On the aromaticity of actinide compounds.

The chemistry of actinides has flourished since the late 2010s with the synthesis of new actinide complexes and clusters. On the theoretical side, a range of tools is available for the characterization of these heavy element-containing compounds, but discrepancies in the assessment of aromaticity using different tools have led to controversies. In this Perspective, we examine the origin of controversies relating to the aromaticity of metallic compounds, with a focus on actinides.

Classical versus Collective Interactions in Asymmetric Trigonal Bipyramidal Alkaline Metal-Boron Halide Complexes.

Collective interactions are a novel type of chemical bond formed between metals and electron-rich substituents around an electron-poor central atom. So far only a limited number of candidates for having collective interactions are reported. In this work, we extend the newly introduced concept of collective bonding to a series of neutral boron complexes with the general formula MBX (M=Li, Na, and K; X=F, Cl, and Br).

Tetraquinolines; four linked quinoline units or porphyrinoids.

Tetraquinolines (TEQs) have been recently synthesized and proposed to be a new member of the porphyrinoid family with highly distorted, nonplanar, geometries. In this contribution by studying several molecules, closely related to TEQs, we have suggested that the origin of the nonplanarity of TEQs and their counterparts is a combination of steric strain and the propensity of the molecules to avoid antiaromaticity. The tendency of TEQs to coordinate with doubly charged metal ions can be interpreted in terms of their transition from potential antiaromaticity to nonaromaticity.

Comparison the salivary levels between caries-active and caries-free children from Birjand, Iran: A case-control study.

Objective: Dental plaque bacteria, including (), play a role in the pathogenesis of the dental caries. There are conflicting results regarding the association of salivary level and dental caries susceptibility. Our aim was to compare salivary levels in colony-forming units (CFU) between children with active caries and caries-free children in Birjand, Iran.

Metallaaromaticity - a protean world.

The nature of magnetically induced current densities (MICD) of metallabenzenes and related compounds has been examined with relativistic DFT calculations to assess the magnetic aromaticity of the molecules. The origin of the total MICD has been analyzed in terms of individual molecular orbital (MO) contributions. Our study reveals that the σ-framework of the molecules always makes a diamagnetic contribution to the MICD.

Composite 5-methylations of cytosines modulate i-motif stability in a sequence-specific manner: Implications for DNA nanotechnology and epigenetic regulation of plant telomeric DNA.

Background: The i-motif is a tetrameric DNA structure based on the formation of hemiprotonated cytosine-cytosine (C.C) base pairs. i-motifs are widely used in nanotechnology.

How Does a Container Affect Acidity of its Content: Charge-Depletion Bonding Inside Fullerenes.

A recent study (Sci. Adv. 2017, 3, e1602833) has shown that FH⋅⋅⋅OH hydrogen bond in a HF⋅H O pair substantially shortens, and the H-F bond elongates upon encapsulation of the cluster in C fullerene.

Unification of ground-state aromaticity criteria - structure, electron delocalization, and energy - in light of the quantum chemical topology.

In the present account we investigate a theoretical link between the bond length, electron sharing, and bond energy within the context of quantum chemical topology theories. The aromatic stabilization energy, ASE, was estimated from this theoretical link without using isodesmic reactions for the first time. The ASE values obtained from our method show a meaningful correlation with the number of electrons contributing to the aromaticity.

Multi-center covalency: revisiting the nature of anion-π interactions.

Exploring the nature of anion-π bonding by means of the Quantum Theory of Atoms in Molecules (QTAIM) and an energy decomposition scheme on the basis of Interacting Quantum Atoms (IQA) theory led us to conclude that these non-classical interactions benefit from "multi-center covalency" far more than from the electrostatics. Comparing anion-π systems to closely related covalent anion-σ complexes reveals that the anion-π systems benefit from an extensive degree of electron sharing between the anions and all atoms of the π-rings. Besides, decomposition of the binding energy into classical (electrostatics) and non-classical (exchange-correlation) components demonstrates that in contrast to previous reports, the anion-π complexes are local minima, if and only if the non-classical contribution to binding energy surpasses that of the electrostatics.

On the non-classical contribution in lone-pair-π interaction: IQA perspective.

In the present work the nature of lone-pair-π interactions between water molecules and a number of π-rings with different substituents/hetero-atoms in the light of quantum chemical topology approaches is studied. The Quantum Theory of Atoms in Molecules (QTAIM) and Interacting Quantum Atoms (IQA) were employed for distinguishing the role of heteroatoms and electron withdrawing substituents in the complex formation between water and π-rings. Our IQA study identified three classes of water-π complexes on the basis of the relative role of electrostatics (classical) and exchange-correlation (non-classical) factors in the interaction energy between the oxygen of water (the lone-pair donor) and the sp(2) atoms of the π-ring, i.

All-Metal Aromaticity: Revisiting the Ring Current Model among Transition Metal Clusters.

We present new insight into the nature of aromaticity in metal clusters. We give computational arguments in favor of using the ring-current model over local indices, such as nucleus independent chemical shifts, for the determination of the magnetic aromaticity. Two approaches for estimating magnetically induced ring currents are employed for this purpose, one based on the quantum theory of atoms in molecules (QTAIM) and the other where magnetically induced current densities (MICD) are explicitly calculated.

Method/basis set dependence of NICS values among metallic nano-clusters and hydrocarbons.

The influence of various all-electron basis sets and effective core potentials employed along with several DFT functionals (B3LYP, B3PW91, BLYP, BP86 and M06) on the magnitude of nucleus independent chemical shift (NICS) values in different metallic nano-clusters and hydrocarbons is studied. In general, it is demonstrated that the NICS values are very sensitive to the applied method/basis set; however, the method/basis set dependence is more prominent for computed NICS values in transition metal clusters. In hydrocarbons, medium-size basis sets perform roughly similar to large basis sets in most cases.

The Laplacian of electron density versus NICSzz scan: measuring magnetic aromaticity among molecules with different atom types.

The electron density versus NICS(zz) (the out-of-plane component of nucleus-independent chemical shifts (NICS)) scan for assessing magnetic aromaticity among similar molecules with different ring sizes is improved by scanning the Laplacian of electron density versus NICS(zz) to include molecules containing different types of atoms. It is demonstrated that the new approach not only reproduces the results of the previous method but also surpasses that in the case of species with different atom types. The relative positions of curves in the plots of the Laplacian of electron density versus NICS(zz) correlate well with the ring current intensities of these molecules both near and far from the ring planes of the considered molecules.