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. The ring currents flow diatropically in the stacked six-membered rings and in the helicene arms. However, these π currents are not interconnected due to the discontinuity of the π delocalization at the C-C single bonds connecting the central six-membered rings to the helicene arms. Electronic indices suggest that the helicene-arm systems have significantly smaller electron delocalization than benzene. The reduction in the delocalization does not compromise their ability to exhibit ring currents in the presence of an external magnetic field. The analysis provides further evidence that the magnetic criteria yield a different degree of aromaticity for the helicene arms than obtained in the calculation of the electronic aromaticity indices. However, both approaches confirm that the studied molecules are not globally aromatic.

Exploring the Aromaticity Differences of Isoelectronic Species of Cyclo[18]carbon (C18), B6C6N6, and B9N9: The Role of Carbon Atoms as Connecting Bridges.

The cyclo[18]carbon (C18) has piqued widespread interest in recent years for its geometrical aesthetic and unique electronic structure. Inspired by it, theoretical investigations of its isoelectronic B9N9 have been published occasionally; however, few studies considered their other companion B6C6N6. In this work, we study the geometric structure, charge distribution, bonding characteristic, aromaticity, and electron delocalization of B6C6N6 and B9N9 for the first time and compare the relevant results with those of C18. Based on the comprehensive analysis of aromaticity indicators such as AV1245, nucleus-independent chemical shifts, anisotropy of the induced current density, magnetically induced current density, iso-chemical shielding surface, and induced magnetic field (Bind), we found that B6C6N6 has definitely a double aromatic character similar to C18 and the aromaticities of the two are very close, while B9N9 is a nonaromatic species. In response to this novel finding, we delved into its nature from an electron delocalization perspective through a localized orbital locator, electron localization function, Fermi hole, and atomic remote delocalization index analyses. The C atom between B and N as an interconnecting bridge strengthens the electron delocalization of the conjugate path, which is the essence of the significant enhancement of the molecular aromaticity from B9N9 to B6C6N6. This work elucidates that within the framework of the isoelectronicity of C18, different methods of atomic doping can achieve molecules with completely different properties.

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.

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. We identified four main current-density pathways of which two are similar to the ones for neutral [12]infinitene. It is difficult to judge from calculations of the nucleus independent shielding constants and the induced magnetic field around the [12]infinitene dianion whether it sustains diatropic or paratropic ring currents.

Correction: Structure and bonding of molecular stirrers with formula B7M2- and B8M2 (M = Zn, Cd, Hg).

Correction for 'Structure and bonding of molecular stirrers with formula B7M2- and B8M2 (M = Zn, Cd, Hg)' by Rui Yu et al., Phys. Chem. Chem. Phys., 2020, 22, 12312-12320, https://doi.org/10.1039/D0CP01603A.

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

We have studied the changes in the aromatic nature of two cyclobutadiene (C4H4) 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 C4H4 rings changes from a strongly antiaromatic character at long distances to an aromatic transition state of stacked C4H4 rings at intermediate internuclear distances when approaching the antiaromatic state of cubane.

CAl11-: a molecular rotor with a quasi-planar tetracoordinate carbon.

In this work, we analyzed the bonding and fluxional character of the global minimum of CAl11-. Its structure is formed by two stacked layers, one of them resembles the well-known planar tetracoordinate carbon CAl4 on top of a hexagonal Al@Al6 wheel. Our results show that the CAl4 fragment rotates freely around the central axis. The exceptional stability and fluxionality of CAl11- derive from its particular electron distribution.

Electronic Structure and Aromaticity of an Unusual Cyclo[18]carbon Precursor, C18 Br6.

Herein, the electronic structure and bonding character of the stable cyclo[18]carbon (C18 ) precursor, C18 Br6 , 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 πout - and πin -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 (Jind ), iso-chemical shielding surface (ICSS), anisotropy of the induced current density (AICD), and the induced magnetic field (Bind ). All these analyses indicate that C18 Br6 is a globally aromatic species with lower aromaticity than C18 , and the blocking of in-plane π-conjugation (labeled as πin -conjugation) by the presence of -Br substituents in it is the underlying cause for the weakening of molecular aromaticity.

B3Al4+: A Three-Dimensional Molecular Reuleaux Triangle.

We systematically explore the potential energy surface of the B3Al4+ combination of atoms. The putative global minimum corresponds to a structure formed by an Al4 square facing a B3 triangle. Interestingly, the dynamical behavior can be described as a Reuleaux molecular triangle since it involves the rotation of the B3 triangle at the top of the Al4 square. The molecular dynamics simulations, corroborating with the very small rotational barriers of the B3 triangle, show its nearly free rotation on the Al4 ring, confirming the fluxional character of the cluster. Moreover, while the chemical bonding analysis suggests that the multicenter interaction between the two fragments determines its fluxionality, the magnetic response analysis reveals this cluster as a true and fully three-dimensional aromatic system.

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. They are deshielded inside and shielded outside the CNO; the latter dominates for larger CNOs. The magnetic response originates from a combination of spherical paratropic current densities on the inside of each carbon layer and diatropic current densities on the outside of them. The quantitative differences in the aromaticity of the CNOs as compared to single fullerenes are discussed in terms of ring-current strengths. The magnetic response of some of the CNOs is approximately the sum of the magnetic response of the individual layers, whereas deviations are significant for CNOs containing C80. For the largest CNOs, the deviation from the sum of the fullerene contributions is larger, especially when the external magnetic field is perpendicular to a six-membered ring.

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 C60 or [14]helicene and the assessment of their aromatic character. We solve this problem by computing the core- and σ-components of the induced magnetic field (and NICS) and the magnetically induced current density by removing the valence electrons (RVE). We estimate the core contributions to the magnetic response by performing calculations on the corresponding highly charged molecules, such as C6H630+ for benzene, using gauge-including atomic orbitals and canonical molecular orbitals (CMOs). The orbital contributions to nuclear magnetic shielding tensors are usually estimated by employing a natural chemical shielding (NCS) analysis in NLMO or CMO bases. The RVE approach shows that the core contribution to the magnetic response is small and localized at the nuclei, contrary to what NCS calculations suggest. This may lead to a completely incorrect interpretation of the magnetic σ-orbital response of nonplanar structures, which may play a major role in the overall magnetic shielding of the system. The RVE approach is thus a simple and inexpensive way to determine the magnetic response of the core- and σ-electrons.

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. The entire structure is completely shielded suggesting that the infinitene molecule is aromatic, contrary to what the Möbius rule for twisted annulene structures predicts. We also studied the dication of [12]infinitene, which sustains two paratropic ring currents flowing along the edges. The space between the stacked rings at the crossing point is shorter for the dication as compared to the neutral molecule. Hence, a strong through-space current density appears at the crossing point of π-π stacked rings.

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 C2016 and C2196) 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 (FIn4 +, FTl4 +, FGaIn3 +, FIn2Tl2 +, FIn3Tl+, and FInTl3 +) whose global minima contain a planar tetracoordinate fluorine. The bonding analyses indicate that the interactions between the fluorine and the peripheral atoms are significantly electrostatic, which is also reflected in the electronic delocalization. As opposed to other planar tetracoordinate systems with carbon, nitrogen, or oxygen atoms, the fluorine in the ptFs does not act as a σ-acceptor, restraining any back-donation. On the other hand, σ-electrons show a diatropic response, which would characterize these clusters as σ-aromatic.

Planar Tetracoordinate Carbons in Allene-Type Structures.

The exhaustive exploration of the potential energy surfaces of CE2M2 (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. The bonding analysis indicated that the ptCs form C-E covalent bonds and C-M electrostatic interactions.

Planar pentacoordinate silicon and germanium atoms.

The global minimum of XMg4Y- (X = Si, Ge; Y = In, Tl) and SiMg3In2 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 XMg52- 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 C6R62+ (R=I, At, SeH, SeCH3, TeH, TeCH3), 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. The role of the relativistic effects in these dications is discussed in detail.

Structure and bonding of molecular stirrers with formula B7M2- and B8M2 (M = Zn, Cd, Hg).

In this work, we systematically explored clusters with formula B7M2- and B8M2 (M = Zn, Cd, Hg). The putative global minima are formed by an M2 dimer and a disk-shaped boron wheel. Moreover, the chemical bonding analysis revealed that charge transfer from the metal atoms to the boron motifs resulted in (B7)3-(M2)2+ and (B8)2-(M2)2+ complexes with double (σ + π) aromatic boron wheels and a single bond for the metallic dimer. Above all, the computed rotational barriers of the M-M fragment with respect to the boron disk and molecular dynamics simulations indicate a virtually barrierless spin, resembling a magnetic stirrer on a baseplate.

A method for designing a novel class of gold-containing molecules.

We propose a novel class of gold-containing molecules, which have been designed using conjugated carbon structures as templates. The sp-hybridized carbons of C2 moieties are replaced with a gold atom and one of the adjacent carbons is replaced by nitrogen. Applying the procedure to hexadehydro[12]annulene yields the well-known cyclic trinuclear gold(i) carbeniate complex. Planar, tubular and cage-shaped complexes can be obtained by taking similar sp-hybridized carbon structures as the starting point.

Percepción de los gerentes y directivos de las IPS públicas del Área Metropolitana del Valle de Aburrá sobre los convenios docencia - servicio en salud / Perception that managers and executives from the public IPS in the Metropolitan Area of Aburrá Valley have of health service - teaching agreements / Percepção dos gerentes e diretivos das IPS públicas da Área Metropolitana do Valle de Aburrá sobre os convênios docência - serviço em saúde

Objetivo: conocer la percepción de gerentes y profesionales con cargos administrativos de hospitales públicos o empresas sociales del Estado de segundo y tercer nivel de complejidad del Área Metropolitana del Valle de Aburrá, en los que hay convenios docencia - servicio, pero que no se encuentran categorizados como hospitales universitarios, acerca del proceso de rotación de estudiantes de medicina, con el fin de indagar sobre el compromiso que las instituciones tienen con estos procesos formativos, qué tan informados están con respecto a la metodología de los mismos y cuáles son los beneficios o limitantes que de ellos se desprenden. Metodología: se realizó una investigación cualitativa con enfoque hermenéutico. Se entrevistaron 14 gerentes y profesionales con cargos administrativos de 6 hospitales públicos del Área Metropolitana del Valle de Aburrá. Resultados: las prácticas de los estudiantes de medicina de primeros semestres se enmarcan en asuntos básicos porque al estar iniciando su formación les es permitida poca práctica, tienen nula relación o intervención directa con los pacientes y les es denegado el acceso a la historia clínica. Conclusiones: los estudiantes de medicina de primeros semestres desarrollan rotaciones básicas y requieren acompañamiento y supervisión por parte de los docentes. Las ventajas que obtienen las IPS a razón del desarrollo de las prácticas son menores en comparación con las limitaciones que este proceso suscita.

Objective: To find out the perception of the personnel with administrative responsibilities from second and third complexity-level public hospitals or State social enterprises in the Aburrá Valley (which have teaching agreements, but that are not considered teaching hospitals), about medicine students' rotation. The aim was to ascertain the institutional commitment to the formative processes, their knowledge of their methodology, as well as benefits or limitations that result from such processes. Methodology: A qualitative hermeneutical study in which 14 managers and professionals with administrative charges from six public hospitals of the Metropolitan Area of the Aburrá Valley were interviewed. Results: the first-semester medical students' practices are framed in basic matters because when they are starting their training, they are allowed little practice, have little or no direct relationship or intervention with patients and are denied access to their clinical history. Conclusions: first-semester Medicine students are framed in basic rotations. They require permanent accompaniment and supervision from teachers. The advantages that IPS obtain due to the development of students' practices are few compared to the limitations that this process causes.

Objetivo: conhecer a percepção de gerentes e profissionais com cargos administrativos de hospitais públicos ou empresas sociais do Estado de segundo e terceiro nível de complexidade da Área Metropolitana do Valle de Aburrá, nos que há convênios docência - serviço, mas que não se encontram categorizados como hospitais universitários, sobre o processo de rodízio de estudantes de medicina, com o fim de indagar sobre o compromisso que as instituições têm com estes processos formativos, que tão informados estão com respeito à metodologia dos mesmos e quais são os benefícios ou limitantes que deles se desprendem. Metodologia: se realizou uma investigação qualitativa com enfoque hermenêutico. Se entrevistaram 14 gerentes e profissionais com cargos administrativos de 6 hospitais públicos da Área Metropolitana do Valle de Aburrá. Resultados: os estágios dos estudantes de medicina de primeiros semestres se quadram em assuntos básicos porque ao estar iniciando sua formação lhes é permitida pouca prática, têm nula relação ou intervenção direta com os pacientes e lhes é denegado o acesso à história clínica. Conclusões: os estudantes de medicina de primeiros semestres desenvolvem rotações básicas e requerem acompanhamento e supervisão por parte dos docentes. As vantagens que obtém as IPS a razão do desenvolvimento dos estágios é menor em comparação com as limitações que este processo suscita.