Pentafluorophenyl salicylamine receptors in anion–π interaction studies

A crystal structure analysis confirms the appropriateness of pentafluorophenyl salicylamine (1a) as a π-acceptor for anion–π interactions. Crystals of 1a·HCl show that the OH-group fixes the anion in a η²-type binding motif above the electron-deficient arene. Attempts to find some relevance for this weak intermolecular force in solution failed. Stronger CH–, NH– and OH–anion interactions are dominant over the weak anion–π interactions. Due to the hydrogen bonding, the non-fluorinated receptor exhibits the highest binding constants within this series.     

An examination of density functionals on aldol, Mannich and ��-aminoxylation reaction enthalpy calculations

The reaction enthalpies of aldol, Mannich and ??-aminoxylation reactions were calculated by density functional theory (DFT) using long-range-corrected (LC), hybrid B3LYP and other up-to-date functionals to show why conventional DFT including B3LYP has given poor enthalpies for these reactions. As a result, we found that long-range exchange interactions significantly affect the reaction enthalpies. We therefore proposed that the poor enthalpies of B3LYP are due to its insufficient long-range exchange effect. On the other hand, LC functionals accurately reproduce reaction enthalpies for these reactions. However, we noticed that even LC functionals present poor reaction enthalpies for specific reactions, in which many branches are produced or very small molecules such as methane molecule participate.     

Assessment of higher-order spin�Corbit effects on electronic g-tensors of d 1 transition-metal complexes by relativistic two- and four-component methods

The electronic g-tensors of a series of V, Cr, Mo, W, Tc, and Re d¹ transition-metal complexes have been studied systematically by density functional theory (DFT) methods. The comparison between one-component second-order perturbation theory calculations with two- and four-component first-order perturbation calculations has allowed an assessment of the importance of higher-order spin-orbit contributions. Using an efficient matrix Dirac?CKohn?CSham implementation with relativistic kinetic balance basis sets, it has been possible for the first time to apply four-component DFT also to g-tensors of larger models for biological vanadium, molybdenum, and tungsten metal sites. Higher-order spin?Corbit effects are generally crucial for an accurate determination of the g-tensors in such complexes, in many cases more important than the choice of non-hybrid or hybrid density functional. A systematic scaling analysis of the spin?Corbit integrals shows that second-order spin?Corbit effects may be of the same size as the leading first-order effects and thus alter the computed g-tensors fundamentally, in particular for the 5d species. In the latter case, even third-order effects may be non-negligible.     

A density functional study on magnetic exchange interaction between Mn(II) ion and nitronyl nitroxide radical in trans- and cis-metal-radical complexes

In the recent few years, transition metal complexeswith radical ligands have received much attentionaiming at a so-called metal-radical approach for novelmolecular magnet design[1]. One of the more popularfamilies is concerned in nitronyl nitroxide radica…     

Additional force field in cooling process of cellular Al alloy

The foaming process of Al alloy is similar to that of Al, but there is a solid-liquid state zone in the solidification process of cellular Al alloy which does not exist in the case of Al. In the unidirectional solidification of cellular Al alloy, the proportion of the solid phase gradually reduces from the solid front to the liquid front. This will introduce a force and result in a serious quick shrinkage. By the mathematic and physical mode, the solidification of the cellular Al alloy is studied. The data measured by experiment are close to the result calculated by the mode. This kind of shrinkage can be solved by suitable cooling method in appropriate growth stage. The compressive strength of the cellular Al alloy made by this way is 40% higher than that of cellular Al.     

Experimental and theoretical study of N-hexylcytosine and N-hexylcytosinium nitrate: the crucial role of hydrophobic and anion–π interactions

We report the synthesis and X-ray characterization of N¹-hexylcytosine (1) and N¹-hexylcytosinium nitrate (2). N¹-hexylcytosine (1) does not follow the same behaviour previously described for N¹-hexylthymine and N¹-hexyluracil in the solid state. This different behavior has been analyzed by means of density functional theory (DFT) calculations including the latest available correction for dispersion (D3). In addition hydrophobic and anion–π noncovalent interactions play a key role in stabilizing the 3D architectures of the compounds, which have been energetically studied using theoretical calculations and compared with similar structures retrieved from the Cambridge Structural Database (CSD). The anion–π–anion binding mode observed for nitrate in compound 2 is also observed in several crystal structures involving cytosine ring coordinated to transition metals.     

Mononuclear and long-range single-bridged binuclear complexes of oxovanadium(IV) involving conjugated heterocyclic nitrogen base and heterocyclic β-diketones

Summary Binuclear complexes of OV^IV have been prepared by reacting aromatic diamines with mixed-ligand (mononuclear) complexes of the type [(diamine), VO(PmAcp or PmbzP)], where (diamine) = 2,2-bipyridine or 1,10-phenanthroline, and PmAcp or PmbzP heterocyclic -diketone ligands = 1-phenyl-3-methyl-4-acetyl or 4-benzoyl-2-pyrazolin-5-one. 2,6-Diaminopyridine orm-phenylenediamine condenses with the MeCO or PhCO groups of PmAcp and PmbzP on two complex molecules, thus bridging the two VO^II centres. The complexes have been characterized by electronic, i.r. and e.s.r. spectra, magnetic measurements, thermogravimetry, conductometry and microanalysis. The magnetic moments and the order of antiferromagnetism are explained on the basis of delocalized -orbitals, orientation of the metal orbitals and the bridging Schiff base. The metal-ligand bond is covalent.     

Influence of anion on the quadratic nonlinearity and depolarization ratios of scattered second harmonic light from cation-π complexes

We have investigated quadratic nonlinearity (β(HRS)) and linear and circular depolarization ratios (D and D('), respectively) of a series of 1:1 complexes of tropyliumtetrafluoroborate as a cation and methyl-substituted benzenes as π-donors by making polarization resolved hyper-Rayleigh scattering measurements in solution. The measured D and D(') values are much lower than the values expected from a typical sandwich or a T-shaped geometry of a complex. In the cation-π complexes studied here, the D value varies from 1.36 to 1.46 and D(') from 1.62 to 1.72 depending on the number of methyl substitutions on the benzene ring. In order to probe it further, β, D and D(') were computed using the Zerner intermediate neglect of differential overlap-correction vector self-consistent reaction field technique including single and double configuration interactions in the absence and presence of BF(4) (-) anion. In the absence of the anion, the calculated value of D varies from 4.20 to 4.60 and that of D(') from 2.45 to 2.72 which disagree with experimental values. However, by arranging three cation-π BF(4)(-) complexes in a trigonal symmetry, the computed values are brought to agreement with experiments. When such an arrangement was not considered, the calculated β values were lower than the experimental values by more than a factor of two. This unprecedented influence of the otherwise "unimportant" anion in solution on the β value and depolarization ratios of these cation-π complexes is highlighted and emphasized in this paper.     

Electron density distribution in endohedral complexes of fullerene C₆₀, calculated based on the Gauss law

This study demonstrates that different partial charge methodologies, consisting of an attribution of the total electron density to particular atoms of a molecule, generate very divergent results in the case of atoms doped into a fullerene cage. A new method of calculating the density distribution inside and outside fullerene complexes has been proposed and applied in the case of C??, [F@C??]?, [Na@C??]?, and He@C??. It allowed for the calculation of the electron density between surfaces, isomorphic with the C?? cage, lying inside and outside the latter, as well as the charge in the space surrounding the central atom (or the central point in the case of empty C??).     

Estimation of σ- and π-donor properties of heterocyclic thioamides by spectroscopic and magnetic resonance methods

The charge-transfer complexes (CTC) of few thioamide: 1-methylimidazoline-2-thione (MMI), 3-methyl-1-ethoxycarbonilimidazoline-2-thione (Carb), 5-methylbenzimidazoline-2-thione (BIZ), benzothiazoline-2-thione (BTZ), benzoxazoline-2-thione (BOZ) as σ-donors and diiodine as σ-acceptor were studied by spectroscopic methods (UV/Vis, (1)H NMR). CTC formation constants of thioamides with diiodine were determined using the function of the average-iodine number. The charge-transfer complexes of thioamides as π-donors with tetracyanoethylene (TCNE) as π-electron acceptor, were studied by UV-spectroscopy in dichloromethane and chloroform solutions. The mechanism of interaction MMI and Carb with TCNE have been studied by EPR spectroscopy. Spectral characteristics and formation constants are discussed in the terms of electron donor affinity of thioamides and the nature of the organic solvent used. The ionization potentials of donors were estimated from the CT transition energies of their complexes. The photolytic equilibrium constants of five thioamides are determined using pH-metric titrations.     

Reactivity of inorganic α-nucleophiles in acyl group transfer processes in water and surfactant micelles: I. Systems based on organic complexes of tribromide anion

Systems based on organic complexes of tribromide anion generate upon dissolution in water nucleophile–oxidant couple HOBr/BrO^– and accelerate hydrolysis of ethyl 4-nitrophenyl ethylphosphonate, diethyl 4-nitrophenyl phosphate, and 4-nitrophenyl p-toluenesulfonate by a factor of 15–90 in the presence of cationic surfactant micelles. As in water, hypobromite ion in surfactant micelles acts as α-nucleophile, and the magnitude of the α-effect almost does not change in going from water to micelles. Micellar effects of surfactants are determined by the nucleophilicity of hypobromite ion in surfactant micelles and by solubilization of the substrate and BrO^–, which largely depend on the counterion concentration in the micelle surface layer. The main factor responsible for the observed acceleration is increased reactant concentration in the micellar pseudophase.     

Topology of the electron density of multicenter bonding in the anion TCNE2 2−

For TCNE₂ ^2? the role of bond paths in the electron density is emphasized to show that the anion contains multicenter bonding interactions across 4 central carbon atoms conferring inherent stability to it, consistent with experimental, and theoretical studies of other authors.     

Vibrational spectra of 1,1-dichloroethanes and βCH stretching interaction force constants

Infrared and Raman spectra are described and assignments are reported for CH₃CDCl₂ and CD₃CHCl₂, together with new i.r. data for CH₃CHCl₂ and CD₂HCHCl₂. Using previously obtained “isolated” CH stretching frequencies, the above data enable the trans and gauche stretch—stretch interaction force constants to be determined:f′_g = ±0.011, f′_t = ∓0.026 mdyn/Å. Similar values, f′_g = +0.016, f′_t = −0.029, may be obtained from the earlier spectra of CHD₂CHD₂ due to Van Riet.The relations between the fundamental deformation bands and their overtones and combinations are examined in order to estimate the accuracy of predictions of v_s (=v₃) for the CH₃ and CD₃ groups from the 4 × 4 refinement and frequency sum rule. The data can be interpreted so as to give good agreement on the values of v^O_s of 2920 cm⁻¹ (CH₃) and 2115 cm⁻¹ (CD₃), provided that there are significance resonance shifts on both 2δ_a and 2δ′_s levels. That this is the case seems to be true for the CD₃ group, but is uncertain for the CH₃ one.     

Different coordination modes of the thiosaccharinate anion in dinuclear and one dimensional polymeric silver–azine complexes

The effect of substituted pyridines bases upon the coordination of thiosaccharinate (tsac, C₇H₄NO₂S₂⁻ in ternary silver complexes is analyzed. Four crystalline silver-substituted pyridine complexes with tsac as a coordinating counter anion, [Ag(tsac)(3-methylpyridine)₂]_n, [Ag₂(tsac)₂(4-methylpyridine)]_n, [Ag₂(tsac)₂(quinoline)₂] and [Ag(tsac)(4-methyloxypyridine)]_n were synthesized and characterized by means of spectroscopic (IR and Raman, UV–Vis, and ¹H and ¹³C NMR) and X-ray diffraction techniques. The thiosaccharinate anion showed its versatility coordinating to the metal in each complex by a different way. In the 3-Mepy complex it was coordinated in a μ₂-S mode and in the 4-MeOpy complex it was bound in a μ₃-S form both resulting in polymeric chains. In the 4-Mepy complex the anion was bound in a μ₂-S,N head to head mode and in the quinoline complex in a μ₂-S,N head to tail mode, both showing dinuclear arrangements.