Comparison of Hydrogen and Gold Bonding in [XHX](-) , [XAuX](-) , and Isoelectronic [NgHNg](+) , [NgAuNg](+) (X=Halogen, Ng=Noble Gas).
TL;DR: Quantum chemical calculations at the MP2/aug-cc-pVTZ and CCSD(T) levels have been carried out for the title compounds and suggest a significant covalent character for the hydrogen bonds to the noble gas atoms in [NgHNg](+) and to the halogen atoms in[XHX](-) .
Abstract: Quantum chemical calculations at the MP2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels have been carried out for the title compounds. The electronic structures were analyzed with a variety of charge and energy partitioning methods. All molecules possess linear equilibrium structures with D∞h symmetry. The total bond dissociation energies (BDEs) of the strongly bonded halogen anions [XHX](-) and [XAuX](-) decrease from [FHF](-) to [IHI](-) and from [FAuF](-) to [IAuI](-) . The BDEs of the noble gas compounds [NgHNg](+) and [NgAuNg](+) become larger for the heavier atoms. The central hydrogen and gold atoms carry partial positive charges in the cations and even in the anions, except for [IAuI](-) , in which case the gold atom has a small negative charge of -0.03 e. The molecular electrostatic potentials reveal that the regions of the most positive or negative charges may not agree with the partial charges of the atoms, because the spatial distribution of the electronic charge needs to be considered. The bonding analysis with the QTAIM method suggests a significant covalent character for the hydrogen bonds to the noble gas atoms in [NgHNg](+) and to the halogen atoms in [XHX](-) . The covalent character of the bonding in the gold systems [NgAuNg](+) and [XAuX](-) is smaller than in the hydrogen compound. The energy decomposition analysis suggests that the lighter hydrogen systems possess dative bonds X(-) →H(+) ←X(-) or Ng→H(+) ←Ng while the heavier homologues exhibit electron sharing through two-electron, three-center bonds. Dative bonds X(-) →Au(+) ←X(-) and Ng→Au(+) ←Ng are also diagnosed for the lighter gold systems, but the heavier compounds possess electron-shared bonds.
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TL;DR: The hydrogen bond interaction and σ-hole and π-hole bonds are steered by the same mechanisms and the increase of the polarization of bonds to this centre seems to be the common effect.
Abstract: The hydrogen bond interaction and σ-hole and π-hole bonds are steered by the same mechanisms. There is electron charge transfer from the Lewis base to the Lewis acid unit, and further, for various interactions the same mechanisms try to protect the former electronic structure of the Lewis acid centre. The increase of the polarization of bonds to this centre seems to be the common effect. In the case of the A-HB hydrogen bond it is the increase of the polarization of the A-H bond connected with the outflow of the electron charge from the H-atom to the A-centre. For other interactions the outflow of electron charge from the Lewis acid centre is also observed. These electron charge shifts try to protect the doublet/octet structure of the acidic centre. The extremely strong interaction is often equivalent to the formation of new covalent bonds or it may lead to chemical reactions. Numerous interactions may be treated as the preliminary stages of chemical reactions: hydrogen bond - proton transfer, dihydrogen bond - molecular hydrogen release, tetrel bond - SN2 reaction, etc.
78 citations
01 Dec 1994
TL;DR: In this paper, the formation of these species is ascribed to optical access of the delocalized X/rare gas charge transfer states, and subsequent charge trapping processes, and the observed second-order decay kinetics are discussed in terms of charge-recombination involving a distribution of barrier heights.
Abstract: Photogeneration of Ar 2 H + , Kr 2 H + and Xe 2 H + and their deuterated counterparts is reported in H(D)Cl doped Ar, and H(D)X (X = Cl, Br or I) doped Kr and Xe matrices, respectively. The formation of these species is ascribed to optical access of the delocalized X/rare gas charge transfer states, and subsequent charge trapping processes. Once generated, the absorptions of the cations bleach thermally at low temperatures ( 12 K). The observed second-order decay kinetics is discussed in terms of charge-recombination involving a distribution of barrier heights. The deuterated cations bleach on a significantly longer time-scale. Bihalide ions, HX − 2 , of D ∞h symmetry are the other products formed in the photolysis. Annealing of the extensively irradiated HCl, HBr and HI doped xenon and HCl doped krypton yields strong infrared absorptions in the 1200–1600 cm −1 spectral region. These bands are tentatively ascribed to linear asymmetric (X-H—X) − ions perturbed by a nearby positive charge, or to (XeHX) + and (KrHX) + species.
66 citations
TL;DR: In this article, a review summarizes the current state of knowledge about the complexes of anions with ligands that engage in these sorts of noncovalent bonds, and how the geometry of the fully coordinated complex varies as the number of surrounding ligands increases.
58 citations
TL;DR: The triel bond may be defined as the interaction of the atom of 13th group that acts as the Lewis acid centre with the electron rich site of the species playing a role of the Lewis base as discussed by the authors.
51 citations
TL;DR: This paper provides a quantitative analysis of the chemical bond between a metal fragment AuCl and a series of 29 different NHCs in [(NHC)AuCl] complexes and shows that information obtained using the metal fragment can be transferred to the PPh moiety and vice versa.
Abstract: In view of their intensive use as ligands in many reactions catalyzed by transition-metal complexes, modulation of the bonding properties of N-heterocyclic carbenes (NHCs) on a rational basis is highly desirable, which should enable optimization of current applications or even promote new functions. In this paper, we provide a quantitative analysis of the chemical bond between a metal fragment AuCl and a series of 29 different NHCs in [(NHC)AuCl] complexes. NHCs electronic properties are modified through: i) variation of the groups attached to the NHC nitrogen atoms or backbone; ii) change of unsaturation/size of the NHC ring; iii) inclusion of paracyclophane moieties; or iv) heteroatom substitution on the NHC ring. For evaluating the donation and back-donation components of the Dewar-Chatt-Duncanson (DCD) model in the NHC-AuCl bond, we apply the charge-displacement (CD) analysis within the NOCV (natural orbitals for chemical valence) framework, a methodology that avoids the constraint of using symmetrized structures. We show that modulation of the NHC bonding properties requires substantial modification of their structure, such as, for instance, insertion of two ketone groups into the NHC backbone (which enhances the π back-donation bond component and introduces an effective electronic communication within the NHC ring) or replacement of a nitrogen atom in the ring with an sp3 or sp2 carbon atom (which increases and decreases the π back-donation bond component, respectively). We extend our investigation by quantitatively comparing the NHC electronic structures for a subset of 13 NHCs in [(NHC)PPh] adducts, the 31 P NMR chemical shift values of which are experimentally available. The latter have been considered as a suitable tool for measuring the NHCs π acceptor properties [Bertrand et al., Angew. Chem. Int. Ed. 2013, 52, 2939-2943]. We show that information obtained using the metal fragment can be transferred to the PPh moiety and vice versa. However, the 31 P NMR chemical shift values only qualitatively correlate with the π acceptor properties of the NHCs, with the stronger π acidic carbenes as the most outliners.
43 citations
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TL;DR: This work reports a gradient-corrected exchange-energy functional, containing only one parameter, that fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more.
Abstract: Current gradient-corrected density-functional approximations for the exchange energies of atomic and molecular systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy density. Here we report a gradient-corrected exchange-energy functional with the proper asymptotic limit. Our functional, containing only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more.
45,683 citations
TL;DR: The revised DFT-D method is proposed as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.
Abstract: The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.
32,589 citations
TL;DR: Numerical results for atoms, positive ions, and surfaces are close to the exact correlation energies, with major improvements over the original LM approximation for the ions and surfaces.
Abstract: Langreth and Mehl (LM) and co-workers have developed a useful spin-density functional for the correlation energy of an electronic system. Here the LM functional is improved in two ways: (1) The natural separation between exchange and correlation is made, so that the density-gradient expansion of each is recovered in the slowly varying limit. (2) Uniform-gas and inhomogeneity effects beyond the randomphase approximation are built in. Numerical results for atoms, positive ions, and surfaces are close to the exact correlation energies, with major improvements over the original LM approximation for the ions and surfaces.
16,378 citations
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TL;DR: In this paper, a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness).
Abstract: The calculation of accurate electron affinities (EAs) of atomic or molecular species is one of the most challenging tasks in quantum chemistry. We describe a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness). This procedure involves the use of the recently proposed correlation‐consistent basis sets augmented with functions to describe the more diffuse character of the atomic anion coupled with a straightforward, uniform expansion of the reference space for multireference singles and doubles configuration‐interaction (MRSD‐CI) calculations. Comparison with previous results and with corresponding full CI calculations are given. The most accurate EAs obtained from the MRSD‐CI calculations are (with experimental values in parentheses) hydrogen 0.740 eV (0.754), boron 0.258 (0.277), carbon 1.245 (1.263), oxygen 1.384 (1.461), and fluorine 3.337 (3.401). The EAs obtained from the MR‐SD...
12,969 citations