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This research article evidences the importance of group-10 π-hole⋯dz2[MII] interactions using a combination of DFT calculations and CSD structures.

Methyltrioxorhenium(VII) (MTO) is a widely employed catalyst for metathesis, olefination, and most importantly, oxidation reactions. It is often preferred to other oxometal complexes due to its stability in air and higher efficiency. The seminal papers of K. B. Sharpless showed that when pyridine derivatives are used as co-catalysts, MTO-catalyzed olefin epoxidation with H

Porous architectures characterized by parallel channels arranged in honeycomb or rectangular patterns are identified in two polymorphic crystals of a zwitterionic 4-(aryliodonio)-benzenesulfonate. The channels are filled with disordered water molecules which can be reversibly removed on heating. Consistent with the remarkable strength and directionality of the halogen bonds (XBs) driving the crystal packing formation, the porous structure is stable and fully preserved on almost quantitative removal and readsorption of water. The porous systems described here are the first reported cases of one-component 3D organic frameworks whose assembly is driven by XB only (XOFs). These systems are a proof of concept for the ability of zwitterionic aryliodonium tectons in affording robust one-component 3D XOFs. The high directionality and strength of the XBs formed by these zwitterions and the geometrical constraints resulting from the tendency of their hypervalent iodine atoms to act as bidentate XB donors might be key factors in determining this ability.

The N+–CH3 unit can function as a tetrel bond donor site both with charged and neutral electron density donor units.

X-ray analyses of some adducts between AuX3 (X = Cl, Br) and several pyridine derivatives show short π-hole CiBs; computational studies reveal the attractive nature of these short contacts, confirming their key role in driving their crystal packing.

The simultaneous binding of a molecular entity through two interactions is a frequently pursued recognition mode due to the advantages it offers in securing molecular self-assembly. Here we report how the planarity of the benzothienoiodolium (BTI) cation allows for preorganizing in the cation plane the hydrogen, halogen, and chalcogen bonds (HB, XB, and ChBs, respectively) formed by the phenyl hydrogen, iodolium iodine, and thienyl sulfur. Crystallographic analyses of some BTI salts show how this interactions coplanarity enables for their coupling to point towards a single anion that is coordinated via the supramolecular and heteroditopic synthon XB/HB or XB/ChB, the latter observed here for the first time. These synthons adopt a Janus like arrangement around iodine. Crystallographic information suggest that interactions of the synthons act synergistically, e.g., when resulting in the unusually short ChBs formed by the thienyl sulfur. Determination of the molecular electrostatic potential, Bader’s quantum theory of “atoms-in-molecules” analysis, natural bond orbital investigations give information on the nature and energetic aspects of the short contacts observed in crystals

The co-crystallization of tetracyanobenzene (TCB) with haloarenes ArX provided six new co-crystals TCB ⋅ ArX (ArX=PhCl, PhBr, 4-MeC

In this communication experimental and theoretical results are reported affording strong evidence that interactions between electron rich atoms and the metal of tetroxide anions of group 7 elements are a new case of attractive and σ-hole interactions. Single crystal X-ray analyses, molecular electrostatic potentials, quantum theory of atoms-in-molecules, and noncovalent interaction plot analyses show that in crystalline permanganate and perrhenate salts the metal in Mn/ReO4- anion can act as electron acceptors, the oxygen of another Mn/ReO4- anion can act as the donor and supramolecular anionic dimers or polymers are formed. The name matere bond (MaB) is proposed to categorize these noncovalent interactions and to differentiate them from the classical metal-ligand coordination bond.

Chalcogen bonds are the specific interactions involving group 16 elements as electrophilic sites. The role of chalcogen atoms as sticky sites in biomolecules is underappreciated, and the few available studies have mostly focused on S. Here, we carried out a statistical analysis over 3562 protein structures in the Protein Data Bank (PDB) containing 18 266 selenomethionines and found that Se···O chalcogen bonds are commonplace. These findings may help the future design of functional peptides and contribute to understanding the role of Se in nature.

This communication reports experimental and theoretical evidences of σ‐hole interactions in adducts between nitrogen or oxygen nucleophiles and tetroxides of osmium or other group 8 elements. Cocrystals between pyridine or pyridine N‐oxide derivatives and osmium tetroxide are characterized through various techniques and rationalized as σ‐hole interactions using DFT calculations and several other computational tools. We propose the term “osme bond” (OmB, Om=Fe, Ru, Os, (Hs)) for naming the noncovalent interactions wherein group 8 elements have the role of the electrophile. The word osme is the transcription of ὀσμή, the ancient Greek word for smell that was used to name the heaviest group 8 element in relation to the smoky odor of its tetroxide., σ‐Hole interactions in adducts between nitrogen or oxygen nucleophiles and tetroxides of osmium or other group 8 elements are reported. Cocrystals between pyridine or pyridine N‐oxide derivatives and osmium tetroxide are characterized through various techniques including computational tools. We propose the term “osme bond” (OmB, Om=Fe, Ru, Os, (Hs)) for naming the noncovalent interactions wherein group 8 elements have the role of the electrophile.

Five structures bearing the

The controlled oxidation reaction of L‐selenocystine under neutral pH conditions affords selenocysteine seleninic acid (3‐selenino‐L‐alanine) which is characterized also by means of single‐crystal X‐ray diffraction. This technique shows that selenium forms three chalcogen bonds (ChBs), one of them being outstandingly short. A survey of seleninic acid derivatives in the Cambridge Structural Database (CSD) confirms that the C−Se(=O)O− functionality tends to act as a ChB donor robust enough to systematically influence the interactional landscape in the solid. Quantum Theory of Atom in Molecules (QTAIM) analysis proves the attractive nature of the short contacts observed in crystals containing the seleninic functionality and calculation of surface molecular electrostatic potential (MEP) reveals that remarkably positive σ‐holes can frequently be found opposite to the covalent bonds at selenium. Both CSD searches and QTAIM and MEP approaches show that also the sulfinic acid moiety can function as a ChB donor, albeit less frequently than the seleninic acid one. These findings may contribute to a better understanding, at the atomic level, of the mechanism of action of the enzymes that control oxidative stress and ROS deactivation and that contain selenocysteine seleninic acid and cysteine sulfinic acid in the active site., L‐selenocysteine seleninic acid displays in the solid state three short chalcogen bonds. Analyses of the Cambridge Structural Database and theoretical studies prove that seleninic acid derivatives frequently show the presence of positive σ‐holes and function as robust chalcogen bond donors. Sulfinic acid derivatives behave similarly, but σ‐holes are less positive and chalcogen bonds are formed less commonly.

Interactions in crystalline tetrachloridoaurates of acetylcholine and dimethylpropiothetine are characterized by Au⋅⋅⋅Cl and Au⋅⋅⋅O short contacts. The former interactions assemble the AuCl4 − units into supramolecular anionic polymers, while the latter interactions append the acetylcholine and propiothetine units to the polymer. The distorted octahedral geometry of the bonding pattern around the gold center is rationalized on the basis of the anisotropic distribution of the electron density, which enables gold to behave as an electrophile (π‐hole coinage‐bond donor). Computational studies prove that gold atoms in negatively charged species can function as acceptors of electron density. The attractive nature of the Au⋅⋅⋅Cl/O interactions described here complement the known aurophilic bonds involved in gold‐centered interactions., The gold atom of the AuCl4 − moiety forms attractive anion⋅⋅⋅anion and anion⋅⋅⋅neutral electron–donor interactions. These interactions are rationalized as π‐hole coinage bonds and give rise to robust and reliable supramolecular synthons which control recognition and organization phenomena in the solid state. Hence, they might be considered for tuning structural and functional features in materials and biosystems.

We carried out a systematic evaluation of the packing forces in co-crystals featuring monoiodo- and diiodo-perfluoroalkanes and 1,2,4-oxadiazoles through single crystal X-ray diffraction and theoretical analysis. The molecules assemble via a combination of halogen bonding and specific dispersive interactions involving the perfluorinated units. We quantitatively elucidated the nature and strength of such interactions through solid-state calculations and Hirshfeld surface analysis. One of the co-crystals, formed by two monoiodoperfluorodecane molecules, the longest perfluorinated chain ever solved at the atomic level, allowed us to fully highlight the role of fluorous interactions.

Here, we demonstrate that introduction of halogen atoms at the tyrosine 10 phenol ring of the DSGYEV sequence derived from the flexible amyloid‐β N‐terminus, promotes its self‐assembly in the solid state. In particular, we report the crystal structures of two halogen‐modified sequences, which we found to be stabilized in the solid state by halogen‐mediated interactions. The structural study is corroborated by Non‐Covalent Interaction (NCI) analysis. Our results prove that selective halogenation of an amino acid enhances the supramolecular organization of otherwise unstructured biologically‐relevant sequences. This method may develop as a general strategy for stabilizing highly polymorphic peptide regions., The power of halogens! The high‐resolution single crystal X‐ray structures of two halogenated derivatives of the amyloid‐β sequence 7–12 demonstrate the role of halogen‐mediated intermolecular interactions in stabilizing the solid‐state supramolecular organization of this otherwise unstructured biologically‐relevant sequence.

Single crystal X-ray analyses show that iodine in pyridinium periodates acts as a halogen bond (HaB) donor forming short and almost linear contacts with neutral and anionic electron donors. A combination of QTAIM and NCIplot computational tools proves the attractive nature of these contacts.

This recommendation proposes a definition for the term “chalcogen bond”; it is recommended the term is used to designate the specific subset of inter- and intramolecular interactions formed by chalcogen atoms wherein the Group 16 element is the electrophilic site.

The distribution of the electron density around covalently bonded atoms is anisotropic, and this determines the presence, on atoms surface, of areas of higher and lower electron density where the electrostatic potential is frequently negative and positive, respectively. The ability of positive areas on atoms to form attractive interactions with electron rich sites became recently the subject of a flurry of papers. The halogen bond (HaB), the attractive interaction formed by halogens with nucleophiles, emerged as a quite common and dependable tool for controlling phenomena as diverse as the binding of small molecules to proteinaceous targets or the organization of molecular functional materials. The mindset developed in relation to the halogen bond prompted the interest in the tendency of elements of groups 13-16 of the periodic table to form analogous attractive interactions with nucleophiles. This Account addresses the chalcogen bond (ChB), the attractive interaction formed by group 16 elements with nucleophiles, by adopting a crystallographic point of view. Structures of organic derivatives are considered where chalcogen atoms form close contacts with nucleophiles in the geometry typical for chalcogen bonds. It is shown how sulfur, selenium, and tellurium can all form chalcogen bonds, the tendency to give rise to close contacts with nucleophiles increasing with the polarizability of the element. Also oxygen, when conveniently substituted, can form ChBs in crystalline solids. Chalcogen bonds can be strong enough to allow for the interaction to function as an effective and robust tool in crystal engineering. It is presented how chalcogen containing heteroaromatics, sulfides, disulfides, and selenium and tellurium analogues as well as some other molecular moieties can afford dependable chalcogen bond based supramolecular synthons. Particular attention is given to chalcogen containing azoles and their derivatives due to the relevance of these moieties in biosystems and molecular materials. It is shown how the interaction pattern around electrophilic chalcogen atoms frequently recalls the pattern around analogous halogen, pnictogen, and tetrel derivatives. For instance, directionalities of chalcogen bonds around sulfur and selenium in some thiazolium and selenazolium derivatives are similar to directionalities of halogen bonds around bromine and iodine in bromonium and iodonium compounds. This gives experimental evidence that similarities in the anisotropic distribution of the electron density in covalently bonded atoms translates in similarities in their recognition and self-assembly behavior. For instance, the analogies in interaction patterns of carbonitrile substituted elements of groups 17, 16, 15, and 14 will be presented. While the extensive experimental and theoretical data available in the literature prove that HaB and ChB form twin supramolecular synthons in the solid, more experimental information has to become available before such a statement can be safely extended to interactions wherein elements of groups 14 and 15 are the electrophiles. It will nevertheless be possible to develop some general heuristic principles for crystal engineering. Being based on the groups of the periodic table, these principles offer the advantage of being systematic.

Experimental and theoretical studies of fluoro-, chloro-, and bromo-substituted derivatives of barbituric acid and indandione show that imide protons form short hydrogen bonds and bromine or, to a ...

Summary Precise control over topologically intricate molecular architectures remains an open challenge for chemists due to their inherent structural complexity. We report a simple solvent-free strategy to selectively prepare two multi-component supramolecular crystalline systems based on the halogen bond, endowed with either an unknot topology or a Borromean-type entanglement. Real-time in situ monitoring of the solvent-free mechanochemical synthesis of these three-component halogen-bonded ionic co-crystals reveals that the choice of milling conditions leads to a switch in the supramolecular reaction trajectory, resulting in the selective formation of an open halogen-bonded network or a halogen-bonded Borromean-type assembly.

We report halogen bonded complexes between 1 polyfluoroalkyl 3 alkylimidazolium iodides and mono iodoperfluoroalkanes of different chain lengths or di iodoperfluorooctane. 19F NMR analyses revealed that the preferred stoichiometry between the donors and acceptors is 1 amp; 8201; amp; 8201;1 in the cases of the mono iodoperfluoroalkanes, and 2 amp; 8201; amp; 8201;1 with di iodoperfluorooctane, as a result of the monodentate behavior of the iodide anion halogen bond acceptor . Single crystal X ray diffraction analyses showed the presence of a perfluorinated superanion, which interdigitates with the cation fluorinated chains, favoring the formation of lamellar structures. All of the obtained supramolecular complexes exhibit enantiotropic liquid crystalline phases over a broad range of temperatures. Most of the obtained complexes show melting points lower than 100 amp; 8201; C, two of them being liquid at room temperature, thus representing a new family of fluorinated ionic liquid crystals

This manuscript reports a combination of crystallographic analysis (Cambridge Structural Database) and theoretical DFT calculations in chalcogen bonding interactions involving radicals in both the Ch bond (ChB) donor and acceptor. As a radical ChB acceptor (nucleophile) we have used benzodithiazolyl radical (BDTA) and as Ch bond donors (electrophile) we have used dithiadiazolyl and diselenadiazolyl radicals of the general formula p-X-C6F4–CNChChN (Ch = S, and Se). We have evaluated how the para substituent (X) affects the interaction energy, spin density and charge/spin transfer from the electron rich BDTA radical to the electron poor dichalcogenadiazolyl ring. The ability of the latter rings to form ChBs in the solid state has been examined by a comprehensive search in the CSD; several cases are used to exemplify the preferred geometric features of the complexes and they are compared with the theory. The molecular surface electrostatic potentials calculated for these ChB donors allow for a very precise rationalization of the self-assembly motifs most frequently adopted in the crystalline state and of their relative robustness.

In crystals of a benzoselenazole dye, a network of hydrogen bonds with the dye cations locks two iodide anions at a distance allowing for an iodine molecule to be pinned at either ends via two halogen bonds. I42− supramolecular anions are formed as discrete species that lie in the confined space defined by cation molecules.

The presence of fluorine atom(s) in a molecule makes the σ-hole potentials of surrounding atoms more positive and thus increases their tendencies to interact attractively with nucleophiles. This review shows that in the crystal structures of fluorinated derivatives of the Group 15 atoms, close contacts between Group 15 atoms and negative sites (e.g. lone pair possessing atoms and anions) are quite common. These close contacts are taken as indications of attractive interactions. The collection of single crystal X-ray structures analysed in this paper demonstrates that the ability of fluorinated atoms of Group 15 to work as electrophilic sites, namely to function as pnictogen bond donors, is fairly general. The directionalities and separations of these pninctogen bonds are convincing experimental evidences that linking a fluorine to a pnictogen atom increases its electrophilicity to the point that pnictogen bonding formation may become a determinant of the lattice structures in crystalline solids. Pnictogen bonding formation may become an heuristic principle for predicting some of the short contacts that are present in the crystal structures of compounds containing fluorinated atoms of Group 15, particularly when polyfluorinated. Pnictogen derivatives containing other moieties may also work as effective electrophilic sites and a convenient design of the used tectons may allow pnictogen bond to become a general and reliable tool in crystal engineering.

Decamethonium diiodide is reported to perform the chemo- and regioselective encapsulation of para-dihalobenzenes through the competitive formation of halogen-bonded cocrystals starting from solutions that also contain ortho and meta isomers. Selective caging in the solid occurs even when an excess ortho or meta isomers, or even a mixture of them, is present in the solution. A prime matching between the size and shape of the dication and the formed dianions plays a key role in enabling the selective self-assembly, as proven by successful encapsulation of halogen-bond donors as weak as 1,4-dichlorobenzene and by the results of cocrystallization trials involving mismatching tectons. Encapsulated para-dihalobenzenes guest molecules can be removed quantitatively by heating the cocrystals under reduced pressure and be recovered as pure materials. The residual decamethonium diiodide can be recycled with no reduction in selectivity.