nanoscale level., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein we report the systematic exploration of the potential energy surfaces of a series of clusters with formula E 5 M 7 + (E=C-Pb and M=Li-Cs). Fifteen of these combinations adopt a D 5h three-dimensional seven-pointed star-like structure in a singlet state, where M atoms interact electrostatically with the E 5 ring. The determining factors in the relative preference of having the D 5h structure over the most competitive isomer or vice-versa are analyzed. These star-shaped systems satisfy the 4n+2 Hückel's rule and exhibit a strong diatropic (σ and π) response to an external magnetic field., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An intriguing structural transition from the quasi-planar form of B 12 cluster upon the interaction with lithium atoms is reported. High-level computations show that the lowest energy structures of LiB 12 , Li 2 B 12 , and Li 3 B 12 have quasi-planar (C s ), tubular (D 6d ), and cage-like (C s ) geometries, respectively. The energetic cost of distorting the B 12 quasi-planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage-like B 12 fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li 2 B 12 ) and cage-like (Li 3 B 12 ) boron structures reported to date., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two low-lying structures are unveiled for the Be 6 B 11 - nanocluster system that are virtually isoenergetic. The first, triple-layered cluster has a peripheral B 11 ring as central layer, being sandwiched by two Be 3 rings in a coaxial fashion, albeit with no discernible interlayer Be-Be bonding. The B 11 ring revolves like a flexible chain even at room temperature, gliding freely around the Be 6 prism. At elevated temperatures (1000 K), the Be 6 core itself also rotates; that is, two Be 3 rings undergo relative rotation or twisting with respect to each other. Bonding analyses suggest four-fold (π and σ) aromaticity, offering a dilute and fluxional electron cloud that lubricates the dynamics. The second, helix-type cluster contains a B 11 helical skeleton encompassing a distorted Be 6 prism. It is chiral and is the first nanosystem with a boron helix. Molecular dynamics also shows that at high temperature the helix cluster readily converts into the triple-layered one., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)