On the halide aggregation into the [Au4(PPh3)4]4+ cluster core. Insights from structural, optical and interaction energy analysis in [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-)

The aggregation of halide atoms into gold clusters offers an interesting scenario for the development of novel metal-based cavities for anion recognition and sensing applications. Thus, further understanding of the different contributing terms leading to efficient cluster-halide aggregation is relevant to guide their synthetic design. In this report, we evaluate the formation of [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-) in terms of different energy contributions underlying the stabilization of the cluster-halide interaction, and the expected UV-vis absorption profiles as a result of the variation in frontier orbital arrangements. Our results denote that a non-planar Au4 core shape enables enhanced halide aggregation, which is similar for Cl-, Br-, and I-, in comparison to the hypothetical planar Au4 counterparts. The electrostatic nature of the interaction involves a decreasing ion-dipole term along with the series, and for iodine species, higher-order electrostatic contributions become more relevant. Hence, the obtained results help in gaining further understanding of the different stabilizing and destabilizing contributions to suitable cluster-based cavities for the incorporation of different monoatomic anions.

Selectivity Rule of Cryptands for Anions: Molecular Rigidity and Bonding Site

Cryptands utilize inside CH or NH groups as hydrogen bond (H-bond) donors to capture anions such as halides. In this work, the nature and selectivity of confined hydrogen bonds inside cryptands were computationally analyzed with the energy decomposition scheme based on the block-localized wavefunction method (BLW-ED), aiming at an elucidation of governing factors in the binding between cryptands and anions. It was revealed that the intrinsic strengths of inward hydrogen bonds are dominated by the electrostatic attraction, while the anion preferences (selectivity) of inner CH and NH hydrogen bonds are governed by the Pauli exchange repulsion and electrostatic interaction, respectively. Typical conformers of cages are classified into two groups, including the C_3(h) -symmetrical conformers, in which all halide anions are located near the centroids of cages, and the "semi-open" conformers, which exhibit shifted bonding sites for different halide anions. Accordingly, the difference in governing factors of selectivity is attributed to either the rigidity of cages or the binding site of anions for these two groups. In details, the C₃ conformers of NH cryptands can be enlarged more remarkably than the C_3(h) -symmetrical conformers of CH cryptands as the size of anion (ionic radius) increases, resulting in the relaxation of the Pauli repulsion and a dramatic reduction in electrostatic attraction, which eventually rules the selectivity of NH cryptands for halide anions. By contrary, the CH cryptands are more rigid and cannot effectively reduce the Pauli repulsion, which subsequently governs the anion preference. Unlike C₃ conformers whose rigidity determines the selectivity, semi-open conformers exhibit different binding sites for different anions. From F^- to I^- , the bonding site shifts toward the outside end of the pocket inside the semi-open NH cryptand, leading to the significant reduction of the electrostatic interaction that dominates the anion preference. Differently, binding sites are much less affected by the size of anion inside the semi-open CH cryptand, in which the Pauli exchange repulsion remains the key factor for the selectivity of inner hydrogen bonds.

Theoretical Study of Macrocyclic Host Molecules: From Supramolecular Recognition to Self-Assembly

Supramolecular chemistry focuses on molecular recognition and self-assembly of various building blocks through weak non-covalent interactions, including anion-π, hydrogen bond (HB), hydrophobic interactions, van der Waals (vdW) interactions, etc, which...

Nature of hydride and halide encapsulation in Ag8 cages: insights from the structure and interaction energy of [Ag8(X){S2P(OiPr)2}6]+ (X = H-, F-, Cl-, Br-, I-) from relativistic DFT calculations

Unraveling the different contributing terms to an efficient anion encapsulation is a relevant issue for further understanding of the underlying factors governing the formation of endohedral species. Herein, we explore the favorable encapsulation of hydride and halide anions in the [Ag₈(X){S₂P(OPr)₂}₆]⁺ (X^- = H, 1, F, 2, Cl, 3, Br, 4, and, I, 5) series on the basis of relativistic DFT-D level of theory. The resulting Ag₈-X interaction is sizable, which decreases along the series: -232.2 (1) > -192.1 (2) > -165.5 (3) > -158.0 (4) > -144.2 kcal mol^-1 (5), denoting a more favorable inclusion of hydride and fluoride anions within the silver cage. Such interaction is mainly stabilized by the high contribution from electrostatic type interactions (80.9 av%), with a lesser contribution from charge-transfer (17.4 av%) and London type interactions (1.7 av%). Moreover, the ionic character of the electrostatic contributions decreases from 90.7% for hydride to 68.6% for the iodide counterpart, in line with the decrease in hardness according to the Pearson's acid-base concept (HSAB) owing to the major role of higher electrostatic interaction terms related to the softer (Lewis) bases. Lastly, the [Ag₈{S₂P(OPr)₂}₆]²⁺ cluster is able to adapt its geometry in order to maximize the interaction towards respective monoatomic anion, exhibiting structural flexibility. Such insights shed light on the physical reasoning necessary for a better understanding of the different stabilizing and destabilizing contributions related to metal-based cavities towards favorable incorporation of different monoatomic anions.

Designing boron and metal complexes for fluoride recognition: a computational perspective

Fluoride anions (F^-) may have beneficial or harmful effects on the environment depending on their concentration. Here, we shed light on F^- recognition by compounds containing boron, tellurium and antimony, which were experimentally demonstrated to be capable of interacting with the F^- ion in a partially aqueous medium. Boron and metal complexes recognize F^- anions primarily using electrostatic energy along with important contributions from orbital interaction energy. The natural orbitals for chemical valence (NOCV) methodology indicates that the main orbital interactions behind fluoride recognition are σ bonds between the receptors and the F^- anions. The charged receptors, which provide (i) two B atoms, (ii) one B atom and one Sb atom, or (iii) one B atom and one Te atom to directly interact with the F^- ions, appear to be some of the best structures for the recognition of F^- anions. This is supported by the combination of favorable electrostatic and σ bond interactions. Overall, the presence of electron donor groups, such as -CH₃ and -OH, in the receptor structure destabilizes the fluoride recognition because it decreases the attractive electrostatic energy and increases the Pauli repulsion energy in the receptor⋯F^- bonds. Notably, electron acceptor groups, for example, -CN and -NO₂, in the receptor structure favor the interaction with the F^- ions, due to the improvement of the electrostatic and σ bond interactions. This study opens the way to find the main features of a receptor for F^- recognition.

The anionic recognition mechanism based on polyol and boronic acid receptors

Chloride, fluoride, dihydrogen phosphate, acetate, bromide, and hydrogen sulfate recognition from polyol and boronic acid receptors is elucidated.

Tracking the role of trans-ligands in ruthenium–NO bond lability: computational insight

Ruthenium–NO tetraamine structures control the nitric oxide bioavailability. The ligand trans to NO modulates the Ru–NO bond stability.

On the recognition of chloride, bromide and nitrate anions by anthracene–squaramide conjugated compounds: a computational perspective

Anionic recognition appears in several biological processes. Here, the interaction between anthracene–squaramide conjugated compounds and Cl⁻, Br⁻ and NO₃⁻ anions has been explored using density functional theory (DFT) calculations.

What is the driving force behind molecular triangles and their guests? A quantum chemical perspective about host–guest interactions

The physical nature of host–guest interactions occurring between molecular triangles and linear anions was explored using DFT calculations combined with energy decomposition analyses, nuclear independent chemical shift, and non-covalent interactions.

The usefulness of energy decomposition schemes to rationalize host–guest interactions

The findings reported here reveal the robustness and practical application of EDA-NOCV in rationalizing molecular recognition situations in host–guest systems.

Impact of confinement in multimolecular inclusion compounds of melamine and cyanuric acid

Supramolecular cavities can be found in clathrates and self-assembling capsules. In these computational experiments, we studied the effect of folding planar hydrogen-bonded supramolecules of melamine (M) and cyanuric acid (CA) into stable cage-like quartets. Based on dispersion-corrected density functional theory calculations at the ωB97XD/6-311++G(d,p) level, we show the flexibility of M and CA molecules to form free confined spaces. Our bonding analysis indicates that only CA can form a cage, which is more stable than its planar systems. We then studied the capacity of the complexes to host ionic and neutral monoatomic species like Na+, Cl- and Ar. The encapsulation energies range from -2 to -65 kcal mol-1. A detailed energy decomposition analysis (EDA) supports the fact that the triazine ring of CA is superior to the M one for capturing chloride ions. In addition, the EDA and the topology of the electron density, by means of the Atoms in Molecules (AIM) theory and electrostatic potential maps, reveal the nature of the host-guest interactions in the confined space. The CA cluster appears to be the best multimolecular inclusion compound because it can host the three species and keep its cage structure, and therefore it could also act as a dual receptor of the ionic pair Na+Cl-. We think these findings could inspire the design of new heteromolecular inclusion compounds based on triazines and hydrogen bonds.

Tracking the absence of anion–π interactions in modified [23](1,3,5)cyclophanes: insights from computation

[2₃](1,3,5)Cyclophanes containing 1,3,5-triazine and 1,3,5-triphosphinine planar rings present different degrees of aromaticity as well as σ-donor and π-acceptor abilities.