Showing papers on "Chemical bond published in 2010"
TL;DR: The geometry of a given B...XY is found to be isomorphic with that of the corresponding hydrogen-bonded system B...HX, an observation that leads an interim definition of the halogen bond similar to that recently proposed for the hydrogen bond.
Abstract: There has been an upsurge of interest in the halogen bond during the last decade. This non-covalent interaction is less familiar than the hydrogen bond, but is similar to it in several respects. In this article, we first discuss the nature of the halogen bond in the gas phase, as established by systematic investigations of the rotational spectra of complexes B⋯XY, where B is a simple Lewis base and XY is a dihalogen molecule. The geometry of a given B⋯XY is found to be isomorphic with that of the corresponding hydrogen-bonded system B⋯HX, an observation that leads an interim definition of the halogen bond similar to that recently proposed for the hydrogen bond. Selected novel applications of the halogen bond made in the last decade in various areas of chemistry/materials (namely crystal engineering, liquid crystals, nano-materials, polymer chemistry and inorganic chemistry) are then reviewed. These applications generally involve molecules of the type XR (where R is an electron-withdrawing group) acting as the electron donor, rather than dihalogens XY.
539 citations
TL;DR: This Perspective summarizes a series of iron-catalyzed C-C bond formation reactions developed by us, which include (asymmetric) carbometalation of olefins, cross-coupling of alkyl halides, and activation of sp(2) and sp(3) C-H bonds.
Abstract: The use of iron as a catalyst for organic synthesis has been increasingly attracting the interest of chemists from economical and ecological points of view. While Fe(III) and Fe(II) catalysts have long been used as Lewis acids for synthesis, we have been interested in exploration of catalysis based on rather unexplored organoiron chemistry since the late 1990s. This Perspective summarizes a series of iron-catalyzed C−C bond formation reactions developed by us, which include (asymmetric) carbometalation of olefins, cross-coupling of alkyl halides, and activation of sp2 and sp3 C−H bonds.
417 citations
TL;DR: Employing the fit functions to assign intramolecular hydrogen bond energies in polypeptides, several side chain CH...O and CH...N hydrogen bonds were detected on the fly and describe rather well intermolescular hydrogen bonds in amino acid dimers and the cooperativity of hydrogen Bond energies in water clusters.
Abstract: First, different approaches to detect hydrogen bonds and to evaluate their energies are introduced newly or are extended. Supermolecular interaction energies of 256 dimers, each containing one single hydrogen bond, were correlated to various descriptors by a fit function depending both on the donor and acceptor atoms of the hydrogen bond. On the one hand, descriptors were orbital-based parameters as the two-center or three-center shared electron number, products of ionization potentials and shared electron numbers, and the natural bond orbital interaction energy. On the other hand, integral descriptors examined were the acceptor-proton distance, the hydrogen bond angle, and the IR frequency shift of the donor-proton stretching vibration. Whereas an interaction energy dependence on 1/r3.8 was established, no correlation was found for the angle. Second, the fit functions are applied to hydrogen bonds in polypeptides, amino acid dimers, and water cluster, thus their reliability is demonstrated. Employing the...
278 citations
TL;DR: In this paper, the adsorption energy, stable geometry, density of state, and magnetic moment of 15 transition metal adatoms on graphene were studied using first-principles density-functional theory with the generalized gradient approximation.
Abstract: The adsorption of 15 different transition metal adatoms on graphene is studied using first-principles density-functional theory with the generalized gradient approximation. The adsorption energy, stable geometry, density of state, and magnetic moment of each adatom–graphene system are calculated. For the adatoms studied from Sc to Zn of the Periodic Table, and noble metals, the distortion of the graphene layer on B of T sites is quite significant in some cases, and the adsorption is characterized by strong hybridization between adatom and graphene electronic states. The favored adsorption site indicates the main chemical bond between adsorbate and graphene. Half filled d shell TM atoms and Au, Ag, Zn have small adsorption energy. The reduction in magnetic moment from the isolated to the adsorbed atom is explained by the perspective of charge transfer, and electron shift between different orbit states of the adatom.
186 citations
TL;DR: The palladium-catalyzed ortho-alkoxylation of N-methoxybenzamides has been demonstrated with the CONHOMe group as a directing group, and the aromatic C-H bond can be functionalized efficiently to generate Ortho-alksoxylated derivatives in moderate to good yields.
Abstract: The palladium-catalyzed ortho-alkoxylation of N-methoxybenzamides has been demonstrated. With the CONHOMe group as a directing group, the aromatic C−H bond can be functionalized efficiently to generate ortho-alkoxylated derivatives in moderate to good yields.
153 citations
TL;DR: This work identifies experimentally, and confirms theoretically, the atomic configuration of maximum chemical bonding to the substrate, and explains why this is the case by considering the various factors that contribute to the bonding at the graphene/metal interface.
Abstract: Resonance tunneling spectroscopy and density functional theory calculations are employed to explore local variations in the electronic surface potential of a single graphene layer grown on Rh(111). A work function modulation of 220 meV is experimentally measured, indicating that the chemical bonding strength varies significantly across the supercell of the Moire pattern formed when graphene is bonded to Rh(111). In combination with high-resolution images, which provide precise knowledge of the local atomic registry at the carbon−metal interface, we identify experimentally, and confirm theoretically, the atomic configuration of maximum chemical bonding to the substrate. Our observations are at odds with reported trends for other transition metal substrates. We explain why this is the case by considering the various factors that contribute to the bonding at the graphene/metal interface.
150 citations
TL;DR: In this paper, the authors provided atomic and electronic structures, formation energies of defects and bond energies in a-IGZO calculated by first-principles density functional theory (DFT), and confirmed that oxygen deficiencies having small formation energies (2-3.6 eV) form either deep fully occupied localized states near the valence band maximum or donor states, which depend on their local structures.
Abstract: Amorphous In-Ga-Zn-O (a-IGZO) is expected for channel layers in thin-film transistors (TFTs). It is known that a-IGZO is sensitive to an O/H-containing atmosphere; therefore, it is important to clarify the roles of oxygen and hydrogen in a-IGZO. This paper provides atomic and electronic structures, formation energies of defects and bond energies in a-IGZO calculated by first-principles density functional theory (DFT). It was confirmed that oxygen deficiencies having small formation energies (2-3.6 eV) form either deep fully-occupied localized states near the valence band maximum or donor states, which depend on their local structures. All the hydrogen doping form -OH bond and work as a donor. The stable -OH bonds have small formation energy of ~0.45 eV and consist of three metal cations coordinated to the O ion. The bond energy of Ga-O is calculated to be ~2.0 eV, which is the largest among the chemical bonds in a-IGZO (1.7 eV for In-O and 1.5 eV for ZnO). This result supports the idea that the incorporation of Ga stabilizes a-IGZO TFTs.
139 citations
TL;DR: It is shown that a tungsten centre can be used to cleave a strong C–C bond that is a component of an unstrained 6-membered aromatic ring, which suggests that other metal centres with suitable ancillary ligands could also accomplish the cleavage of strong C-C bonds of aromatic substrates and thereby provide new ways of functionalizing such molecules.
Abstract: The cleavage of C-H and C-C bonds by transition metal centres is of fundamental interest and plays an important role in the synthesis of complex organic molecules from petroleum feedstocks. But while there are many examples for the oxidative addition of C-H bonds to a metal centre, transformations that feature oxidative addition of C-C bonds are rare. The paucity of transformations that involve the cleavage of C-C rather than C-H bonds is usually attributed to kinetic factors arising from the greater steric hindrance and the directional nature of the sp(n) hybrids that form the C-C bond, and to thermodynamic factors arising from the fact that M-C bonds are weaker than M-H bonds. Not surprisingly, therefore, most examples of C-C bond cleavage either avoid the kinetic limitations by using metal compounds in which the C-C bond is held in close proximity to the metal centre, or avoid the thermodynamic limitations by using organic substrates in which the cleavage is accompanied by either a relief of strain energy or the formation of an aromatic system. Here, we show that a tungsten centre can be used to cleave a strong C-C bond that is a component of an unstrained 6-membered aromatic ring. The cleavage is enabled by the formation of an unusual chelating di(isocyanide) ligand, which suggests that other metal centres with suitable ancillary ligands could also accomplish the cleavage of strong C-C bonds of aromatic substrates and thereby provide new ways of functionalizing such molecules.
137 citations
TL;DR: Large bond elongations accompanied by red-shifts are obtained for the ion pairs investigated, and this points to a disturbing rather than stabilizing role of hydrogen bonding on the interaction of the counterions in imidazolium-based ionic liquids.
Abstract: The intermediate bond forces in ionic liquids are investigated from static quantum chemical calculations at various methods and two basis sets. The experimentally observed red-shift of the donor-proton bond stretching frequency due to a bond elongation is confirmed by all methods. Comparing Hartree-Fock to second-order Moller-Plesset perturbation theory, the Hartree-Fock method gives in many cases an erroneous description of the geometries. Furthermore, the Hartree-Fock interaction energies can deviate up to 60 kJ mol(-1) from Moller-Plesset perturbation theory indicating the importance of dispersion interaction. While the usual trends of decreasing stability or interaction energies with increasing ion sizes are found, the geometries involving hydrogen atoms do not change this order of total interaction energies. Therefore, the hydrogen bond is not the most important interaction for ion pairs with regard to the total interaction energy. On the other hand, the different established analysis methods give rise to hydrogen bonding in several ion pairs. Charge analysis reveals the hydrogen-bonding character of the ion pair and shows, depending on the type of ions combined and further on the type of conformers considered, that a hydrogen bond can be present. The possibility of hydrogen bonding is also shown by an analysis of the frontier orbitals. Calculating potential energy surfaces and observing from this the change in the donor proton bond indicates that regular hydrogen bonds are possible in ion pairs of ionic liquids. Thereby, the maximum of bond elongation exceeds the one of a usual hydrogen bond by far. The more salt-like hydrogen-bonded ion pair [NH(4)][BF(4)] exhibits a steeper maximum than the more ionic liquid like ion pair [EtNH(3)][BF(4)]. The fact that imidazolium-based ionic liquids as [Emim][Cl] can display two faces, hydrogen bonding and purely ionic bonding, points to a disturbing rather than stabilizing role of hydrogen bonding on the interaction of the counterions in imidazolium-based ionic liquids. While geometry and charge analysis provides attributes of weak (blue-shifted) hydrogen bonds, large bond elongations accompanied by red-shifts are obtained for the ion pairs investigated. This can be understood by the simple fact that these imidazolium-based ionic liquid ion pairs constitute weak hydrogen bonds placed between two delocalized charges.
121 citations
TL;DR: Amminelithium borohydride, LiBH(4) x NH(3) which has two temperature sensitive chemical bonds N:-->Li(+) and N-H...H-B, is shown to release hydrogen at low temperatures by stabilizing the ammonia and promoting the recombination of the NH...HB bond.
111 citations
TL;DR: The chemical bonding, electronic structure, and optical properties of metal-organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations to contribute to a comprehensive understanding about this kind of material and shed insight into the synthesis and application of novel and stable MOFs.
Abstract: The chemical bonding, electronic structure, and optical properties of metal−organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations. The unit cell volume and atomic positions were optimized with the Perdew−Burke−Ernzerhof (PBE) functional leading to a good agreement between the experimental and the theoretical equilibrium structural parameters. The calculated bulk modulus indicates that MOF-5 is a soft material. The estimated band gap from a density of state (DOS) calculation for MOF-5 is about 3.4 eV, indicating a nonmetallic character. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, and electroluminescence cells, the optical properties of this material were investigated. The detailed analysis of chemical bonding in MOF-5 reveals the nature of the Zn−O, O−C, H−C, and C−C bonds, that is, Zn−O having mainly ionic interaction whereas O−C, H−C, and C−C exhibit mainly covalent interactions. The find...
TL;DR: A chelation-assisted copper(II)-catalyzed ortho-acyloxylation of the 2-arylpyridine sp(2) C-H bond with anhydride is described, affording the mono- or diacylOxylated products in moderate to good yields.
Abstract: A chelation-assisted copper(II)-catalyzed ortho-acyloxylation of the 2-arylpyridine sp2 C−H bond with anhydride is described. The procedure tolerates various functional groups, such as carbomethoxyl, methoxyl, fluoro, bromo, chloro, and cyano groups, affording the mono- or diacyloxylated products in moderate to good yields. Importantly, this procedure uses O2 as a clean terminal oxidant.
TL;DR: To demonstrate the utility of isocyanides in catalytic C-H bond functionalization reactions, a palladium-catalyzed cyclocoupling reaction of 2-halobiaryls with isocianides was developed, allowing the construction of a wide range of ring system.
Abstract: To demonstrate the utility of isocyanides in catalytic C−H bond functionalization reactions, a palladium-catalyzed cyclocoupling reaction of 2-halobiaryls with isocyanides was developed. The reaction afforded an array of fluorenone imine derivatives via the cleavage of a C−H bond at the 2′-position of 2-halobiaryls. The use of 2,6-disubstituted phenyl isocyanide was crucial for this catalytic cyclocoupling reaction to proceed. The reaction was applicable to heterocyclic and vinylic substrates, allowing the construction of a wide range of ring system. The large kinetic isotope effect observed (kH/kD = 5.3) indicates that C−H bond activation was the turnover-limiting step in this catalysis.
TL;DR: In this paper, temperature-dependent two-dimensional infrared spectroscopy of dilute HOD in H2O was used to investigate hydrogen bond rearrangements in water, and they found the barrier to dephasing and hydrogen bond switching to be Ea = 3.4 ± 0.5 kcal/mol, although the trend is slightly non-Arrhenius.
Abstract: We use temperature-dependent two-dimensional infrared spectroscopy (2D IR) of dilute HOD in H2O to investigate hydrogen bond rearrangements in water. The OD stretching frequency is sensitive to its environment, and loss of frequency correlation provides a picture of local and collective hydrogen bond dynamics. The time scales for hydrogen bond rearrangements decrease from roughly 2 ps at 278 K to 0.5 ps at 345 K. We find the barrier to dephasing and hydrogen bond switching to be Ea = 3.4 ± 0.5 kcal/mol, although the trend is slightly non-Arrhenius. The value is in good agreement with the reported barrier height for OD reorientation observed in pump−probe anisotropy measurements. This provides evidence for the proposal that hydrogen bond switching occurs through concerted large angular jump reorientation. MD simulations of temperature-dependent OD vibrational dephasing and orientational correlation functions are used to support our conclusions.
TL;DR: In this paper, the formation of a self-assembled monolayer is explained through a two-step mechanism, S−H bond breaking and Au−S bond formation, and the authors found that the production of H2 is more favorable than the formation in Au−H species.
Abstract: The bonding of propanethiol molecules on a Au(111) surface is investigated using period DFT calculations within the framework of our model for chemical bond breaking that was recently proposed. The S−H bond breaking and the Au−S bond formation are analyzed through the evolution of the density of states. The energetics confirms the complexity of the reaction emerging from the interthiol chain interaction. The formation of a self-assembled monolayer is explained through a two-step mechanism, S−H bond breaking and Au−S bond formation. The production of H2 is found to be more favorable than the formation of Au−H species. The bonding and antibonding electronic states of the S−H bond have been identified and their evolutions during the process of bond breaking carefully analyzed. The corresponding bonding and antibonding states for the C−S bond are practically not affected during this process, indicating that the bond is preserved. The s orbital of the hydrogen atom strongly interacts with the gold surface and ...
TL;DR: The results of DFT calculations on cation radicals of the model compounds show that the C1-C2 bond dissociation energies of theβ-1 lignin model compounds are significantly lower than those of the β-O-4 models, providing clear evidence for the source of the rate differences.
Abstract: Features of the oxidative cleavage reactions of diastereomers of dimeric lignin model compounds, which are models of the major types of structural units found in the lignin backbone, were examined. Cation radicals of these substances were generated by using SET-sensitized photochemical and Ce(IV) and lignin peroxidase promoted oxidative processes, and the nature and kinetics of their C−C bond cleavage reactions were determined. The results show that significant differences exist between the rates of cation radical C1−C2 bond cleavage reactions of 1,2-diaryl-(β-1) and 1-aryl-2-aryloxy-(β-O-4) propan-1,3-diol structural units found in lignins. Specifically, under all conditions C1−C2 bond cleavage reactions of cation radicals of the β-1 models take place more rapidly than those of the β-O-4 counterparts. The results of DFT calculations on cation radicals of the model compounds show that the C1−C2 bond dissociation energies of the β-1 lignin model compounds are significantly lower than those of the β-O-4 mod...
TL;DR: Theoretical studies using the Electron Localizability Indicator (ELI-D) suggest the metal-metal bonding is more significant, while the delocalization indices imply that both Fe-Fe bonding and Fe···C(alkylidyne) bonding are equally important.
Abstract: The charge density in the tri-iron methoxymethylidyne cluster Fe3(μ-H)(μ-COMe)(CO)10 (1) has been studied experimentally at 100 K and by DFT calculations on the isolated molecule using the Quantum Theory of Atoms in Molecules (QTAIM). The COMe ligand acts as a nearly symmetric bridge toward two of the Fe atoms (Fe−C = 1.8554(4), 1.8608(4) A) but with a much longer interaction to the third Fe atom, Fe−C = 2.6762(4) A. Complex 1 provides a classic example where topological QTAIM catastrophes render an exact structure description ambiguous. While all experimental and theoretical studies agree in finding no direct metal−metal interaction for the doubly bridged Fe−Fe vector, the chemical bonding between the Fe(CO)4 unit and the Fe2(μ-H)(μ-COMe)(CO)6 moiety in terms of conventional QTAIM descriptors is much less clear. Bond paths implying direct Fe−Fe interactions and a weak interaction between the COMe ligand and the Fe(CO)4 center are observed, depending on the experimental or theoretical density model examin...
TL;DR: In this article, the first-principles pseudopotential total energy method is used to predict the structural, electronic and elastic properties of the M3AlC2 (MAX) phases, where M = 3d,4 d, and 5d early transition metals.
TL;DR: In this article, the interacting quantum atoms approach (IQA) was used to examine the chemical bonding in simple transition metal carbonyls under the QA framework. But the authors focused on the interaction of atoms in the atom lattice.
Abstract: Chemical bonding in simple transition metal carbonyls is examined under the interacting quantum atoms approach (IQA), which provides an energetic viewpoint within the quantum theory of atoms in mol...
TL;DR: The role of the long-range correction of the potential to obtain a balanced description of excitation energies and excited-state structures is confirmed and it is pointed out that, for a small system, B3LYP and PBE0 also give results close to CASPT2.
Abstract: We present an analysis on the behavior of the TD-DFT approach in the determination of excited-state structures with particular attention to single and double bonds. The analysis is based on a direct comparison with the highly correlated CASPT2 ab initio approach. Six DFT exchange-correlation functionals differing in the Hartree−Fock exchange percentage and the type of correlation functional are considered and applied to the study of seven prototype organic molecules characterized by two families of excitations (acrolein, acetone, diazomethane, and propanoic acid anion for n−π* and cis-1,3-butadiene, trans-1,3-butadiene, and pyrrole for π−π*), and three protonated Schiff bases, used as model chromophores for 11-cis retinal. Our analysis allows pinpointing specific correlations between accuracy of the various functionals and category of excitation and/or type of chemical bond involved in the corresponding geometry relaxation. We confirm the role of the long-range correction of the potential to obtain a bala...
TL;DR: In this paper, the theoretical hardness is described as a function of the bond density and bond strength, and the bond strength may be characterized by energy gap, reference potential, electron-holding energy or Gibbs free energy.
Abstract: Recent developments in the field of microscopic hardness models have been reviewed. In these models, the theoretical hardness is described as a function of the bond density and bond strength. The bond strength may be characterized by energy gap, reference potential, electron-holding energy or Gibbs free energy, and different expressions of bond strength may lead to different hardness models. In particular, the hardness model based on the chemical bond theory of complex crystals has been introduced in detail. The examples of the hardness calculations of typical crystals, such as spinel Si3N4, stishovite SiO2, B12O2, ReB2, OsB2, RuB2, and PtN2, are presented. These microscopic models of hardness would play an important role in search for new hard materials.
TL;DR: The results plead in favor of a systematic recourse to dispersion including DFT approximations when addressing organometallic and coordination complexes.
Abstract: The concept of a dative metal−metal bond is generally used to designate the donor−acceptor (DA) interaction of an electron-saturated metal center with another electron-deficient—or unsaturated—metal center. This type of DA bonding extended to the field of coordination complexes constitutes a borderline case of weak metal−metal interaction, among which the so-called metallophilic interactions occurring with 4d, 5d, and other late-transition-metal complexes are the most documented and representative examples. From a general standpoint, the peculiar position of the so-called dative metal−metal bond in chemical bonding stems from its presumed covalent character, which contrasts with the situation encountered with metallophilic interactions, which are essentially supported by dispersion and electrostatic forces and somewhat sustained by relativistic effects. In this study, the nature of the metal−metal bond in nonbridged 5d−3d Os−Cr and 5d−5d Os−W adducts, i.e., (Me3P)(CO)4Os−M(CO)5 (M = Cr, W) and (CO)5Os−Cr(...
TL;DR: It is believed that, particularly for this kind of molecule, molecular orbital concepts are of limited help for a consistent rationalization of the bond formation.
Abstract: The diatomic neutral oxides and their ions, MO(0,+/-), M = Sc, Ti, Cr, and Mn, have been studied through multireference configuration interaction and coupled-cluster methods. With the purpose to paint a more comprehensive and detailed picture on these not so easily tamed systems, we have constructed complete potential energy curves for a large number of states of all MO(0,+/-)'s reporting structural and spectroscopic properties. Our overall results are in very good agreement with the, in general limited, experimental data. The always difficult to be pinpointed "nature of the chemical bond" becomes more recondite for these highly open ionic-covalent species. We have tried to give some answers as to the bonding interactions using simple valence-bond-Lewis diagrams in conjunction with Mulliken populations and the symmetry of the in situ atoms. It is our belief that, particularly for this kind of molecule, molecular orbital concepts are of limited help for a consistent rationalization of the bond formation.
TL;DR: In this article, the adsorption of fluorine, chlorine, bromine, and iodine diatomic molecules on graphene has been investigated using density functional theory with taking into account nonlocal correlation effects by means of van der Waals density functional approach.
Abstract: The adsorption of fluorine, chlorine, bromine, and iodine diatomic molecules on graphene has been investigated using density functional theory with taking into account nonlocal correlation effects by means of van der Waals density functional approach. It is shown that the van der Waals interaction plays a crucial role in the formation of chemical bonding between graphene and halogen molecules, and is therefore important for a proper description of adsorption in this system. In-plane orientation of the molecules has been found to be more stable than the orientation perpendicular to the graphene layer. In the cases of ${\text{F}}_{2}$, ${\text{Br}}_{2}$, and ${\text{I}}_{2}$ we also found an ionic contribution to the binding energy, slowly vanishing with distance. Analysis of the electronic structure shows that ionic interaction arises due to the charge transfer from graphene to the molecules. Furthermore, we found that the increase in impurity concentration leads to the conduction-band formation in graphene due to interaction between halogen molecules. In addition, graphite intercalation by halogen molecules has been investigated. In the presence of halogen molecules the binding between graphite layers becomes significantly weaker, which is in accordance with the results of recent experiments on sonochemical exfoliation of intercalated graphite.
TL;DR: Recent research has shown that 7-azaindolyl and derivatives are excellent blue emitters for organic light emitting diodes, they have rich coordination chemistry with both main group elements and transition metal ions, and their metal complexes display not only phosphorescence but also unusual and often unprecedented reactivity toward C-H and C-X bonds
Abstract: 7-Azaindole and its derivatives have been extensively investigated for uses in biological probes and imaging In contrast, there have been very limited studies on the coordination chemistry and the applications of 7-azaindole and derivatives in materials science and in chemical bond activation Our recent research has shown that 7-azaindolyl and derivatives are excellent blue emitters for organic light emitting diodes, they have rich coordination chemistry with both main group elements and transition metal ions, and their metal complexes display not only phosphorescence but also unusual and often unprecedented reactivity toward C–H and C–X bonds This critical review discusses recent advances in these fields with focuses on new 7-azaindolyl derivatives and their metal complexes developed by our group The luminescent properties and applications of 7-azaindolyl-based compounds will be presented The reactivity of Pt(II) complexes toward C–H and C–X bonds, especially the steric impact of the bis(7-azaindolyl) chelate ligands and bimetallic cooperativity will be discussed (86 references)
TL;DR: These results have important implications for metal/organic interfaces in organic electronics or photovoltaic devices based on pi-conjugated semiconducting metal complexes, because the character of the chemical bond at the interface determines important parameters such as charge injecting rates.
Abstract: Monolayers and multilayers of cobalt octaethylporphyrin (CoOEP), cobalt tetraphenylporphyrin (CoTPP) and the corresponding free-base porphyrins 2HOEP and 2HTPP on an Au(111) surface were investigated with X-ray and UV photoelectron spectroscopy (XPS and UPS) For CoTPP and CoOEP monolayers, the XP spectra show a characteristic splitting of the Co 2p3/2 signal, which suggests that only a fraction of the Co ions forms coordinative bonds to the Au(111) surface, while the others interact more weakly This is a remarkable difference to previous results for CoOEP and CoTPP on Ag(111), where all Co ions in the monolayer were found to interact strongly and uniformly with the silver surface Presumably, the lateral structural and electronic inhomogeneities of the reconstructed Au(111) surface are responsible for the more complex interaction behaviour on the gold surface UP spectra of CoOEP and CoTPP monolayers show a new electronic state around 03 eV below the Fermi energy (EF), ie, at lower binding energy than in the case of Ag(111), where a strong signal appeared at 06 eV below EF In contrast, the free-base porphyrins 2HOEP and 2HTPP show no additional valence states in the monolayer, indicating that the Co ion plays a central role in the electronic interaction between the metal complexes and the substrate These results have important implications for metal/organic interfaces in organic electronics or photovoltaic devices based on π-conjugated semiconducting metal complexes, because the character of the chemical bond at the interface determines important parameters such as charge injecting rates
TL;DR: This technique shows that the fluorescence-yield spectra of aqueous ionic species exhibit additional features compared with those of non-aqueous solvents, even for fully ligated metal atoms, which indicates a direct interaction with the water molecules.
Abstract: Aqueous ions are central to catalysis and biological function and play an important role in radiation biology as sources of damage-inducing electrons. Detailed knowledge of solute-solvent interactions is therefore crucial. For transition-metal ions, soft X-ray L-edge spectroscopy allows access to d orbitals, which are involved in chemical bonding. Using this technique, we show that the fluorescence-yield spectra of aqueous ionic species exhibit additional features compared with those of non-aqueous solvents. Some features dip below the fluorescence background of the solvent and this is rationalized by the competition between the fluorescence yields of the solute and solvent species, and between the solute radiative (fluorescence) and non-radiative channels; in particular, electron transfer to the water molecules. This method allows us to determine the nature, directionality and timescale of the electron transfer. Remarkably, we observe such features even for fully ligated metal atoms, which indicates a direct interaction with the water molecules.
TL;DR: The results show that the fluorine atom has the capability to interact with the π−cloud to form an aromatic halogen bond, as long as the donor group is highly electron withdrawing.
Abstract: In this work, the intermolecular distribution of the electronic charge density in the aromatic hydrogen/halogen bonds is studied within the framework of the atoms in molecules (AIM) theory and the molecular electrostatic potentials (MEP) analysis. The study is carried out in nine complexes formed between benzene and simple lineal molecules, where hydrogen, fluorine and chlorine atoms act as bridge atoms. All the results are obtained at MP2 level theory using cc-pVTZ basis set. Attention is focused on topological features observed at the intermolecular region such as bond, ring and cage critical points of the electron density, as well as the bond path, the gradient of the density maps, molecular graphs and interatomic surfaces. The strength of the interaction increases in the following order: F⋅⋅⋅π < Cl⋅⋅⋅π < H⋅⋅⋅π. Our results show that the fluorine atom has the capability to interact with the π−cloud to form an aromatic halogen bond, as long as the donor group is highly electron withdrawing. The Laplacian topology allows us to state that the halogen atoms can act as nucleophiles as well as electrophiles, showing clearly their dual character.
TL;DR: In this article, the gas-phase fragmentation reactions of the group 11 organometallates [CH3MR] were studied by density functional theory (DFT) calculations and, for those accessible in the gas phase, via collision-induced dissociation (CID) and selected deuterium labeling experiments.