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An analysis of the thermodynamic and kinetic stability and the nature of the chemical bond in hypercoordinated compounds with the formula BeH3Ng+ (Ng = He–Rn) through high-level calculations is presented in this work. Thermochemical calculations show that, for the heavier noble gases (Ar–Rn), these systems are thermodynamically stable at room temperature; however, this stability decreases due to a weakening of the Be–H2 interaction, while the Be–Ng bond strengthens going down the periodic table. These results are complemented by Born Oppenheimer molecular dynamics simulations, in which the increasing tendency to dissociate the Be–H2 bond is evidenced. The nature of the chemical bonding depends on the analysis performed. On the one hand, the interacting quantum atoms method indicates that the covalent contribution is around 25 to 30%. On the other hand, the electron density topology indicates a covalent nature for compounds with Kr–Rn, while Hirshfeld population analysis in conjunction with Mayer's bond order establishes polar covalent behavior. The geometrical parameters and natural energy decomposition analysis (NEDA) indicate a covalent nature, allowing us to consider that the Be–Ng bond has a partially covalent character. [ABSTRACT FROM AUTHOR]

In this study, we delved into the structure of B5H5 and questioned some of its accepted assumptions. By exploring the potential energy surface, we found a new three-dimensional structure as the global minimum. This finding is in contrast with the previously hypothesized planar and cage-like models. Our exploration extends to the kinetic stability of various B5H5 isomers, offering insights into the dynamic behavior of these molecules. [ABSTRACT FROM AUTHOR]

Thermodynamic, kinetic, and chemical bonding analysis at the coupled cluster level has been carried out for a series of hypercoordinated carbon compounds with formula CH4Ng2+ (Ng = He–Rn). Results show that these compounds could be stable at room temperature and Born–Oppenheimer molecular dynamics simulations (BOMD) in conjunction with activation energies indicate high kinetic stability. In addition, all chemical bonding descriptors agree with a strong C–Ng covalent bond and a bonding pattern similar to that of CH5+. Finally, BOMD simulations showed that these compounds are fluxional, with a continuous formation/breaking of H–H and C–H bonds. To the best of the authors' knowledge, these results represent the first series of fluxional compounds possessing a covalent bond between a main group element and a noble gas atom. [ABSTRACT FROM AUTHOR]

Using various exploration strategies, in this study, we investigated the potential energy surfaces (PES) of CBe5H5+ and CnBe3n+2H2n+22+ (n = 2–4) clusters. Previous studies proposed that the planar pentacoordinate carbons (ppCs) were the global minima of these clusters. However, our study identified new putative global minima and competitive isomers, refuting some previous assignments. We employed several methods, including evolutive-inspired stochastic approaches guided by "chemical criteria", and ab initio molecular dynamics simulations at elevated temperatures. Our results showed that the size of the scanned population significantly affected the evolutive method and that constrained or guided procedures showed an advantage in identifying better minima for larger systems. This study demonstrated that using multiple complementary strategies can result in a wider variety of minima in a given energy range. Our findings provide valuable insights into exploring the potential energy surfaces of clusters, mainly medium-sized clusters, which could be the connections between small clusters and nanomaterials. [ABSTRACT FROM AUTHOR]

The relativistic effects on the aromaticity of a set of benzene analogues, E3M3H3 (E = C–Pb; M = N–Bi) heterocycles, using magnetically induced current density (MICD) and the NICSzz component of the conventional nucleus independent chemical shift (NICS), is hereby examined. The relativistic effects were evaluated by means of four-component relativistic MICD, and two-component NMR relativistic shielding tensor methods. MICD and NICS were also computed in a non-relativistic fashion, to assess the influence of scalar-relativistic and spin–orbit effects. Most of the studied compounds exhibit a net diatropic ring current (aromatic), excluding the nitrogen-containing compounds which are non-aromatic (except for C3N3H3), in agreement with their higher E–N electronegativity difference. Only in the case of bismuth compounds, E3Bi3H3, aromaticity is substantially decreased when relativistic effects are included (mainly due to the spin–orbit contribution). The larger the mass of the system, the larger the magnitude of this change, in line with the expected relativistic effects for heavier elements. The analysis based on the NICSzz computations agrees with that of the MICD, thus supporting both the magnetic behavior and the aromatic character of these compounds. [ABSTRACT FROM AUTHOR]

The aromaticity and dynamics of a set of recently proposed neutral 5- and 6-membered heterocycles that are closed by dative (donor–acceptor) or multi-center σ bonds, and have resonance forms with a Hückel number of π-electrons, are examined. The donors and acceptors in the rings include N, O, and F, and B, Be, and Mg, respectively. The planar geometry of the rings, coupled with evidence from different measures of aromaticity, namely the NICSzz, and NICSπzz components of the conventional nucleus independent chemical shifts (NICS), and ring current strengths (RCS), indicate non-trivial degrees of aromaticity in certain cases, including the cyclic C3B2OH6 and C3BOH5 isomers, both with three bonds to the O site in the ring. The former is lower in energy by at least 17.6 kcal mol−1 relative to linear alternatives obtained from molecular dynamics simulations in this work. Some of the other systems examined are best described as non-aromatic. Ring opening, closing, and isomerization are observed in molecular dynamics simulations for some of the systems studied. In a few cases, the ring indeed persists. [ABSTRACT FROM AUTHOR]

The potential energy surfaces (PESs) of Lin(BH)5n−6 systems (where n = 5, 6, and 7) were explored using the gradient embedded genetic algorithm (GEGA) program, in order to find their global minima conformations. This search predicts that the lowest-energy isomers of Li6(BH)5 and Li7(BH)5+ contain a (BH)56− pentagonal fragment, which is isoelectronic and structurally analogous to the prototypical aromatic hydrocarbon anion C5H5−. Li7(BH)5+, along with Li7C5+, Li7Si5+ and Li7Ge5+, joins a select group of clusters that adopt a seven-peak star-shape geometry, which is favored by aromaticity in the central five-membered ring, and by the preference of Li atoms for bridging positions. The theoretical analysis of chemical bonding, based on magnetic criteria, supports the notion that electronic delocalization is an important stabilization factor in all these star-shaped clusters. [ABSTRACT FROM AUTHOR]