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Many organic dyes are fluorescent in solution. In the solid state, however, quenching processes often dominate, hampering material science applications such as light filters, light‐emitting devices, or coding tags. We show that the dimethylene‐cyclopropanide scaffold can be used to form two structurally different types of chromophores, which feature fluorescence quantum yields up to 0.66 in dimethyl sulfoxide and 0.53 in solids. The increased fluorescence in the solid state for compounds bearing malonate substituents instead of dicyanomethide ones is rationalized by the induced twist between the planes of the cyclopropanide core and a pyridine ligand. [ABSTRACT FROM AUTHOR]

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The use of noncovalent interactions based on electrophilic halogen, chalcogen, pnictogen, or tetrel centers in organocatalysis has gained noticeable attention. Herein, we provide an overview on the most important developments in the last years with a clear focus on experimental studies and on catalysts which act via such non‐transient interactions. [ABSTRACT FROM AUTHOR]

The four Industry 4.0 design principles information transparency, technical assistance, interconnection and decentralized decisions pose challenges in integrating Information Technology (IT) and Operational Technology (OT) solutions in industrial systems. These different solutions have conflicting requirements, making interfaces between them problematic for both systems and organizations. An Industrial Business Process Twin (IBPT) entity, acting as an intermediary between the realms of IT and OT, has been proposed in a previous work, to effectively reduce the amount of required IT/OT interfaces in an attempt of overcoming this situation. In this work, we investigate the effects of this approach during the design phase. We argue that, by eliminating potentially conflicting direct interfaces between IT and OT stakeholders within the organizational structure, this approach effectively eliminates conflicting communication channels within the system design. To verify our argument, we develop a model of our IBPT concept according to the Reference Architecture Model Industrie 4.0 (RAMI4.0) using an Industry 4.0 scenario addressing the four essential Industry 4.0 design principles. Results show that the IBPT approach indeed eliminates potentially conflicting IT/OT interfaces during the system design phase. [ABSTRACT FROM AUTHOR]

For a comparison of the interaction modes of various chalcogen‐bond donors, 2‐chalcogeno‐imidazolium salts have been designed, synthesized, and studied by single crystal X‐ray diffraction, solution NMR and DFT as well as for their ability to act as activators in an SN1‐type substitution reaction. Their interaction modes in solution were elucidated based on NMR diffusion and chemical shift perturbation experiments, which were supported by DFT‐calculations. Our finding is that going from lighter to the heavier chalcogens, hydrogen bonding plays a less, while chalcogen bonding an increasingly important role for the coordination of anions. Anion‐π interactions also show importance, especially for the sulfur and selenium derivatives. [ABSTRACT FROM AUTHOR]

Applications of both halogen and chalcogen bonding in organocatalysis are by now well established with various examples. However, the combination of both interactions within one catalyst is currently unknown. Herein, we describe the synthesis of such a mixed chalcogen‐ and halogen‐bond donor and present a first indication of its catalytic activity in a benchmark reaction. [ABSTRACT FROM AUTHOR]

1,3‐Bis(benzimidazoliumyl)benzene‐based chalcogen‐bonding catalysts were previously successfully applied in different benchmark reactions. In one of those examples, i.e. the activation of quinolines, sulfur‐ and selenium‐based chalcogen‐bonding catalysts showed comparable properties, which is unexpected, as the selenium‐containing catalysts should show superior catalytic properties due to the increased polarizability of selenium compared to sulfur. Herein, we present four crystal structures of the respective 1,3‐bis(benzimidazoliumyl)benzene‐based chalcogen‐bonding catalyst containing sulfur (3S) and selenium (3Se, three forms) as Lewis acidic centres. The sulfur‐containing catalyst shows weaker chalcogen bonding compared to its selenium analogue, as well as anion–π interactions. The selenium‐based analogues, on the other hand, show stronger chalcogen‐bonding motifs compared to the sulfur equivalent, depending on the crystallization conditions, but in every case, the intermolecular interactions are comparable in strength. Other interactions, such as hydrogen bonding and anion–π, were also observed, but in the latter case, the interaction distances are longer compared to those of the sulfur‐based equivalent. The solid‐state structures could not further explain the high catalytic activity of the sulfur‐containing catalysts. Therefore, a comparison of their σ‐hole depths from density functional theory (DFT) gas‐phase calculations was performed, which are again in line with the previously found properties in the solid‐state structures. [ABSTRACT FROM AUTHOR]

Carbenes with conjugatively connected redox system act as "auto‐umpolung" ligands. Due to their electronic flexibility, they should also be particularly suitable to stabilize open‐shell species. Herein, the first neutral radical of such sort is described in form of a dialkylamino‐substituted bis(dicyanomethylene)cyclopropanide. Despite the absence of steric shielding, the radical is stable for an extended amount of time and was consequently characterized in solution via EPR measurements. These data and accompanying X‐ray structural analyses indicate that the radical species is in equilibrium with aggregates (formed via π‐stacking) and dimers (obtained via σ‐bond formation between methylene carbons). [ABSTRACT FROM AUTHOR]

Recently, chalcogen bonding has been investigated in more detail in organocatalysis and the scope of activated functionalities continues to increase. Herein, the activation of imines in a Povarov [4+2] cycloaddition reaction with bidentate cationic chalcogen bond donors is presented. Tellurium‐based Lewis acids show superior properties compared to selenium‐based catalysts and inactive sulfur‐based analogues. The catalytic activity of the chalcogen bonding donors increases with weaker binding anions. Triflate, however, is not suitable due to its participation in the catalytic pathway. A solvent screening revealed a more efficient activation in less polar solvents and a pronounced effect of solvent (and catalyst) on endo : exo diastereomeric ratio. Finally, new chiral chalcogen bonding catalysts were applied but provided only racemic mixtures of the product. [ABSTRACT FROM AUTHOR]

Noncovalent organocatalysts utilizing halogen bonding have emerged in the last decade as efficient alternatives to more established hydrogen bonding donors. However, currently they often cannot be recycled and, in some cases, even stoichiometric amounts need to be used. Herein, we present the first generation of recyclable, polymer‐bound halogen bonding catalysts which are able to catalyze a halide‐abstraction reaction. To this end, bis(benzimidazolium)‐based halogen bonding units were attached to a polystyrene polymer, yielding insoluble catalysts. These could be recycled up to three times with little loss in catalytic activity. The overall performance of the catalysts is comparable to that of a free (non‐polymer‐bound) halogen bond donor. Interestingly, catalysts featuring a preorganized and a non‐preorganized halogen bond donating unit showed comparable activity, in contrast to the situation of the free donors. This proof‐of‐principle study provides the basis for further steps towards more sustainable halogen bonding organocatalysts. [ABSTRACT FROM AUTHOR]

6‐Halo‐2‐pyridones and their pyridol tautomers show different grades of polarization on their halogen substituents in DFT calculations. This and the fact that the tautomeric equilibrium is affected by the surrounding medium make them interesting candidates for a new platform of halogen bond donors. We therefore probed four simple halopyridones for their halogen bonding properties both in the solid state and in solution. Concurring with hydrogen bonding, halogen bonding indeed is found to be an interaction governing the packing motif in pyridone crystals, which is more pronounced in N‐methylated congeners. Solution studies using a halide abstraction reaction, and NMR titrations against bromide salts, however, showed no clear evidence for halogen bonding in solution. [ABSTRACT FROM AUTHOR]

Halogen bonding occurs between molecules featuring Lewis acidic halogen substituents and Lewis bases. It is often rationalized as a predominantly electrostatic interaction and thus interactions between ions of like charge (e. g. of anionic halogen bond donors with halides) seem counter‐intuitive. Herein, we provide an overview on such complexes. First, theoretical studies are described and their findings are compared. Next, experimental evidences are presented in the form of crystal structure database analyses, recent examples of strong "anti‐electrostatic" halogen bonding in crystals, and the observation of such interactions also in solution. We then compare these complexes to select examples of "counter‐intuitive" adducts formed by other interactions, like hydrogen bonding. Finally, we comment on key differences between charge‐transfer and electrostatic polarization. [ABSTRACT FROM AUTHOR]

α‐Metallated ylides have revealed themselves to be versatile reagents for the introduction of ylide groups. Herein, we report the synthesis of the thiophosphinoyl and piperidyl (Pip) substituted α‐metallated ylide [Ph2(Pip)P=C−P(S)Ph2]M (M=Li, Na, K) through a four‐step synthetic procedure starting from diphenylmethylphosphine sulfide. Metallation of the ylide intermediate was successfully accomplished with different alkali metal bases delivering the lithium, sodium and potassium salts, the latter isolable in high yields. Structure analyses of the lithium and potassium compounds in the solid state with and without crown ether revealed different aggregates (monomer, dimer and hexamer) with the metals coordinated by the thiophosphoryl moiety and ylidic carbon atom. Although the piperidyl group does not coordinate to the metal, it significantly contributes to the stability of the yldiide by charge delocalization through negative hyperconjugation. [ABSTRACT FROM AUTHOR]

Halogen bonding, the non‐covalent interaction of Lewis bases with an electron‐deficient region of halogen substituents, received increased attention recently. Consequently, the design and evaluation of numerous halogen‐containing species as halogen bond donors have been subject to intense research. More recently, organoiodine compounds at the iodine(III) state have been receiving growing attention in the field. Due to their electronic and structural properties, they provide access to unique binding modes. For this reason, our groups have been involved in the development of such compounds, in the quantification of their halogen bonding strength (through the evaluation of their Lewis acidities), as well as in the evaluation of their activities as catalysts in several model reactions. This account will describe these contributions. [ABSTRACT FROM AUTHOR]

An enantioselective sulfimidation of 3‐thiosubstituted 2‐quinolones and 2‐pyridones was achieved with a stoichiometric nitrene source (PhI=NNs) and a silver‐based catalyst system. Key to the success of the reaction is the use of a chiral phenanthroline ligand with a hydrogen bonding site. The enantioselectivity does not depend on the size of the two substituents at the sulfur atom but only on the binding properties of the heterocyclic lactams. A total of 21 chiral sulfimides were obtained in high yields (44–99 %) and with significant enantiomeric excess (70–99 % ee). The sulfimidation proceeds with high site‐selectivity and can also be employed for the kinetic resolution of chiral sulfoxides. Mechanistic evidence suggests the intermediacy of a heteroleptic silver complex, in which the silver atom is bound to one molecule of the chiral ligand and one molecule of an achiral 1,10‐phenanthroline. Support for the suggested reaction course was obtained by ESI mass spectrometry, DFT calculations, and a Hammett analysis. [ABSTRACT FROM AUTHOR]

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In contrast to iodine(I)‐based halogen bond donors, iodine(III)‐derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro‐Michael addition reaction as well as in a Diels–Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)‐based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF3. [ABSTRACT FROM AUTHOR]

Diaryliodonium(III) salts have recently received increasing interest as a new class of strong halogen bonding noncovalent organocatalysts. Even though this utilization of their Lewis acidity has only been investigated in few studies, their high potential in comparison to classical monovalent iodine based XB donors has become very apparent. So far, only acyclic and cyclic five‐membered core structures have been used, and titration studies have shown the latter to be superior in terms of binding constants towards Lewis bases. Herein, we now compare the Lewis acidity and activity of these five‐membered iodolium salts with those of six‐membered iodininium derivatives. X‐Ray structural analyses, ITC measurements and the reaction kinetics of a Ritter‐type solvolysis reaction in wet acetonitrile (a typical halogen bond donor benchmark reaction) all demonstrate that iodolium salts are stronger halogen bond donors and catalysts than iodininium salts. Subsequently, we were able to improve the activity of both core structures significantly by introducing electron‐withdrawing substituents. [ABSTRACT FROM AUTHOR]

ZrW2 and HfW2 were prepared by melting the constituent elements in an arc‐furnace. By cooling through perictectic phase lines above approximately 2000 °C, samples of the nominal 1:2 composition were obtained as products consisting of two phases, of which approximately 95 % adopts the MgCu2 type structure and 5 % the W structure. In ZrW2 and in HfW2, the MgCu2 type structure enables efficient topological compact spacefilling of the smaller W atoms into the cavities of the three‐dimensional net constructed by the larger tetravalent metals Zr and Hf. Correspondingly, very dense and hard alloys are obtained which burn at a crash in air in a strong exothermic ignition reaction. These materials are non‐toxic. [ABSTRACT FROM AUTHOR]

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In recent years, the non‐covalent interaction of halogen bonding (XB) has found increasing application in organocatalysis. However, reports of the activation of metal‐ligand bonds by XB have so far been limited to a few reactions with elemental iodine or bromine. Herein, we present the activation of metal‐halogen bonds by two classes of inert halogen bond donors and the use of the resulting activated complexes in homogenous gold catalysis. The only recently explored class of iodolium derivatives were shown to be effective activators in two test reactions and their activity could be modulated by blocking of the Lewis acidic sites. Bis(benzimidazolium)‐based halogen bonding activators provided even more rapid conversion, while the non‐iodinated reference compound showed little activity. The role of halogen bonding in the activation of metal‐halogen bonds was further investigated by NMR experiments and DFT calculations, which support the mode of activation occurring via halogen bonding. [ABSTRACT FROM AUTHOR]

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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 chiral phosphoric acid with a 2,2'‐binaphthol core was prepared that displays two thioxanthone moieties at the 3,3'‐position as light‐harvesting antennas. Despite its relatively low triplet energy, the phosphoric acid was found to be an efficient catalyst for the enantioselective intermolecular [2+2] photocycloaddition of β‐carboxyl‐substituted cyclic enones (e.r. up to 93:7). Binding of the carboxylic acid to the sensitizer is suggested by NMR studies and by DFT calculations to occur by means of two hydrogen bonds. The binding event not only enables an enantioface differentiation but also modulates the triplet energy of the substrates. [ABSTRACT FROM AUTHOR]

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Even though halogen bonding—the noncovalent interaction between electrophilic halogen substituents and Lewis bases—has now been established in molecular recognition and catalysis, its use in enantioselective processes is still very rarely explored. Herein, we present the synthesis of chiral bidentate halogen‐bond donors based on two iodoimidazolium units with rigidly attached chiral sidearms. With these Lewis acids, chiral recognition of a racemic diamine is achieved in NMR studies. DFT calculations support a 1:1 interaction of the halogen‐bond donor with both enantiomers and indicate that the chiral recognition is based on a different spatial orientation of the Lewis bases in the halogen‐bonded complexes. In addition, moderate enantioselectivity is achieved in a Mukaiyama aldol reaction with a preorganized variant of the chiral halogen‐bond donor. This represents the first case in which asymmetric induction was realized with a pure halogen‐bond donor lacking any additional active functional groups. [ABSTRACT FROM AUTHOR]

Halogen‐bond donors (halogen‐based Lewis acids) have now found various applications in diverse fields of chemistry. The goal of this study was to identify a parameter obtainable from a single DFT calculation that reliably describes halogen‐bonding strength (Lewis acidity). First, several DFT methods were benchmarked against the CCSD(T) CBS binding data of complexes of 17 carbon‐based halogen‐bond donors with chloride and ammonia as representative Lewis bases, which revealed M05‐2X with a partially augmented def2‐TZVP(D) basis set as the best model chemistry. The best single parameter to predict halogen‐bonding strengths was the static σ‐hole depth, but it still provided inaccurate predictions for a series of compounds. Thus, a more reliable parameter, Ωσ*, has been developed through the linear combination of the σ‐hole depth and the σ*(C−I) energy, which was further validated against neutral, cationic, halogen‐ and nitrogen‐based halogen‐bond donors with very good performance. [ABSTRACT FROM AUTHOR]

The combination of singly or doubly bidentate halogen‐bond donors with double bidentate acceptors was investigated as a supramolecular synthon in crystal engineering. The crystal topologies obtained feature novel halogen‐bonding motifs like double two‐point recognition and infinite chains or networks based on two‐point interactions. Induced conformational changes in the double bidentate halogen‐bond donors could be exploited to obtain different 1D and 2D networks. All solid‐state studies were accompanied by DFT calculations to predict and rationalize the outcome. [ABSTRACT FROM AUTHOR]

Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra‐ and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)‐based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)‐based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding. [ABSTRACT FROM AUTHOR]

In the last years the use of chalcogen bonding—the noncovalent interaction involving electrophilic chalcogen centers—in noncovalent organocatalysis has received increased interest, particularly regarding the use of intermolecular Lewis acids. Herein, we present the first use of tellurium‐based catalysts for the activation of a carbonyl compound (and only the second such activation by chalcogen bonding in general). As benchmark reaction, the Michael‐type addition between trans‐crotonophenone and 1‐methylindole (and its derivatives) was investigated in the presence of various catalyst candidates. Whereas non‐chalcogen‐bonding reference compounds were inactive, strong rate accelerations of up to 1000 could be achieved by bidentate triazolium‐based chalcogen bond donors, with product yields of >90 % within 2 h of reaction time. Organotellurium derivatives were markedly more active than their selenium and sulphur analogues and non‐coordinating counterions like BArF4 provide the strongest dicationic catalysts. [ABSTRACT FROM AUTHOR]

Verdichtungskontrolle von Sekundärbaustoffen im Erdbau: Unerlässlicher Bestandteil der Qualitätssicherung im Erdbau und wesentlich für die Gewährleistung der Standsicherheit und dauerhaften Gebrauchstauglichkeit von Erdbauwerken ist die Verdichtungskontrolle. Da die direkte Bestimmung des Verdichtungsgrades bei grobkörnigen Materialien sehr zeitaufwändig ist, kommen hierzu häufig Plattendruckversuche zur Anwendung. Die Praxis zeigt jedoch, dass die Verdichtungskontrolle mittels Plattendruckversuchen bei Sekundärbaustoffen nicht immer so einfach möglich ist, wie es im erdbautechnischen Regelwerk vorgeschlagen wird. Diese Feinheiten sind allerdings leider nicht allgemein bekannt und führen typischerweise trotz ausreichender Verdichtung der Schichten zu deren Ablehnung. Dieser Beitrag fasst die Ergebnisse von Verdichtungsfeldversuchen an mehreren Sekundärbaustoffen, die im Feld auf unterschiedliche Verdichtungsgrade verdichtet wurden, zusammen. Die Felduntersuchungen umfassten die Ermittlung der im Feld erreichten Trockendichte sowie die Durchführung von statischen und dynamischen Plattendruckversuchen. Die Ergebnisse dieser Feldversuche werden im Rahmen dieses Beitrages vorgestellt und diskutiert. Die Ergebnisse zeigen, dass sich die mittels Plattendruckversuchen bestimmten Parameter (Verformungsmoduln) in Bezug auf die Trockendichte im Vergleich zu natürlichen Materialien unterschiedlich verhalten. Es werden daher Vorschläge für die praktikabelste Vorgehensweise zur Verdichtungskontrolle von Sekundärbaustoffen innerhalb des bestehenden erdbautechnischen Regelwerkes in Deutschland und Österreich gemacht. [ABSTRACT FROM AUTHOR]

Chalkogenbrücken sind nicht‐kovalente Wechselwirkungen zwischen Lewis‐aziden Chalkogensubstituenten und Lewis‐Basen. Hierin präsentieren wir die erste Anwendung dikationischer, Tellur‐basierter Chalkogenbrückendonoren als Katalysatoren in einer Nitro‐Michael‐Reaktion zwischen trans‐β‐Nitrostyrol und Indolen. Dies ist außerdem die erste Aktivierung einer Nitro‐Gruppe durch Chalkogenbrücken (und Halogenbrücken). Die Katalysatoren zeigten eine mehr als 300‐fache Beschleunigung der Reaktionsgeschwindigkeit im Vergleich zu stark Lewis‐sauren Wasserstoffbrückendonoren. Durch mehrere Vergleichsexperimente, Titrationen und DFT‐Rechnungen konnte die Aktivierung des Nitrostyrols durch Chalkogenbrücken nachgewiesen werden. [ABSTRACT FROM AUTHOR]

Chalcogen bonding is the non‐covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium‐based chalcogen bond donors in the nitro‐Michael reaction between trans‐β‐nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen‐bonding‐based mode of activation of β‐nitrostyrene. [ABSTRACT FROM AUTHOR]

A common method to dissolve elemental gold involves the combination of an oxidant with a Lewis base that coordinates to the gold surface, thus lowering the metal's redox potential. Herein we report the usage of organic iodide salts, which provide both oxidative power and a coordinating ligand, to dissolve gold under formation of organo‐gold complexes. The obtained products were identified as AuIII complexes, all featuring Au−C bonds, as shown by X‐ray single‐crystal analysis, and can be isolated in good yields. Additionally, our method provides direct access to N‐heterocyclic carbene (NHC‐type) complexes and avoids costly organometallic precursors. The investigated complexes show dynamic behavior in acetonitrile and in the case of the NHC(‐type) complexes, the involved species could be identified as a monocarbene [AuI3(carbene)] and biscarbene complex [AuI2(carbene)2]+. [ABSTRACT FROM AUTHOR]

In the last few decades, "unusual" noncovalent interactions like anion‐π and halogen bonding have emerged as interesting alternatives to the ubiquitous hydrogen bonding in many research areas. This is also true, to a somewhat lesser extent, for chalcogen bonding, the noncovalent interaction involving Lewis acidic chalcogen centers. Herein, we aim to provide an overview on the use of chalcogen bonding in crystal engineering and in solution, with a focus on the recent developments concerning intermolecular chalcogen bonding in solution‐phase applications. In the solid phase, chalcogen bonding has been used for the construction of nano‐sized structures and the self‐assembly of sophisticated self‐complementary arrays. In solution, until very recently applications mostly focused on intramolecular interactions which stabilized the conformation of intermediates or reagents. In the last few years, intermolecular chalcogen bonding has increasingly also been exploited in solution, most notably in anion recognition and transport as well as in organic synthesis and organocatalysis. Building bridges: Chalcogen bonds are noncovalent interactions similar to hydrogen bonds that are based on electrophilic chalcogen substituents. This Minireview provides an overview on the origin and features of chalcogen bonding as well as its applications in the solid state and in solution. A certain focus will be on the latter and particularly on the recent introduction of chalcogen bonding in noncovalent organocatalysis. LB=Lewis base. [ABSTRACT FROM AUTHOR]

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Motivated by the need to calculate liquid‐phase free energies of species and equilibria involving halogen bonding, recent experimental data were used to optimize new Coulomb radii for Br and I for use in the SMD universal solvation model for calculating free energies of solvation. The use of the SMD model with these parameters for Br and I and the SMD values of all other parameters is called SMD18. After parametrization, the SMD18 model was tested for data not used in the parametrization. These data are standard‐state free energies (equivalent to equilibrium constants) for 18 ionic equilibria involving Cl, Br, and I halogen bonding in acetonitrile, and the agreement of theory and experiment is satisfactory. The SMD18 model is then used to compare hydrogen bonding to halogen bonding and to reassess the interpretation of recent experiments. Experimental data on halogen bonded complexes has been used to reoptimize the iodine and bromine radius in the SMD intrinsic solvation model. Subsequent testing of this new SMD18 model on several ionic equilibria provided very good agreement between experiment and theory. [ABSTRACT FROM AUTHOR]

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Abstract: Hypervalent iodine(III) derivatives are known as versatile reagents in organic synthesis, but there is only one previous report on their use as Lewis acidic organocatalysts. Herein, we present first strong indications for the crucial role of halogen bonding in this kind of catalyses. To this end, the solvolysis of benzhydryl chloride and the Diels–Alder reaction of cyclopentadiene with methyl vinyl ketone served as benchmark reactions for halide abstraction and the activation of neutral compounds. Iodolium compounds (cyclic diaryl iodonium species) were used as activators or catalysts, and we were able to markedly reduce or completely switch off their activity by sterically blocking one or two of their electrophilic axes. Compared with previously established bidentate cationic halogen bond donors, the monodentate organoiodine derivatives used herein are at least similarly active (in the Diels–Alder reaction) or even decidedly more active (in benzhydryl chloride solvolysis). [ABSTRACT FROM AUTHOR]

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Abstract: We performed a comparative study on the interaction modes of 2‐haloimidazolium salts with anions in solution, particularly with regard to halogen bonding, hydrogen bonding and anion–π interactions. The syntheses and solid‐state analyses of a series of sterically and electronically modified 2‐haloimidazolium structures are presented. Detailed isothermal titration calorimetry (ITC) measurements, quantum mechanics/molecular mechanics (QM/MM), classical molecular dynamics simulations (MD) and free‐energy calculations together with NMR spectroscopy were used to elucidate the binding modes in solution. Our work reveals the absence of a potential anion–π interaction between the cationic imidazolium ring and the Lewis basic counteranion, and corroborates a formation of halogen bonding via the Lewis acidic iodine moiety and hydrogen bonding via the backbone hydrogen atoms, with repercussions in the field of organocatalysis. [ABSTRACT FROM AUTHOR]

Chalcogen bonding is a noncovalent interaction based on electrophilic chalcogen substituents, which shares many similarities with the more well-known hydrogen and halogen bonding. Herein, the first application of selenium-based chalcogen bond donors in organocatalysis is described. Cationic bifunctionalized organoselenium compounds activate the carbon-chlorine bond of 1-chloroisochroman in a benchmark reaction. While imidazolium-based derivatives showed no noticeable activation, benzimidazolium backbones yielded potent catalysts. In all cases, syn-isomers were markedly more active, presumably due to bidentate coordination, which was confirmed by DFT calculations. Comparison experiments with the corresponding non-selenated as well as the non-cationic reference compounds clearly indicate that the catalytic activity can be ascribed to chalcogen bonding. The rate acceleration by the catalyst-compared to the non-selenated derivative-was about 10 fold. [ABSTRACT FROM AUTHOR]

Low-energy electrons effectively decompose the isomers 2-nitroimidazole and 4(5)-nitroimidazole by dissociative electron attachment (DEA) into a variety of fragment anions and radicals. The present study shows that a distinct selectivity for the two isomers occurs in the DEA reactions. Several new decay channels are observed for 2-nitroimidazole, including a dominant one leading to the loss of molecular H2O by attachment of a low-energy electron. In contrast, the loss of a single hydrogen atom is a much more efficient reaction in DEA to 4(5)-nitroimidazole. Quantum chemical calculations were carried out to explain the pronounced isomer effect found in the DEA experiment. Although the free energies of the reactions are similar for the different isomers, the very different natures of the dipole-bound states and valence-bound anions lead to preference for or hindrance of a particular dissociation channel. Nitroimidazolic compounds are considered as radiosensitizing compounds in tumor radiation therapy. The enhanced formation of fragments, including the highly reactive hydroxyl radical, in DEA to 2-nitroimidazole suggests that it may be a more efficient radiosensitizing agent than 4(5)-nitroimidazoles. [ABSTRACT FROM AUTHOR]

Chalcogen bonding is a little explored noncovalent interaction similar to halogen bonding. This manuscript describes the first application of selenium-based chalcogen bond donors as Lewis acids in organic synthesis. To this end, the solvolysis of benzhydryl bromide served as a halide abstraction benchmark reaction. Chalcogen bond donors based on a bis(benzimidazolium) core provided rate accelerations relative to the background reactivity by a factor of 20-30. Several comparative experiments provide clear indications that the observed activation is due to chalcogen bonding. The performance of the chalcogen bond donors is superior to that of a related brominated halogen bond donor. [ABSTRACT FROM AUTHOR]

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Sex differences in mathematical performance have frequently been examined over the last decades indicating an advantage for males especially when numerical problems cannot be solved by (classroom-)learnt strategies and/or estimation. Even in basic numerical tasks such as number line estimation, males were found to outperform females - with sex differences argued to emerge from different solution strategies applied by males and females. We evaluated the latter using two versions of the number line estimation task: a bounded and an unbounded task version. Assuming that women tend more strongly to apply known procedures, we expected them to be at a particular disadvantage in the unbounded number line estimation task, which is less prone to be solved by specific strategies such as proportion judgement but requires numerical estimation. Results confirmed more pronounced sex differences for unbounded number line estimation with males performing significantly more accurately in this task version. This further adds to recent evidence suggesting that estimation performance in the bounded task version may reflect solution strategies rather than numerical estimation. Additionally, it indicates that sex differences regarding the spatial representation of number magnitude may not be universal, but associated with spatial-numerical estimations in particular. [ABSTRACT FROM AUTHOR]

In multi‐digit numbers, the value of each digit is determined by its position within the digit string. Children's understanding of this place‐value structure constitutes a building block for later arithmetic skills. We investigated whether a number line estimation task can provide an assessment of place‐value understanding in first grade. We hypothesized that estimating the position of two‐digit numbers requires place‐value understanding. Therefore, we fitted a linear function to children's estimates of two‐digit numbers and considered the resulting slope as a measure of children's place‐value understanding. We observed a significant correlation between this slope and children's performance in a transcoding task known to require place‐value understanding. Additionally, the slope for two‐digit numbers assessed at the beginning of grade 1 predicted children's arithmetic performance at the end of grade 1. These results indicate that the number line estimation task may indeed constitute a valid measure for first‐graders' place‐value understanding. Moreover, these findings are hard to reconcile with the view that number line estimation directly assesses a spatial representation of numbers. Instead, our results suggest that numerical processes involved in performing the task (such as place‐value understanding) may drive the association between number line estimation and arithmetic performance. [ABSTRACT FROM AUTHOR]

Halogen bonding is a noncovalent interaction similar to hydrogen bonding, which is based on electrophilic halogen substituents. Hydrogen-bonding-based organocatalysis is a well-established strategy which has found numerous applications in recent years. In light of this, halogen bonding has recently been introduced as a key interaction for the design of activators or organocatalysts that is complementary to hydrogen bonding. This Concept features a discussion on the history and electronic origin of halogen bonding, summarizes all relevant examples of its application in organocatalysis, and provides an overview on the use of cationic or polyfluorinated halogen-bond donors in halide abstraction reactions or in the activation of neutral organic substrates. [ABSTRACT FROM AUTHOR]