Pnicogen-hydride interaction between FH2X (X = P and As) and HM (M = ZnH, BeH, MgH, Li, and Na).
29 Feb 2012-Journal of Physical Chemistry A (J Phys Chem A)-Vol. 116, Iss: 10, pp 2547-2553
TL;DR: By comparison with some related systems, it is concluded that the pnicogen-hydride interactions are stronger than dihydrogen bonds and lithium-Hydride interactions.
Abstract: A pnicogen-hydride interaction has been predicted and characterized in FH(2)P-HM and FH(2)As-HM (M = ZnH, BeH, MgH, Li, and Na) complexes at the MP2/aug-cc-pVTZ level. For the complexes analyzed here, P(As) and HM are treated as a Lewis acid and a Lewis base, respectively. This interaction is moderate or strong since, for the strongest interaction of the FH(2)As-HNa complex, the interaction energy amounts to -24.79 kcal/mol, and the binding distance is equal to about 1.7 A, much less than the sum of the corresponding van der Waals radii. By comparison with some related systems, it is concluded that the pnicogen-hydride interactions are stronger than dihydrogen bonds and lithium-hydride interactions. This interaction has been analyzed with natural bond orbitals, atoms in molecules, electron localization function, and symmetry adapted perturbation theory methods.
TL;DR: An ab initio MP2/aug'-cc-pVTZ study has been carried out on complexes formed between PO2X (X = F and Cl) as the Lewis acids and a series of nitrogen bases ZN, including NH3, H2C═NH, NH2F, NP, NCH, NCF, NF3, and N2.
Abstract: An ab initio MP2/aug′-cc-pVTZ study has been carried out on complexes formed between PO2X (X = F and Cl) as the Lewis acids and a series of nitrogen bases ZN, including NH3, H2C═NH, NH2F, NP, NCH, NCF, NF3, and N2. Binding energies of these complexes vary from −10 to −150 kJ/mol, and P—N distances from 1.88 to 2.72 A. Complexes ZN:PO2F have stronger P...N bonds and shorter P—N distances than the corresponding complexes ZN:PO2Cl. Charge transfer from the N lone pair through the π-hole to the P—X and P—O σ* orbitals leads to stabilization of these complexes, although charge-transfer energies can be evaluated only for complexes with binding energies less than −71 kJ/mol. Complexation of PO2X with the strongest bases leads to P···N bonds with a significant degree of covalency, and P—N distances that approach the P—N distances in the molecules PO2NC and PO2NH2. In these complexes, the PO2X molecules distort from planarity. Changes in 31P absolute chemical shieldings upon complexation do not correlate with chan...
TL;DR: Analysis of the frontier orbitals of monomer and dimer in connection with the investigation of electron difference densities, and atomic charges lead to a simple rationalization of the various facets of pnicogen bonding.
Abstract: A set of 36 pnicogen homo- and heterodimers, R3E···ER3 and R3E···E′R3′, involving differently substituted group Va elements E = N, P, and As has been investigated at the ωB97X-D/aug-cc-pVTZ level of theory to determine the strength of the pnicogen bond with the help of the local E···E′ stretching force constants ka. The latter are directly related to the amount of charge transferred from an E donor lone pair orbital to an E′ acceptor σ* orbital, in the sense of a through-space anomeric effect. This leads to a buildup of electron density in the intermonomer region and a distinct pnicogen bond strength order quantitatively assessed via ka. However, the complex binding energy ΔE depends only partly on the pnicogen bond strength as H,E-attractions, H-bonding, dipole–dipole, or multipole–multipole attractions also contribute to the stability of pnicogen bonded dimers. A variation from through-space anomeric to second order hyperonjugative, and skewed π,π interactions is observed. Charge transfer into a π* subs...
TL;DR: The energy decomposition analysis highlights the importance of the electrostatic interaction in the formation of the tetrel Bond, although the dispersion part is also non-negligible for the weak tetrel bond.
Abstract: A single-electron tetrel bond was predicted and characterized in FXH3⋯CH3 (X = C, Si, Ge, and Sn) complexes by performing quantum chemical calculations, where the methyl radical acts as the Lewis base and the σ-hole on the X atom in FXH3 as the Lewis acid. The interaction between the methyl radical and FXH3 is characterized by a red shift of F–X stretching frequency. The strength of the tetrel bond becomes stronger by not only increasing the atomic number of the central atom X (X = C, Si, Ge, and Sn) but also by enhancing the electron-withdrawing ability of substituents in the Lewis acid. The energy decomposition analysis highlights the importance of the electrostatic interaction in the formation of the tetrel bond, although the dispersion part is also non-negligible for the weak tetrel bond. There is a competition between the formation of single-electron tetrel bonds and hydrogen bonds for the complexes composed of the methyl radical and CNCH3 or NCCH3. Furthermore, the single-electron tetrel bond exhibits the cooperative effect not only with the hydrogen bond in the complex of NCH⋯NCCH3⋯CH3, but also with the conventional tetrel bond in NCCH3⋯NCCH3⋯CH3.
TL;DR: In this article, the sensitivity of noncovalent bonds to stretching from their equilibrium intermolecular separation was examined and compared to stretches of hydrogen, halogen, chalcogen, and pnicogen bonds.
Abstract: It is well known that noncovalent bonds are weakened when stretched from their equilibrium intermolecular separation. Quantum chemical calculations are used to examine and compare the sensitivity to stretches of hydrogen, halogen, chalcogen, and pnicogen bonds. NH3 was taken as the universal electron donor, paired with HOH and FH in H-bonds, as well as with FPH2, FSH, and FCl. Even though the binding energies span a wide range, stretching the intermolecular separation by 1 A cuts this quantity by the same proportion, roughly in half, for each system. Taking the sum of van der Waals radii as an arbitrary cutoff, the H-bond energy in FH⋯NH3 remains at 5.5 kcal mol−1 while the binding energy of the other three bond types is only slightly smaller at 4.5–4.7 kcal mol−1.
TL;DR: The NBO analysis indicates that the N(lp → P-Fσ* charge-transfer transition has a much greater stabilizing effect than the P(lp) → N-Fρσ* transition, which leads to shorter P···N distances, increased strength of P··N bonds, and synergistic energetic effects.
Abstract: Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the influence of F–H···F hydrogen bonds on the P···N pnicogen bond in complexes nFH:(H2FP:NFH2) for n = 1–2, and a selected complex with n = 3. The NBO analysis indicates that the N(lp) → P–Fσ* charge-transfer transition has a much greater stabilizing effect than the P(lp) → N–Fσ* transition. When hydrogen bonding occurs at P–F, charge transfer associated with the pnicogen bond and the hydrogen bond are in the same direction but are in opposite directions when hydrogen bonding occurs at N–F. As a result, the formation of F–H···F hydrogen bonds at P–F leads to shorter P···N distances, increased strength of P···N bonds, and synergistic energetic effects; hydrogen bonding at N–F has opposite effects. 31P and 15N chemical shieldings do not correlate with charges on P and N, respectively, but 31P shieldings correlate quadratically with the P–N distance. 1pJ(P–N) coupling constants do not correlate with the intermolecular P–N distance....
TL;DR: In this paper, a direct difference method for the computation of molecular interactions has been based on a bivariational transcorrelated treatment, together with special methods for the balancing of other errors.
Abstract: A new direct difference method for the computation of molecular interactions has been based on a bivariational transcorrelated treatment, together with special methods for the balancing of other errors. It appears that these new features can give a strong reduction in the error of the interaction energy, and they seem to be particularly suitable for computations in the important region near the minimum energy. It has been generally accepted that this problem is dominated by unresolved difficulties and the relation of the new methods to these apparent difficulties is analysed here.
TL;DR: In this article, the topological properties of ρ(r) at the intermolecular critical points of 83 experimentally observed hydrogen bonds [X-H⋯O (X=C,N,O)], using accurate X-ray diffraction experiments, were analyzed.
TL;DR: In this paper, a set of criteria are proposed based on the theory of "atoms in molecules" to establish hydrogen bonding, even for multiple interactions involving C-H-O hydrogen bonds.
Abstract: It is shown that the total charge density is a valid source to confirm hydrogen bonding without invoking a reference charge density. A set of criteria are proposed based on the theory of “atoms in molecules” to establish hydrogen bonding, even for multiple interactions involving C-H-O hydrogen bonds. These criteria are applied to several van der Waals complexes. Finally a bifurcated intramolecular C-H-O hydrogen bond is predicted in the anti-AIDS drug AZT, which may highlight a crucial feature of the biological activity of a whole class of anti-AIDS drugs. Almost all the methods of physical chemistry, spectroscopy, and diffraction can be used to recognize and study hydrogen bonding.] Each technique focuses on specific properties in order to detect and characterize this phenomenon in its own way. This work is concerned with the manifestation of hydrogen bonding in the charge density obtained from ab initio calculations. Whereas crystallographers have concluded upon hydrogen bonding via purely geometrical criteria, recent deformation density2 studies allow one to observe hydrogen bonding beyond mere ge~metry.~ However, it is not necessary to subtract an arbitrary (promolecular) charge density from the total density to reveal hydrogen bonding, not even in the interpretation of X-ray experiment^.^ Boyd and Choi have shown in two important contribution^^^^ that the theory of “atoms in molecules’’ (AIM)7,8 can be used to characterize hydrogen bonding solely from the (total) charge density for a large set of acceptor molecules, involving HF and HC1 as donors. In a next stage Carroll and Bader performed a more extended analysis on a large set of BASE-HF comple~es.~ This theory has not only provided new insights in conventional intermolecular hydrogenI0.’ ] bonding but has also been successful in intramolecularI33l4 and x-type hydrogen bonds.I5 Drawing from earlier ob~ervations~~~~ ~.’~~~~ and the present work, we formulate eight concerted effects occurring in the charge density which are indicative of hydrogen bonding. All of these effects can be viewed as necessary criteria to conclude that hydrogen bonding is present. By observation one of these conditions has proven to be sufficient as well. This case study on C-H-O interactions shows that this less common type of hydrogen bonding obeys all of the proposed criteria. Moreover, the multiple interactions appearing in the present five examples do not impair the consistency of the global phenomenon of hydrogen bonding as it expresses itself in the charge density. In spite of an early affirmative infrared review,I6 the old controversy on whether C-H-O hydrogen bonds really exist continued for another decade,” but now the dust has settled’* (for an entertaining account of this controversy, see ref 19). The importance of these bonds has been recognized in crystal engineering’9,20 since C-H-O contacts have a determining influence on packing motifs.21
TL;DR: In this paper, the authors carried out a natural bond order B3LYP analysis of the molecules CF(3)X, with X = F, Cl, Br and I. The results showed that the Cl and Br atoms in these molecules closely approximate the [Formula: see text] configuration, where the z-axis is along the R-X bond.
Abstract: Halogen bonding refers to the non-covalent interactions of halogen atoms X in some molecules, RX, with negative sites on others. It can be explained by the presence of a region of positive electrostatic potential, the sigma-hole, on the outermost portion of the halogen's surface, centered on the R-X axis. We have carried out a natural bond order B3LYP analysis of the molecules CF(3)X, with X = F, Cl, Br and I. It shows that the Cl, Br and I atoms in these molecules closely approximate the [Formula: see text] configuration, where the z-axis is along the R-X bond. The three unshared pairs of electrons produce a belt of negative electrostatic potential around the central part of X, leaving the outermost region positive, the sigma-hole. This is not found in the case of fluorine, for which the combination of its high electronegativity plus significant sp-hybridization causes an influx of electronic charge that neutralizes the sigma-hole. These factors become progressively less important in proceeding to Cl, Br and I, and their effects are also counteracted by the presence of electron-withdrawing substituents in the remainder of the molecule. Thus a sigma-hole is observed for the Cl in CF(3)Cl, but not in CH(3)Cl.