Search

Halogen⋯halogen interaction is a highly debated and important topic in crystal engineering and supramolecular chemistry. There are controversies about the nature and geometry of these interactions. F, Cl, Br and I are the four halogens involved in these interactions. Very often the lighter and the heavier halogens behave differently. The nature of the interactions also depends upon the nature of the atom which is covalently bonded to the halogens. In this review different homo‐halogen⋯halogen, hetero‐halogen⋯halogen, halogen⋯halide interactions, their natures, and preferred geometries have been discussed. Different motifs of halogen⋯halogen interactions, interchangeability of the halogen⋯halogen interactions with other supramolecular synthons and interchangeability between different halogens and other functional groups also have been discussed. Some of the important applications, in which halogen⋯halogen interactions have been successfully employed, are mentioned. [ABSTRACT FROM AUTHOR]

The co‐crystallization of tetracyanobenzene (TCB) with haloarenes ArX provided six new co‐crystals TCB ⋅ ArX (ArX=PhCl, PhBr, 4‐MeC6H4Cl, 4‐MeC6H4Br, 4‐MeOC6H4Cl, 1,2‐Br2C6H4) which were studied by X‐ray diffraction. In these systems, the strong collective effect of π⋅⋅⋅π stacking interactions and lone pair‐(X)⋅⋅⋅π‐hole‐(C) bondings between TCB and ArX promote the strength of X⋅⋅⋅Ncyano halogen bonding (HaB). Theoretical studies showed that the stacking interactions affect the σ‐hole depth of the haloarenes, thus significantly boosting their ability to function as HaB donors. According to the molecular electrostatic potential calculations, the σ‐ hole‐(Cl) value (1.5 kcal/mol) in the haloarene 4‐MeOC6H4Cl (featuring an electron‐rich arene moiety and exhibiting very poor σ‐hole‐(Cl) ability) increases significantly in the stacked trimer (TCB)2 ⋅ 4‐MeOC6H4Cl (12.5 kcal/mol). Theoretical DFT calculations demonstrate the dramatic increase of X⋅⋅⋅Ncyano HaB strength for stacked trimers in comparison with parent unstacked haloarenes. [ABSTRACT FROM AUTHOR]

Polymers have long been known to us for their versatile utility in our daily lives. With many years of successful advancement in controlled polymer synthesis and supramolecular chemistry, currently an amalgamation of these two fields is becoming increasingly important for generating modern‐day emerging polymeric materials. Hydrogen bonding and other noncovalent interactions like π‐stacking, host‐guest interaction, electrostatic interaction, metal‐ligand coordination have been explored much to this context, unlike the recently emerged halogen bonding, which indeed shows advantageous features like superior hydrophobicity, directionality and polar solvent resistance compared to ubiquitous hydrogen bonding. Hence, rendering these properties of halogen bonding into polymeric domain for generating functional materials for application in advance nanotechnologies is highly desirable. In the recent years, substantial progress has been made in fulfilling this challenging goal. This is evident from the escalating number of scientific publications in this research area every year. In this minireview, we have summarized the most recent developments in the field of halogen bonded polymeric assemblies and supramolecular polymers and discussed them in the context of their emerging materials properties and functions. Emphasis is given on highlighting various design criteria adopted in crystal engineering, covalent and supramolecular polymers in the past five years for constructing diverse organic functional materials, viz. liquid crystals, photoresponsive and photochromic materials, biomaterials and gels, self‐healing materials and many others by virtue of this highly directional supramolecular tool. In conclusion, a brief perspective on the advantages, challenges and future prospects in this rapidly growing field of research is discussed. [ABSTRACT FROM AUTHOR]

An interplay between 4‐bromo‐ and 4‐iodo‐5‐nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4‐dimethylaminopyridine 2, isoquinoline 3, 4‐cyanopyridine 4, 2‐methylpyridine 5, 2‐aminopyridine 6, quinoline 7, 1‐methylisoquinoline 8, and 2,2'‐bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1–3 underwent N‐arylation to give the corresponding azinium salts (characterized by 1H and 13C{H} NMR and high‐resolution ESI‐MS). In contrast, azines 4–9 with sterically hindered N atoms or bearing an electron‐withdrawing substituent, form stable co‐crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co‐crystals, X⋅⋅⋅N structure‐directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0‐D3/def2‐TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from −7.6 kcal/mol (for 6 ⋅ INPN) to −11.4 kcal/mol (5 ⋅ INPN). [ABSTRACT FROM AUTHOR]

Halogen bonding is often described as being driven predominantly by electrostatics, and thus adducts between anionic halogen bond (XB) donors (halogen‐based Lewis acids) and anions seem counterintuitive. Such "anti‐electrostatic" XBs have been predicted theoretically but for organic XB donors, there are currently no experimental examples except for a few cases of self‐association. Reported herein is the synthesis of two negatively charged organoiodine derivatives that form anti‐electrostatic XBs with anions. Even though the electrostatic potential is universally negative across the surface of both compounds, DFT calculations indicate kinetic stabilization of their halide complexes in the gas phase and particularly in solution. Experimentally, self‐association of the anionic XB donors was observed in solid‐state structures, resulting in dimers, trimers, and infinite chains. In addition, co‐crystals with halides were obtained, representing the first cases of halogen bonding between an organic anionic XB donor and a different anion. The bond lengths of all observed interactions are 14–21 % shorter than the sum of the van der Waals radii. [ABSTRACT FROM AUTHOR]

A study of the strong N−X⋅⋅⋅−O−N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from −47.5 to −120.3 kJ mol−1; the strongest N−I⋅⋅⋅−O−N+ XBs approaching those of 3‐center‐4‐electron [N−I−N]+ halogen‐bonded systems (ca. 160 kJ mol−1). 1H NMR association constants (KXB) determined in CDCl3 and [D6]acetone vary from 2.0×100 to >108 m−1 and correlate well with the calculated donor×acceptor complexation enthalpies found between −38.4 and −77.5 kJ mol−1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (RXB) between 0.65–0.67 for the N−I⋅⋅⋅−O−N+ halogen bond. [ABSTRACT FROM AUTHOR]

A study of the strong N−X⋅⋅⋅−O−N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from −47.5 to −120.3 kJ mol−1; the strongest N−I⋅⋅⋅−O−N+ XBs approaching those of 3‐center‐4‐electron [N−I−N]+ halogen‐bonded systems (ca. 160 kJ mol−1). 1H NMR association constants (KXB) determined in CDCl3 and [D6]acetone vary from 2.0×100 to >108 m−1 and correlate well with the calculated donor×acceptor complexation enthalpies found between −38.4 and −77.5 kJ mol−1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (RXB) between 0.65–0.67 for the N−I⋅⋅⋅−O−N+ halogen bond. [ABSTRACT FROM AUTHOR]

Owing to their dynamic attributes, non‐covalent supramolecular interactions have enabled a new paradigm in the design and fabrication of multifunctional material systems with programmable properties, performances, and reconfigurable traits. Recently, the "halogen bond" has become an enticing supramolecular synthetic tool that displays a plethora of promising and advantageous characteristics. Consequently, this versatile and dynamic non‐covalent interaction has been extensively harnessed in various fields such as crystal engineering, self‐assembly, materials science, polymer chemistry, biochemistry, medicinal chemistry and nanotechnology. In recent years, halogen bonding has emerged as a tunable supramolecular synthetic tool in the design of functional liquid‐crystalline materials with adjustable phases and properties. In this Concept article, the use of halogen bond in the field of stimuli‐responsive smart soft materials, that is, liquid crystals is discussed. The design, synthesis and characterization of molecular and macromolecular liquid crystalline materials are described and the modulation of their properties has been emphasized. The power of halogen bonding in offering a large variety of functional liquid crystalline materials from readily accessible mesomorphic and non‐mesomorphic complementary building blocks is highlighted. The article concludes with a perspective on the challenges and opportunities in this emerging endeavor towards the realization of enabling and elegant dynamic functional materials. Holy halogens: The halogen bond is increasingly used in the realization of advanced functional materials. In this Concept article, we discuss the usage of halogen bond as an enabling supramolecular tool in the preparation of different kinds of functional liquid crystalline materials towards the understanding of their structure–property and structure–function relationships. [ABSTRACT FROM AUTHOR]

Abstract: Structural evidence obtained from in situ X‐ray diffraction shows that halogen bonding is responsible for the formation of a dynamic porous molecular solid. This material is surprisingly robust and undergoes reversible switching of its pore volume by activation or by exposure to a series of gases of different sizes and shapes. Volumetric gas sorption and pressure‐gradient differential scanning calorimetry (P‐DSC) data provide further mechanistic insight into the breathing behavior. [ABSTRACT FROM AUTHOR]

Recent theoretical studies suggested that hydrogen bonds between ions of like charges are of a covalent nature due to the dominating nD→σ*H‐A charge‐transfer (CT) interaction. In this work, energy profiles of typical hydrogen (H) and halogen (X) bonding systems formed from ions of like charges are explored using the block‐localized wavefunction (BLW) method, which can derive optimal geometries and wave functions with the CT interaction “turned off.” The results demonstrate that the kinetic stability, albeit reduced, is maintained for most investigated systems even after the intermolecular CT interaction is quenched. Further energy decomposition analyses based on the BLW method reveal that, despite a net repulsive Coulomb repulsion, a stabilizing component exists due to the polarization effect that plays significant role in the kinetic stability of all systems. Moreover, the fingerprints of the augmented electrostatic interaction due to polarization are apparent in the variation patterns of the electron density. All in all, much like in standard H‐ and X‐bonds, the stability of such bonds between ions of like charges is governed by the competition between the stabilizing electrostatic and charge transfer interactions and the destabilizing deformation energy and Pauli exchange repulsion. While in most cases of “anti‐electrostatic” bonds the CT interaction is of a secondary importance, we also find cases where CT is decisive. As such, this work validates the existence of anti‐electrostatic H‐ and X‐bonds. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Being electrostatic interactions in nature, hydrogen bonding (HB) and halogen bonding (XB) are considered to be two parallel worlds. In principle, all the applications that HB have could also be applied to XB. However, there has been no report on an anionic, metallic XB acceptor, but metal anions have been observed to be good HB acceptors. This missing mosaic piece of XB theory is because common metal anions are reactive for XB donors. In view of this, two strategies are proposed for designing metallic acceptor-containing XB using ab initio calculations. The first one is to utilize a metal cluster anion with a high electron detachment energy, such as the superatom, Al13− as the XB acceptor. The second strategy is to design a ligand-passivated/protected metal core that can maintain the negative charge; several exotic clusters, such as PtH5−, PtZnH5−, and PtMgH5−, are used as examples. Based on these two strategies, it is anticipated that more metallic acceptor-containing XBs will be discovered. [ABSTRACT FROM AUTHOR]

N-Salicilideneanilines are among the most studied thermo- and photochromic systems in the solid state. Although thermochromism is a general property of crystalline N-salicilideneanilines, photochromism is known in a limited number of cases. As a method for the construction of thermo- and photo-responsive molecular architectures, the co-crystallisation of 1,2,4,5-tetrafluoro-3,6-diiodobenzene ( I2F4) with three selected imines of o-vanillin, named 1, 2 and 3, obtained through a condensation reaction with 3-aminopyridine, 4-bromoaniline and 4-iodoaniline, respectively, is reported herein. All crystals and co-crystals have been characterised by means of solid-state complementary techniques (X-ray diffraction, solid-state NMR spectroscopy, absorption and emission spectroscopy). The role of halogen bonding and crystal packing in the optical and chromic properties of all solid materials is discussed. All solids exhibit thermochromic behaviour, and three of them ( 2, 22⋅I2F4 and 32⋅I2F4) are also photochromic. Imine derivative 3 crystallises in two different polymorphic forms ( 3 A and 3 B) and a solvate ( 3Solv). The bromo and iodo derivatives, 2 and 3 B, are isomorphous and form isomorphous co-crystals with I2F4, but behave differently when exposed to UV light because only crystalline 2 is photochromic. Interestingly, the replacement of bromine with iodine seems to turn off the photochromism because crystalline 3 A and 3Solv, and even the 20.7 30.3 solid solution, do not manifest photochromic behaviour. [ABSTRACT FROM AUTHOR]

The synthesis and comprehensive characterization of a systematic series of cleft-type anion receptors imbedded into a polymeric architecture is presented. For the first time, isothermal calorimetric titrations on polymeric halogen-bond-based donors were exploited to evaluate the dependence of the anion affinity on different key parameters (i.e. monomeric versus polymeric receptor, halogen versus hydrogen bonding, charge assistance). The combination of these donor systems with a copolymer bearing accepting carboxylate groups led to supramolecular cross-linked polymer networks showing excellent intrinsic self-healing behavior. FT-Raman spectroscopy and nano-indentation measurements were utilized to clarify the thermally induced self-healing mechanism based on the formation of halogen bonds. These first self-healing materials based on halogen bonds pave the way for new applications of halogen-bond donors in polymer and material science. [ABSTRACT FROM AUTHOR]

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [C nF2 n+1-I⋅⋅⋅I⋅⋅⋅I-C nF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. [ABSTRACT FROM AUTHOR]

A homologous series of donor-π-acceptor dyes was synthesized, differing only in the identity of the halogen substituents about the triphenylamine (TPA; donor) portion of each molecule. Each Dye-X (X=F, Cl, Br, and I) was immobilized on a TiO2 surface to investigate how the halogen substituents affect the reaction between the light-induced charge-separated state, TiO2(e−)/ Dye-X+, with iodide in solution. Transient absorption spectroscopy showed progressively faster reactivity towards nucleophilic iodide with more polarizable halogen substituents: Dye-F < Dye-Cl < Dye-Br < Dye-I. Given that all other structural and electronic properties for the series are held at parity, with the exception of an increasingly larger electropositive σ-hole on the heavier halogens, the differences in dye regeneration kinetics for Dye-Cl, Dye-Br, and Dye-I are ascribed to the extent of halogen bonding with the nucleophilic solution species. [ABSTRACT FROM AUTHOR]

Iodothyronine deiodinases (IDs) are mammalian selenoenzymes that play an important role in the activation and inactivation£ of thyroid hormones. It is known that iodothyronamines (TnAMs), produced by the decarboxylation of thyroid hormones, act as substrates for deiodinases. To understand whether decarboxylation alters the rate and/or regioselectivity of deiodination by using synthetic deiodinase mimics, we studied the deiodination of different iodothyronamines. The triiodo derivative 3,3′,5-triiodothyronamine (T3 AM) is deiodinated at the inner ring by naphthyl-based deiodinase mimics, which is similar to the deiodination of 3,3′,5-triiodothyronine (T3). However, T3 AM undergoes much slower deiodination than T3. Detailed experimental and theoretical investigations suggest that T3 AM forms a weaker halogen bond with selenium donors than T3. Kinetic studies and single-crystal X-ray structures of T3 and T3 AM reveal that intermolecular I⋅⋅⋅I interactions may play an important role in deiodination. The formation of hydrogen- and halogen-bonding assemblies, which leads to the formation of a dimeric species of T3 in solution, facilitates the interactions between the selenium and iodine atoms. In contrast, T3 AM, which does not have I⋅⋅⋅I interactions, undergoes much slower deiodination. [ABSTRACT FROM AUTHOR]

Halogen bonding is the formation of a non-covalent interaction between an electrophilic halogen substituent and a Lewis base, for instance, a halide. These kinds of relatively weak interactions have found applications in crystal engineering and initial applications in solution-phase chemistry are starting to appear. We report on the exploration of bis(iodoimidazolium) compounds as halogen-based Lewis acids in the activation of glycosyl halides. We show that these dicationic halogen-bond donors can be used to activate glycosyl halides if the carbohydrate core is sufficiently reactive enough. Furthermore, we provide comparison experiments which indicate that the mode of activation is indeed based on halogen bonding. This represents the first glycosylation reaction mediated by a (carbon-backbone-based) halogen-bond donor. [ABSTRACT FROM AUTHOR]

Insight into the key factors driving the competition of halogen and hydrogen bonds is obtained by studying the affinity of the Lewis bases trimethylamine (TMA), dimethyl ether (DME), and methyl fluoride (MF) towards difluoroiodomethane (CHF2I). Analysis of the infrared and Raman spectra of solutions in liquid krypton containing mixtures of TMA and CHF2I and of DME and CHF2I reveals that for these Lewis bases hydrogen and halogen-bonded complexes appear simultaneously. In contrast, only a hydrogen-bonded complex is formed for the mixtures of CHF2I and MF. The complexation enthalpies for the CH ⋅⋅⋅Y hydrogen-bonded complexes with TMA, DME, and MF are determined to be −14.7(2), −10.5(5) and −5.1(6) kJ mol−1, respectively. The values for the CI ⋅⋅⋅Y halogen-bonded isomers are −19.0(3) kJ mol−1 for TMA and −9.9(8) kJ mol−1 for DME. Generalization of the observed trends suggests that, at least for the bases studied here, softer Lewis bases such as TMA favor halogen bonding, whereas harder bases such as MF show a substantial preference for hydrogen bonding. [ABSTRACT FROM AUTHOR]

Bis(I2) ‐ Addukte von Hexamethoniumdihalogeniden sind so organisiert, dass sie auf dynamisches Heizen reagieren und eine Struktur annehmen können, aus der die Bildung von relativ instabilen, bisher unbekannten [I2Br2]2− ‐ und [I2Cl2]2− ‐ Tetrahalogeniden möglich ist, die in Lösung nicht erhalten werden können (siehe Bild). Die kavitätsgesteuerte Reaktivität bietet neue Möglichkeiten für die Synthese und Umwandlung von Polyhalogenanionen. [ABSTRACT FROM AUTHOR]

This study targets the construction of porphyrin assemblies directed by halogen bonds, by utilizing a series of purposely synthesized Sn(axial ligand)2-(5,10,15,20-tetraarylporphyrin) [Sn(L)2-TArP] complexes as building units. The porphyrin moiety and the axial ligands in these compounds contain different combinations of complimentary molecular recognition functions. The former bears p-iodophenyl, p-bromophenyl, 4′-pyridyl, or 3′-pyridyl substituents at the meso positions of the porphyrin ring. The latter comprises either a carboxylate or hydroxy anchor for attachment to the porphyrin-inserted tin ion and a pyridyl-, benzotriazole-, or halophenyl-type aromatic residue as the potential binding site. The various complexes were structurally analyzed by single-crystal X-ray diffraction, accompanied by computational modeling evaluations. Halogen-bonding interactions between the lateral aryl substituents of one unit of the porphyrin complex and the axial ligands of neighboring moieties was successfully expressed in several of the resulting samples. Their occurrence is affected by structural (for example, specific geometry of the six-coordinate complexes) and electronic effects (for example, charge densities and electrostatic potentials). The shortest intermolecular I⋅⋅⋅N halogen-bonding distance of 2.991 Å was observed between iodophenyl (porphyrin) and benzotriazole (axial ligand) moieties. Manifestation of halogen bonds in these relatively bulky compounds without further activation of the halophenyl donor groups by electron-withdrawing substituents is particularly remarkable. [ABSTRACT FROM AUTHOR]

Charge-assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge-transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT-TTFI2)2(TCNQF n), n=0-2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT-TTFI2, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF2) through highly directional CI⋅⋅⋅N≡C halogen-bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge-transfer complex is isolated whereas with the more oxidizing TCNQF2 acceptor, an ionic, highly conducting charge-transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral-ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the CI⋅⋅⋅N≡C halogen-bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen-bonding interaction. The neutral-ionic conversion in (EDT-TTFI2)2(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups. [ABSTRACT FROM AUTHOR]

The article presents a study on organocatalysis through halogen-bond donors. It states that 2,6-diiodo-3,4,5-trifluoropheny group was usually selected as building block due to electron-withdrawing fluorine substituents, high rigidity to be achieved through aryl moieties coupling, and avoidance from atrop-isomers formation. It adds that neutral multidentate halogen-bond donors were able to catalyze the chemical reaction between silyl enol ethers and ketene silyl acetals with 1-chloroisochroman.

Multi-component organic nanocrystals that are comprised of two or more supramolecular building blocks can be used to extend the design and assembly scope of solid molecular materials. Herein, we report the use of ultrasonication to prepare halogen-bonded stilbene-based nano-cocrystals that exhibit different photoemission properties, including one- and two-phonon emission and fluorescence lifetimes, relative to those of macrodimensional crystals. The structural transformation from nano-cocrystals into nanocrystals upon heating results in a luminescence red-shift from greenish blue to yellow. The temperature-dependent ratiometric luminescence may allow such nano-cocrystals to be used as fluorescent sensors and thermosensitive materials. [ABSTRACT FROM AUTHOR]

Photoresponsive supramolecular gels with various applications are being constantly pursued; however, achieving well‐defined morphology changes of gels via light irradiation remains a formidable challenge. In this study, a gel is prepared through halogen bond between azopyridine‐containing Azopy‐C10 and 1,4‐tetrafluorodiiodobenzene. The gel exhibits gel–sol transition due to trans–cis isomerization of the azopyridine moiety upon UV irradiation. During this transition, the morphologies vary from flake to fluffy bobble‐like and finally to peony‐like with increasing exposure time, which is difficult to achieve in traditional assembly systems. The microstructure change is attributed to the variations of cis‐isomer content and halogen‐bonding strength. The supramolecular gel provides a novel method to achieve photomodulated morphologies and broadens the applications of such kind of materials, ranging from information storage to high‐tech anticounterfeit. Herein, halogen bond acts as an important driving force to fabricate a supramolecular gels between azopyridine‐containing Azopy‐C10 and 1,4‐diiodotetrafluorobenzene. During the gel–sol transition upon UV irradiation, the morphological changes from flake to fluffy bobble‐like and finally to peony‐like can be achieved, which are difficult to achieve by traditional assembly systems. [ABSTRACT FROM AUTHOR]