Sigma Hole Research Articles

Investigation of Supramolecular Self-Assembly in Sn(IV)-5,10,15,20-tetra(4-bromo-2,6-difluorophenyl) Porphyrins Mediated through Activated Sigma Hole

Investigation of Supramolecular Self-Assembly in Sn(IV)-5,10,15,20-tetra(4-bromo-2,6-difluorophenyl) Porphyrins Mediated through Activated Sigma Hole

New global minimum conformers for the Pt19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{19}$$\\end{document} and Pt20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{20}$$\\end{document} clusters: low symmetric species featuring different active sites

ContextThe study of platinum (Pt) clusters and nanoparticles is essential due to their extensive range of potential technological applications, particularly in catalysis. The electronic properties that yield optimal catalytic performance at the nanoscale are significantly influenced by the size and structure of Pt clusters. This research aimed to identify the lowest-energy conformers for Pt18\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{18}$$\\end{document}, Pt19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{19}$$\\end{document}, and Pt20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{20}$$\\end{document} species using Density Functional Theory (DFT). We discovered new low-symmetry conformers for Pt19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{19}$$\\end{document} and Pt20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{20}$$\\end{document}, which are 3.0 and 1.0 kcal/mol more stable, respectively, than previously reported structures. Our study highlights the importance of using density functional approximations that incorporate moderate levels of exact Hartree-Fock exchange, alongside basis sets of at least quadruple-zeta quality. The resulting structures are asymmetric with varying active sites, as evidenced by sigma hole analysis on the electrostatic potential surface. This suggests a potential correlation between electronic structure and catalytic properties, warranting further investigation.MethodsAn equivariant graph neural network interatomic potential (NequIP) within the Atomic Simulation Environment suite (ASE) was used to provide initial geometries of the aggregates under study. DFT calculations were performed with the ORCA 5 package, using functional approximations that included Generalized Gradient Approximation (PBE), meta-GGA (TPSS, M06-L), hybrid (PBE0, PBEh), meta-GGA hybrid (TPSSh), and range-separated hybrid (ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega $$\\end{document}B97x) functionals. Def2-TZVP and Def2-QZVP as well as members of the cc-pwCVXZ-PP family to check basis set convergence were used. QTAIM calculations were performed using the AIMAll suite. Structures were visualized with the AVOGADRO code.

Structural consequences in differently substituted haloarylcarboxylates and non-covalent interactions on crystal packing and biological efficacy of copper(II) complexes with N,N,N′,N′-tetramethylethylenediamine N-donor ligand

In this work, we reported four new copper(II) halo-benzoate complexes (2-chloro-4-nitrobenzoate (2-Cl-4-NO2-BZ), 3,5-DICBZ, 2-chloro-5-nitrobenzoate (2-Cl-5-NO2-BZ), 3,5-difluoro benzoate (3,5-DIFBZ), and 3,5-dichlorobenzene (3,5-DICBZ) respectively in complexes 1–4) with N,N,N’,N’- tetramethylethylene diamine (temed) N-donor ligand in order to study the interesting coordination features and biological evaluation of such complexes under ambient reaction conditions. All the complexes 1–4 were characterized by elemental analyses, and spectroscopic techniques, including FT-IR, UV–vis, and EPR etc. Single crystal X-ray structure determination (SCXRD) of complexes revealed the distorted octahedral geometry in all complexes. Notably, the halobenzoate ligands exhibited a bidentate chelation mode in complexes 1 and 2, while they showed a monodentate mode in complex 3. In complex 4, the carboxylate ligand exhibited both monodentate as well as bidentate coordination. Furthermore, detailed packing analyses of complexes 1–4 highlighted the significance of halogen bonding in lattice stabilization besides hydrogen bonding and π∙∙∙π interactions as evidenced by Hirshfeld surface analyses and crystal analysis. Moreover, packing analyses displayed that complex 1 exhibited a layered or wave-like arrangement, while complex 2 featured a helical arrangement supported by a supramolecular halogen-bonded network guided by Cl∙∙∙O interactions. Complex 3 displayed a zig-zag layered arrangement with a stacking topology, and Complex 4 showcased a ribbon-like arrangement stabilized by F∙∙∙F and Cl∙∙∙Cl halogen bonding interactions. Furthermore, sigma hole on halogen atoms has also been examined (which play an important role in halogen bonding) by electrostatic-potential isosurfaces. In order to exploit the biological efficacy of complexes 1–4 owing to the inherent biological activity of copper metal, molecular docking analyses against gram +ve bacteria i.e. S. epidermidis (PDB ID; 8DO6), B. subtilis (1QD9), as well as two gram -ve bacteria, namely, P. aeruginosa (5WZE) and S. dysenteriae (1DM0), have also been carried out. Interestingly, values of docking scores and inhibition constant of all complexes 1–4 (with a maximum binding score (inhibition constant) of -9.8 kcal/mol (0.063 µMol) in 1 against 8DO6 and 1DM0) revealed higher biological efficacy than that of standard drugs.

Sigma Hole Potentials as Tools: Quantifying and Partitioning Substituent Effects.

Empirical substituent constants, such as the Hammett parameters, have found important utility in organic and other areas of chemistry. They are useful both in predicting the impact of substitutions on chemical processes and in rationalizing after-the-fact observations on chemical bonding and reactivity. We assess the impact of substitutions on monoiodinated benzene rings and find that the modifications that substituents induce on the electrostatic potentials at the sigma hole on the terminal I center correlate strongly with established trends of common substituents. As an alternative to the experimental procedures involved in obtaining empirically based substituent constants, the computationally determined constants based on induced electrostatic potentials offer a model for quantifying the influence of mono- and polyatomic, neutral, and ionic substituents on their compounds. A partitioning scheme is proposed that allows us to discretely separate σ and π contributions to generate quantitative measures of substituent effects.

Dispersion-Corrected DFT-D4 Study of the Adsorption of Halobenzenes and 1,3,5-Trihalobenzenes on the Cu(111) Surface─Effect of Sigma Hole Properties.

Halogen bonds, characterized by directionality, tunability, hydrophobicity, and variable sizes, are ideal noncovalent interactions to design and control the formation of self-assembled nanostructures. The specific self-assembly cases formed by the halogen-bonding interaction have been well studied by scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. However, there is a lack of systematic theoretical adsorption studies on halogenated molecules. In this work, the adsorption of halobenzenes and 1,3,5-trihalobenzenes on the Cu(111) surface was examined by dispersion-corrected DFT methods. The adsorption geometries, noncovalent molecule-surface interactions, electronic densities, and electrostatic potential maps were examined for their most stable adsorption sites using the DFT-D4 method. Our calculations revealed that the iodo compounds favor a different adsorption geometry from aryl chlorides and bromides. Down the halogen group (Cl to I), the adsorption energy increases and the distance between the halogen atom and Cu surface decreases, which indicates stronger molecule-surface interactions. This is supported by the changes in the density of states upon adsorption. Noncovalent interaction analysis was also employed to further understand the nature and relative strength of the molecule-surface interactions. Electrostatic potential maps revealed that the positive character of the halogen sigma hole becomes stronger upon adsorption. Thus, surface adsorption of the halogenated molecule will enhance the formation of intermolecular halogen bonds. The present theoretical findings are expected to contribute toward a more comprehensive understanding of halogen bonding on the Cu(111) surface.

Impact of Electron-Withdrawing Effect on Sigma Hole Via Bromine-Based Interactions in Zn-5,10,15,20-tetra(4-bromo-2,6-difluoro Phenyl) Porphyrin

Impact of Electron-Withdrawing Effect on Sigma Hole Via Bromine-Based Interactions in Zn-5,10,15,20-tetra(4-bromo-2,6-difluoro Phenyl) Porphyrin

Molecular Dynamics with Conformationally Dependent, Distributed Charges.

Accounting for geometry-induced changes in the electronic distribution in molecular simulation is important for capturing effects such as charge flow, charge anisotropy, and polarization. Multipolar force fields have demonstrated their ability to correctly represent chemically significant features such as anisotropy and sigma holes. It has also been shown that off-center point charges offer a compact alternative with similar accuracy. Here, it is demonstrated that allowing relocation of charges within a minimally distributed charge model (MDCM) with respect to their reference atoms is a viable route to capture changes in the molecular charge distribution depending on geometry, i.e., intramolecular polarization. The approach, referred to as "flexible MDCM" (fMDCM), is validated on a number of small molecules and provides accuracies in the electrostatic potential (ESP) of 0.5 kcal/mol on average compared with reference data from electronic structure calculations, whereas MDCM and point charges have root mean squared errors of a factor of 2 to 5 higher. In addition, MD simulations in the NVE ensemble using fMDCM for a box of flexible water molecules with periodic boundary conditions show a width of 0.1 kcal/mol for the fluctuation around the mean at 300 K on the 10 ns time scale. For water, the equilibrium valence angle in the gas phase is found to increase by 2° for simulations in the condensed phase which is consistent with experiment. The accuracy in capturing the geometry dependence of the ESP together with the long-time stability in energy conserving simulations makes fMDCM a promising tool to introduce advanced electrostatics into atomistic simulations.

Influence of halogen substitution on crystal packing, molecular properties and electrochemical sensing

Halogen atoms are commonly present in organic molecules and halogen functionalization is of great significance in organic synthesis, to achieve desired material and biological functions. In crystal engineering, the halogen bond is an intriguing interaction utilized to design molecular solids. Herein we report the development of halogen functional red tri-halo Schiff bases/Anils 1–4 in which the nature of halogen atoms is rationally changed, to explore the impact of halogen atoms on molecular packing and physicochemical properties. The trichloro (1), tribromo (2) and triiodo (3) Anils crystallize in the same centrosymmetric triclinic crystal systems and the 2 and 3 are isomorphous. The molecular solids exhibit similar 2-dimensional packing induced by halogen atoms, however, the molecules differ significantly in the third-dimensional packing propagated by π-stackings. It is observed that π-π interactions are stronger in triiodo Anil. To further understand the effect of the nature of halogen on molecular packing a mixed dichloro-iodo Anil (4) was synthesized. The introduction of different halogens on the Anil skeleton greatly alters the packing behavior and the molecules pack in monoclinic P21/n space group. 4 undergoes halogen bonded interactions to arrange as zig-zag solid, further stabilized by π-stackings. The Hirshfeld studies validate the formation of a significant sigma hole on a para-iodine atom in 3 (0.0161 a.u), while the tip of p-chlorine in 1 is not electron-deficient (−0.0128 a.u.), which also reflects in more contribution of halogen-halogen interactions in 3 than 1 and 2, in their fingerprint plots. Theoretical and experimental studies indicate lower band gap values in triiodo form 3 than others. The framework analyses of the molecular solids indicate nature of intermolecular contacts is predominantly dispersive. The physicochemical property investigation of the Anils validates relatively better chemical and thermal stability and optical properties of the trihalo form. Solubility studies of the molecular solids 1–4 validate their hydrophobic nature and the iodo functional groups enhance the hydrophobicity of the molecules, while the solubility investigations of these solids in DCM and toluene indicate higher solubilities with relatively lower values for iodo-functionalized molecules. The molecular solids have been employed for electrochemical sensing of picric acid with the limit of the detection value of 0.72, 0.84, 0.74 and0.73 ​μM for 1–4, respectively.

Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics.

Intermolecular bonding attraction at π-bonded centers is often described as “electrostatically driven” and given quasi-classical rationalization in terms of a “pi hole” depletion region in the electrostatic potential. However, we demonstrate here that such bonding attraction also occurs between closed-shell ions of like charge, thereby yielding locally stable complexes that sharply violate classical electrostatic expectations. Standard DFT and MP2 computational methods are employed to investigate complexation of simple pi-bonded diatomic anions (BO−, CN−) with simple atomic anions (H−, F−) or with one another. Such “anti-electrostatic” anion–anion attractions are shown to lead to robust metastable binding wells (ranging up to 20–30 kcal/mol at DFT level, or still deeper at dynamically correlated MP2 level) that are shielded by broad predissociation barriers (ranging up to 1.5 Å width) from long-range ionic dissociation. Like-charge attraction at pi-centers thereby provides additional evidence for the dominance of 3-center/4-electron (3c/4e) nD-π*AX interactions that are fully analogous to the nD-σ*AH interactions of H-bonding. Using standard keyword options of natural bond orbital (NBO) analysis, we demonstrate that both n-σ* (sigma hole) and n-π* (pi hole) interactions represent simple variants of the essential resonance-type donor-acceptor (Bürgi–Dunitz-type) attraction that apparently underlies all intermolecular association phenomena of chemical interest. We further demonstrate that “deletion” of such π*-based donor-acceptor interaction obliterates the characteristic Bürgi–Dunitz signatures of pi-hole interactions, thereby establishing the unique cause/effect relationship to short-range covalency (“charge transfer”) rather than envisioned Coulombic properties of unperturbed monomers.

Halogen bonding and chalcogen bonding mediated sensing.

Sigma–hole interactions, in particular halogen bonding (XB) and chalcogen bonding (ChB), have become indispensable tools in supramolecular chemistry, with wide-ranging applications in crystal engineering, catalysis and materials chemistry as well as anion recognition, transport and sensing. The latter has very rapidly developed in recent years and is becoming a mature research area in its own right. This can be attributed to the numerous advantages sigma–hole interactions imbue in sensor design, in particular high degrees of selectivity, sensitivity and the capability for sensing in aqueous media. Herein, we provide the first detailed overview of all developments in the field of XB and ChB mediated sensing, in particular the detection of anions but also neutral (gaseous) Lewis bases. This includes a wide range of optical colorimetric and luminescent sensors as well as an array of electrochemical sensors, most notably redox-active host systems. In addition, we discuss a range of other sensor designs, including capacitive sensors and chemiresistors, and provide a detailed overview and outlook for future fundamental developments in the field. Importantly the sensing concepts and methodologies described herein for the XB and ChB mediated sensing of anions, are generically applicable for the development of supramolecular receptors and sensors in general, including those for cations and neutral molecules employing a wide array of non-covalent interactions. As such we believe this review to be a useful guide to both the supramolecular and general chemistry community with interests in the fields of host–guest recognition and small molecule sensing. Moreover, we also highlight the need for a broader integration of supramolecular chemistry, analytical chemistry, synthetic chemistry and materials science in the development of the next generation of potent sensors.

Chirally modified cobalt-vanadate grafted on battery waste derived layered reduced graphene oxide for enantioselective photooxidation of 2-naphthol: Asymmetric induction through non-covalent interaction

The cobalt oxide-vanadium oxide (Co3O4-V2O5) combined with reduced graphene oxide (rGO) having band gap of ∼ 3.3 eV appeared as a suitable photocatalyst for selective oxidation of 2-naphthol to BINOL. C2-symmetric BINOL was achieved with good yield using hydrogen peroxide as the oxidant under UV-light irradiation. The same catalyst was chirally modified with cinchonidine and a newly synthesized chiral Schiff base ligand having a sigma-hole center. The strong interaction of the chiral modifiers with the cobalt-vanadium oxide was truly evident from various spectroscopic studies and DFT calculations. The chirally modified mixed metal oxide transformed the oxidative CC coupling reaction with high enantioselectivity. High enantiomeric excess upto 92 % of R-BINOL was obtained in acetonitrile solvent and hydrogen peroxide as the oxidant. A significant achievement was the formation of S-BINOL in the case of the cinchonidine modified catalyst and R-BINOL with the Schiff base ligand anchored chiral catalyst. The UV-light induced catalytic reaction was found to involve hydroxyl radical as the active reactive species. The spin trapping ESR and fluorescence experiment provided relevant evidence for the formation of such species through photodecomposition of hydrogen peroxide on the catalyst surface. The chiral induction to the resultant product was found to induce through supramolecular interaction like OH…π, H…Br interaction. The presence of sigma hole center was believed to play significant role in naphtholate ion recognition during the catalytic cycle.

Evaluating Halogen-Bond Strength as a Function of Molecular Structure Using Nuclear Magnetic Resonance Spectroscopy and Computational Analysis.

Halogen bonding (XB) is a highly directional, non-covalent intermolecular interaction between a molecule (XB donor) presenting a halogen with an electron-deficient region or sigma hole (σ-hole) and an electron-rich or Lewis-base molecule (XB acceptor). A systematic, experimental, and theoretical study of solution-phase XB strength as a function of the molecular structure for both XB donor and acceptor molecules is presented. The impact of specific structural features is assessed using 19F and 1H nuclear magnetic resonance (NMR) titrations to determine association constants, density functional theory calculations for interaction energies and bond lengths, as well as 19F-1H HOESY NMR measurements of intermolecular cross-relaxation between the interacting XB donor-acceptor adducts. For XB donor molecules (perfluoro-halogenated benzenes), results indicate the critical importance of iodine coupled with electron-withdrawing entities. Prominent structural components of XB acceptor molecules include a central atom working in conjunction with a Lewis-base atom to present high electron density directed at the σ-hole (e.g., tributylphosphine oxide). Additionally, larger surrounding aliphatic R groups (e.g., butyl and octyl) were found to significantly stabilize strong XB, particularly in solvents that promote the interaction. With a more thorough understanding of structure-optimized XB, one can envision harnessing XB interactions more strategically for specific design of optimal materials and chemical applications.

Qualitative and Quantitative Study of Intermolecular Interactions in Imidazo[2,1‐b] [1,3,4] Thiadiazoles

AbstractThe crystal structures of three Imidazo [2, 1‐b] [1, 3, 4] thiadiazole derivatives were determined by single crystal x‐ray diffraction method. All compounds are crystallized under monoclinic crystal system, P21 space group. In solid‐state, the crystal structures are primarily stabilized by C−H…O hydrogen bonds. The chloro and bromo substituted structures exhibits sigma hole involved S…O and S…N non‐bonding interactions. A detailed analysis of crystal packing with the evaluation of interaction energies of molecular pairs extracted from both PIXEL and quantum chemical methods were presented in detail. In addition, Hirshfeld 2D fingerprint plots are used to estimate intermoleular interactions quantitatively. The iso‐structurality present in the crystal packing was investigated using XPAC analysis. The molecular electrostatic potential (MEP) was mapped to identify the reaction sites of the molecules. Further nonlinear optical properties are calculated using Density functional theory.

Copper (II)-based halogen-substituted chromone antitumor drug entities: Studying biomolecular interactions with ct-DNA mediated by sigma hole formation and cytotoxicity activity

Copper-based antitumor drug entities 1–3 derived from substituted (F−, Br−, –CH3) 3-formylchromone pharmacophore were synthesized and thoroughly characterized by spectroscopic and single X-ray crystallographic studies. These complexes show structural novelty due to presence of the X-bonds in chromone scaffold which could facilitate higher propensity for nucleic acids via sigma σ-hole interactions. Therefore, structure-activity relationship of 1–3 was studied by performing ct-DNA binding, pBR322 cleavage and cytotoxicity activity to validate their potential to act as chemotherapeutic drug entities. The binding studies of 1–3 with ct- DNA were carried out employing many biophysical techniques and the corroborative results of these experiments showed intercalation mode of binding and the order of binding was found to be 2 > 1 > 3. The structure of drug entities could facilitated strong halogen bonding interaction (in case of 1 &2) and stability of X bond was rationalized by sigma hole region of positive electrostatic potential on the surface of C-X covalent bond, as determined by gas phase B3LYP computational DFT studies. Interestingly, 2 exhibited most avid binding affinity due to presence of Br− electron withdrawing and polarizable group. Further, cleavage studies of 1–3 with pBR322 plasmid DNA were performed which demonstrated significant cleavage activity, the supercoiled form (Form I) of plasmid DNA was converted to nicked form (Form II) with the appearance of linearized form (Form III) in between two, implicating lethal double strand breaks of DNA. 2 showed predominantly higher cleavage activity following the similar trend as observed for binding studies. The cytotoxicity of the complexes 1–3 was evaluated by MTT assay against the human liver carcinoma (Huh-7) and prostate cancer (DU-145) cell lines; complex 2 exhibited specific and selective cytotoxicity for the DU-145 cancer cell line with LC50 value of 1.6 μM.

Automated parameterization of quantum-mechanically derived force-fields including explicit sigma holes: A pathway to energetic and structural features of halogen bonds in gas and condensed phase.

In classical molecular dynamics, general purpose atomistic force-fields (FFs) often deliver inaccurate results when dealing with halogen bonds (XBs), notwithstanding their crucial role in many fields of science, ranging from material design to drug development. Given the large dimensions of the systems of interest, it would be therefore desirable to increase the FF accuracy maintaining the simplicity of the standard Lennard-Jones (LJ) plus point charge description to avoid an excessive computational cost. A simple yet effective strategy consists in introducing a number of virtual sites able to mimic the so-called "explicit σ-hole." In this work, we present an automated FF parameterization strategy based on a global optimization of both LJ and charge parameters with respect to accurate quantum mechanical data, purposely computed for the system under investigation. As a test case, we report on two homologue series, characterized either by weak or strong XBs, namely, the di-halogenated methanes and the mono-, di-, and tri-substituted acetonitriles, taking into consideration Cl, Br, and I substituents. The resulting quantum mechanically derived FFs are validated for each compound in the gas and in the condensed phase by comparing them to general purpose and specific FFs without virtual sites and to highly accurate reference quantum mechanical data. The results strongly support the adoption of the specific FFs with virtual sites, which overcome the other investigated models in representing both gas phase energetics and the structural patterns of the liquid phase structure related to the presence of XBs.

Spectroscopic (FTIR and UV‐Vis) Analysis, Supramolecular Studies, XRD Structural Characterization and Theoretical Studies of Two Flavone‐Oxime Derivatives

AbstractTwo flavone oxime derivatives, (E)‐2‐phenyl‐4H‐chromen‐4‐one O‐(2‐bromoallyl)oxime (C18H14BrNO2) (1) and (E)‐2‐phenyl‐4H‐chromen‐4‐one O‐benzyloxime (C22H17NO2) (2), were analyzed by XRD, IR (FT‐IR), and UV‐Vis spectroscopies. Supramolecular studies of the two compounds revealed the existence of weak C−Br…Cg halogen bonds as well as weak C−H…O interactions in the first oxime derivative and even weaker interactions dominated by dispersion forces in the second derivative. These interactions were further analyzed by observing the Hirshfeld surfaces. To evaluate the features of the halogen interactions, molecular electrostatic studies (MEP) were performed. These studies showed positive charges on the surface of the halogen atom, demonstrating the presence of a “sigma hole”. The maximum and minimum values of the molecular electrostatic potential indicate low molecular reactivity, and difficult access of the electrophilic or nucleophilic agents to the molecule, in the case of a hypothetical reaction, is observed. Spectroscopic studies in the IR region showed similar results for the two compounds, finding specific differences in the behavior of the N−O and N=C frequencies that characterize the oxime group. UV–visible spectra of both compounds were also recorded and the electronic properties, such as HOMO, LUMO and band gap energies were measured by time‐dependent DFT (TD‐DFT) approach. Analysis of the interaction energies of the two compounds between pairs of neighboring molecules within a radius of 3.8 Å, using the CrystalExplorer program at the DFT/6‐31G level, showed that the Edis term essentially contributed to the total interaction energy in the process of crystal formation.

Chalcogen Bond Mediated Enhancement of Cooperative Ion‐Pair Recognition

AbstractA series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5‐bis‐triazole pyridine structure covalently linked to benzo‐15‐crown‐5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi‐nuclear 1H, 13C, 125Te and 19F NMR, ion pair binding investigations reveal sodium cation–benzo‐crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred‐fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.

Chalcogen Bond Mediated Enhancement of Cooperative Ion-Pair Recognition.

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5‐bis‐triazole pyridine structure covalently linked to benzo‐15‐crown‐5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi‐nuclear 1H, 13C, 125Te and 19F NMR, ion pair binding investigations reveal sodium cation–benzo‐crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred‐fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.

Computational insight into the halogen bonded self-assembly of hexa-coordinated metalloporphyrins.

We demonstrate herein a computational study probing the influence of metalloporphyrins on intermolecular halogen bonding (XB) during supramolecular self-assembly. The results demonstrate that porphyrin aromatic rings can activate or deactivate halogen bonding interactions, especially those on axial ligands, and further influence the preference type of halogen···halogen bonding during the supramolecular self-assembly. Calculations show that the halogen atom present at the equatorial position has a higher sigma hole potential (VS,max) than that at the axial position. The computational analysis and our observations from the X-ray structure analysis are in good agreement. From structural analysis it is clear that equatorial halogen atoms prefer to participate in Type-II XB interactions whereas the axial halogen atoms either participate in Type-I XB interaction or reluctant to participate in XB interactions due to the decrease of their sigma hole potential. Thus, we demonstrate, herein, for the first time a computational study probing the direct influence of the porphyrin's ring current on the sigma hole potential (VS,max) of the halogen atoms and subsequently the effects of the supramolecular self-assembly.

C-GeM: Coarse-Grained Electron Model for Predicting the Electrostatic Potential in Molecules.

We have developed a new coarse-grained electron model, C-GeM, in which atoms are represented by a positive core and an electron shell described by Gaussian charge distributions, with the interaction energy between the core and shell reflecting the electronegativity of a given atomic element. By minimizing the electronic shell positions in the field of atomic core positions, the model can provide accurate electrostatic properties of molecules and their interactions. We have tested the performance of the C-GeM model for a set of molecules containing H, C, O, and Cl atoms to show that it can predict the electrostatic potential with high accuracy, and correctly describe the dissociation of HCl into ionic fragments in solution and to neutral atoms in the gas phase. The resulting C-GeM approach offers many advantages over expensive ab initio methods and reactive force field charge equilibration methodologies: it can rapidly predict the electrostatic potential surfaces of molecules, molecules dissociate into integer charge fragments so that redox reactions are easily described, there is no unphysical long-range charge transfer, it can account for out-of-plane polarization, and charges are not required to be centered on atoms, thereby accounting for electrostatic features such as sigma holes.