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The regioselective deiodinations of L‐thyroxine (T4) play key roles in the thyroid hormone homeostasis. These reactions are catalyzed by three isoforms of the selenoenzymes, iodothyronine deiodinases (Dio1, Dio2 and Dio3), which are highly homologous in nature. Dio1 mediates 5′‐ or 5‐deiodinations of T4 to produce T3 and rT3, respectively. In contrast, Dio2 and Dio3 are selective to 5′‐ or 5‐deiodination to produce T3 and rT3, respectively. Understanding of the regioselectivity of deiodination at the molecular level is important as abnormal levels of thyroid hormone have been implicated in various clinical conditions, such as hypoxia, myocardial infarction, neuronal ischemia and cancer. In this paper, we report that the electronic properties of the iodine atoms in thyroxine (T4) can be modulated through a simple substitution in the 4′‐phenolic moiety. This leads to the change in the regioselectivity of deiodination by different small molecule mimics of Dio enzymes. By using this chemical approach, we also show that the substitution of a strong electron withdrawing group facilitates the removal of all four iodine atoms in the T4 derivative. Theoretical investigations on the hydrogen bonded adducts of T4 with imidazole indicate that the charge on the iodine atoms depend on the nature of hydrogen bond between the −OH group of T4 and the imidazole moiety. While the imidazole can act as either hydrogen bond acceptor (HBA) or hydrogen bond donor (HBD), the protonated imidazole acts exclusively as HBD in T4‐imidazole complex. These studies support the earlier observations that the histidine residue at the active sites of the deiodinases play an important role not only in the substrate binding, but also in altering the regioselectivity of the deiodination reactions. [ABSTRACT FROM AUTHOR]

Keywords: computational chemistry; hydrogen bonds; NBO; noncovalent interactions; QTAIM EN computational chemistry hydrogen bonds NBO noncovalent interactions QTAIM 1 1 1 04/17/23 20230413 NES 230413 B The main idea b of the paper "the acceptor rules and the donor chooses" is illustrated by representing the different binding modes as the available "vegetables" offered in the market, ruled by the hydrogen bond acceptors. Computational chemistry, hydrogen bonds, NBO, noncovalent interactions, QTAIM. [Extracted from the article]

Helical architectures with controllable helical sense bias have recently attracted considerable interest for mimicking biological helices and developing novel chiral materials. Coordination polymers (CPs), composed of metal ion nodes and organic linkers, are intriguing systems showing tunable structures and functions. However, CPs with helical morphologies have rarely been explored so far. Particularly, chirality inversion through external stimulus has not been achieved in helical CPs. In this work, we carried out an in‐depth investigation on the self‐assembly of 1D gadolinium(III) phosphonate CPs using GdX3 (X=Cl, Br, I) and Gd(RSO3) (R=CH3, C6H5, CF3) as metal sources and R‐(1‐phenylethylamino)methyl phosphonic acid (R‐pempH2) as ligand. Superhelices were formed by precise control of the interchain interactions through different intercalated anions. Furthermore, the twisting direction of superhelices could be controlled by synergistic effect of anions and pH. This study may provide a new route to fabricate helical nanostructures of CPs with a desirable chiral sense and help understand the inner mechanism of the self‐assembly process of macroscopic helical structures of molecular systems. [ABSTRACT FROM AUTHOR]

Organosilanols typically show a high condensation tendency and only exist as stable isolable molecules under very specific steric and electronic conditions at the silicon atom. In the present work, various novel representatives of this class of compounds were synthesized by hydrolysis of alkoxy‐ or chlorosilanes. Phenyl, 1‐naphthyl, and 9‐phenanthrenyl substituents at the silicon atom were applied to systematically study the influence of the aromatic substituents on the structure and reactivity of the compounds. Chemical shifts in 29Si NMR spectroscopy in solution, correlated well with the expected electronic situation induced by the substitution pattern on the Si atom. 1H NMR studies allowed the detection of strong intermolecular hydrogen bonds. Single‐crystal X‐ray structures of the alkoxides and the chlorosilanes are dominated by π‐π interactions of the aromatic systems, which are substituted by strong hydrogen bonding interactions representing various structural motifs in the respective silanol structures. [ABSTRACT FROM AUTHOR]

Combining metal complexes with amphiphilic molecules leads to a wide variety of functional self‐assembled nanostructures. Metal complexes exhibiting spin transitions can be good candidates as the trigger to cause structural conversion of such assembly because they respond to various external stimuli. In this work, we studied a structural conversion of a supramolecular assembly containing a [Co2Fe2] complex through a thermally induced electron transfer‐coupled spin transition (ETCST). With an amphiphilic anion, the [Co2Fe2] complex formed reverse vesicles in solution and showed thermal ETCST. In contrast, thermal ETCST in the presence of a bridging hydrogen‐bond donor caused structural conversion from the reverse vesicle structure to entangled one‐dimensional chains through hydrogen bond formation. [ABSTRACT FROM AUTHOR]

Deployment of adhesives in natural seawater to in situ bonds is urgently needed in engineering fields. However, stable adhesion in natural seawater remains a challenge due to the turbulent environment and high ion concentration. Herein, we reported a viscous, macromolecular underwater adhesive enhanced by Hofmeister effect (EHUA) for practical application in dynamic seawater. EHUA was synthesized via a facile one‐step copolymerization. After transferred into seawater, the solvent of EHUA was exchanged to seawater, and thereby hydrogen bonds inside the adhesive were activated and enhanced by Hofmeister effect. We demonstrated EHUA can adhere on the surface in turbulent seawater, and the adhesive strength could reach 1.691 MPa. In addition, the adhesives also exhibited long‐term storage stability and convenient recyclability. These fascinating properties enable adhesives to seal leaky pipelines, repair damaged ships and construct buildings in turbulent seawater. This work may open an avenue for the design of adhesives for seawater environments. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue is the group of Cristina Trujillo at Trinity College Dublin and the University of Manchester. The image depicts a market run by hydrogen bond acceptors in which hydrogen‐bond‐donor "customers" are choosing their preferred binding mode "vegetable". Read the full text of the article at 10.1002/chem.202203577. [ABSTRACT FROM AUTHOR]

Regioselective di‐functionalization of a cyclodextrin allows hydrophobic domains to be directed in a geometrically controlled manner. This controlled orientation ultimately gives access to an original hierarchical assembly in the solid state. This assembly spans over three levels of hierarchy which are governed by synergistic host‐guest inclusions, directed hydrophobic effect and hydrogen bonding. This combination of interactions precisely positioned in space through regioselective functionalization of a cyclodextrin creates a porous organic architecture. [ABSTRACT FROM AUTHOR]

A biomimetic receptor for glucose has been developed with high affinity and selectivity. The receptor was efficiently synthesized in three steps through dynamic imine chemistry followed by imine‐to‐amide oxidation. The receptor features two parallel durene panels, forming a hydrophobic pocket for [CH⋅⋅⋅π] interactions, and two pyridinium residues directing four amide bonds towards the pocket. These pyridinium residues not only improve solubility but also provide polarized C−H bonds for hydrogen bonding. Experimental data and DFT calculations show that these polarized C−H bonds significantly enhance substrate binding. These findings demonstrate the power of dynamic covalent chemistry for creating molecular receptors and using polarized C−H bonds for boosted carbohydrate recognition in water, providing a foundation for developing glucose‐responsive materials and sensors. [ABSTRACT FROM AUTHOR]

The design of a well‐ordered arrangement of atoms on a solid surface has long been sought due to the envisioned applications in many different fields. On‐surface synthesis of metal‐organic networks is one of the most promising fabrication techniques. Hierarchical growth, which involves coordinative schemes with weaker interactions, favours the formation of extended areas with the desired complex structure. However, the control of such hierarchical growth is in its infancy, particularly for lanthanide‐based architectures. Here the hierarchical growth of a Dy‐based supramolecular nanoarchitecture on Au(111) is described. Such an assembly is based on a first hierarchical level of metallo‐supramolecular motifs, which in a second level of hierarchy self‐assemble through directional hydrogen bonds, giving rise to a periodic two‐dimensional supramolecular porous network. Notably, the size of the metal‐organic based tecton of the first level of hierarchy can be tailored by modifying the metal‐ligand stoichiometric ratio. [ABSTRACT FROM AUTHOR]

Indenone azines, in which the exocyclic C=C bond in dibenzopentafulvalene is replaced by an azine moiety (C=N−N=C), have been synthesized as novel electron‐accepting π‐conjugated scaffolds. Structural modulation at the 7,7′‐positions of indenone azines enabled stereoselective syntheses of diastereomers in which the configurations of the two C=N bonds are E,E or Z,Z. X‐ray crystallographic analyses revealed that all the indenone azines exhibit high coplanarity in contrast to the twisted frameworks of dibenzopentafulvalene derivatives, resulting in the formation of densely π‐stacked structures. Electrochemical measurements and quantum chemical calculations revealed the electron‐accepting character of indenone azines comparable to isoindigo dyes. In particular, the intramolecular hydrogen bonds of 7,7′‐dihydroxy‐substituted derivatives impart enhanced electron‐accepting character and significantly red‐shifted photoabsorption. This study demonstrates that indenone azines represent a promising candidate as electron‐accepting building blocks for optoelectronic materials. [ABSTRACT FROM AUTHOR]

Two ionic hydrogen‐bonded organic frameworks (iHOF‐10, iHOF‐11) were prepared using 1,1′‐diamino‐4,4′‐bipyridine diiodide (Dbpy ⋅ 2I) and tetrakis(4‐sulfophenyl)ethylene (H4TPE). With increasing RH and temperature, water molecules induce single crystal to single crystal (SCSC) transformation of iHOF‐10, resulting in the formation of iHOF‐11. At 90 °C, 98 % RH, the proton conductivity of iHOF‐11 (7.03×10−3 S cm−1) is 2.09 times higher than iHOF‐10 (3.37×10−3 S cm−1). At 50 °C, 98 % RH, iHOF‐11 (9.49×10−4 S cm−1) is 19.06 times higher than iHOF‐10 (4.98×10−5 S cm−1). The proton conductivity shows water molecules enter the crystal and induce crystal transformation and reorganization of the hydrogen bonding structure, thus increasing the proton conductivity and stability. [ABSTRACT FROM AUTHOR]

Gold(I) centers can form moderately strong (Au⋅⋅⋅H) hydrogen bonds with tertiary ammonium groups, as has been demonstrated in the 3AuCl+ (3+=1‐(tert‐butyl)‐3‐phenyl‐4‐(2‐((dimethylammonio)methyl)phenyl)‐1,2,4‐triazol‐5‐ylidene) complex. However, similar hydrogen bonding interactions with isoelectronic silver(I) or copper(I) centers are unknown. Herein, we first explored whether the Au⋅⋅⋅H bond originally observed in 3AuCl+ can be strengthened by replacing Cl with Br or I. Experimental gas‐phase IR spectra in the ∼3000 cm−1 region showed only a small effect of the halogen on the Au⋅⋅⋅H bond. Next, we measured the spectra of 3AgCl+, which exhibited significant differences compared to its 3AuX+ counterparts. The difference has been explained by DFT calculations which indicated that the Ag⋅⋅⋅H interaction is only marginal in this complex, and a Cl⋅⋅⋅H hydrogen bond is formed instead. Calculations predicted the same for the 3CuCl+ complex. However, we noticed that for Ag and Cu complexes with less flexible ligands, such as dimethyl(2‐(dimethylammonio)phenyl)phosphine (L7H+), the computations predict the presence of the respective Ag⋅⋅⋅H and Cu⋅⋅⋅H hydrogen bonds, with a strength similar to the Au⋅⋅⋅H bond in 3AuCl+. We, therefore, propose possible complexes where the presence of (Ag/Cu)⋅⋅⋅H bonds could be experimentally verified to broaden our understanding of these unusual interactions. [ABSTRACT FROM AUTHOR]

The synthesis of self‐assembly systems that can mimic partial biological behaviours require ingenious and delicate design. For decades, scientists are committed to exploring new base pairing patterns using hydrogen bonds directed self‐assembly of nucleotides. A fundamental question is the adaptive circumstance of the recognition between base pairs, namely, how solvent conditions affect the domain of base pairs. Towards this question, three nucleotide complexes based on 2'‐deoxycytidine‐5'‐monophosphate (dCMP) and cytidine‐5'‐monophosphate (CMP) were synthesized in different solvents and pH values, and an unusual cytosine‐cytosine base paring pattern (named full C : C base pairing) has been successfully obtained. Systematic single crystal analysis and 1H NMR titration spectra have been performed to explore factors influencing the formation of base paring patterns. Moreover, supramolecular chirality of three complexes were studied using circular dichroism (CD) spectroscopy in solution and solid‐state combined with crystal structure analysis. [ABSTRACT FROM AUTHOR]

Herein, we have utilized 2‐(2‐hydroxyphenyl)benzimidazole (HBI) to synthesize 3‐(1H‐benzoimidazol‐2‐yl)‐2‐hydroxy‐5‐methyl‐benzaldehyde (HBIA) followed by three Schiff bases by using –ortho (H2BIo), ‐meta (H3BIdm) and ‐para (H2BIp) substituted amino benzoic acids and studied their photophysical properties. We have successfully derived molecular structures of HBI, HBIA and H3BIdm which reveals that in HBI and HBIA, the phenolic −OH is intramolecularly hydrogen bonded with sp2 N of benzimidazole group whereas in H3BIdm, it is hydrogen bonded with imine C=N of Schiff base moiety, which is responsible for different solid state emission properties of the reported compounds. Extensive experimental and theoretical studies show that for all three Schiff bases, in solution due to activation of C=N isomerization, ESIPT operates through benzimidazole site and displays different emission from the solid state. Furthermore, H2BIo, H3BIdm and H2BIp selectively sense Cu2+ in semi aqueous medium with nano‐molar detection limit and in HuH‐7 cells through the inhibition of ESIPT of process. [ABSTRACT FROM AUTHOR]

The syntheses of two novel mechanically chiral rotaxanes containing urea and squaramide motifs (in yields of 33 % and 22 %, respectively) are presented. 1H NMR spectroscopic titrations reveal shuttling of the macrocycle – detectable by modulation of the expression of mechanical chirality in the NMR spectrum – is possible through the addition of achiral chloride anions, a process which is reversed by the addition of sodium cations. [ABSTRACT FROM AUTHOR]

Self‐healable and stretchable elastomeric material is essential for the development of flexible electronics devices to ensure their stable performance. In this study, a strain sensor (PIH2T1‐tri/CNT‐3) composed of self‐repairable crosslinked elastomer substrate (PIH2T1‐tri, containing multiple reversible repairing sites such as disulfide, imine, and hydrogen bonds) and conductive layer (carbon nanotube, CNT) was prepared. The PIH2T1‐tri elastomer had excellent self‐healing ability (healing efficiency=91 %). It exhibited good mechanical integrity in terms of elongation at break (672 %), tensile strength (1.41 MPa). The Young's modulus (0.39 MPa) was close to that of human skin. The PIH2T1‐tri/CNT‐3 sensor also demonstrated an effective self‐healing function for electrical conduction and sensing property. Meanwhile, it had high sensitivity (gauge factor (GF)=24.1), short response time (120 ms), and long‐term durability (4000 cycles). This study offers a novel self‐healable elastomer platform with carbon based conductive components to develop flexible strain sensors towards high performance soft electronics. [ABSTRACT FROM AUTHOR]

Hydrogen‐bonding interactions are assumed to play a critical role in the long‐range transport of light or charge recently observed in supramolecular assemblies of C3‐symmetrical discotic molecules. Herein, the structure of mixed valence assemblies formed by irradiating triarylamine trisamide (TATA) molecules was determined by multifarious techniques under various conditions with the aim of probing the interplay between the hydrogen bonding network and the rate of electron transport in different states (solution, gel, film). Irradiation was performed under initial states that vary by the degree of association of TATA monomers through hydrogen bonds. Firstly, a significant shift of the N−H and C=O stretching frequencies was observed by FTIR upon irradiation thus revealing an overlooked signature of TATA⋅+ species and interacting mixed valence aggregates. Secondly, gels and films both mostly consist of hydrogen‐bonded TATA polymers but their EPR spectra recorded at 293 K reveal very different behaviors: localized electrons in the gels versus fully delocalized electrons in the films. Hydrogen bonding thus appears as a necessary but not sufficient condition to get fast electron transfer rates and a packing of the TATA monomers particularly suitable for charge transport is assumed to exist in the solid state. Finally, defects in the hydrogen bonding network are detected upon increasing the number of radical species in the mixed valence assemblies present in the film state without impeding the delocalization of the unpaired electrons. A delicate balance between hydrogen bonds and packing is thus necessary to get supramolecular polarons in mixed valence TATA assemblies. [ABSTRACT FROM AUTHOR]

The reaction of the Pt complexes cis‐[Pt(CH3)(Ar){Ph2P(Ind)}2] (Ind=2‐(3‐methyl)indolyl, Ar=4‐tBuC6H4 (1 a), 4‐CH3C6H4 (1 b), Ph (1 c), 4‐FC6H4 (1 d), 4‐ClC6H4 (1 e), 4‐CF3C6H4 (1 f)) with HF afforded the polyfluorido complexes trans‐[Pt(F(HF)2)(Ar){Ph2P(Ind)}2] 2 a–f, which can be converted into the fluoride derivatives trans‐[Pt(F)(Ar){Ph2P(Ind)}2] (3 a–f) by treatment with CsF. The compounds 2 a–f and 3 a–f were characterised thoroughly by multinuclear NMR spectroscopy. The data reveal hydrogen bonding of the fluorido ligand with HF molecules and the indolylphosphine ligand. Polyfluorido complexes 2 a–f show larger |1J(F,Pt)|, but lower 1J(H,F) coupling constants when compared to the fluorido complexes 3 a–f. Decreasing 1J(P,Pt) coupling constants in 2 a–f and 3 a–f suggest a cis influence of the aryl ligands in the following order: 4‐tBuC6H4 (a) ≈4‐CH3C6H4 (b)

Thiourea S‐oxides can be viewed as formal analogs of the currently unknown diamino‐substituted Criegee intermediates (urea O‐oxides). However, the preparation of such S‐oxides is rather challenging, and the direct oxidation of thioureas typically only leads to formation of desulfurized products. Employing the accurate revDSD‐PBEP86‐D4 double hybrid density functional, it was found that the peracid mediated oxidation of thiourea S‐oxides exhibits a lower reaction barrier than the oxidation of the corresponding thiourea itself in contrast to most other ordinary thioketones. The undesired overoxidation reactivity, which is associated with strong π‐donation from the thiourea's nitrogen atoms, can be partially suppressed by introduction of bulky substituents and the utilization of protic solvents. In this regard, we managed to prepare two sterically encumbered thiourea S‐oxides in isolated yields of 35–40 %. The S‐oxides are stable in the solid state and in alcoholic solutions at room temperature for extended periods of time, but swiftly decompose in aprotic solvents by disproportionation. A dimesityl‐substituted thiourea S‐oxide complexed with residual mCBA could be characterized by means of X‐ray crystallography, confirming the importance of hydrogen bonding in the stabilization of the amino‐substituted C=S+−O− moiety. [ABSTRACT FROM AUTHOR]

The development of an efficient strategy for fabricating two‐dimensional metal‐organic framework (MOF) nanosheets with high yield and high stability is desirable. Herein, we demonstrate for the first time that large, single‐layer 2D nickel‐benzene dicarboxylate (Ni−BDC) MOF nanosheets can be fabricated with the assistance of supercritical (SC) CO2 in a pure aqueous system. Detailed experimental evidence reveals that the SC CO2 molecule can exchange with the lattice‐coordinated H2O molecules, side‐on coordinate with the metal Ni1 sites on the Ni−BDC surface, and finally break the interlayer hydrogen bond to exfoliate the bulk Ni−BDC into a 2D MOF. More importantly, a thin SC CO2 layer building up at the water−Ni−BDC interfaces can transform the pristine hydrophilic interface into a super‐hydrophobic one. This super‐hydrophobic layer at the water‐MOF interface can effectively prevent dissociation, thus promoting the stability of Ni−BDC in aqueous system. [ABSTRACT FROM AUTHOR]

As hydrogen bonded frameworks are held together by relatively weak interactions, they often form several different frameworks under slightly different synthesis conditions and respond dynamically to stimuli such as heat and vacuum. However, these dynamic restructuring processes are often poorly understood. In this work, three isoreticular hydrogen bonded organic frameworks assembled through charge‐assisted amidinium⋅⋅⋅carboxylate hydrogen bonds (1C/C, 1Si/C and 1Si/Si) are studied. Three distinct phases for 1C/C and four for 1Si/C and 1Si/Si are fully structurally characterized. The transitions between these phases involve extreme yet recoverable molecular‐level framework reorganization. It is demonstrated that these transformations are related to water content and can be controlled by humidity, and that the non‐porous anhydrous phase of 1C/C shows reversible water sorption through single crystal to crystal restructuring. This mechanistic insight opens the way for the future use of the inherent dynamism present in hydrogen bonded frameworks. [ABSTRACT FROM AUTHOR]

The dynamic nature of excited‐state intramolecular proton transfer (ESIPT) and its effect on emission spectra is an attractive strategy to create multi‐emissive dyes. Here we describe the behavior of a series of hydrogen‐bonded triphenylpyridines with a set of donor–acceptor combinations that allowed us to perceive the influence of each substitution on the photophysical properties of the dyes. The susceptibility of these ESIPT moieties to pH variations was also studied, elucidating that the level of protonation had a significant effect on the emission color. The assignment of each emission band was made by using DFT and td‐DFT calculations that were in agreement with the experimental results. This study emphasizes the versatility of triphenylpyridines that can be synthesized effortlessly with a logical and independent C‐2, C‐4 and C‐6 substitution in order to have the desired ESIPT modulation and subsequent multi‐emission response. [ABSTRACT FROM AUTHOR]

The reaction of a cyclic alkyl(amino)carbene (CAAC)‐stabilized thiazaborolo[5,4‐d]thiazaborole (TzbTzb) with strong Brønsted acids, such as HCl, HOTf (Tf=O2SCF3) and [H(OEt2)2][BArF4] (ArF=3,5‐(CF3)2C6H3), results in the protonation of both TzbTzb nitrogen atoms. In each case X‐ray crystallographic data show coordination of the counteranions (Cl−, OTf−, BArF4−) or solvent molecules (OEt2) to the doubly protonated fused heterocycle via hydrogen‐bonding interactions, the strength of which strongly influences the 1H NMR shift of the NH protons, enabling tuning of both the visible (yellow to red) and fluorescence (green to red) colors of these salts. DFT calculations reveal that the hydrogen bonding of the counteranion or solvent to the protonated nitrogen centers affects the intramolecular TzbTzb‐to‐CAAC charge transfer character involved in the S0→S1 transition, ultimately enabling fine‐tuning of their absorption and emission spectral features. [ABSTRACT FROM AUTHOR]

A family of novel halogen bonding (XB) and hydrogen bonding (HB) heteroditopic [2]rotaxane host systems constructed by active metal template (AMT) methodology, were studied for their ability to cooperatively recognise lithium halide (LiX) ion‐pairs. 1H NMR ion‐pair titration experiments in CD3CN:CDCl3 solvent mixtures revealed a notable "switch‐on" of halide anion binding in the presence of a co‐bound lithium cation, with rotaxane hosts demonstrating selectivity for LiBr over LiI. The strength of halide binding was shown to greatly increase with increasing number of halogen bond donors integrated into the interlocked cavity, where an all‐XB rotaxane was found to be the most potent host for LiBr. DFT calculations corroborated these findings, determining the mode of LiX ion‐pair binding. Notably, ion‐pair binding was not observed with the corresponding XB/HB macrocycles alone, highlighting the cooperative, heteroditopic, rotaxane axle‐macrocycle component mechanical bond effect as an efficient strategy for ion‐pair recognition in general. [ABSTRACT FROM AUTHOR]

We show that the carboxyl‐functionalized ionic liquid 1‐(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC‐CH2‐py][NTf2] exhibits three types of hydrogen bonding: the expected single hydrogen bonds between cation and anion, and, surprisingly, single and double hydrogen bonds between the cations, despite the repulsive Coulomb forces between the ions of like charge. Combining X‐ray crystallography, differential scanning calorimetry, IR spectroscopy, thermodynamic methods and DFT calculations allows the analysis and characterization of all types of hydrogen bonding present in the solid, liquid and gaseous states of the ionic liquid (IL). We find doubly hydrogen bonded cationic dimers (c+=c+) in the crystalline phase. With increasing temperature, this binding motif opens in the liquid and is replaced by (c+−c+−a− species, with a remaining single cationic hydrogen bond and an additional hydrogen bond between cation and anion. We provide clear evidence that the IL evaporates as hydrogen‐bonded ion pairs (c+−a−) into the gas phase. The measured transition enthalpies allow the noncovalent interactions to be dissected and the hydrogen bond strength between ions of like charge to be determined. [ABSTRACT FROM AUTHOR]

Achiral 2‐hydroxy‐N‐(diphenylmethyl)acetamide (HNDPA) crystallizes in the P61 chiral space group as a hydrate, building up permeable chiral crystalline helical water channels. The crystallization‐driven chiral self‐resolution process is highly robust, with the same air‐stable crystalline form readily obtained under a variety of conditions. Interestingly, the HNDPA supramolecular helix inner pore is filled by a helical water wire. The whole edifice is mainly stabilized by robust hydrogen bonds involving the HNDPA amide bonds and CH...π interactions between the HNDPA phenyl groups. The crystalline structure shows breathing behavior, with completely reversible release and re‐uptake of water inside the chiral channel under ambient conditions. Importantly, the HNDPA channel is able to transport water very efficiently and selectively under biomimetic conditions. With a permeability per channel of 3.3 million water molecules per second in large unilamellar vesicles (LUV) and total selectivity against NaCl, the HNDPA channel is a very promising functional nanomaterial for future applications. [ABSTRACT FROM AUTHOR]

We report the synthesis of two [2]rotaxanes containing an interlocked three dimensional binding cavity formed from a pyridinium bis(amide) axle component containing two phenol donors, and an isophthalamide based macrocycle. In the competitive solvent mixture 1 : 1 CDCl3 : CD3OD, one of the receptors exhibits a much higher selectivity preference for chloride than an analogous rotaxane without the hydroxy groups. X‐ray crystal structures reveal the chloride anion guest encapsulated within the interlocked binding cavity, though not all of the hydrogen bond donors are utilised. Computational semi‐empirical simulations indicate that secondary intermolecular interactions occur between the axle hydroxy hydrogen bond donors and the [2]rotaxane macrocycle components, contributing to a more preorganised binding pocket, which may be responsible for the observed enhanced selectivity. [ABSTRACT FROM AUTHOR]

The intramolecular hydrogen bond (intra‐HB) is one of the best‐known examples of non‐covalent interactions in molecules. Among the different types of intramolecular hydrogen bonding, the NH⋅⋅⋅O hydrogen bond in amino‐alcohols and amino‐ethers is one of the weakest. In contrast to the strong OH⋅⋅⋅N intramolecular hydrogen bond, the strength of the NH⋅⋅⋅O bond can hardly be measured with conventional spectroscopic methods, even for simple amino‐alcohols, since the band belonging to the NH⋅⋅⋅O conformer merges with the free OH band. In this work, we developed a combination of G4 calculations, and a method based on experimental vaporization enthalpies to determine the NH⋅⋅⋅O hydrogen bonding strength. The archetypal compounds for this study are 2‐amino‐1‐ethanol and 3‐amino‐1‐propanol as well as their respective methoxy analogs. Based on these molecules, different series were studied to investigate various factors influencing NH⋅⋅⋅O intra‐HB strength. In the first series, the influence of alkylation near the hydroxy or methoxy group and the amino group in sterically hindered aminoalcohols was examined. In the second series, the influence of alkylation of the amino‐group was investigated. In the third series, the effect of extending the alkyl chain between functional groups was studied. [ABSTRACT FROM AUTHOR]

Inclusion of a second nitrogen atom in the aromatic core of phosphorus‐nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X‐ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs. To study the difference in solution vs. solid‐state heterocycles, alkylated analogues that lock in the quinoidal tautomer were synthesized and their different 1H NMR and UV/Vis spectra studied. Ultimately, we determined that all heterocycles are the aromatic tautomer in solution and all but 2 e switch to the quinoidal tautomer in the solid state. Better understanding of this transformation and under what circumstances it occurs suggest future use in a switchable on/off hydrogen‐bond‐directed receptor that can be tuned for complementary hydrogen bonding. [ABSTRACT FROM AUTHOR]

Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C12H30N8)]3+ ⋅ 3 NO3− is reported to undergo a disorder‐order phase transition at Tc1 ≈133 K upon cooling. Temperature‐dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below Tc1. The modulation wave vector varies as function of temperature and locks in at Tc3≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in Tc1

As appreciation for nonclassical hydrogen bonds has progressively increased, so have efforts to characterize these interesting interactions. Whereas several kinds of C−H hydrogen bonds have been well‐studied, much less is known about the R3N+−C−H⋅⋅⋅X variety. Herein, we present crystallographic and spectroscopic evidence for the existence of these interactions, with special relevance to Selectfluor chemistry. Of particular note is the propensity for Lewis bases to engage in nonclassical hydrogen bonding over halogen bonding with the electrophilic F atom of Selectfluor. Further, the first examples of 1H NMR experiments detailing R3N+−C−H⋅⋅⋅X (X=O, N) hydrogen bonds are described. [ABSTRACT FROM AUTHOR]

An H2O2 molecule was isolated inside hydroxylated open‐cage fullerene derivatives by mixing an H2O2 solution with a precursor molecule followed by reduction of one of carbonyl groups on its orifice. Depending on the reduction site, two structural isomers for H2O2@open‐fullerenes were obtained. A high encapsulation ratio of 81 % was attained at low temperature. The structures of the peroxosolvate complexes thus obtained were studied by 1H NMR spectroscopy, X‐ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H2O2 and the hydroxy group located at the center of the orifice. This OH group was found to act as a kinetic stopper, and the formation of the hydrogen bonding caused thermodynamic stabilization of the H2O2 molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H2O2@open‐fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen‐bonding interaction. [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]

The solution and mechanochemical synthesis of two cocrystals that differ in the stoichiometric ratio of the components (stoichiometric cocrystals) is reported. The components in the stoichiometric cocrystals interact through hydrogen or hydrogen/halogen bonds and differ in π‐stacking arrangements. The difference in structure and noncovalent interactions affords dramatically different thermal expansion behaviors in the two cocrystals. At certain molar ratios, the cocrystals are obtained concomitantly; however, by varying the ratios, a single stoichiometric cocrystal is achieved using mechanochemistry. [ABSTRACT FROM AUTHOR]

The reaction of [PtCl2(COD)] (COD=1,5‐cyclooctadiene) with diisopropyl‐2‐(3‐methyl)indolylphosphine (iPr2P(C9H8N)) led to the formation of the platinum(ii) chlorido complexes, cis‐[PtCl2{iPr2P(C9H8N)}2] (1) and trans‐[PtCl2{iPr2P(C9H8N)}2] (2). The cis‐complex 1 reacted with NEt3 yielding the complex cis‐[PtCl{κ2‐(P,N)‐iPr2P(C9H7N)}{iPr2P(C9H8N)}] (3) bearing a cyclometalated κ2‐(P,N)‐phosphine ligand, while the isomer 2 with a trans‐configuration did not show any reactivity towards NEt3. Treatment of 1 or 3 with (CH3)4NF (TMAF) resulted in the formation of the twofold cyclometalated complex cis‐[Pt{κ2‐(P,N)‐iPr2P(C9H7N)}2] (4). The molecular structures of the complexes 1–4 were determined by single‐crystal X‐ray diffraction. The fluorido complex cis‐[PtF{κ2‐(P,N)‐iPr2P(C9H7N)}{iPr2P(C9H8N)}] ⋅ (HF)4 (5 ⋅ (HF)4) was formed when complex 4 was treated with different hydrogen fluoride sources. The Pt(ii) fluorido complex 5 ⋅ (HF)4 exhibits intramolecular hydrogen bonding in its outer coordination sphere between the fluorido ligand and the NH group of the 3‐methylindolyl moiety. In contrast to its chlorido analogue 3, complex 5 ⋅ (HF)4 reacted with CO or the ynamide 1‐(2‐phenylethynyl)‐2‐pyrrolidinone to yield the complexes trans‐[Pt(CO){κ2‐(P,C)‐iPr2P(C9H7NCO)}{iPr2P(C9H8N)}][F(HF)4] (7) and a complex, which we suggest to be cis‐[Pt{C=C(Ph)OCN(C3H6)}{κ2‐(P,N)‐iPr2P(C9H7N)}{iPr2P(C9H8N)}][F(HF)4] (9), respectively. The structure of 9 was assigned on the basis of DFT calculations as well as NMR and IR data. Hydrogen bonding of HF and NH to fluoride was proven to be crucial for the existence of 7 and 9. [ABSTRACT FROM AUTHOR]

Recent years have witnessed various fascinating phenomena arising from the interactions of noncovalent bonds with homogeneous external electric fields (EEFs). Here we performed a computational study to interpret the sensitivity of intrinsic bond strengths to EEFs in terms of steric effect and orbital interactions. The block‐localized wavefunction (BLW) method, which combines the advantages of both ab initio valence bond (VB) theory and molecular orbital (MO) theory, and the subsequent energy decomposition (BLW‐ED) approach were adopted. The sensitivity was monitored and analyzed using the induced energy term, which is the variation in each energy component along the EEF strength. Systems with single or multiple hydrogen (H) or halogen (X) bond(s) were also examined. It was found that the X‐bond strength change to EEFs mainly stems from the covalency change, while generally the steric effect rules the response of H‐bonds to EEFs. Furthermore, X‐bonds are more sensitive to EEFs, with the key difference between H‐ and X‐bonds lying in the charge transfer interaction. Since phenylboronic acid has been experimentally used as a smart linker in EEFs, switchable sensitivity was scrutinized with the example of the phenylboronic acid dimer, which exhibits two conformations with either antiparallel or parallel H‐bonds, thereby, opposite or consistent responses to EEFs. Among the studied systems, the quadruple X‐bonds in molecular capsules exhibit remarkable sensitivity, with its interaction energy increased by −95.2 kJ mol−1 at the EEF strength 0.005 a.u. [ABSTRACT FROM AUTHOR]