Ππ Interaction Research Articles

Ferromagnetic coupling in copper benzimidazole chloride: structural, mass spectrometry, magnetism, and DFT studies.

Herein, quasi-square planar CuII(Hmbm)Cl2 (CBC, Hmbm = (1-methyl-1H-benzo[d]imidazol-2-yl)methanol) was arranged in a pseudo orthogonal way to form Cl-bridged chains, and further ππ interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu-Cl > Cu-O/N ≫ CuCl. ESI-MS data reveal several small fragments from CBC, but oligomeric [Cu], [Cu], and [Cu] for non-zero in-source energies; MS data indicates the occurrence of several chemical processes, viz. splitting of the ligand, oligomerization, and redox reaction of alcohol to aldehyde and CuII to CuI. Gibbs free energies for the fragments were estimated using DFT. The magnetic susceptibility was modeled with the ferromagnetic coupling J(Cu-Cl2aCu) = +0.99(30) cm-1 and J'(ππ) = +0.35(16) cm-1 and g = 2.38(2). HF-EPR determined the anisotropic g-values, gx = 2.24, gy = 2.16, and gz = 2.09, and a hyperfine constant of Az = 450 G. DFT calculations from crystal structure data reveal a J(Cu-Cl2aCu) of +3.6 at 296 K and +4.1 cm-1 at 90 K that dominates the magnetic properties, whereas J'(ππ) = 0.04 cm-1 is negligibly small.

Dispersive analysis of KS → γγ and KS → γl+l−

We calculate the decay rates for KS → γγ and KS → γl+l− (l = e or μ)within a dispersive framework in which the weak Hamiltonian carries momentum. Given input from KS → ππ and γγ(*)→ππ, we solve the once-subtracted dispersion relations numerically and find that final-state ππ interactions generate sizeable corrections to the predictions from 3-flavour chiral perturbation theory. Our analysis predicts BR(KS → γγ) = (2.34 ± 0.31) × 10−6, BR(KS → γe+e−) = (4.38 ± 0.57) × 10−8, and BR(KS → γμ+μ−) = (1.45 ± 0.27) × 10−9.

Carbon-nanorings ([10]CPP and [6]CPPA) as fullerene (C60 and C70) receptors: a comprehensive dispersion-corrected DFT study.

A comprehensive computational analysis of all possible complexes between the carbon-nanorings, CNRs, [10]CPP and [6]CPPA with the fullerenes C60 and C70, was carried out. The B97-D2 functional together with the def2-TZVP basis set was used through the work, although comparisons with other different functionals (BLYP-D2, B3LYP-D3(BJ), TPSS-D3(BJ), PBE0-D3(BJ) and M06-2X) were also performed. In order to find all the possible rearrangements of the fullerenes inside the CNRs, two methods of different complexities and computational costs were employed. After localization of all minima of interest, the corresponding complexation energies were evaluated, and subsequently, the different minima were compared both from a structural and an energetic point of view. According to our results, the largest complexation energy clearly corresponds to the C70@[10]CPP complex: -53.32 kcal mol-1. This complex shows a structure where each of the ten rings of [10]CPP directly faces a six-membered ring of C70. That is to say, the best possible overlap between the hexagonal rings of C70 and [10]CPP takes place, showing an arrangement that clearly favours the dispersive ππ interaction. To achieve this spatial disposition, C70 is placed fully vertically (its major diameter perpendicular to the plane of the CNR), and undergoes a small displacement of 0.769 Å from the centre of the CNR. With C60, exactly the same interaction pattern is reproduced, and it is indeed the reason for this fullerene to be just inside the CNR, since for C60 the belt formed by the six-membered rings is placed exactly at the centre of the buckyball. Basically due to the smaller dispersion arising for this C60@[10]CPP complex, the complexation energy is somewhat smaller: -49.78 kcal mol-1. All the calculations show that the ability of [6]CPPA as a fullerene receptor is rather smaller than that of [10]CPP (about ten kcal mol-1, regarding complexation energy), both for C60 and C70. This is basically due to the loss of the interaction of four phenyl rings with the fullerenes, not adequately counterbalanced by the weaker interaction with the alkyne bonds.

3-D Framework {[Cu(L)nX][X] (H<sub>2</sub>O)<sub>2</sub>} L= bipy,n=2 Constructed through C-H….Cl Hydrogen Bondings and π-π Interactions

The reaction of copper 2,2-dichloroacetic acid, heterocyclic diimine (bipy) ligands under mildconditions affords one novel supramolecular complexes, [Cu (bipy)2[[H22 (bipy=2,2-bipyridine X=dichloroacetic acid). The compounds were constituted through hydrogen bonding and ππ interactions between the heterocyclic rings.

Crystal Structure and Synthesis of {[Cu(L)nX][X] (H<sub>2</sub>O)<sub>2</sub>} L= benz,n=3

The reaction of copper 2,2-dichloroacetic acid and heterocyclic diimine (benz) ligands under mildconditions affords one supramolecular complexes, [Cu (bipy)2[[H22 (bipy=benz, X=dichloroacetic acid). The compounds involves a regular square based pyramidal one and were constituted through hydrogen bonding and ππ interactions between the heterocyclic rings.

Simple trigonometric proof for the new parameters of the sigma meson

Correctness of the results obtained in the recent analysis of the ππ interactions using new dispersion relations with imposed crossing symmetry condition is checked. The performed proof is based on purely mathematical relations and properties of analytic functions and concerns position of the scalar-isoscalar ƒ0(500) (former σ) pole. Mere analysis of amplitudes expressed by the trigonometric functions and their derivatives clearly defines the area in which mass of the σ and its width must be located.

Coordination polymers (NiII and CoII) based on the rigid bridging ligand, 4,4′-bis(imidazol-1-yl)biphenyl, with (46) topology

Two coordination polymers, {[Ni0.5(4,4′-bib)Cl][(4,4′-bib)0.5]·H2O} n (1) and {[Co(4,4′-bib)3(H2O)2][NO3]2·H2O} n (2) (4,4′-bib = 4,4′-bis(imidazol-1-yl)biphenyl) have been hydrothermally synthesized. Their structures have been determined by single-crystal X-ray diffraction analyses and are further characterized by elemental analyses, IR, thermogravimetric analyses, and powder X-ray diffraction. In 1, each NiII is linked by four μ 2–4,4′-bib ligands in 2-D (4,4)-networks, which are further connected through host–guest interaction to form a 3-D packing diagram with 1-D channels. In 2, each CoII is linked by two μ 2–4,4′-bib and two μ 1–4,4′-bib ligands in a 1-D zigzag chain, further connected through non-covalent interactions (including O–HN, O–HO, C–Hπ, and ππ interactions) to form a 3-D supramolecular structure. 4,4′-bib exhibits μ 2-, μ 1-, and μ 0-coordination during the construction of 1 and 2. From the topological view, the overall structures of 1 and 2 possess (46) topology.

Photochemical reduction of graphene oxide in colloidal solution

Stable aqueous colloidal solutions of graphene oxide stabilized with sodium polyphosphate were obtained. During irradiation of the colloids the oxygen-containing groups of the graphene oxide are eliminated, and the aromatic graphite-like regions in its composition are expanded. This is accompanied by decrease in the energy of the electronic transitions Ebg in such sp2-hybridized fragments. Photoreduction of the colloidal particles of graphene oxide leads to changes in their hydrodynamic size, resulting from 𝜋𝜋 interactions between the aromatic fragments in the particles. It was shown that the Ebg value can be varied purposefully in the range of 0.5-1.9 eV by varying the experimental conditions.

Measurement ofη′ →ηπ+π−with KLOE and KLOE-2

The investigation of η ′ → ππη allows to study ππ and ηπ interactions and the possible influence of the scalar states f 0 (600) and a 0 (980) on the decay dynamics. 1.7 fb −1 of data taken with the KLOE detector at the DAΦ NE e+ e− collider have been analyzed with respect to the charged decay mode η ′ → π + π − η . 7900 ± 90 event candidates have been extracted and can be used for a Dalitz plot analysis.

Role of the ππ interaction in pairwise photoproduction of π 0 mesons on a proton

Photoproduction of two neutral pions on a proton is considered. Qualitative analysis of the available experimental data demonstrates that a linear dependence of the total cross section on the energy testifies to the dominating contribution of s-waves for Eγ < 800 MeV. Since in the tree approximation, the s-wave is almost completely absent from the π0π0 channel, the effects of π+π− meson rescattering into the neutral channel are included in calculations. Owing to the high intensity of π+π− pair formation, the influence of rescattering appears considerable. Its consideration yields a better agreement with the available experimental data.

DOUBLE PION PHOTOPRODUCTION OFF 7Li

Data for quasi-free photoproduction of π0π0 and π0π+/- pairs from 7 Li have been analyzed in view of the in-medium properties of hadrons. Data have been measured with the CB/TAPS detector setup using the Glasgow photon tagging spectrometer for incident photon energies up to 820 MeV. The double π0 invariant mass distributions show an enhancement with respect to the mixed charged channel at small invariant masses. This enhancement could be consistent with an in-medium modification of the ππ interaction in the I = J = 0 channel, however effects from final state interactions must also be considered.

ππ interaction in kaon decay

NA48 coll. measured the ππ scattering lengths from a large statistics sample of kaon decays. The excellent agreement between experimental results and theoretical prediction is an important validation of the Chiral Dynamics approach.

The role of aromatic interactions in the structure and energetics of benzyl ketones

A qualitative and quantitative energetic and structural study of dibenzyl ketone (DBK) and benzyl ethyl ketone (BEK) was carried out in order to obtain insights into the type and magnitude of aromatic interactions that these systems present in their different phases. The crystal structure of DBK was obtained by X-ray crystallography, and it shows that the conformation adopted in the crystalline state is governed by the intermolecular interactions. The standard (p(0) = 10(5) Pa) molar enthalpy of formation in the gaseous state at T = 298.15 K was derived by Calvet and combustion calorimetry. Using a homodesmic reaction scheme, the first calorimetric evaluation of the interaction enthalpy between two stacked phenyl rings is presented. A stabilizing enthalpic effect of (12.9 ± 4.9) kJ mol(-1) associated with the intramolecular π-π interaction in DBK was found. The gas phase intramolecular ππ interaction in DBK is in agreement with quantum chemical calculations at B3LYP/6-311++G(d,p) and MP2 with various basis-sets. An intramolecular ππ interaction in DBK and a weak C-Hπ interaction in BEK were found by variable-temperature (1)H-NMR spectroscopy in MeOD. These observations are consistent with a hindered rotor interpretation, supported by ab initio calculations for the gas phase at the MP2/cc-pVDZ level. The global results indicate a distinct molecular structure on going from crystalline DBK to liquid, gas, and solution phases, ruled by the overall contribution of the intra- and intermolecular interactions.

Pion-pion scattering lengths from Ke4 and Cusp at NA48/2 experiment

In kaon decays the measurement of ππ scattering lengths ( a 0 and a 2 ) are accessible mainly through the study of kinematical properties in two decay modes. The classic way is based on the form factors analysis in K ± → π + π − e ± ν ( K e 4 ) decay. Thanks to the absence of other hadrons in the final state the ππ interaction can be analyzed in terms of phase shift variation with the ππ invariant mass. The preliminary results on a set of ∼ 1150000 K ± events collected in two years of data taking, will be discussed. The second way to evaluate the ππ scattering lengths is based on the accurate study of K ± → π ± π 0 π 0 Dalitz plot, in which the strong rescattering process π + π − → π 0 π 0 introduces a singularity in the shape of the distribution. The preliminary result based on more than ∼ 60 ⋅ 10 6 K ± → π ± π 0 π 0 decays is in good agreement with the measurement in K e 4 .

Measurement of ππ scattering lengths in Kaon decay by NA48/2

In kaon decays the measurement of ππ scattering lengths (a0 and a2) are accessible mainly through the study of kinematical properties in two decay modes. The classic one is based on the analysis of the form factors in the K± → π+π−e±v (Ke4). Thanks to the absence of other hadrons in the final state the ππ interaction can be analyzed in terms of variation of phase shift with the ππ invariant mass. The preliminary results on a partial set of ~ 670000 K± will be discussed. The second way to evaluate the ππ scattering lengths is based on the accurate study of K± → πππ0π0 Dalitz plot, in which the strong rescattering process π+π− → π0π0 introduces a singularity in the shape of the distribution. The preliminary result based on ~ 50 · 106 K± → π±π0π0 decays is in good agreement with the measurement in Ke44.

Forward dispersion relations and Roy equations in ππ scattering

We first review the results of an analysis of ππ interactions in S, P and D waves for the two-pion effective mass from threshold to about 1.4 GeV. In particular, we show a recent improvement of this analysis above the K \( \bar K \) threshold using more data for phase shifts and including the S0-wave inelasticity from ππ → K \( \bar K \). In addition, we have improved the fit to the f 2(1270)-resonance and used a more flexible P-wave parametrization above the K \( \bar K \) threshold and included an estimation of the D2-wave inelasticity. The better accuracy thus achieved also required a refinement of the Regge analysis above 1.42 GeV. Finally, in this work we check that the ππ scattering amplitudes obtained in this approach satisfy remarkably well forward dispersion relations and Roy’s equations.

A novel degradation pathway of Zn (dmid) (phen)2 in pyridine

The light-oxidation degradation processes of Zn(dmid)(phen)2 (dmid=4,5-dimercapto-1, 3-dithiole-2-one, phen=1, 10-phenanthroaline) in pyridine solvent has been monitored. It has been found under the light, dmid2− of Zn(dmid)(phen)2 in pyridine solution could generate NCS− and NCS− replaces dmid2− to form Zn(NCS)2 (phen)2 simultaneously. The crystal structure of Zn(NCS)2(phen)2 has been determined. In the crystal of Zn(NCS)2(phen)2, two NCS− ligands are arranged in syn-configuration, and there is strong ππ interaction between the two adjacent parallel phen.

New study of the isotensor ππ interaction

With t-channel ρ, f 2(1270) exchange and the ππ→ ρρ→ ππ box diagram contribution, we reproduce the ππ isotensor S-wave and D-wave scattering phase shifts and inelasticities up to 2.2 GeV quite well in a K-matrix formalism. The t-channel ρ exchange provides repulsive negative phase shifts while the t-channel f 2(1270) gives an attractive force to increase the phase shifts for ππ scattering above 1 GeV, and the coupled-channel box diagram causes the inelasticities. The implication to the isoscalar ππ S-wave interaction is discussed.

CP violation in K S, L → π + π − γ and K S, L → π + π − e + e − decays

The dependence of K S, L → π + π − γ decay probabilities on photon polarization is calculated. The phases of the terms of the amplitude that arise from the pion-pion interaction are obtained by using a simple realistic model of pion-pion interaction via virtual ρ meson, instead of chiral perturbation theory (ChPT). The results are compared with those of other authors and the origin of the discrepancies is explained. It is shown that the standard ChPT approach for K S, L → π + π − γ decays cannot reproduce the contribution of the ρ meson to the P-wave ππ interaction. The departure of the photon spectrum from pure bremsstrahlung due to the pion-loop contribution to the electric direct emission amplitude is calculated. It is shown that the interference between the terms of amplitude with different CP parity appears only when the photon is polarized (linearly or circularly). Instead of measuring the linear polarization, the angular correlation between the π + π − and e + e − planes in K S, L → π + π − e + e − decay can be studied.

Experimental signals of $\sigma$ -mesons in nuclei and chiral symmetry

The ππ interaction in the scalar isoscalar channel is studied as a function of the baryonic density in the framework of a chiral unitary approach which successfully reproduces vacuum π-π phase shifts. We present some results on the a-meson pole, which is generated dynamically in our model, in nuclear matter. Finally, we analyze the (γ, ππ) reaction on nucleons and nuclei in the kinematical region where the scalar isoscalar ππ scattering amplitude is influenced by the low mass of the σ in nuclei, and thus, presents a large enhancement close to the position of its pole. Indeed, we find, that the final-state interaction of the pions modified by the nuclear medium produces a large shift of strength of the two-pion invariant-mass distribution in the (γ, π 0 π 0) channel consistent with recent experimental data.