Evaluating Aromaticity in AgRu and AgRu as Electron-Precise Superatom Clusters.

Herein, the superatomic characteristics of the favorable global minima of electron precise clusters are evaluated, leading to stable species featuring catalytic reactive sites and inherent aromaticity in both planar and spherical realms. The results show that AgRu exhibits an electron-precise ten-electron 1S1P 1D planar superatomic electron shell structure, related to the 1S1P1D 18-electron structure of the spherical AgRu cluster, involving seven and ten reactive sites. The favorable electronic structure in such related clusters exhibits diatropic ring currents and long-range shielded regions, supporting the respective planar- and 3D aromatic character.

Planar Tetracoordinate Oxygen Atoms.

Planar tetracoordinate oxygen (ptO) atoms are rare, with only a few examples confirmed to date. This study systematically investigates 515 potential structures, formulated as OXY , where n+m=4, q ranging from +2 to -2, and following the 18-valence electron rule. High-level ab initio calculations identified 35 global minima containing a ptO atom, predominantly stabilized by Group 13 elements.

Planar tetracoordinate beryllium in σ-aromatic Li4Be and Na4Be clusters: A missing member in first-octal row planar tetracoordinate family.

While planar tetracoordinate (pt) centers have been extensively explored from carbon to other octal-row elements or their heavier analogs, their counterparts involving alkali (A) and alkaline-earth metals (Ae) remain elusive due to the large atomic radius and absence of p orbitals. In this work, we found six hitherto unknown anionic ptA (A4A-) and neutral ptAe (A4Ae) centers through an extensive exploration of potential energy surfaces. The D4h-symmetry ptBe structures in Li4Be and Na4Be emerge as the lowest-energy configurations, and all the other ptA/ptAe structures are higher in energy or saddle points.

H©CuH: a covalently bonded planar pentacoordinate hydrogen star.

A hydrocopper H©CuH star with planar pentacoordinate hydrogen (ppH) was designed. This structure is the global minimum, exhibiting dynamic stability. Its planar geometry is supported by five peripheral Cu-H-Cu 3c-2e σ-bonds and a central 6c-2e σ-bond.

Dicyclopenta[4,3,2,1-cde:4',3',2',1'-pqr]-peri-tetracene: Synthesis and an Example of Annulene-within-an-Annulene Aromaticity in Different Redox States.

We report a robust strategy for tuning the electronic structure and chemical stability of π-conjugated polycyclic hydrocarbons (PHs). By fusing two cyclopentadienyl rings in the peri-tetracene bay regions, we introduce antiaromatic character into the π-system, leading to unique photophysical and electronic properties. A stable mesityl-substituted dicyclopenta-peri-tetracene derivative was synthesized through stepwise formylation/intramolecular cyclization at the bay regions of the dihydro peri-tetracene precursor, followed by oxidative dehydrogenation.

Planar Pentacoordinate Halogens.

Planar hypercoordinate motifs represent an intriguing frontier in chemistry, challenging traditional bonding norms. As electronegativity of the central atom increases, achieving planar hypercoordination becomes more difficult due to restricted delocalization, making the design of planar hypercoordinate halogens particularly puzzling. Here, we conduct an extensive computational survey of LiX (n=4, 5, 6; X=F, Cl, Br, I) clusters, revealing a starlike D-symmetry global minimum in LiX (X=F, Cl, Br) with a planar pentacoordinate halogen (ppX), where X is located at the center of LiX crown.

Core-electron contributions to the magnetic response of molecules with heavy elements and their significance in aromaticity assessments.

This study delves into the magnetic response of core electrons and their influence on the global magnetic response of planar and three-dimensional systems containing heavy elements, employing the removing valence electron (RVE) approximation. We also explore electronic aromaticity indices to understand the potential role of core electrons on electron delocalization in the absence of an external perturbation. The study reveals that core electrons significantly contribute to the overall magnetic response, especially to the magnetic shielding, affecting the interpretation of aromaticity.

Understanding Aromaticity in [5]Helicene-Bridged Cyclophanes: A Comprehensive Study.

This study explores the aromaticity of doubly [5]helicene-bridged (1,4)cyclophane and triply [5]helicene-bridged (1,3,5)cyclophane via calculations of the magnetic response and of electronic aromaticity indices. The primary objective is to assess the π-electron delocalization to determine whether they sustain global ring currents associated with π aromaticity. The molecules show local ring currents in the presence of an external magnetic field.

Exploring the Aromaticity Differences of Isoelectronic Species of Cyclo[18]carbon (C), BCN, and BN: The Role of Carbon Atoms as Connecting Bridges.

The cyclo[18]carbon (C) has piqued widespread interest in recent years for its geometrical aesthetic and unique electronic structure. Inspired by it, theoretical investigations of its isoelectronic BN have been published occasionally; however, few studies considered their other companion BCN. In this work, we study the geometric structure, charge distribution, bonding characteristic, aromaticity, and electron delocalization of BCN and BN for the first time and compare the relevant results with those of C.

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 computations reveal that the global minimum of a series of interalkali and interalkali-alkaline earth clusters (LiNa, LiMg, NaMg, KCa, CaRb, RbSr, and SrCs) adopts a singlet structure with a planar pentacoordinate lithium or alkaline earth metal (AE = Mg, Ca, Sr).

Correction: Structure and bonding of molecular stirrers with formula BM and BM (M = Zn, Cd, Hg).

Correction for 'Structure and bonding of molecular stirrers with formula BM and BM (M = Zn, Cd, Hg)' by Rui Yu , , 2020, , 12312-12320, https://doi.org/10.1039/D0CP01603A.

The magnetically induced current density of the [12]infinitene dianion.

The magnetically induced current-density susceptibility (MICD) of the [12]infinitene dianion and the induced magnetic field around it have been calculated at the density functional theory level. Separation of the MICD into diatropic and paratropic contributions shows that the MICD is dominated by the diatropic contribution in contrast to the notion that it is antiaromatic, which was reported in a recently published article. The MICD of the [12]infinitene dianion exhibits several through-space MICD pathways, whereas it sustains only weak local paratropic current-density contributions.

On the antiaromatic-aromatic-antiaromatic transition of the stacked cyclobutadiene dimer.

We have studied the changes in the aromatic nature of two cyclobutadiene (CH) molecules on decreasing the intermolecular distance and approaching the cubane structure in a face-to-face fashion. The analysis based on the calculations of the magnetically induced current density and the induced magnetic field shows that the aromaticity of the two CH rings changes from a strongly antiaromatic character at long distances to an aromatic transition state of stacked CH rings at intermediate internuclear distances when approaching the antiaromatic state of cubane.

CAl: a molecular rotor with a quasi-planar tetracoordinate carbon.

In this work, we analyzed the bonding and fluxional character of the global minimum of CAl. Its structure is formed by two stacked layers, one of them resembles the well-known planar tetracoordinate carbon CAl on top of a hexagonal Al@Al wheel. Our results show that the CAl fragment rotates freely around the central axis.

Electronic Structure and Aromaticity of an Unusual Cyclo[18]carbon Precursor, C Br.

Herein, the electronic structure and bonding character of the stable cyclo[18]carbon (C ) precursor, C Br , are thoroughly characterized by molecular orbital (MO), density of states (DOS), bond order (BO), and interaction region indicator (IRI) analyses. The delocalization characters of out-of-plane and in-plane π-electrons (labeled as π - and π -electrons, respectively) in bonding regions were examined using localized orbital locator (LOL) and electron localization function (ELF). The aromaticity was investigated, studying the molecular magnetic response to external magnetic field by computing the magnetically induced current density (J ), iso-chemical shielding surface (ICSS), anisotropy of the induced current density (AICD), and the induced magnetic field (B ).

BAl: A Three-Dimensional Molecular Reuleaux Triangle.

We systematically explore the potential energy surface of the BAl combination of atoms. The putative global minimum corresponds to a structure formed by an Al square facing a B triangle. Interestingly, the dynamical behavior can be described as a Reuleaux molecular triangle since it involves the rotation of the B triangle at the top of the Al square.

Magnetic response properties of carbon nano-onions.

The magnetic response of a number of double- and triple-layer carbon nano-onions (CNOs) is analyzed by calculating the magnetically induced current density and the induced magnetic field using the pseudo-π model. Qualitatively the same magnetic response was obtained in calculations at the all-electron level. The calculations show that the CNOs exhibit strong net diatropic (paratropic) ring currents when the external magnetic field points perpendicularly to one of the six-membered (five-membered) rings.

Core-electron contributions to the molecular magnetic response.

Orbital contributions to the magnetic response depend on the method used to compute them. Here, we show that dissecting nuclear magnetic shielding tensors using natural localized molecular orbitals (NLMOs) leads to anomalous core contributions. The arbitrariness of the assignment might significantly affect the interpretation of the magnetic response of nonplanar molecules such as C or [14]helicene and the assessment of their aromatic character.

Non-intersecting ring currents in [12]infinitene.

The aromaticity of the newly synthesized [12]infinitene is addressed via analysis of the magnetically induced current density and the induced magnetic field. Our calculations reveal that [12]infinitene responds to an external magnetic field by creating two current-density pathways that flow diatropically along the edges of the molecule. The current-density pathways do not intersect.

Magnetically Induced Ring-Current Strengths of Planar and Nonplanar Molecules: New Insights from the Pseudo-π Model.

The pseudo-π model yields current densities and induced magnetic fields that mimic the π-component, allowing investigations of large molecular structures, whether they are planar or not, at a low computational cost but with high accuracy. Herein the π-contribution to the magnetically induced current densities and induced magnetic fields of large planar molecules and nonplanar molecules (such as [10]cyclophenacene and chiral toroidal nanotubes C and C) were computed using the pseudo-π model with the gauge-including magnetically induced currents method. Additionally, we provide a way to determine the π-component of the ring-current strengths, which can be used for assessing the aromatic character of large carbon molecules.

Planar tetracoordinate fluorine atoms.

Among the list of planar tetracoordinate atoms, fluorine is missing. So far, there are no theoretical or experimental reports suggesting their existence. Herein, we introduce the first six combinations (FIn , FTl , FGaIn , FInTl , FInTl, and FInTl ) whose global minima contain a planar tetracoordinate fluorine.

Planar Tetracoordinate Carbons in Allene-Type Structures.

The exhaustive exploration of the potential energy surfaces of CEM (E = Si-Pb; M = Li and Na) revealed seven global minima containing a planar tetracoordinate carbon (ptC). The design, based on a π-localization strategy, resulted in a ptC with two double bonds forming a linear or a bent allene-type E═C═E motif. The magnetic response of the bent E═C═E fragments support a σ-aromaticity.

Planar pentacoordinate silicon and germanium atoms.

The global minimum of XMgY (X = Si, Ge; Y = In, Tl) and SiMgIn contains a planar pentacoordinate atom of group 14 other than carbon. Its design is based on the "localization" approach, replacing one or two peripheral atoms in XMg by more electronegative ones. This change diminishes the repulsion and leads to stronger covalent X-Y bonds, stabilizing the planar pentacoordinate atom species.

Delocalization in Substituted Benzene Dications: A Magnetic Point of View.

In this work, the induced magnetic field is analyzed for a series of substituted benzenes dications with formula CR (R=I, At, SeH, SeCH, TeH, TeCH), presumably exhibiting concentric aromaticity. Previous studies concluded that in the carbon skeleton, just π-electrons are delocalized. However, our results support that both the σ- and π-electrons are delocalized in the carbon skeleton, combined with a σ-delocalization in the external ring.