Showing papers on "Hydrogen bond published in 2017"
TL;DR: It was found that the difluoromethyl group acts as a hydrogen bond donor on a scale similar to that of thiophenol, aniline, and amine groups but not as that of hydroxyl.
Abstract: There is a growing interest in organic compounds containing the difluoromethyl group, as it is considered a lipophilic hydrogen bond donor that may act as a bioisostere of hydroxyl, thiol, or amine groups. A series of difluoromethyl anisoles and thioanisoles was prepared and their druglike properties, hydrogen bonding, and lipophilicity were studied. The hydrogen bond acidity parameters A (0.085–0.126) were determined using Abraham’s solute 1H NMR analysis. It was found that the difluoromethyl group acts as a hydrogen bond donor on a scale similar to that of thiophenol, aniline, and amine groups but not as that of hydroxyl. Although difluoromethyl is considered a lipophilicity enhancing group, the range of the experimental Δlog P(water–octanol) values (log P(XCF2H) – log P(XCH3)) spanned from −0.1 to +0.4. For both parameters, a linear correlation was found between the measured values and Hammett σ constants. These results may aid in the rational design of drugs containing the difluoromethyl moiety.
351 citations
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TL;DR: The carbonyl group holds a prominent position in chemistry and biology not only because it allows diverse transformations but also because it supports key intermolecular interactions, including hydrogen bonding, in what is termed an n→π* interaction, which is likely to play an important role in dictating protein structure.
Abstract: ConspectusThe carbonyl group holds a prominent position in chemistry and biology not only because it allows diverse transformations but also because it supports key intermolecular interactions, including hydrogen bonding. More recently, carbonyl groups have been found to interact with a variety of nucleophiles, including other carbonyl groups, in what we have termed an n→π* interaction. In an n→π* interaction, a nucleophile donates lone-pair (n) electron density into the empty π* orbital of a nearby carbonyl group. Mixing of these orbitals releases energy, resulting in an attractive interaction. Hints of such interactions were evident in small-molecule crystal structures as early as the 1970s, but not until 2001 was the role of such interactions articulated clearly.These non-covalent interactions were first discovered during investigations into the thermostability of the proline-rich protein collagen, which achieves a robust structure despite a relatively low potential for hydrogen bonding. It was found t...
293 citations
TL;DR: A simple one-pot strategy to prepare a fully physically cross-linked nanocomposite hydrogel through the formation of the hydrogen bonds and dual metal-carboxylate coordination bonds within supramolecular networks, in which iron ions and TEMPO oxidized cellulose nanofibrils (CNFs) acted as cross-linkers and led to the improved mechanical strength, toughness, time-dependent self-recovery capability and self-healing property.
Abstract: Dynamic noncovalent interactions with reversible nature are critical for the integral synthesis of self-healing biological materials. In this work, we developed a simple one-pot strategy to prepare a fully physically cross-linked nanocomposite hydrogel through the formation of the hydrogen bonds and dual metal-carboxylate coordination bonds within supramolecular networks, in which iron ions (Fe3+) and TEMPO oxidized cellulose nanofibrils (CNFs) acted as cross-linkers and led to the improved mechanical strength, toughness, time-dependent self-recovery capability and self-healing property. The spectroscopic analysis and rheological measurements corroborated the existence of hydrogen bonds and dual coordination bonds. The mechanical tests and microscopic morphology were explored to elucidate the recovery properties and toughening mechanisms. The hydrogen bonds tend to preferentially break prior to the coordination bonds associated complexes that act as skeleton to maintain primary structure integrity, and th...
279 citations
TL;DR: In this article, a hybrid polymer network is constructed by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks.
Abstract: Self-healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to "dry" elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid "dry" elastomer that is very tough with fracture energy 13500 Jm-2 comparable to that of natural rubber. Moreover, the elastomer can self-heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self-healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self-healing polymers of practical usage.
274 citations
TL;DR: The bioisosterism of the OH and CF2H groups and the important roles of CF2-H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences are demonstrated.
Abstract: The CF2H group, a potential surrogate for the OH group, can act as an unusual hydrogen bond donor, as confirmed by crystallographic, spectroscopic, and computational methods. Here, we demonstrate the bioisosterism of the OH and CF2H groups and the important roles of CF2–H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences. Experimental evidence, corroborated by theory, reveals the distinctive nature of CF2H hydrogen bonding interactions relative to their normal OH hydrogen bonding counterparts.
270 citations
TL;DR: The authors' experimental results confirm that oleylammonium ions act as capping ligands by substituting Cs+ ions from the surface of CsPbBr3 NCs, and DFT calculations shows that the substitution mechanism does not require much energy for surface reconstruction and stabilizes the nanocrystal by the formation of three hydrogen bonds.
Abstract: Optoelectronic properties of CsPbBr3 perovskite nanocubes (NCs) depend strongly on the interaction of the organic passivating molecules with the inorganic crystal. To understand this interaction, we employed a combination of synchrotron-based X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) spectroscopy, and first-principles density functional theory (DFT)-based calculations. Variable energy XPS elucidated the internal structure of the inorganic part in a layer-by-layer fashion, whereas NMR characterized the organic ligands. Our experimental results confirm that oleylammonium ions act as capping ligands by substituting Cs+ ions from the surface of CsPbBr3 NCs. DFT calculations shows that the substitution mechanism does not require much energy for surface reconstruction and, in contrast, stabilizes the nanocrystal by the formation of three hydrogen bonds between the −NH3+ moiety of oleylammonium and surrounding Br– on the surface of NCs. This substitution mechanism and its origin ar...
262 citations
TL;DR: In this paper, an electrostatic self-assembly method to form a unique core-shell architecture of a colloid of carbon spheres with graphitic carbon nitride (g-C3N4) has been developed by a one-step chemical solution route.
Abstract: The development of new, appealing metal-free photocatalysts is of great significance for photocatalytic hydrogen evolution. Herein, an electrostatic self-assembly method to form a unique core–shell architecture of a colloid of carbon spheres with graphitic carbon nitride (g-C3N4) has been developed by a one-step chemical solution route. The chemical protonation of g-C3N4 solids with strong oxidizing acids (such as HNO3) is an efficient pathway toward the sol procedure of stable carbon nitride colloids, which can cover the surface of carbon spheres via electrostatic adsorption. On account of the unique polymeric matrix of g-C3N4 and reversible hydrogen bonding, the carbon@g-C3N4 derived from the sol solution showed high mechanical stability with broadened light absorption and enhanced conductivity for charge transport. Thus, the carbon@g-C3N4 core–shell structure exhibited remarkably enhanced photoelectrochemical performance. This polymer system is envisaged to hybridize with desirable functionalities (suc...
234 citations
TL;DR: Simulations show that the structure of the bulk hydrogen bond donor is largely preserved for hydroxyl based hydrogen bond donors (ChCl:Gly and ChCl:EG), resulting in a smaller melting point depression, while ChCl?:U exhibits a well-established hydrogen bond network between the salt and hydrogen Bond donor, leading to a larger melting point depressed.
Abstract: Deep eutectic solvents (DESs) are a mixture of a salt and a molecular hydrogen bond donor, which form a eutectic liquid with a depressed melting point. Quantum mechanical molecular dynamics (QM/MD) simulations have been used to probe the 1 : 2 choline chloride–urea (ChCl : U), choline chloride–ethylene glycol (ChCl : EG) and choline chloride–glycerol (ChCl : Gly) DESs. DES nanostructure and interactions between the ions is used to rationalise differences in DES eutectic point temperatures and viscosity. Simulations show that the structure of the bulk hydrogen bond donor is largely preserved for hydroxyl based hydrogen bond donors (ChCl:Gly and ChCl:EG), resulting in a smaller melting point depression. By contrast, ChCl:U exhibits a well-established hydrogen bond network between the salt and hydrogen bond donor, leading to a larger melting point depression. This extensive hydrogen bond network in ChCl:U also leads to substantially higher viscosity, compared to ChCl:EG and ChCl:Gly. Of the two hydroxyl based DESs, ChCl:Gly also exhibits a higher viscosity than ChCl:EG. This is attributed to the over-saturation of hydrogen bond donor groups in the ChCl:Gly bulk, which leads to more extensive hydrogen bond donor self-interaction and hence higher cohesive forces within the bulk liquid.
230 citations
TL;DR: A new class of cobalt-based complexes among the most promising CO2-to-formic acid reducing catalysts developed to date is reported, and the role of amine groups for stabilizing key intermediates through hydrogen bonding with water molecules during hydride transfer from the Co center to the CO2 molecule is confirmed.
Abstract: We report here on a new series of CO2-reducing molecular catalysts based on Earth-abundant elements that are very selective for the production of formic acid in dimethylformamide (DMF)/water mixtures (Faradaic efficiency of 90 ± 10%) at moderate overpotentials (500-700 mV in DMF measured at the middle of the catalytic wave). The [CpCo(PR2NR'2)I]+ compounds contain diphosphine ligands, PR2NR'2, with two pendant amine residues that act as proton relays during CO2-reduction catalysis and tune their activity. Four different PR2NR'2 ligands with cyclohexyl or phenyl substituents on phosphorus and benzyl or phenyl substituents on nitrogen were employed, and the compound with the most electron-donating phosphine ligand and the most basic amine functions performs best among the series, with turnover frequency >1000 s-1. State-of-the-art benchmarking of catalytic performances ranks this new class of cobalt-based complexes among the most promising CO2-to-formic acid reducing catalysts developed to date; addressing the stability issues would allow further improvement. Mechanistic studies and density functional theory simulations confirmed the role of amine groups for stabilizing key intermediates through hydrogen bonding with water molecules during hydride transfer from the Co center to the CO2 molecule.
218 citations
TL;DR: In this article, the adsorptive removal of pharmaceuticals and personal care products (PPCPs) from water was carried out using metal-organic framework (MOF, here MIL-101) with or without modifications, i.e., introduction of hydroxyl groups.
179 citations
TL;DR: The absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute is shown.
Abstract: Hydrophobicity plays an important role in numerous physicochemical processes from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that, in the presence of a hydrophobic solute, water forms transient microscopic “icebergs” arising from strengthened water hydrogen bonding, but there is no experimental evidence for enhanced hydrogen bonding and/or icebergs in such solutions. Here, we have used the redshifts and line shapes of the isotopically decoupled IR oxygen–deuterium (O-D) stretching mode of HDO water near small purely hydrophobic solutes (methane, ethane, krypton, and xenon) to study hydrophobicity at the most fundamental level. We present unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10–15 per methane molecule. Ab initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous, and more tetrahedrally oriented hydrogen bonds than those in bulk water and that their mobility is restricted. We show the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration.
TL;DR: Application of the procedure to hybrid lead halide perovskites shows that these compounds have significantly weaker hydrogen-bonding energies of 0.09 to 0.27 eV/cation, correlating with lower order–disorder transition temperatures.
Abstract: Hybrid organic–inorganic perovskites represent a special class of metal–organic framework where a molecular cation is encased in an anionic cage. The molecule–cage interaction influences phase stability, phase transformations, and the molecular dynamics. We examine the hydrogen bonding in four AmBX3 formate perovskites: [Am]Zn(HCOO)3, with Am+ = hydrazinium (NH2NH3+), guanidinium (C(NH2)3+), dimethylammonium (CH3)2NH2+, and azetidinium (CH2)3NH2+. We develop a scheme to quantify the strength of hydrogen bonding in these systems from first-principles, which separates the electrostatic interactions between the amine (Am+) and the BX3– cage. The hydrogen-bonding strengths of formate perovskites range from 0.36 to 1.40 eV/cation (8–32 kcalmol–1). Complementary solid-state nuclear magnetic resonance spectroscopy confirms that strong hydrogen bonding hinders cation mobility. Application of the procedure to hybrid lead halide perovskites (X = Cl, Br, I, Am+ = CH3NH3+, CH(NH2)2+) shows that these compounds have s...
TL;DR: In this article, the authors studied the electrochemical interface between rutile IrO2(110) and water to investigate how the inclusion of an explicit solvent influences the stabilities of adsorbed intermediates in the oxygen evolution reaction.
Abstract: We study the electrochemical interface between rutile IrO2(110) and water to investigate how the inclusion of an explicit solvent influences the stabilities of adsorbed intermediates in the oxygen evolution reaction. Solvent is modeled by explicit nondissociated water molecules, and their structure is determined by a global optimization method. We find that the inclusion of an explicit solvent can significantly affect the geometry of adsorbed intermediates, changing from an interaction with the surface to an interaction with the water bilayer. These water structures consist of stacked octagonal sheets in an ordered network. Solvent stabilization is pronounced for adsorbed *OH and *OOH, which are capable of donating hydrogen bonds. We find little to no change in adsorbate binding energy as the number of layers of solvent is increased from 1 to 3, suggesting a single water bilayer is sufficient to describe the system. With either *O or *OH coadsorbates, the energetics of the reaction pathway are relatively ...
TL;DR: In this article, the authors demonstrate that control of the competition between hydrogen bonds and halogen bonds, the two most highly studied directional intermolecular interactions, can be exerted by choice of solvent (polarity) to direct the selfassembly of co-crystals.
Abstract: Control of intermolecular interactions is integral to harnessing self-assembly in nature. Here we demonstrate that control of the competition between hydrogen bonds and halogen bonds, the two most highly studied directional intermolecular interactions, can be exerted by choice of solvent (polarity) to direct the self-assembly of co-crystals. Competitive co-crystal formation has been investigated for three pairs of hydrogen bond and halogen bond donors, which can compete for a common acceptor group. These competitions have been examined in seven different solvents. Product formation has been determined and phase purity has been examined by analysis of powder X-ray diffraction patterns. Formation of hydrogen-bonded co-crystals is favoured from less polar solvents and halogen-bonded co-crystals from more polar solvents. The solvent polarity at which the crystal formation switches from hydrogen-bond to halogen-bond dominance depends on the relative strengths of the interactions, but is not a function of the solution-phase interactions alone. The results clearly establish that an appreciation of solvent effects is critical to obtain control of the intermolecular interactions.
TL;DR: In this paper, three types of ionic liquids, including [Bmim][NTf2], [Bim] and [HOOC(CH2), were designed and synthesized with various hydrogen bond donating abilities and characterized based on their thermodynamic dissociation constants (pKa).
TL;DR: This study aimed to assess the chemical interaction and to demonstrate the mechanisms of coordination between 10-MDP and zirconium oxide using 1H and 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) and two dimensional (2D) 1H → 31P heteronuclear correlation (HETCOR) NMR.
Abstract: Currently, the functional monomer 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) was documented to chemically bond to zirconia ceramics. However, little research has been conducted to unravel the underlying mechanisms. This study aimed to assess the chemical interaction and to demonstrate the mechanisms of coordination between 10-MDP and zirconium oxide using 1H and 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) and two dimensional (2D) 1H → 31P heteronuclear correlation (HETCOR) NMR. In addition, shear bond-strength (SBS) tests were conducted to determine the effect of 10-MDP concentration on the bonding effectiveness to zirconia. These SBS tests revealed a 10-MDP concentration-dependent SBS with a minimum of 1-ppb 10-MDP needed. 31P-NMR revealed that one P-OH non-deprotonated of the PO3H2 group from 10-MDP chemically bonded strongly to zirconia. 1H-31P HETCOR NMR indicated that the 10-MDP monomer can be adsorbed onto the zirconia particles by hydrogen bonding between the P=O and Zr-OH groups or via ionic interactions between partially positive Zr and deprotonated 10-MDP (P-O−). The combination of 1H NMR and 2D 1H-31P HETCOR NMR enabled to describe the different chemical states of the 10-MDP bonds with zirconia; they not only revealed ionic but also hydrogen bonding between 10-MDP and zirconia.
TL;DR: In this paper, the ascorbic acid/TBAI binary system was applied for the cycloaddition of CO2 to various epoxides under ambient or mild conditions.
Abstract: Readily available ascorbic acid was discovered as an environmentally benign hydrogen bond donor for the synthesis of cyclic organic carbonates from CO2 and epoxides in the presence of nucleophilic cocatalysts. The ascorbic acid/TBAI (TBAI: tetrabutylammonium iodide) binary system could be applied for the cycloaddition of CO2 to various epoxides under ambient or mild conditions. Density functional theory calculations and catalysis experiments revealed an intriguing bifunctional mechanism in the step of CO2 insertion involving different hydroxyl moieties (enediol, ethyldiol) of the ascorbic acid scaffold.
TL;DR: In this paper, the authors synthesized and characterized the (E)-1-(5-bromo-2-hydroxybenzylidene)semicarbazide (15BHS) by FT-IR, FT-Raman, UV, 1HNMR and 13CNMR spectral analysis.
TL;DR: There are strong acid-base interactions between SO2 and -COO- on HBA, which shows that environmentally benign solvents, deep eutectic solvent (DESs) could be designed with a function to absorb low-partial pressure SO2 from simulated flue gas.
TL;DR: Results indicated that controlled-release of EGCG from zein/CS NPs and its corresponding antioxidant activities in 95% ethanol fatty simulant may provide long-term protection against oxidation for fatty foods.
TL;DR: In this paper, four thermostable functional deep eutectic solvents (DESs) based on imidazole (Im), 2-methylimidazoles, 2-ethylimidsazole and 2-propylimidazesole as hydrogen bond acceptor (HBA) and glycerol (Gly) as HBD donor were prepared.
TL;DR: A nearly discontinuous shift of the peak frequencies and areas of vibrational bands across the LCST transition for PNIPAM whereas NIPAM exhibits a continuous linear change with temperature, which supports the crucial role of the polymer backbone with respect to hydration changes in the amide group in combination with cooperative interactions of bound water along the backbone chain.
Abstract: Thermo-responsive polymers undergo a reversible coil-to-globule transition in water after which the chains collapse and aggregate into bigger globules when passing to above its lower critical solution temperature (LCST). The hydrogen bonding with the amide groups in the side chains has to be contrasted with the hydration interaction of the hydrophobic main-chain hydrocarbons. In the present investigation we study molecular changes in the polymer poly(N-isopropyl acrylamide) (PNIPAM) and in its monomer N-isopropyl acrylamide (NIPAM) in solution across the LCST transition. Employing Fourier-transform infrared spectroscopy we probe changes in conformation and hydrogen bonding. We observe a nearly discontinuous shift of the peak frequencies and areas of vibrational bands across the LCST transition for PNIPAM whereas NIPAM exhibits a continuous linear change with temperature. This supports the crucial role of the polymer backbone with respect to hydration changes in the amide group in combination with cooperative interactions of bound water along the backbone chain.
TL;DR: Searching transition state (TS) structures in different polar aprotic solvents, this work successfully regulate and control the stepwise ESDPT behaviors of BP(OH)2 through solvent polarity.
Abstract: In this work, we theoretically investigate the sequential excited state double proton transfer (ESDPT) mechanism of a representative intramolecular hydroxyl (OH)-type hydrogen molecule 2,2′-bipyridyl-3,3′-diol (BP(OH)2). We mainly adopt three kinds of different polar solvents (nonpolar cyclohexane (CYH), polar acetonitrile (ACN), and moderate chloroform (CHCl3)) to explore solvent effects on this system. Two intramolecular hydrogen bonds of BP(OH)2 are testified to be strengthened in the S1 state, which provides possibility for ESDPT process. Explorations of charge redistribution and potential energy surfaces (PESs) reveal ESDPT process. Searching transition state (TS) structures in different polar aprotic solvents, we successfully regulate and control the stepwise ESDPT behaviors of BP(OH)2 through solvent polarity.
TL;DR: In this article, the mechanism of lignin dissolution in imidazolium-based ionic liquids (ILs) was investigated using density functional theory (DFT), atoms in molecules (AIM) theory, natural bond orbital (NBO) analysis, and reduced density gradient (RDG) analysis.
Abstract: Density functional theory (DFT), atoms in molecules (AIM) theory, natural bond orbital (NBO) analysis, and reduced density gradient (RDG) analysis were employed to investigate the mechanism of lignin dissolution in imidazolium-based ionic liquids (ILs). Lignin was modeled with guaiacyl glycerol-β-guaiacyl ether (GG), which is one type of β-O-4 linked dimers. Hydrogen bonds (H-bonds) are studied specifically and characterized by different methods to evaluate the strength of interaction between ILs and the lignin model compound. From the theoretical results, it is observed that H-bonds between anions and the GG model are stronger than those between cations and the GG model. Also, anions have the strongest interaction at the α-OH position of GG, while cations have the strongest interaction at the γ-OH position of GG. In addition, anions Cl, OAc and MeSO4 have much stronger H-bonding ability than PF6, and the length of the alkyl chain does not have a significant influence on the cation–GG interaction. This work also simulates the interaction between the GG model and ion pairs, with the results suggesting that anions in ion pairs play a key role in forming H-bonds, and cations have a π-stacking interaction with GG. The calculation data provide the interaction mechanism of lignin dissolution in ILs to some extent.
TL;DR: In this paper, the authors show that the interlayer hydrogen bonds can be disrupted by solvents such as DMSO, leading to solvent-induced delamination of 2D metal-organic nanosheets.
Abstract: Trigonal 3-connecting imidazole-annulated triptycene triacid (H3TPA) is a molecular module that is programmed for orthogonal self-assembly. Upon treatment with metal salts such as CoCl2, Mn(NO3)2, Zn(NO3)2 and Cd(NO3)2, highly porous isostructural MOFs are obtained in which the TPA linker undergoes metal–ligand coordination and hydrogen bonding through carboxylate groups and imidazole moieties, respectively. The MOFs are constructed by hydrogen bond-mediated offset stacking of porous (3,3) honeycomb layers formed by the self-assembly of TPA with 3-connecting triangular bimetallic SBUs. We show that the interlayer hydrogen bonds can be disrupted by solvents such as DMSO, leading to solvent-induced delamination of 2D metal–organic nanosheets. The delamination is signaled by turn-on of fluorescence, which is suppressed in the bulk state. Indeed, the extent of exfoliation with different solvents – as reflected from fluorescence quantum yields as well as solvent-induced shifts in emission maxima – can be nicely correlated with Gutmann's solvent DN numbers, which are a measure of the ability of solvents to accept hydrogens in hydrogen bonds. The results demonstrate how the bulk materials with layered structures can be (i) engineered in a ‘bottom-up’ approach by orthogonal self-assembly of an organic linker created by de novo design and (ii) in turn be exfoliated in a ‘top-down’ approach by solvent-induced ultrasonication. As bulk materials, the hydrogen-bonded MOFs lend themselves to selective as well as high adsorption of CO2 under ambient conditions as a result of the nitrogenous environment of pores conferred by the benzimidazole moieties.
TL;DR: It is shown how all of these interactions - and hydrogen bonds - can be readily understood through their common origin in the redistribution of electron density that results from chemical bonding.
Abstract: Structure–property relationships are the key to modern crystal engineering, and for molecular crystals this requires both a thorough understanding of intermolecular interactions, and the subsequent use of this to create solids with desired properties. There has been a rapid increase in publications aimed at furthering this understanding, especially the importance of non-canonical interactions such as halogen, chalcogen, pnicogen, and tetrel bonds. Here we show how all of these interactions – and hydrogen bonds – can be readily understood through their common origin in the redistribution of electron density that results from chemical bonding. This redistribution is directly linked to the molecular electrostatic potential, to qualitative concepts such as electrostatic complementarity, and to the calculation of quantitative intermolecular interaction energies. Visualization of these energies, along with their electrostatic and dispersion components, sheds light on the architecture of molecular crystals, in turn providing a link to actual crystal properties.
TL;DR: There is competition between the hydrogen and hydrogen bonds in the protonated complexes, in which the hydrogen bond is favored in the complexes of H+-p-PyCF3 but the tetrel bond is preferred in thecomplexs of H-o/m-PySiF3 and H--o-Py SiF3.
Abstract: Ab initio calculations have been performed for the complexes H+–PyTX3⋯NH3 and H+–furanTF3⋯NH3 (T = C, Si, and Ge; X = F and Cl) with focus on geometries, energies, orbital interactions, and electron densities to study the influence of protonation on the strength of tetrel bonding. The primary interaction mode between α/β-furanCF3/p-PyCF3 and NH3 changes from an F⋯H hydrogen bond to a C⋯N tetrel bond as a result of protonation. Importantly, the protonation has a prominent enhancing effect on the strength of tetrel bonding with an increase in binding energy from 14 to 30 kcal mol−1. The tetrel bonding becomes stronger in the order H+–p-PySiF3⋯NH3 < H+–m-PySiF3⋯NH3 < H+–o-PySiF3⋯NH3, showing a reverse trend from that of the neutral analogues. In addition, there is competition between the tetrel and hydrogen bonds in the protonated complexes, in which the hydrogen bond is favored in the complexes of H+–p-PyCF3 but the tetrel bond is preferred in the complexes of H+–p-PyTX3 (T = Si, Ge; X = F, Cl) and H+–o/m-PySiF3.
TL;DR: The direct involvement of reactive oxygen in the kinetically relevant step leads to more effective CH4 turnovers and complete elimination of coke deposition on Ni-Co bimetallic clusters.
Abstract: This study describes a new C–H bond activation pathway during CH4–CO2 reactions on oxophilic Ni-Co and Co clusters, unlike those established previously on Ni clusters. The initial C–H bond activation remains as the sole kinetically relevant step on Ni-Co, Ni, and Co clusters, but their specific reaction paths vary. On Ni clusters, C–H bond activation occurs via an oxidative addition step that involves a three-center (H3C···*···H)⧧ transition state, during which a Ni-atom inserts into the C–H bond and donates its electron density into the C–H bond’s antibonding orbital. Ni-Co clusters are more oxophilic than Ni; thus, their surfaces are covered with oxygen adatoms. An oxygen adatom and a vicinal Co-atom form a metal–oxygen site-pair that cleaves the C–H bond via a σ bond metathesis reaction, during which the Co inserts into the C–H bond while the oxygen abstracts the leaving H-atom in a concerted, four-center (H3C···*···H···O*)⧧ transition state. Similarly, Co clusters also catalyze the σ bond metathesis s...
TL;DR: A range of interactions can be placed in one big tent, related by a combination of σ hole and n→σ* bonding contributions with retention of the octet by the central element, E, and a strong symmetrical HB can be considered as containing hypervalent hydrogen.
Abstract: In hypervalent bonding (HVB), secondary bonding (SB) and hydrogen bonding (HB) a nucleophilic and an electrophilic partner form a new bond that is based on a similar bonding pattern across the whole series of interactions. The electrostatic contribution is reflected in the ‘σ hole’ model in which a positive patch on E attracts the nucleophilic component. The nucleophile, Y, possesses a corresponding negative patch, resulting in a linear structure Y⋯E–X having one strong E–X bond and one weaker, longer Y⋯E interaction; this is considered as a SB interaction between Y and E. The covalent component, more important in the stronger interactions, HVB and strong HB, involves charge transfer between the lone pair (n) of Y, and the σ* orbital of E–X as emphasized in the ‘n→σ*’ bonding model. For example, charge transfer from I− to I2 gives rise to the linear, symmetrical [I–I–I]− anion. We now have two short (2.95 A) bonds of equal strength corresponding to true HVB. In HB the central element, E, is H, and we can have strong or weak hydrogen bonding. On the HVB/HB analogy, a strong symmetrical HB, as in [F–H–F]−, can be considered as containing hypervalent hydrogen. In the weak HB case, we have a lesser degree of interaction, leading to normal hydrogen bonds of type Y⋯H–X analogous to secondary bonding. Within both the HB and HVB series, strong and weak types form a smooth continuum with no sharp break in properties. HVB was once considered to involve the expansion of the octet to 10, 12 or even higher valence electron counts. Whether the σ hole or n→σ* model applies, any octet expansion is now seen as largely formal, however, because the central element essentially retains its eight valence electrons. Thus a range of interactions can be placed in one big tent, related by a combination of σ hole and n→σ* bonding contributions with retention of the octet by the central element, E.
TL;DR: In this article, the authors demonstrate that the solubility of GO and the stability of the as-formed solutions depend not only on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface.
Abstract: One of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface. By the DFT and QTAIM calculations, we demonstrate that the solubility of GO is afforded by strong hydrogen bonding established between GO functional groups and solvent molecules. The main functional groups taking part in hydrogen bonding are tertiary alcohols; epoxides play only a minor role. The magnitude of the bond energy values is significantly higher than that for typical hydrogen bonding. The hydrogen bond energy between GO functional groups and solvent molecules decreases in the sequence: water > methanol > ethanol. We support our theoretical results by several experimental observations including solution calorimetry. The enthalpy of GO dissolution in water, methanol and ethanol is −0.1815 ± 0.0010, −0.1550 ± 0.0012 and −0.1040 ± 0.0010 kJ g−1, respectively, in full accordance with the calculated trend. Our findings provide an explanation for the well-known, but poorly understood solvent exchange phenomenon.