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This study computationally investigates the properties and competition of complexes formed by the interaction between hypohalous acids (HOX, where X = F, Cl, Br, and I) and carbonyl selenide (COSe) at the MP2/aug-cc-pVTZ computational level. Three distinct groups of complexes were obtained. The first group, consisting of complexes with a cyclic structure (HB-TB), exhibited the highest stability. remaining two groups formed less stable linear structures with different characteristics (ChB and XB). In the first group, the electronegativity of the halogen atom significantly influenced the stability of the complexes. Conversely, the stability of complexes in groups II and III was primarily determined by the acid and base strengths of the interacting monomers. To comprehensively evaluate the obtained results, various analyses were employed, including Molecular electrostatic potential (MEP), geometry Optimization, Spectroscopic, Interaction energy (SE), Natural bond orbital (NBO) analysis, Atoms in molecules (AIM) analysis, Non-covalent interaction (NCI) index, Energy decomposition analysis (EDA), and Electron density difference(EDD) analysis. [ABSTRACT FROM AUTHOR]

Halogen bonds find application in supramolecular chemistry, DNA Holliday junction, drug design, organic catalysis and various other fields. Coumarin derivatives are high in demand due to their application in photochemotherapy, drugs and other cancer treatments. Halogenated coumarins are widely known for their biological activities. There exists a competition between the halogen bond and hydrogen bond in singly hydrated halogenated coumarins. The competition between hydrogen and halogen bonding interactions in 3-halogenated 4-hydroxyl coumarin [coumarin derivative; halogen, X = F (A), Cl (B), Br (C), I (D)] with water molecule in the corresponding binding regions C3–X and C2=O4 is studied. This study was conducted using PBE0 D3BJ with augmented correlation consistent basis set in order to include the diffuse functions. Improved findings for non-bonded distances and much more distinct intramolecular effects were obtained using BJ-damping. In the singly-hydrated systems, the water molecule forms a hydrogen bond with C2=O4 in all the halogenated molecules, whereas halogen bonding between the water oxygen and C2–X exists only in the case of X = Br (C) and I (D). The absence of a halogen-bonded structure in singly-hydrated chlorine and fluorine substituted coumarin derivative is therefore attributed to the competing hydrogen-bonding interaction with C2=O4. RDG scatter plot as well QTAIM analysis implied that halogen bond exists between water molecule and the coumarin derivative. Further, the most modern local energy decomposition (LED) analysis of intermolecular interaction was also studied using DLPNO-CCSD(T). Finally, ab initio molecular dynamics was also performed. [ABSTRACT FROM AUTHOR]

Neutral complex [L2CoCl2] is obtained by the reaction of cobalt(II) chloride with E-(((4-iodophenyl)imino)methyl)phenol (L), and its structure is studied by single crystal X-ray diffraction. The structure contains I⋯Cl halogen bonds whose energies are estimated by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

The importance of halogen bonds (XBs) in the regulation of material properties through a variation in the electrostatic potential of the halogen atom is not attracted much attention. Herein, this study utilizes in situ single crystal X‐ray diffraction and synchrotron‐based X‐ray techniques to investigate the cooling‐triggered irreversible single‐crystal‐to‐single‐crystal transformation of the DMF solvated iodo‐substituted squaraine dye (SQD‐I). Transformation is observed to be mediated by solvent‐involved XB formation and strengthening of electrostatic interaction between adjacent SQD‐I molecules. By immersing a DMF solvate in acetonitrile a solvent exchange without loss of long‐range ordering is observed. This is attributed to conservation of the molecular charge distribution of SQD‐I molecules during the process. The different solvates can be used in combination for temperature‐dependent image encryption. This work emphasizes the changes caused by XB formation to the electrostatic potentials of halogen containing molecules and their influence on material properties and presents the potential utility of XBs in the design of soft‐porous crystals and luminescent materials. [ABSTRACT FROM AUTHOR]

The crystal structure of the title 2:1 molecular complex between 2-(allylthio)pyridine and 1,2,4,5-tetrafluoro-3,6-diiodobenzene, C6F4I2·2C8H9NS, at 100 K has been determined in the monoclinic space group P21/c. The most noteworthy characteristic of the complex is the halogen bond between iodine and the pyridine ring with a short N...I contact [2.8628 (12) Å]. The Hirshfeld surface analysis shows that the hydrogen...hydrogen contacts dominate the crystal packing with a contribution of 32.1%.

Halogen bonding permeates many areas of chemistry. A wide range of halogen-bond donors including neutral, cationic, monovalent, and hypervalent have been developed and studied. In this work we used density functional theory (DFT), natural bond orbital (NBO) theory, and quantum theory of atoms in molecules (QTAIM) to analyze aryl halogen-bond donors that are neutral, cationic, monovalent and hypervalent and in each series we include the halogens Cl, Br, I, and At. Within this diverse set of halogen-bond donors, we have found trends that relate halogen bond length with the van der Waals radii of the halogen and the non-covalent or partial covalency of the halogen bond. We have also developed a model to calculate ΔG of halogen-bond formation by the linear combination of the % p-orbital character on the halogen and energy of the σ-hole on the halogen-bond donor.

Halogen bonding acknowledged as a noteworthy weak interaction, has gained growing recognition in the field of supramolecular chemistry. In this study, we selected structurally rigid diaryliodonium ions (I(III)) with two biaxial σ‐holes as halogen‐bond donors, to bind with three chiral acceptor molecules bearing cholesteryl and naphthalimides with distinct geometries. The abundant carbonyl oxygen atoms in side‐arm substituents function as multiple acceptors for halogen bonding. The self‐aggregation of chiral acceptor molecules demonstrates adaptiveness to solvent media, evidenced by the inversion of the Cotton effect and the morphological evolution from spherical to rod‐like nanoarchitectures in different solvent systems. The distinct geometries of the acceptor molecules conferred various binding modes with I(III). The introduction of I(III) as a halogen‐bond donor regulates the aggregation of the donors, achieving amplification of chiroptical signals and inheriting solvent responsiveness from the self‐aggregated assembly. This study successfully utilized rational structural design and multimodal control strategies to achieve regulation of supramolecular chirality. [ABSTRACT FROM AUTHOR]

The complexation of an alkali metal ion by a model macrocycle is examined using the M05-2X/DGDZVP DFT method. The macrocycle is built by connecting three cyclopenta[b]pyrrole motifs with alternating acetylene and ethylene linkages. Replacing one of the C-H bonds in each motif with a C-I bond allows for the formation of three intramolecular C-I···N halogen bonds. Two distinct binding modes were found for the complexation of each metal ion. In one mode, the binding of the ion occurs solely by the iodine atoms, via I···M+ interactions, while maintaining the integrity of the halogen bonds. The complexation energies are in the range −66 to −35 kcal/mol. In the other mode, the binding of the ion includes one nitrogen atom as well, with binding energies in the range of −71 to −38 kcal/mol. In this binding mode, the halogen bond network is weakened. The presence and strength of the interactions are further examined using AIM and NBO calculations. Lastly, the geometries for the transition state structures linking the less stable to the more stable metal ion complexes were obtained, and their calculated Gibbs free energy barriers were found in the range of 1.6 to 1.9 kcal/mol. [ABSTRACT FROM AUTHOR]

A cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene has been prepared and its crystal structure has been determined via single-crystal X-ray diffraction. Infinite chains of roughly coplanar donor and acceptor molecules are held together by two crystallographically distinct and highly linear Br···N halogen bonds. Four further crystallographically distinct Br···Br halogen bonds are also observed. Each of the two Br atoms in the 3 and 5 positions on the benzene ring acts simultaneously as a halogen bond donor and acceptor to two additional bromines on two neighbouring 1,3,4,5-tetrabromo-2,6-difluorobenzene molecules. These halogen bonds are also classified as type II halogen-halogen contacts. As a result of these contacts, a staggered herringbone arrangement of the infinite chains results. These structural features are shown to be consistent with computed molecular electrostatic potential and Hirshfeld surfaces. The insights gained through this analysis imply that additional systematic variations in the substitution motifs of aromatic halogen bond donors may lead to new structures and properties. As part of this work, a single-crystal X-ray structure of 1,3,4,5-tetrabromo-2,6-difluorobenzene of moderate quality is also reported. The single-crystal X-ray diffraction structure of a 1:1 cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene is reported. Bromine-nitrogen halogen bonds link the two types of molecules together, forming infinite chains. Bromine-bromine halogen bonds (type II contacts) between aromatic molecules stabilize a herringbone-like packing arrangement. [ABSTRACT FROM AUTHOR]

The theoretical study of the complexes produced from the interactions between hypohalous acids (HOX; X = F, Cl, Br, and I) and acetonitrile (AN) was carried out at the MP2/aug-cc-pVTZ level of theory. Three different conformations were produced, namely, A, B, and C, in which conformations B and C were stabilized by only the N···H HB and the N···X XB interactions, respectively. In contrast, conformation A was stabilized by two O···C TB and H···X HB interactions through a cyclic structure. The characteristics of product complexes were analyzed by various methods such as molecular electrostatic potential (MEP), spectroscopy, binding energy (ΔE0), quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), energy decomposition analysis (EDA), electron density differences (EDD), and non-covalent interaction (NCI) index. [ABSTRACT FROM AUTHOR]

We present a luminescent Ir(III) complex featuring a bidentate halogen bond donor site capable of strong anion binding. The tailor‐made Ir(III)(L)2 moiety offers a significantly higher emission quantum yield (8.4 %) compared to previous Ir(III)‐based chemo‐sensors (2.5 %). The successful binding of chloride, bromide and acetate is demonstrated using emission titrations. These experiments reveal association constants of up to 1.6×105 M−1. Furthermore, a new approach to evaluate the association constant by utilizing the shift of the emission was used for the first time. The experimentally observed characteristics are supported by quantum chemical simulations. [ABSTRACT FROM AUTHOR]

In this study, we propose an alternative metal‐free methodology for the synthesis of Streptindole and its derivatives. This approach employs economically viable and easily handled molecular iodine (I2) as the catalyst in an aqueous medium. The method demonstrates remarkable tolerance towards a diverse array of functional groups. The versatility of the developed protocol is highlighted by its application in the efficient total syntheses of the alkaloid natural products, Streptindole and Arsindoline B accomplished in a single step from indole. Furthermore, the methodology is also useful for the synthesis of pharmaceutically significant compounds, specifically anti‐TMV agents (5 c, 5 d, and 5 e) and an anticancer agent (5 f). Control experiments have been carried out to study the plausible catalytic cycle by finding the key intermediates. The experimental findings support the mechanistic pathway involving halogen bond activation in molecular iodine catalysis. [ABSTRACT FROM AUTHOR]

Non‐covalent interactions play an important role in all sub‐fields of chemistry, including catalysis, where interactions of different natures can work together to improve reactivitiy and selectivity. Several families of molecules that incorporate both hydrogen bond (HB) and halogen bonding (XB) donors have already been studied. However, there is a lack of data on how grafting HB donors to iodoazolium salts could impact their association and reactivity properties. Herein, we disclose the synthesis of a library of iodoazolium salts bearing varied HB donors, along with a study of their physico‐chemical properties using different techniques (X‐ray diffraction, 31P NMR, ITC) and their behavior in catalysis. Even though no clear‐cut evidence of cooperation between XB and HB could be obtained through physico‐chemical evaluations, a iodoazolium salt bearing a urea function displayed better conversion and product selectivity in a Ritter reaction than all other activators lacking one or the other function. [ABSTRACT FROM AUTHOR]

It is widely recognized that electrostatics plays a central role in the intermolecular interactions in condensed phases, as evidenced by the "electrostatics + Lennard-Jones" form of the potential functions that are commonly used in classical molecular dynamics simulations. Then, do we understand all about electrostatics in condensed phases? In this review, recent theoretical advances in relation to this topic will be discussed: (1) vibrational spectroscopic probing of the electrostatics in condensed phases, and (2) some phenomena affected by deviation from the scheme of isotropic fixed atomic partial charges, i.e., anisotropy and intermolecular transfer of electron distributions. A theoretical basis for better understanding on them and some theoretical models for practical calculations will be shown with some typical example cases of hydrogen- and halogen-bonded systems. [ABSTRACT FROM AUTHOR]

The substituent effects on cooperativity between pnicogen and halogen bonds in ternary complexes involving pyrimidine with substituents X in the 5-position (X = CN, NC, CF3, Br, Cl, F, H, CH3, C(CH3)3, NH2, N(CH3)2), H2FP, and ClF are investigated using theoretical calculations at the MP2/aug-cc-pVDZ level. The reduced density gradient (RDG) analysis indicates that the halogen and pnicogen interactions clearly stand out as attractive interactions. The calculated synergetic energies in ternary complexes are positive, which demonstrates the antagonist effect of pnicogen and halogen interactions upon each other. According to geometrical parameters, binding energies, molecular electrostatic potentials (MEPs), and the results of natural bond orbital (NBO), atoms in molecules (AIM), and nuclear magnetic resonance (NMR) analyses, pnicogen and halogen bonds are weakened in the ternary complexes where two pnicogen and halogen bonds coexist. The results indicate reduced electron density values, second-order perturbation energies, charge transfer values, and two-bonded spin–spin coupling constants for both pnicogen and halogen bonds in the ternary complex as compared to the isolated binary systems. Also, the results show that substituent effects on cooperativity between N...P pnicogen and N...Cl halogen bonds in considered system can be expressed by Hammett constants. [ABSTRACT FROM AUTHOR]

The title compound, C10H8BrN3OS2, a brominated dithiocarbazate imine derivative, was obtained from the condensation reaction of S-methyldithiocarbazate (SMDTC) and 5-bromoisatin. The essentially planar molecule exhibits a Z configuration, with the dithiocarbazate and 5-bromoisatin fragments located on the same sides of the C=N azomethine bond, which allows for the formation of an intramolecular N—H...Ob (b = bromoisatin) hydrogen bond generating an S(6) ring motif. In the crystal, adjacent molecules are linked by pairs of N—H...O hydrogen bonds, forming dimers characterized by an R22(8) loop motif. In the extended structure, molecules are linked into a three-dimensional network by C—H...S and C—H...Br hydrogen bonds, C—Br...S halogen bonds and aromatic π–π stacking.

Abstract The N─Oxide oxygen in the 111 C─I···⁻O─N+ halogen bond (XB) complexes, formed by five perfluoroiodobenzene XB donors and 32 pyridine N‐oxides (PyNO) XB acceptors, exhibits three XB modes: bidentate, tridentate, and monodentate. Their C─I···O XB angles range from 148° to 180°, reflecting the iodine σ‐hole's structure‐guiding influence. The I···⁻O─N+ angles range from 87° to 152°. On the contrary, the I···⁻O─N+ angles have a narrower range from 107° to 125° in stronger monodentate N─I···⁻O─N+ XBs of N‐iodoimides and PyNOs. The C─I···⁻O─N+ systems exhibit a larger variation in I···⁻O─N+ angles due to weaker XB donor perfluoroiodoaromatics forming weak I···O XBs, which allows wider access to electron‐rich N‐O group regions. Density Functional Theory analysis shows that I···O interactions are attractive even when the I···⁻O─N+ angle is ≈80°. Correlation analysis of structural parameters showed that weak I···O XBs in perfluoroiodobenzene‐PyNO complexes affect the C─I bond via n(O)→σ*(C─I) donation less than the N─I bond via n(O)→σ*(N─I) donation in very strong I···O XBs of N‐iodoimide‐PyNO complexes. This implies that PyNOs' oxygen self‐tunes its XB acceptor property, dependent on the XB donor σ‐hole strength affecting the bonding denticity, geometry, and interaction energies.

Abstract The importance of halogen bonds (XBs) in the regulation of material properties through a variation in the electrostatic potential of the halogen atom is not attracted much attention. Herein, this study utilizes in situ single crystal X‐ray diffraction and synchrotron‐based X‐ray techniques to investigate the cooling‐triggered irreversible single‐crystal‐to‐single‐crystal transformation of the DMF solvated iodo‐substituted squaraine dye (SQD‐I). Transformation is observed to be mediated by solvent‐involved XB formation and strengthening of electrostatic interaction between adjacent SQD‐I molecules. By immersing a DMF solvate in acetonitrile a solvent exchange without loss of long‐range ordering is observed. This is attributed to conservation of the molecular charge distribution of SQD‐I molecules during the process. The different solvates can be used in combination for temperature‐dependent image encryption. This work emphasizes the changes caused by XB formation to the electrostatic potentials of halogen containing molecules and their influence on material properties and presents the potential utility of XBs in the design of soft‐porous crystals and luminescent materials.

The coordination nature of 2‐mono‐ and 2,6‐disubstituted pyridines with electron‐withdrawing halogen and electron‐donating methyl groups for [N−X−N]+ (X=I, Br) complexations have been studied using 15N NMR, X‐ray crystallography, and Density Functional Theory (DFT) calculations. The 15N NMR chemical shifts reveal iodine(I) and bromine(I) prefer to form complexes with 2‐substituted pyridines and only 2,6‐dimethylpyridine. The crystalline halogen(I) complexes of 2‐substituted pyridines were characterized by using X‐ray diffraction analysis, but 2,6‐dihalopyridines were unable to form stable crystalline halogen(I) complexes due to the lower nucleophilicity of the pyridinic nitrogen. In contrast, the halogen(I) complexes of 2,6‐dimethylpyridine, which has a more basic nitrogen, are characterized by X‐crystallography, which complements the 15N NMR studies. DFT calculations reveal that the bond energies for iodine(I) complexes vary between −291 and −351 kJ mol−1 and for bromine between −370 and −427 kJ mol−1. The bond energies of halogen(I) complexes of 2‐halopyridines with more nucleophilic nitrogen are 66‐76 kJ mol−1 larger than those of analogous 2,6‐dihalopyridines with less nucleophilic nitrogen. The experimental and DFT results show that the electronic influence of ortho‐halogen substituents on pyridinic nitrogen leads to a completely different preference for the coordination bonding of halogen(I) ions, providing new insights into bonding in halogen(I) chemistry. [ABSTRACT FROM AUTHOR]

Halogen bonds are typically observed to have a linear arrangement with a 180° angle between the nucleophile and the halogen bond acceptor X−R. This linearity is commonly explained using the σ‐hole model, although there have been alternative explanations involving exchange repulsion forces. We employ two‐dimensional Distortion/Interaction and Energy Decomposition Analysis to examine the archetypal H3N⋯X2 halogen bond systems. Our results indicate that although halogen bonds are predominantly electrostatic, their directionality is largely due to decreased Pauli repulsion in linear configurations as opposed to angled ones in the I2 and Br2 systems. As we move to the smaller halogens, Cl2 and F2, the influence of Pauli repulsion diminishes, and the energy surface is shaped by orbital interactions and electrostatic forces. These results support the role of exchange repulsion forces in influencing the directionality of strong halogen bonds. Additionally, we demonstrate that the 2D Energy Decomposition Analysis is a useful tool for enhancing our understanding of the nature of potential energy surfaces in noncovalent interactions. [ABSTRACT FROM AUTHOR]

Human interleukin‐5 (IL‐5) cytokine mediates the development of eosinophils and is involved in a variety of immune inflammatory responses that play a major role in the pathogenesis of childhood asthma, leukemia, and other pediatric allergic diseases. The immunomodulatory cytokine functions by binding to its cognate cell surface receptor IL‐5R in a sheet‐by‐sheet manner, which can be conformationally mimicked and competitively disrupted by a double‐stranded cyclic AF18748 peptide. In this study, we systematically examined the co‐crystallized complex structure of human IL‐5R with AF18748 peptide and rationally designed a halogen bond to glue at the protein–peptide complex interface by substituting the indole moiety of AF18748 Trp13 residue with a halogen atom (X = F, Cl, Br, or I). High‐level theoretical calculations imparted presence of the halogen bond between the oxygen atom (O) of IL‐5R Glu58 backbone and the halogen atom (X) of AF18748 Trp13 side chain. Experimental assays confirmed that the halogen bond can promote peptide binding moderately or considerably. More importantly, the halogen bond not only enhances peptide affinity to IL‐5R, but also improves peptide selectivity for its cognate IL‐5R over other noncognate IL‐R proteins. As might be expected, the affinity and selectivity conferred by halogen bond increase consistently in the order: H < F < Cl < Br < I. Structural modeling revealed that the halogen bond plus its vicinal π–cation–π stacking co‐define a ringed noncovalent system at the complex interface, which involves a synergistic effect to effectively improve the peptide binding potency and recognition specificity. [ABSTRACT FROM AUTHOR]

The nature of (imide)N–X⋯N(pyridine) halogen‐bonded complexes formed by six N‐haloimides and sixteen 2‐substituted pyridines are studied using X‐ray crystallography (68 crystal structures), Density Functional Theory (DFT) (86 complexation energies), and NMR spectroscopy (90 association constants). Strong halogen bond (XB) donors such as N‐iodosuccinimide form only 1:1 haloimide:pyridine crystalline complexes, but even stronger N‐iodosaccharin forms 1:1 haloimide:pyridine and three other distinct complexes. In 1:1 haloimide:pyridine crystalline complexes, the haloimide's N─X bond exhibits an unusual bond bending feature that is larger for stronger N‐haloimides. DFT complexation energies (ΔEXB) for iodoimide–pyridine complexes range from −44 to −99 kJ mol−1, while for N‐bromoimide–pyridine, they are between −31 and −77 kJ mol−1. The ΔEXB of I⋯N XBs in 1:1 iodosaccharin:pyridine complexes are the largest of their kind, but they are substantially smaller than those in [bis(saccharinato)iodine(I)]pyridinium salts (−576 kJ mol−1), formed by N‐iodosaccharin and pyridines. The NMR association constants and ΔEXB energies of 1:1 haloimide:pyridine complexes do not correlate as these complexes in solution are heavily influenced by secondary interactions, which DFT studies do not account for. Association constants follow the σ‐hole strengths of N‐haloimides, which agree with DFT and crystallography data. The haloimide:2‐(N,N‐dimethylamino)pyridine complex undergoes a halogenation reaction resulting in 5‐iodo‐2‐dimethylaminopyridine. [ABSTRACT FROM AUTHOR]

The formation of a halogen-bonded network using four NHX-(CH2)3-NX-(CH2)3-NHX molecules (X = Cl, Br, or I) is investigated using DFT. The self-assembly of the four basic motifs results in a tube-like structure with C4h symmetry, with one halogen-bonded network located at each end of the structure and one at its center. Each halogen-bonded network has four quasi-planar N-X···N interactions with binding energies that increase with the size of X. The structure is found to bind Li+ at each of the halogen-bonded networks, albeit more strongly at its center. The binding of Li+ is driven by halogen atom lone pairs that produce a rich electron density orthogonal to the halogen bond. The presence and strength of the interactions are further examined using AIM and NBO calculations. Lastly, IRC calculations are performed to examine the transitions between the Li+ complex minima and, thus, the potential for transporting the metal ion from one end of the tube to the other. Based on the tetrameric structure, a model intramolecular structure is built and considered as a potential host for Li+. In this case, the central intermolecular N-X···N network is replaced by an intramolecular Si-C≡C-Si network. Interestingly, both intermolecular and intramolecular structures exhibit similar Li+ binding abilities. [ABSTRACT FROM AUTHOR]

The crystal structure of 1,2,3,4-tetrabromo,1-phenylbutane determined by single crystal synchrotron X-ray diffraction is described. Molecules of the compound compose a layered structure of the Langmuir–Blodgett film type (with tail-to-tail, head-to-head orientations of molecules of the neighboring layers) in which phenyl radicals of one layer contact with those of another. Halogen bonds and Br⋯Br contacts (four per each molecule) have the key importance for the molecular packing in the layer. The distance between bromine atoms in these bonds and contacts is 3.656-4.002 Å. The thermal analysis shows that the tetrabromophenylbutane melting point is 148 °C, with the compound starting to decompose at 150-280 °C in one step with releasing HBr and benzene. [ABSTRACT FROM AUTHOR]

The synthesis of a chiral isothiourea, namely, (4aR,8aR)‐3‐phenyl‐4a,5,6,7,8,8a‐hexahydrobenzo[4,5]imidazo[2,1‐b]thiazol‐9‐ium bromide, C15H17N2S+·Br−, with potential organocatalytic and anti‐inflammatory activity is reported. The preparation of the heterocycle of interest was carried out in two high‐yielding steps. The hydrobromide salt of the isothiourea of interest provided suitable crystals for X‐ray diffraction analysis, the results of which are reported. Salient observations from this analysis are the near perpendicular arrangement of the phenyl ring and the mean plane of the heterocycle. This conformational characteristic may be relevant with regard the stereoselectivity induced by the chiral isothiourea in asymmetric reactions. Furthermore, evidence was found for the existence of an S...Br− halogen bond. [ABSTRACT FROM AUTHOR]

Human interleukin‐5 (IL‐5) functions as an important pro‐inflammatory factor by binding to its specific receptor, IL‐5Rα, which has been implicated in the pathogenesis of asthma. Previously, a disulfide‐bonded cyclic peptide AF17121 obtained from random library screening and sequence variation was found to competitively disrupt the cognate IL‐5Rα/IL‐5 interaction with moderate potency. In this study, the crystal complex of IL‐5Rα with AF17121 was investigated at structural and energetic levels. It is revealed that the side‐chain indole moiety of the AF17121 Trp5 residue is a potential site for a stem putative halogen bond (X‐bond) with IL‐5Rα, which is just located within the key 3EXXR6 motif region recognized specifically by IL‐5Rα. We systematically examined four halogen substitution types at five positions of the indole moiety; QM/MM calculations theoretically unraveled that only halogenations at 5 and 6 positions can form effective X‐bonds with the side‐chain hydroxyl oxygen of the IL‐5Rα Thr21 residue and the backbone carbonyl oxygen of Ala66 residue, respectively. Binding assays observed that I‐substitution at the 5 position and Br‐substitution at the 6 position can result in two potent halogenated peptides, [5I]AF17121 and [6Br]AF17121, which are improved by 1.6‐fold and 3.5‐fold relative to the native AF17121, respectively. 5I/6Br‐double substitution, resulting in [5I/6Br]AF17121, can further enhance the peptide affinity by 7.5‐fold. Structural analysis revealed that the X‐bond stemming from 6Br‐substitution is also involved in an orthogonal interaction system with a H‐bond; they share a common backbone carbonyl oxygen acceptor of IL‐5Rα Ala66 residue and exhibit a significant synergistic effect between them. [ABSTRACT FROM AUTHOR]

Abstract We present a luminescent Ir(III) complex featuring a bidentate halogen bond donor site capable of strong anion binding. The tailor‐made Ir(III)(L)2 moiety offers a significantly higher emission quantum yield (8.4 %) compared to previous Ir(III)‐based chemo‐sensors (2.5 %). The successful binding of chloride, bromide and acetate is demonstrated using emission titrations. These experiments reveal association constants of up to 1.6×105 M−1. Furthermore, a new approach to evaluate the association constant by utilizing the shift of the emission was used for the first time. The experimentally observed characteristics are supported by quantum chemical simulations.

Iodine-induced cleavage at phosphorothioate DNA (PT-DNA) is characterized by extremely high sensitivity (∼1 phosphorothioate link per 106 nucleotides), which has been used for detecting and sequencing PT-DNA in bacteria. Despite its foreseeable potential for wide applications, the cleavage mechanism at the PT-modified site has not been well established, and it remains unknown as to whether or not cleavage of the bridging P-O occurs at every PT-modified site. In this work, we conducted accurate ωB97X-D calculations and high-performance liquid chromatography-mass spectrometry to investigate the process of PT-DNA cleavage at the atomic and molecular levels. We have found that iodine chemoselectively binds to the sulfur atom of the phosphorothioate link via a strong halogen-chalcogen interaction (a type of halogen bond, with binding affinity as high as 14.9 kcal/mol) and thus triggers P-O bond cleavage via phosphotriester-like hydrolysis. Additionally, aside from cleavage of the bridging P-O bond, the downstream hydrolyses lead to unwanted P-S/P-O conversions and a loss of the phosphorothioate handle. The mechanism we outline helps to explain specific selectivity at the PT-modified site but also predicts the dynamic stoichiometry of P-S and P-O bond breaking. For instance, Tris is involved in the cascade derivation of S-iodo-phosphorothioate to S-amino-phosphorothioate, suppressing the S-iodo-phosphorothioate hydrolysis to a phosphate diester. However, hydrolysis of one-third of the Tris-O-grafting phosphotriester results in unwanted P-S/P-O conversions. Our study suggests that bacterial DNA phosphorothioation may more frequently occur than previous bioinformatic estimations have predicted from iodine-induced deep sequencing data.

This article discusses the synthesis of halogen-bond-donor-site-introduced functional monomers through the Wittig reaction of perfluorohalogenated benzaldehydes. The study focuses on the potential utility of perfluorohalogenated styrenes as functional monomers in smart polymer materials. The authors report on the Wittig reaction of perfluorohalogenated benzaldehydes and provide insights into the key factors for obtaining these functional monomers. The research aims to facilitate future research endeavors in the field of small-molecule synthesis. The given text appears to be a table showing various reactions and their conditions. It also includes information about molecular electrostatic potential maps, V s,min, and NBO charges. The table provides data on different organic bases and their corresponding values for V s,min and NBO charges. The information seems to be relevant for research on organic chemistry and may be useful for understanding the properties and behavior of different organic bases. This article discusses the development of an organic-base-mediated Wittig reaction for the synthesis of 2,3,5,6-tetrafluoro-4-halobenzaldehydes (TFXSs) from 2,3,5,6-tetrafluoro-4-halobenzaldehydes. The authors conducted experiments using different bases and solvents to optimize the reaction conditions and improve the yield of TFXSs. They also performed density functional theory (DFT) calculations [Extracted from the article]

Herein, we reported a practical and metal‐free synthesis of 2,3‐dihydroindolizines using N‐alkyl pyridinium salts and electron‐deficient alkenes with ambient air as a sole oxidant. Interestingly, a halogen bond donor (penta‐fluoroiodobenzene 20 mol %) was successfully applied to promote this partial oxidation by slowing down the undesired decomposition processes, probably because of the formation of a halogen‐bonded adduct. Moreover, the C1 position of 2,3‐dihydroindolizines was utilized as a good nucleophile for nucleophilic aromatic substitution with 4‐iodo‐1‐methylpyridin‐1‐ium trifluoromethanesulfonate as electrophile and provided a new‐type dipyridinium compound effectively. [ABSTRACT FROM AUTHOR]

The halogenated volatile solid additives can delicately optimize the active layer morphology of organic solar cells, improving the devices' performance, stability, and reproducibility. However, what type of intermolecular interaction occurs between the solid additives and the active layer and whether the interaction truly impacts the donor or acceptor remains debatable. Herein, the focus is on halogenated volatile solid additives with conjugated benzene rings and their influence on the morphology of the active layer composed of PM6:Y6 as they evaporated. The absorbance spectra exhibit apparent red‐shift features in Y6 absorption regions, while the donor part is unaffected. The theoretical calculation results reveal that the additives can stay between two Y6 molecules and form halogen bonds, affecting the π–π aggregation properties of Y6. As a result, the crystalline features of the active layer are altered, leading to increased charge carrier mobilities, extended charge carrier diffusion lengths, reduced bimolecular charge recombination, and thus the device performance. Especially when 1,3,5‐tri bromobenzene is used, a champion power conversion efficiency of 17.9% is attained, among the best‐performed organic solar cells comprising PM6:Y6. The findings shed light on theoretical and experimental guidelines for designing and developing volatile solid additives for highly efficient nonfullerene organic solar cells. [ABSTRACT FROM AUTHOR]

The reaction of tellurium(IV) oxide with trimethylammonium chloride in the presence of gaseous chlorine in concentrated hydrochloric acid gives supramolecular dichlorohexachlorotellurate (Me3NH)2{[TeCl6](Cl2)} (I), whose structure is determined by X-ray diffraction (XRD) (CIF file CCDC no. 2217752). The data of elemental and XRD analyses suggest a restricted stability of the synthesized compound. Specific features of noncovalent Cl···Cl interactions in the crystal structure of compound I are studied by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Shape‐changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape‐morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self‐healing ability. Here, we report halogen‐bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape‐programmed and that self‐heal under mild thermal or photothermal stimulation. We incorporate halogen‐bond‐donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self‐healing. Utilizing the halogen‐bonded LCEs, we demonstrate proof‐of‐concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators. [ABSTRACT FROM AUTHOR]

This study reports the synthesis and characterization of a "click‐able" iridium(III) complex as halogen bond‐based anion sensor. The functionalization is exemplarily demonstrated by the attachment of poly(ethylene glycol) azide via a "copper‐click"‐reaction. Subsequently, the polymeric XB donor complex is characterized in depth with 1H NMR spectroscopy, size exclusion chromatography, and MALDI‐ToF‐MS. Moreover, the anion binding capabilities are demonstrated with emission titrations revealing strong anion complexation. These findings emphasize the great potential of this approach to tune the complex's properties or include other functions such as cation complexation sites to exploit cooperative effects by using polymeric substituents on the iridium complex. [ABSTRACT FROM AUTHOR]

We designed 0D, 1D, and 2D supramolecular assemblies made of diaryliodonium salts (functioning as double σ-hole donors) and carboxylates (as σ-hole acceptors). The association was based on two charge-supported halogen bonds (XB), which occurred between IIII sites of the iodonium cations and the carboxylate anions. The sequential introduction of the carboxylic groups in the aryl ring of the benzoic acid added a dimension to the 0D supramolecular organization of the benzoate, which furnished 1D-chained and 2D-layered structures when terephthalate and trimesate anions, correspondingly, were applied as XB acceptors. The structure-directing XB were studied using DFT calculations under periodic boundary conditions and were followed by the one-electron-potential analysis and the Bader atoms-in-molecules topological analysis of electron density. These theoretical methods confirmed the existence of the XB and verified the philicities of the interaction partners in the designed solid-state structures. [ABSTRACT FROM AUTHOR]

Abstract The nature of (imide)N–X⋯N(pyridine) halogen‐bonded complexes formed by six N‐haloimides and sixteen 2‐substituted pyridines are studied using X‐ray crystallography (68 crystal structures), Density Functional Theory (DFT) (86 complexation energies), and NMR spectroscopy (90 association constants). Strong halogen bond (XB) donors such as N‐iodosuccinimide form only 1:1 haloimide:pyridine crystalline complexes, but even stronger N‐iodosaccharin forms 1:1 haloimide:pyridine and three other distinct complexes. In 1:1 haloimide:pyridine crystalline complexes, the haloimide's N─X bond exhibits an unusual bond bending feature that is larger for stronger N‐haloimides. DFT complexation energies (ΔEXB) for iodoimide–pyridine complexes range from −44 to −99 kJ mol−1, while for N‐bromoimide–pyridine, they are between −31 and −77 kJ mol−1. The ΔEXB of I⋯N XBs in 1:1 iodosaccharin:pyridine complexes are the largest of their kind, but they are substantially smaller than those in [bis(saccharinato)iodine(I)]pyridinium salts (−576 kJ mol−1), formed by N‐iodosaccharin and pyridines. The NMR association constants and ΔEXB energies of 1:1 haloimide:pyridine complexes do not correlate as these complexes in solution are heavily influenced by secondary interactions, which DFT studies do not account for. Association constants follow the σ‐hole strengths of N‐haloimides, which agree with DFT and crystallography data. The haloimide:2‐(N,N‐dimethylamino)pyridine complex undergoes a halogenation reaction resulting in 5‐iodo‐2‐dimethylaminopyridine.

Strategies commonly used for the synthesis of functionalised bicyclo[1.1.1]pentanes (BCP) rely on the reaction of [1.1.1]propellane with anionic or radical intermediates. In contrast, electrophilic activation has remained a considerable challenge due to the facile decomposition of BCP cations, which has severely limited the applications of this strategy. Herein, we report the electrophilic activation of [1.1.1]propellane in a halogen bond complex, which enables its reaction with electron-neutral nucleophiles such as anilines and azoles to give nitrogen-substituted BCPs that are prominent motifs in drug discovery. A detailed computational analysis indicates that the key halogen bonding interaction promotes nucleophilic attack without sacrificing cage stabilisation. Overall, our work rehabilitates electrophilic activation of [1.1.1]propellane as a valuable strategy for accessing functionalised BCPs.

The complexation of an alkali metal ion by a model macrocycle is examined using the M05-2X/DGDZVP DFT method. The macrocycle is built by connecting three cyclopenta[b]pyrrole motifs with alternating acetylene and ethylene linkages. Replacing one of the C-H bonds in each motif with a C-I bond allows for the formation of three intramolecular C-I···N halogen bonds. Two distinct binding modes were found for the complexation of each metal ion. In one mode, the binding of the ion occurs solely by the iodine atoms, via I···M+ interactions, while maintaining the integrity of the halogen bonds. The complexation energies are in the range −66 to −35 kcal/mol. In the other mode, the binding of the ion includes one nitrogen atom as well, with binding energies in the range of −71 to −38 kcal/mol. In this binding mode, the halogen bond network is weakened. The presence and strength of the interactions are further examined using AIM and NBO calculations. Lastly, the geometries for the transition state structures linking the less stable to the more stable metal ion complexes were obtained, and their calculated Gibbs free energy barriers were found in the range of 1.6 to 1.9 kcal/mol.

We presented a cascade transformation of N, N‐diallylamines and fluoroalkyl iodides into various functionalized fluoroalkylated pyrrolidines through a visible light‐induced synthetic process in the solvent‐free conditions. In this reaction system, the substrate N, N‐diallylamine acted both as the base and the electron donor. We further demonstrated the practicality of this protocol by the direct modification of amino acids and pharmaceutical molecules. [ABSTRACT FROM AUTHOR]

Due to their high electron density, fluoride anions can be considered the most effective halogen bond (HaB) acceptors among the halides. However, under common experimental conditions, F− uncommonly acts as HaB acceptor, expectedly as it is present in hydrated form. Herein we report that under specific crystallization conditions a hydrogen bond‐free F− functioning as donor of electron density can be obtained, with the formed HaBs constituting the driving force of the observed crystal packings. Computations confirm the strength of these HaBs compared to analogous interactions involving other halides. [ABSTRACT FROM AUTHOR]

2,3,5,6-Tetramethyl-1,4-diisocyanobenzene (1), 1,4-diisocyanobenzene (2), and 1,4-dicyanobenzene (3) were co-crystallized with 1,3,5-triiodotrifluorobenzene (1,3,5-FIB) to give three cocrystals, 1·1,3,5-FIB, 2·2(1,3,5-FIB), and 3·2(1,3,5-FIB), which were studied by X-ray diffraction. A common feature of the three structures is the presence of I···Cisocyanide or I···Nnitrile halogen bonds (HaBs), which occurs between an iodine σ-hole and the isocyanide C-(or the nitrile N-) atom. The diisocyanide and dinitrile cocrystals 2·2(1,3,5-FIB) and 3·2(1,3,5-FIB) are isostructural, thus providing a basis for accurate comparison of the two types of noncovalent linkages of C≡N/N≡C groups in the composition of structurally similar entities and in one crystal environment. The bonding situation was studied by a set of theoretical methods. Diisocyanides are more nucleophilic than the dinitrile and they exhibit stronger binding to 1,3,5-FIB. In all structures, the HaBs are mostly determined by the electrostatic interactions, but the dispersion and induction components also provide a noticeable contribution and make the HaBs attractive. Charge transfer has a small contribution (<5%) to the HaB and it is higher for the diisocyanide than for the dinitrile systems. At the same time, diisocyanide and dinitrile structures exhibit typical electron-donor and π-acceptor properties in relation to the HaB donor. [ABSTRACT FROM AUTHOR]

N−X⋅⋅⋅−O−N+ halogen‐bonded systems formed by 27 pyridine N‐oxides (PyNOs) as halogen‐bond (XB) acceptors and two N‐halosuccinimides, two N‐halophthalimides, and two N‐halosaccharins as XB donors are studied in silico, in solution, and in the solid state. This large set of data (132 DFT optimized structures, 75 crystal structures, and 168 1H NMR titrations) provides a unique view to structural and bonding properties. In the computational part, a simple electrostatic model (SiElMo) for predicting XB energies using only the properties of halogen donors and oxygen acceptors is developed. The SiElMo energies are in perfect accord with energies calculated from XB complexes optimized with two high‐level DFT approaches. Data from in silico bond energies and single‐crystal X‐ray structures correlate; however, data from solution do not. The polydentate bonding characteristic of the PyNOs' oxygen atom in solution, as revealed by solid‐state structures, is attributed to the lack of correlation between DFT/solid‐state and solution data. XB strength is only slightly affected by the PyNO oxygen properties [(atomic charge (Q), ionization energy (Is,min) and local negative minima (Vs,min)], as the σ‐hole (Vs,max) of the donor halogen is the key determinant leading to the sequence N‐halosaccharin>N‐halosuccinimide>N‐halophthalimide on the XB strength. [ABSTRACT FROM AUTHOR]

As a new type of non‐covalent interaction similar to hydrogen bond, halogen bond has become an important supramolecular tool in crystal engineering, material chemistry, biological science, etc., due to its unique properties. In fact, halogen bond has been confirmed on the effect of molecular assemblies and soft materials, and widely used in various functional soft materials including liquid crystals, gels and polymers. In recent years, halogen bonding has aroused strong interest in inducing molecular assembly into low‐molecular‐weight gels (LMWGs). To the best of our knowledge, there is still a lack of in‐depth review of this field. So, in this paper, the recent progress of LMWGs driven by halogen bonding is reviewed. According to the number of components forming halogen bonded gels, the structural characteristics of halogen bonded supramolecular gels, the relationship between halogen bonding and other non‐covalent interactions, as well as the application fields of halogen bonded gels are introduced, respectively. In addition, the challenges faced by halogenated supramolecular gels at present and their development prospects in future have been proposed. We believe that the halogen bonded gel will have more impressive applications in the next few years, opening exciting new opportunities for the development of soft materials. [ABSTRACT FROM AUTHOR]

The development of high-performance fluorescence probes has been an active area of research. In the present work, two new pH sensors Zn-3,5-Cl-saldmpn and Zn-3,5-Br-saldmpn based on a halogenated Schiff ligand (3,5-Cl-saldmpn = N, N′-(3,3′-dipropyhnethylamine) bis (3,5-chlorosalicylidene)) with linearity and a high signal-to-noise ratio were developed. Analyses revealed an exponential intensification in their fluorescence emission and a discernible chromatic shift upon pH increase from 5.0 to 7.0. The sensors could retain over 95% of their initial signal amplitude after 20 operational cycles, demonstrating excellent stability and reversibility. To elucidate their unique fluorescence response, a non-halogenated analog was introduced for comparison. The structural and optical characterization suggested that the introduction of halogen atoms can create additional interaction pathways between adjacent molecules and enhance the strength of the interaction, which not only improves the signal-to-noise ratio but also forms a long-range interaction process in the formation of the aggregation state, thus enhancing the response range. Meanwhile, the above proposed mechanism was also verified by theoretical calculations. [ABSTRACT FROM AUTHOR]

We report here on the status of research on halogen bonds and other σ‐hole interactions involving p‐block elements in Lewis acidic roles, such as chalcogen bonds, pnictogen bonds and tetrel bonds. A brief overview of the available literature in this area is provided via a survey of the many review articles that address this field. Our focus has been to collect together most review articles published since 2013 to provide an easy entry into the extensive literature in this area. A snapshot of current research in the area is provided by an introduction to the virtual special issue compiled in this journal, comprising 11 articles and entitled `Halogen, chalcogen, pnictogen and tetrel bonds: structural chemistry and beyond.'A compilation of review articles on σ‐hole interactions published since 2013 is presented alongside an overview of the 11 articles in the special issue on this topic. [ABSTRACT FROM AUTHOR]