Showing papers on "Pi interaction published in 2013"

Electron Sharing and Anion–π Recognition in Molecular Triangular Prisms

Abstract: Stacking on a full belly: Triangular molecular prisms display electron sharing among their triangularly arranged naphthalenediimide (NDI) redox centers. Their electron-deficient cavities encapsulate linear triiodide anions, leading to the formation of supramolecular helices in the solid state. Chirality transfer is observed from the six chiral centers of the filled prisms to the single-handed helices.

Molecular architecture using novel types of non-covalent π-interactions involving aromatic neutrals, aromatic cations and π-anions

Abstract: A solid-state complex utilizing non-covalent interactions between two aromatic cations is synthesized and characterized. The X-ray study of the structure shows that the anion templated π+–π+ interactions are the major driving force in the crystal packing, while π+–π, π–π, π–anion and π+–anion interactions assist the overall stabilization of self-assembly. In addition, we also identify the cation-mediated non-covalent interaction between two π anions (π−–π− interaction). The interaction energies of the important driving forces (π+–π+, π+–π, π–anion, π+–anion, and π−–π− interactions) observed in the crystal structure are calculated using dispersion-corrected density functional theory (DFT-D).

A successive layer-by-layer assembly of supramolecular frameworks driven by a novel type of face-to-face π+–π+ interactions

Abstract: The solid-state complex [PTPH3](NO3)3·2(HNO3) (1) has been synthesized and characterized by X-ray studies, where PTPH3 is the triply protonated form of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine (PTP). The solid-state structure of the complex reveals that the π+–π+ interactions are the major driving force in the crystal packing while π+–π, π–π and π–anion interactions assist the overall stabilization of self-assembly. Complex 1 exhibits two different π-stack layers, where layer 1 is generated through π+–π+ interactions and the mutual forces of π+–π+ and π+–π form layer 2. The interaction energies of the main driving forces (π+–π+, π+–π and π–anion interactions) observed in the crystal structure have been calculated using dispersion-corrected density functional theory (DFT-D). An analysis of the Hirshfeld surface of complex 1 shows the intermolecular interactions involved within the crystal structure and corresponding quantitative information are presented by fingerprint plots.

Catalysis with Gold Complexes Immobilised on Carbon Nanotubes by π–π Stacking Interactions: Heterogeneous Catalysis versus the Boomerang Effect

Abstract: A new pyrene-tagged gold(I) complex has been synthesised and tested as a homogeneous catalyst. First, a simple 1,6-enyne was chosen as a model substrate for cyclisation by using different solvents to optimise the reaction conditions. The non-covalent immobilisation of our pyrene-tagged gold complex onto multi-walled carbon nanotubes through π-π stacking interactions was then explored to obtain a supported homogeneous catalyst. The heterogenised catalyst and its homogeneous counterpart exhibited similar activity in a range of enyne cyclisation reactions. Bearing in mind that π-π interactions are affected by temperature and solvent polarity, the reuse and robustness of the supported homogeneous catalyst was tested to explore the scope and limitations of the recyclability of this catalyst. Under the optimised conditions, recyclability was observed by using the concept of the boomerang effect. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dimensional matching of polycyclic aromatics with rectangular metallacycles: insertion modes determined by [C-H···π] interactions.

Abstract: A family of PdII/PtII dinuclear receptors, designed to give a smooth increase in their cavity lengths (from 7.46–13.78 A), is presented. Their inclusion complexes with a representative set of polycyclic aromatic substrates (naphthalene, carbazol, pyrene, and benzo[a]pyrene), were characterized and studied in aqueous solution and the solid state. By taking into account the dimensions of both receptors and substrates, an excellent complementarity was found between the size of the receptors and their ability to complex a given substrate. Furthermore, this dimensional matching results in specific binding modes depending on the ability of the guest to establish stabilizing [CH⋅⋅⋅π] interactions with the host.

Control of Exchange Interactions in π Dimers of 6‐Oxophenalenoxyl Neutral π Radicals: Spin‐Density Distributions and Multicentered–Two‐Electron Bonding Governed by Topological Symmetry and Substitution at the 8‐Position

Abstract: The tri-tert-butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phenalenyl-based air-stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X-ray crystal structure analyses showed that 8-tert-butyl- and 8-(p-XC6H4)-6OPOs (X=I, Br) also form π dimers in the crystalline state. The π-dimeric structure of 8-tert-butyl-6OPO is seemingly similar to that of TBPLY even though its SOMO-SOMO overlap is small compared with that of TBPLY. The 8-(p-XC6H4) derivatives form slipped stacking π dimers in which the SOMO-SOMO overlaps are greater than in 8-tert-butyl-6OPO, but still smaller than in TBPLY. The solid-state electronic spectra of the 6OPO derivatives show much weaker intradimer charge-transfer bands, and SQUID measurements for 8-(p-BrC6H4)-6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl-based π dimer. The formation of the relevant multicenter-two-electron bonds is discussed.

Multiple anion...π interactions in tris(1,10‐phenanthroline‐κ2N,N′)iron(II) bis[1,1,3,3‐tetracyano‐2‐(2‐hydroxyethyl)propenide] monohydrate

Abstract: In the ionic structure of the title compound, [Fe(C12H8N2)3](C9H5N4O2)2·H2O, the octahedral tris-chelate [Fe(phen)3](2+) dications [Fe-N = 1.9647 (14)-1.9769 (14) A; phen is 1,10-phenathroline] afford one-dimensional chains by a series of slipped π-π stacking interactions [centroid-to-centroid distances = 3.792 (3) and 3.939 (3) A]. The 1,1,3,3-tetracyano-2-(2-hydroxyethyl)propenide anions, denoted tcnoetOH(-), reveal an appreciable delocalization of π-electron density, involving the central propenide [C-C = 1.383 (3)-1.401 (2) A] fragment and four nitrile groups, and this is also supported by density functional theory (DFT) calculations at the B97D/6-311+G(2d,2p) level. Primary noncovalent inter-moiety interactions comprise conventional O-H...O(N) and weak C-H...O(N) hydrogen bonding [O...O(N) = 2.833 (2)-3.289 (5) A and C...O(N) = 3.132 (2)-3.439 (2) A]. The double anion...π interaction involving a nitrile group of tcnoetOH(-) and two cis-positioned pyridine rings (`π-pocket') of [Fe(phen)3](2+) [N...centroid = 3.212 (2) and 3.418 (2) A] suggest the relevance of anion...π stackings for charge-diffuse polycyanoanions and common M-chelate species.

Influence of the Li···π Interaction on the H/X···π Interactions in HOLi···C6H6···HOX/XOH (X=F, Cl, Br, I) complexes.

Abstract: The influences of the Li···π interaction of C6H6···LiOH on the H···π interaction of C6H6···HOX (X=F, Cl, Br, I) and the X···π interaction of C6H6···XOH (X=Cl, Br, I) are investigated by means of full electronic second-order Moller-Plesset perturbation theory calculations and "quantum theory of atoms in molecules" (QTAIM) studies. The binding energies, binding distances, infrared vibrational frequencies, and electron densities at the bond critical points (BCPs) of the hydrogen bonds and halogen bonds prove that the addition of the Li···π interaction to benzene weakens the H···π and X···π interactions. The influences of the Li···π interaction on H···π interactions are greater than those on X···π interactions; the influences of the H···π interactions on the Li···π interaction are greater than X···π interactions on Li···π interaction. The greater the influence of Li···π interaction on H/X···π interactions, the greater the influences of H/X···π interactions on Li···π interaction. QTAIM studies show that the intermolecular interactions of C6H6···HOX and C6H6···XOH are mainly of the π type. The electron densities at the BCPs of hydrogen bonds and halogen bonds decrease on going from bimolecular complexes to termolecular complexes, and the π-electron densities at the BCPs show the same pattern. Natural bond orbital analyses show that the Li···π interaction reduces electron transfer from C6 H6 to HOX and XOH.

Reactions of 13-vertex carboranes with strong bases: synthesis and structural characterization of carborane monoanions with exo-π bonding.

Abstract: Several monoanions of 13- vertex carboranes were prepared in high yields from the reactions of C,C'- linked 13-vertex carboranes with tBuOK or NaH in dry THF at room temperature. These monoanions were characterized by various spectroscopic methods, elemental analysis, and single-crystal X-ray diffraction. The re- sults showed substantial double-bond character between the cage-carbon atom and the exo vicinal carbon atom, thus leading to charge delocalization into the cage. As a result, the atom atom distances within the cage were elongated, with one broken CB bond. However, the cage geometry of the monoanions remained very similar to that of their corresponding neutral 13- vertex closo-carboranes. These mono- anions represent the first examples of 13-vertex carboranes with exo-p bond- ing to hypercarbon atoms.

Di(4-pyridyl) Sulfoxide as an Angled Building Block for Zigzag-Chain Silver(I) Complexes Stabilized by Supramolecular O=S···π Interactions

Abstract: The angled ligand di-4-pyridyl sulfoxide (L1) and five of its silver(I) complexes that bear various counteranions, namely, {[Ag(L1)](BF4)·(CH3CN)}∞ (1), {[Ag(L1)(CF3SO3)]·(CH3CN)}∞ (2), {[Ag(L1)(CF3CO2)]·CH3CN}∞ (3), {[Ag(L1)(NO3)]·H2O}∞ (4), and {[Ag2(L1)2(SO4)]·6H2O}∞ (5), have been synthesized and characterized by X-ray crystallography, FTIR spectroscopy, elemental analysis, and luminescent emission measurements. Complexes 1–5 exhibit a common [Ag(L1)]nn+ zigzag-chain motif generated by the μ2-N,N-bridging L1 ligand. The common dominant intermolecular O=S(sulfinyl)···π(pyridyl) interaction with the S=O group embraced by the pyridyl wings of an adjacent butterfly-like L1 ligand plays a crucial role in the supramolecular aggregation of 1–5. Replacement of the sulfinyl (S=O) group of L1 by a sulfonyl (O=S=O) group to yield related ligand L2 led to {[Ag(L2)](NO3)}∞ (6) (L2 = di-4-pyridyl sulfone), which exhibits a markedly different supramolecular architecture from those of 1–5 because of the absence of the O=S(sulfinyl)···π(pyridyl) contact. Density functional calculations confirm that there is a π orbital interaction between the sulfinyl S atom and the intermolecular pyridyl rings, which significantly contributes to the O=S···π affinity.

Cyclic π electron delocalization in fluoroborazines.

Abstract: How does the most electronegative atom, fluorine, affect cyclic π electron delocalization (aromaticity) of an inorganic counterpart of benzene, borazine? Previous studies have shown that N-fluorination decreases the aromatic character, whereas conclusions about the effect of B-fluorination oppose each other ( J. Phys. Chem. A 1997 , 101 , 9410 and J. Mol. Struct.: THEOCHEM 2005 , 715 , 91 ). The aim of this study is to resolve this discrepancy and also to evaluate a degree of cyclic π electron delocalization in all possible polyfluoroborazines. This was done by employing four aromaticity indices, HOMA, NICS, ECRE, and PDI. NICS, ECRE, and PDI gave a satisfactory description of aromaticity of the studied molecules. It was found that N-monofluoroborazine, N-difluoroborazine, and N-trifluoroborazine are the only fluorinated derivatives that exhibit a higher degree of aromaticity compared to borazine. This result opposes the previous ones regarding the influence of N-fluorination.

Ionic semiconductor: DC and AC conductivity of anilinium tetrathiafulvalene-2-carboxylate

Abstract: A single crystal of anilinium tetrathiafulvalene-2-carboxylate exhibits a characteristic electrical conduction; it is a semiconductor with activation-type transport above 200 K; σrt = 0.16 S cm−1 with an activation energy of 0.11 eV. On the other hand, below 200 K, it does not obey the Arrhenius relation but is conductive even at 4 K with 2.1 × 10−4 S cm−1 at a frequency of 2 MHz. Its behavior exhibits strong frequency dependence and suggests a particular conduction coupled with dielectric relaxation, reflecting its ionic nature. The crystal structure of the salt shows that conducting molecules are assembled supramolecularly with multiple nonbonding interactions, such as the hydrogen bond, and the π/π and CH/π interactions. The hydrogen bond and CH/π interactions have a short bond length, which is similar to the charge-assisted-type interaction observed in organometallics.

Radiative corrections to the charged pion-pair production process π−γ → π+π−π− at low energies

Abstract: We calculate the one-photon loop radiative corrections to the charged pion-pair production process π − γ → π + π − π −. In the low-energy region this reaction is governed by the chiral pion-pion interaction. The pertinent set of 42 irreducible photon-loop diagrams is calculated by using the package FeynCalc. Electromagnetic counterterms with two independent low-energy constants $$\hat k_1$$ and $$\hat k_2$$ are included in order to remove the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved by including soft photon radiation below an energy cut-off Λ. The purely electromagnetic interaction of the charged pions mediated by one-photon exchange is also taken into account. The radiative corrections to the total cross section (in the isospin limit) vary between +10% close to threshold and about −1% at a center-of-mass energy of 7m π . The largest contribution comes from the simple one-photon exchange. Radiative corrections to the π + π − and π − π − mass spectra are studied as well. The Coulomb singularity of the final-state interaction produces a kink in the dipion mass spectra. The virtual radiative corrections to elastic π − π − scattering are derived additionally.

Non-covalent interactions in solution

Abstract: This chapter gives general overview of non-covalent interactions. It introduces different classes of non-covalent interactions and goes on to present popular models and methods for quantifying these weak interactions. The chapter concludes with a focus on dispersion interactions in gas phase and in solution. 1.1 General classes of non-covalent interactions The covalent bond, as has long been known by chemists, involves two atoms sharing a pair of electrons. 1 Since covalent bonds commonly have energies of hundreds of kJmol –1 , breaking a bond always requires large energy input either from an external energy source or from energy differences in other bonds that might be broken or formed in a chemical reaction. In contrast to strong covalent bonds, non-covalent interactions are relatively weak, and do not involve fully overlapping valence orbitals. Although weak, non-covalent interactions are fundamental parts in biological systems. Taking advantage of the non-bonded nature of interactions, which are normally reversible and easy to control, chemists are keen to exploit non-covalent interactions in building blocks for materials 2 , molecular recognition 3 and in molecular machines 4 . The classification of non-covalent interaction is sometimes indistinct and classification boundaries are often blurred, or overlapping. Here we introduce several typical types of non-covalent interactions, including ionic interactions, hydrogen bonds (H bonds), halogen bonds, the hydrophobic effect, Van der Waals forces and aromatic interactions (Fig 1.1).

Structure and Fluorescence Property of a 2D Bilayer Cd(II) Coordination Polymer Induced by H-bonding and pi-pi Interaction

Abstract: Solvothermal reaction of 1,3-dipyridyl benzene(1,3-dpb) with 4,4′-oxybis(benzoic acid)(H2oba) produced a two dimensional(2D) zinc(Ⅱ) coordination polymer {[Zn(oba)(dpb)]·H2O}n(1).The complex was characterized by elemental analysis,IR spectroscopy,and X-ray single-crystal diffraction.It crystallizes in the monoclinic system,space group C2/c.The neighboring Zn(Ⅱ) ions are linked by oba2-anions and 1,3-dpb to form infinitely 2D sheet,two 2D sheets are interlocked each other to form 2D→2D structure,and these two 2D sheets were linked each other by H-bonding.Two groups of interlocked structures further linked to form bilayer 2D supermolecule network by π-π interaction.In addition,the fluorescence property of 1 was also studied.CCDC:917714.

CP Violation and Strong Pion-Pion Interactions in the Weak $${B^\pm \to \pi^\pm \pi^\mp \pi^\pm}$$ Decays

Abstract: An analysis of \({B^\pm \to \pi^\pm \pi^\mp \pi^\pm}\) decay data in a quasi two-body B± → π± [π+π−]S, P, D QCD factorization framework is performed. The short distance amplitudes are calculated including next-to-leading order in αs vertex and penguin corrections. The long distance amplitudes due to the [π+π−]S, P, D final state interactions are described by the pion non-strange scalar and vector form factors for the [π+π−]SS-wave state and [π+π−]PP-wave state, respectively and by a relativistic Breit–Wigner formula for the[π+π−]DD-wave state. We achieve a good fit of the data with only three parameters for the S wave, one for the P wave and one for the D wave. Our model gives a unified unitary description of the three scalar resonances, f0(600), f0(980) and f0(1400) in terms of the pion scalar form factor. We predict for the B to f2(1270) transition form factor, \({F^{Bf_2}(m_\pi^2)=0.098\pm0.007}\) .

The π Bond of C2H4 and 2HX(X=F,Cl,Br,I) Interaction

Abstract: We applied ab initio theoretical studies on the complex of C2H4 and 2HX,the results demonstrated that C2H4???2HX(X=F,Cl,Br,I),with increasing halogen atomic number,from HF to HI,the bond length have all increasing,however,the binding energy of complex present in the overall decreasing trend.The π bond C2H4 molecule at least interacting with 2HX(X=F,Cl,Br,I) to formation of the X-H???π bond complex.