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A new method based on frontier orbital theory is used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. Useful predictions of the binding sites can be made based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function f(super -)(sub Ff) and it is found that Cu3, Cu5 and Cu5- have the highest reactivity toward molecular oxygen.

The potential energy surfaces of the [Si.sub.5][Li.sub.n.sup.5-6] (n = 5?7) systems were explored in detail to find feasible way to design three-dimensional star-like silicon structures using the appropriate ligands. The calculation results revealed that the important contribution of ionic character of the Si-Li interactions to induce the formation of a bridged structure and the contribution of reduction of the Pauli repulsion and the maximization of the orbital towards formation of star-like structure.

A range of cyclin-dependent kinases (CDK2) inhibitors are analyzed by a model of active site called the hinge region (HR) by utilizing a group of global reactivity indices decided with respect to density of states. It is proposed that in the HR-ligand interaction, the polarization effect is more than the charge transfer contribution by comparing the biological activity and global softness.

A simple model is presented to develop an empirical nucleophilicity scale based on the stretching force constants of the vibrational spectrum, where the B-HX hydrogen bonding system (where B is a base Lewis and HX is a dipole) is the benchmark to test the model. The results have shown that Legon and Millen nucleophilicity scale and the electrostatic potential derived scales can elucidate in good approximation the reactivity order of the nucleophiles only when the interactions with a probe electrophile is of the hard-hard type.

The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable σ-orbital interactions involved in the formation of two C--N bonds in comparison with the generation of C--C and N--N bonds in the 1,2-isomers. [ABSTRACT FROM AUTHOR]

Recently, Guha and co-workers (Sarmah, K.; Kalita, A.; Purkayastha, S.; Guha, A. K. Pushing The Extreme of Multicentre Bonding: Planar Pentacoordinate Hydride. Angew. Chem. Int. Ed. 2024 , e202318741) reported a highly intriguing bonding motif: planar pentacoordinate hydrogen (ppH) in Li 5 H 6 - , featuring C 2 v symmetry in the singlet state with two distinct H-Li (center-ring) bond distances. We herein revisited the potential energy surface of Li 5 H 6 - by using a target-oriented genetic algorithm. Our investigation revealed that the lowest-energy structure of Li 5 H 6 - exhibits a ppH configuration with very high D 5 h symmetry and a 1 A 1 ' electronic state. We did not find any electronic effect like Jahn-Teller distortion that could be responsible for lowering its symmetry. Moreover, our calculations demonstrated significant differences in the relative energies of other low-lying isomers. An energetically very competitive planar tetracoordinate hydrogen (ptH) isomer is also located, but it corresponds to a very shallow minimum on the potential energy surface depending on the used level of theory. Chemical bonding analyses, including AdNDP and EDA-NOCV, uncover that the optimal Lewis structure for Li 5 H 6 - involves H - ions stabilized by the Li 5 H 5 crown. Surprisingly, despite the dominance of electrostatic interactions, the contribution from covalent bonding is also significant between ppH and the Li 5 H 5 moiety, derived from H - (1s) → Li 5 H 5 σ donation. Magnetically induced current density analysis revealed that due to minimal orbital overlap and the highly polar nature of the H-Li covalent interaction, the ppH exhibits local diatropic ring currents around the H centers, which fails to result in a global aromatic ring current. The coordination of Li 5 H 6 - with Lewis acids, BH 3 and BMe 3 , instantly converts the ppH configuration to (quasi) ptH. These Lewis acid-bound ptH complexes show high electronic stability and high thermochemical stability against dissociation and, therefore, will be ideal candidates for the experimental realization.

The quest for planar hypercoordinate atoms (phA) beyond six has predominantly focused on transition metals, with dodecacoordination being the highest reported thus far. Extending this bonding scenario to main-group elements, which typically lack d orbitals despite their larger atomic radius, has posed significant challenges. Intrigued by the potentiality of covalent bonding formation using the d orbitals of the heavier alkaline-earth metals (Ae = Ca, Sr, Ba), the so-called "honorary transition metals", we aim to push the boundaries of planar hypercoordination. By including rings formed by 12-15 atoms of boron-carbon and Ae centers, we propose a design scheme of 180 candidates with a phA. Further systematic screening, structural examination, and stability assessments identified 10 potential clusters with a planar hypercoordinate alkaline-earth metal (phAe) as the lowest-energy form. These unconventional structures embody planar dodeca-, trideca-, tetradeca-, and pentadecacoordinate atoms. Chemical bonding analyses reveal the important role of Ae d orbitals in facilitating covalent interactions between the central Ae atom and the surrounding boron-carbon rings, thereby establishing a new record for coordination numbers in the two-dimensional realm.

Here, we introduce a hybrid method, named Kick-Fukui, to explore the potential energy surface (PES) of clusters and molecules using the Coulombic integral between the Fukui functions in the first screening of the best individuals. In the process, small stable molecules or clusters whose combination has the stoichiometry of the explored species are used as assembly units. First, a small set of candidates has been selected from a large and stochastically generated (Kick) population according to the maximum value of the Coulombic integral between the Fukui functions of both fragments. Subsequently, these few candidates are optimized using a gradient method and density functional theory (DFT) calculations. The performance of the program has been evaluated to explore the PES of various systems, including atomic and molecular clusters. In most cases studied, the global minimum (GM) has been identified with a low computational cost. The strategy does not allow to identify the GM of some silicon clusters; however, it predicts local minima very close in energy to the GM that could be used as the initial population of evolutionary algorithms.

The exhaustive exploration of the potential energy surfaces of CE 2 M 2 (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.

The synthesis and structural characterization of the dimer [(Sn 6 Ge 2 Bi) 2 ] 4- raise the possibility of obtaining a broad variety of analogous compounds with different Sn/Ge/Bi proportions. Several combinations of nine atoms have been detected by electrospray mass spectrometry as potential assembly units. However, [(Sn 6 Ge 2 Bi) 2 ] 4- remains as the unique experimentally characterized species in this series. This fact has motivated us to explore its potential energy surface, as well as its monomers' [Sn 6 Ge 2 Bi] 3-/2- , in an effort to gain insight into the factors that might be privileging the experimental viability of this species. Our results show that the lowest-energy [Sn 6 Ge 2 Bi] 3- structure remains in its oxidized product [Sn 6 Ge 2 Bi] 2- , which corresponds to that identified in the dimer [(Sn 6 Ge 2 Bi) 2 ] 4- . Additionally, local minima, very close in energy to the lowest-energy monomer, are chiral mixtures that dimerize into diverse structures with a probable energetic cost, making them noncompetitive isomers. Finally, the global minimum of the dimer [(Sn 6 Ge 2 Bi) 2 ] 4- presents the most stable monomers as assembly units. These results show the importance of considering the simultaneity of all of these conditions for the viability of these types of compounds.

We have theoretically evaluated the behavior of the Re3(μ-Cl)3Cl6 cluster under magnetic perturbation, and it clearly shows that the magnetic response within the Re3(μ-Cl)3 plane is highly diatropic in nature. An analysis of both the magnetically induced current density (MICD) and induced magnetic field (B(ind)) allows us to classify this cluster as doubly σ- and also π-aromatic on the magnetic criterion. These findings contradict the classical Re-Re double bond representation and favor a chemical bonding pattern that involves delocalized bonds.

A recently proposed molecular orbital localization procedure, based on the electron localization function (ELF) technique, has been used to describe chemical bonding in the cluster series Sin(BH)(5-n)(2-) (n = 0-5). The method combines the chemically intuitive information obtained from the traditional ELF analysis with the flexibility and generality of canonical molecular orbital theory. This procedure attempts to localize the molecular orbitals in regions that have the highest probability for finding a pair of electrons, providing a chemical bonding description according to the classical Lewis theory. The results confirm that conservation of the structures upon isoelectronic replacement of a B-H group by a Si atom, allowing evolution from B5H5(2-) to Si5(2-), is in total agreement with the preservation of the chemical bonding pattern.

In this article, we employed the induced magnetic field method to show that the Al2X6 (X = F, Cl, Br, I) clusters cannot be classified as aromatic systems. Interestingly, even nucleus independent chemical shift (NICS) reveals the same conclusion when analyzed in greater detail, showing that a superficial analysis of this index can easily lead to incorrect interpretations. In view of the fact that the NICS index is extensively used by computational and theoretically oriented experimental chemists, this is an important warning against superficial analyses, as it can lead to erroneous chemical interpretation.

In this work, we present a methodology inspired by criteria of "maximum matching" between the Fukui functions to predict the best interaction between small silicon clusters to form larger ones. The model is based on the topological analysis of the Fukui functions. We tested the methodology in the formation of Si4-Si8 using a set of small Si2-Si6 clusters as building blocks in ground state structures in singlet and triplet multiplicities. In all of the cases, the Fukui function predicts the formation of the large cluster in its ground state structure, but the number of reaction channels increases with the cluster size.

In the course of a reaction it is the shape of the Fukui potential that guides a distant reagent toward the site where an electrophile/nucleophile is willing to accept/donate charge. In this paper we explore the mathematical characteristics of the Fukui potential and demonstrate its relationship to the hardness and the ability of an atom in a molecule to change its charge. The Fukui potential not only determines the active site for electron transfer, but it also approximates the distribution of hardness of a molecule: it is the Coulomb contribution to the frontier local hardness. The Fukui potential at the position of the nuclei is equal to the variation of the chemical potential with the nuclear charge and therefore measures the sensitivity of the system to changes in atom type. In the specific case of atoms and slightly charged ions, the Fukui potential at the nucleus measures the hardness. The strong correlation between the hardness and the Fukui potential at the nucleus suggests that the Fukui potential at the nucleus is an alternative definition for the chemical hardness.

Can relativistic effects modify the NICS and the B(ind) values? In this manuscript we evaluate the relativistic corrections incorporated via the zeroth-order regular approximation to the calculations of nucleus-independent chemical shifts and the induced magnetic field (B(ind)) in the E12(2-) spherenes (E = Ge, Sn, Pb). We found that both electron delocalization descriptors are strongly affected by the relativistic corrections. For instance, for plumbaspherene, the difference in values from the nonrelativistic to the relativity-included calculation is almost 40 ppm! Our results show that the changes observed in the NICS and B(ind) values in the title cages are a consequence of the treatment of the relativistic effects. If these effects are included as scalar or spin-orbit calculations, then we can establish the next trend: Ge12(2-) is a nonaromatic species, Sn12(2-) is a low aromatic species, and Pb12(2-) is strongly aromatic, according to calculated NICS and B(ind) values. Thus, any prediction of electron delocalization in molecules containing heavy elements without considering an adequate treatment for relativistic effects may lead to an erroneous chemical interpretation.

In this work an alternative to the analysis of the Fukui function will be presented and compared with the traditional condensed function. The topological analysis allows us to define basins corresponding to different regions of the space, and the numerical integration of the density over those volumes gives a number amenable of a chemical interpretation in line with the Fukui function applications. Various examples are shown, a series of small molecules, a couple of clusters, and aromatic molecules. They are discussed in comparison with other methodologies and with the experimental evidence.

A theoretical study of two series of small clusters, Si3On(-) and Si6On(-) (n = 1-6), has been carried out. The minimum energy structures were produced adding an electron to neutral species followed by relaxation at the B3LYP-6-311G(2d) level. The vertical ionization energies (VIEs) were computed using the electron propagator theory (EPT) in two approximations, Unrestricted Outer Valence Green Functions (UOVGF) and partial third-order approximation (P3). In the series Si3On(-) the theoretical VIEs of the minimum energy structures agree well with experimental data. For the second series there are not experimental VIEs, and the theoretical results are predictions. The performance of EPT methodologies in conjunction with all-electron or pseudopotentials (PP) calculations is analyzed. The conjunction of P3 and PP approximation proves to be the most efficient and economical methodology to calculate the VIEs of small anionic silicon oxide clusters. In the series Si6On(-) different channels of fragmentation have been calculated. The results suggest that the fragments do not have drastic geometric changes and the anionic fragment corresponds to the atoms where the spin density of the initial large cluster is localized. The Fukui function calculated over selected optimized fragments predicts adequately the interaction between them to form large stable clusters.

We report a theoretical study on a series of CDK2 inhibitors using a set of global reactivity indices defined in terms of the density of states. The statistical analysis was performed on the basis of two groups of 11 and 6 compounds, respectively, reported by Hardcastle et al. (J. Med. Chem. 2004, 47, 3710-3722). Both series were classified on the basis of the correlations obtained for the complete set of compounds and the sites targeted within the active site of CDK2. The comparison between the biological activity and the electronic chemical potential approached as the Fermi level yields poor results, thereby suggesting that the interaction between the hinge region (HR) of CDK2 and the ligands may have a marginal contribution from the charge transfer (CT) component. Comparison between the biological activity and global softness shows a better correlation, thereby suggesting that polarization effects outweigh the CT contribution in the HR-ligand interaction. We stress the importance to include in the evaluation of the reactivity indices all of the occupied energy states in order to assess the effects coming from the internal electronic structure involved in the HR-ligand interaction.