Solid State C NMR of 30-Crown-10 Ether and 30-Crown-10.4H2O

The ¹³C NMR solution spectra of 30-crown-10 ether and its tetrahydrate show only one resonance at all accessible temperatures. In contrast, the solid state ¹³C NMR spectrum of the 30-crown-10.4H₂O shows two resonances in the ratio of 4:1, separated by 1.2 ppm. In the case of 30-crown-10 itself, six resolvable ¹³C resonances in the ratio of 4:1:1:2:1:1 are observed in the solid with an overall chemical shift dispersion of 5 ppm. The remarkably different spectral behavior of these two systems in the solid state is discussed in terms of the torsional environments of the crystallographically unique carbons and the results of GIAO calculations of isotropic ¹³C shieldings for simpler model compounds. Results of dipolar dephased ¹³C CPMAS spectra indicate that 30-crown-10 does not undergo a large amplitude molecular motion, in contrast to earlier results for 18-crown-6. Only a small amount of residual intensity is found in the dipolar dephased spectrum of 30-crown-10.4H₂O, indicating that it also is relatively rigid in the solid.     

Quadrupole relaxation enhancement and polarisation transfer in DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6 in solid state

ABSTRACT

¹H spin-lattice relaxation studies have been performed for pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 in powder and its solution in dimethyl sulfoxide (DMSO). The experiments have been carried out in the frequency range of 10?kHz–30?MHz and the temperature range of 240–277?K; at 277?K the solution is already frozen. The ¹H relaxation of pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 has been interpreted in terms of three dynamical processes. Quadrupole Relaxation Enhancement effects have been observed in the frozen DMSO solution of [Bi(NO₃)₃(H₂O)₃]*18-crown-6. The specific mechanisms of the ¹H spin-lattice relaxation enhancement have been discussed distinguishing between effects caused by time independent (residual) and fluctuating ¹H-²⁰⁹Bi dipole-dipole interactions.     

冠醚铕镧异核配合物的合成表征及荧光性质

以 18冠 6为配体 ,分别与高氯酸铕和高氯酸镧在乙腈介质中反应 ,合成冠醚铕和冠醚镧配合物 ;两种冠醚配合物与交联配体———对苯二甲酸反应 ,形成了对苯二甲酸冠醚铕镧异核稀土超分子配合物。由元素分析数据推测 ,超分子配合物的组成式为EuLaL2 L′(ClO4) 4 ·6H2 　 [L =18 C 6 ,L′ =p C6H4(COO-) 2 ],测定了超分子配合物的红外光谱 ,紫外光谱 ,摩尔电导及荧光光谱。结果表明 ,冠醚和对苯二甲酸根与稀土离子配位 ,而高氯酸根离子处于配合物的外界 ,铕镧异核稀土超分子配合物的荧光强度是冠醚铕的 8倍多。     

Analysis of newly synthesized disulfides of aryldithiocarbonates and vanadium(V) and niobium(V) complexes of aryldithiocarbonates based on spectroscopic,thermogravimetric, SEM and DFT studies

ABSTRACT

Oxidation of the sodium salt of 2-methyl, 3-methyl, 4-methyl and 4-chloro-3-methylphenyldithiocarbonic acid by I₂ affords the disulfides of respective dithiocarbonates [(ArOCS₂)₂] (Ar?=?2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃. Vanadium(V) and Niobium(V) complexes of 2-methyl, 3-methyl, 4-methyl and 4-chloro-3-methylphenyldithiocarbonates have also been synthesised by one-step synthetic route. The metal salt (VOCl₃ and NbCl₅) were reacted with 2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃OCS₂Na in 1:2 stoichiometric molar ratio yielding the complexes corresponding to the molecular formula [(ArOCS₂)₂VO(Cl)] and [(ArOCS₂)₂NbCl₃] [Ar?=?2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃OCS₂)]. The compounds were characterised by elemental analyses, infrared, mass and heteronuclear NMR (¹H and ¹³C) spectroscopic studies. Thermogravimetric analysis and scanning electron microscopic analyses were also carried out for deeper investigation of the structural features. Comprehensive theoretical investigation was performed by applying density functional theory (DFT) calculations on vanadium and niobium complexes by the DFT/B3LYP/LANL2DZ method to obtain the optimised molecular geometry, vibrational frequencies, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), thermodynamic properties and various other quantum-mechanical parameters.     

A Comparison of Complexation of Li<Superscript>+</Superscript> Ion with Macrocyclic Ligands 15-Crown-5 and Benzo-derivatives in Binary Nitromethane–Acetonitrile Mixtures by Using Lithium-7 NMR Technique and Ab Initio Calculation

Abstract  

Lithium-7 nuclear magnetic resonance (NMR) measurements were used to investigate the stoichiometry and stability of Li⁺ complexes with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) and dibenzo-15-crown-5 (DB15C5) in a number of nitromethane (NM)–acetonitrile (AN) binary mixtures. In all cases, the exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. While all crown ethers form 1:1 complexes with Li⁺ ion in the binary mixtures used, stepwise formation constants of the 1:1 (ligand/metal) complexes were evaluated from computer fitting of the NMR-mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of AN in the solvent mixtures. The stability order of the 1:1 complexes was observed to be 15C5.Li⁺ > B15C5.Li⁺ > DB15C5.Li⁺. The optimized structures of the free ligands and their 1:1 complexes with the Li⁺ ion were predicted by ab initio theoretical calculations using the Gaussian 98 software. The results of calculations are discussed.     

O,O′-Dimethyl diphenyldithiophosphates of titanium(IV): synthesis,spectroscopic, DFT and biological studies

Dimethyl diphenyldithiophosphate complexes of titanium(IV), [(C₅H₅)₂Ti{S₂P(OAr)₂}_nCl_2-n] (Ar?= 2,4-(CH₃)C₆H₃, 2,5-(CH₃)C₆H₃, 3,4-(CH₃)C₆H_3, 3,5-(CH₃)C₆H_3, 3-CH₃-4-Cl-C₆H₃O; n?=?1 and 2) have been synthesised and characterised by various physicochemical techniques along with computational analysis of the complexes (2), (9) and (10) using density functional theory (DFT) and time-dependent DFT (TDDFT). Comparison of antimicrobial activity of the free ligands and complexes has shown that the complexes are more effective than the free ligands. The in vitro cytotoxic by using a MTT staining method with RAW 264.7 cells (mouse macrophages) have been investigated. On the basis of analytical and DFT data, a distorted trigonal bipyramidal around titanium(IV) may be assigned to the complexes (1–5) and distorted octahedral geometries for the complexes (6–10).     

DFT study of hydrogen storage in Pd-decorated C60 fullerene

Hydrogen storage reactions on Pd-doped C₆₀ fullerene are investigated by using the state-of-the-art density functional theory calculations. The Pd atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to four hydrogen molecules with average adsorption energies of 0.61, 0.45, 0.32, and 0.21 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.8 wt%. While the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 1 are outside the department of energy (DOE) domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 2–4 are inside this domain. While the interaction of 1H₂ with Pd + C₆₀ is irreversible at 459 K, the interaction of 2H₂ with Pd + C₆₀ is reversible at 529 K. The hydrogen storage of the irreversible 1H₂ + Pd–C₆₀ and reversible 2H₂ + Pd–C₆₀ interactions are characterised in terms of densities of states, infrared, Raman, and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability.     

Crown ether enhancement of ionic conductivity in a polymer-salt system

Crown ethers are a class of organic compounds that form complexes with inorganic cations. When crown ethers are added to poly (vinylene carbonate) containing dissolved lithium salt, ionic charge transport in the solid electrolyte is assisted. The ionic conductivity of the polymer containing 12-crown-4 is three orders of magnitude greater than the conductivity in the polymer without crown ether. The conductivity of this system at room temperature is approximately 2.5×10⁻⁴ S cm⁻¹, higher than any polymer-lithium salt system yet reported. The effects of various crown compounds as well as their concentration effects are examined.     

Density functional theory study on a fluorescent chemosensor device of aza‐crown ether

Three derivatives of alkyl anthracene covalently bonded to aza‐18‐crown‐6 at the nitrogen position, anthracene(CH₂)_n, (n = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6‐31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza‐18‐crown‐6 ( L ) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between L and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time‐dependent density functional theory with the basis set 6‐31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza‐crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza‐crown ether‐based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza‐crown ether part of L indicate that the presence of the alkali metal cations Li⁺, Na⁺ and K⁺ play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Sensing and fluorescence behaviors of complex formation between new lariat crown ethers bearing fluorescence sidearm and metal ions in methanol solution

Fluorescence spectroscopic properties of the complex formation between six new C-pivot16-crown-5 ethers bearing fluorescence side arms and metal ions are studied. Six new C-pivot 16-crown-5 ethers that carry fluorescence side arms were synthesized. The research also included the examination of different fluorescent behavior of the new lariat ethers in the presence of silver and sodium ions (Ag⁺ and Na⁺) in methanol. Because of the good fit of the cavity size of these 16-crown-5 ethers with the Ag⁺ and Na⁺ ions, remarkable change in fluorescent spectra were observed. The results showed that the new lariat crown ethers exhibited enhanced selectivity towards sodium ion, but silver ion show quenching abilities towards the ligands. Cooperative participations of the C-pivot side arm oxygen with the ring oxygen molecules in complexation was also confirmed by the single crystal X-ray crystallography of the complex, (C₂₇H₃₀O₇)·NaClO₄. The freezing of crown ring conformation and the diminishment of the chance of sidearm oscillation that occurred upon complexation with sodium ion are the main causes of fluorescent enhancement. The quenching caused by the addition of silver ion was found to explainable by the photo-induced electron transfer that results in the reduction of silver ions.     

A hydrogen bonded complex C2H2…HBr isolated and characterized in the gas phase using pulsed-jet,Fourier transform microwave spectroscopy

A complex formed from ethyne and hydrogen bromide has been isolated and characterized by using a fast-mixing nozzle in conjunction with a pulsed-jet, Fourier transform microwave spectrometer. Any possible chemical reaction between the two components when mixed in the usual way was thereby precluded. The rotational constants A, B and C, the quartic centrifugal distortion constants δ_J, δ_Jk and δ_J and the Br nuclear hyperfine coupling constants X_aa and X_bb—X_cc (nuclear quadrupole) and M_bb (spin-rotation) were determined for each of the five isotopomers C₂H₂…H⁷⁹Br, C₂H₂…H⁸¹ Br, C₂H₂…D⁷⁹Br, C₂H₂…D⁸¹Br and C₂D₂…H⁷⁹Br. Interpretations of the spectroscopic constants show that the complex is planar and T shaped in the equilibrium conformation, with HCCH internuclear axis forming the cross of the T and the HBr internuclear axis lying along the C₂ axis of C₂H₂. The H of HBr is closer to the centre (?) of the π bond of ethyne, and therefore HBr is involved in a hydrogen bond to the π system, in which the distance of H from ? is r (?…H) = 2.469(1) A. The intermolecular stretching force constant is estimated as kσ = 5.38(2) Nm^?1 for the species involving a hydrogen bond (C₂H₂…H⁷⁹Br, C₂H₂…H⁸¹Br and C₂D₂…H⁷⁹Br) while this quantity increases to kσ = 5.68(2)Nm^?1 for those complexes bound through a deuterium bond (C₂H₂…D⁷⁹Br and C₂H₂…D⁷⁹Br). The opportunity is taken to consider similarities in the properties of complexes within the two series B…HBr and B…HC1 for a range of Lewis bases B, including B = C₂H₂. Some family relationships are identified in the two series.     

Investigation of cation complexation behavior of azacrown ether substituted benzochromene

The study of the complex formation of 3,3‐diphenyl‐3H‐benzo[f]chromenes containing aza‐18‐crown‐6‐ether, diaza‐18‐crown‐6‐ether or morpholine units with alkali, alkaline earth, heavy and transition metal cations in acetonitrile is reported. The spectroscopic and kinetic behavior of the photomerocyanine isomers of these chromenes is strongly affected by complexation with a metal cation. In order to interpret some of experimental data, an ab initio theoretical analysis of photochromic‐crown ether and its cation complexes was conducted. The different site of coordination of mono‐ and divalent cations to determine the minimum‐energy structure of benzochromene complexes in gas phase as well as in acetonitrile as solvent was explored. The coordination of both carbonyl oxygen and crown‐ether macrocyle with divalent cations in carbonyl‐capped structure is found to be the most stable isomer in gas as well as in condensed media. The crown‐containing benzochromenes were studied in liquid‐liquid extraction experiments toward there capacity to transfer metallic salts from water into an organic phase.The high selectivity to extraction of Ag⁺ was found. Copyright © 2007 John Wiley & Sons, Ltd.     

E.P.R. study of Mn2+ in lithium potassium tartrate (LPT) and its isomorphism with lithium ammonium tartrate (LAT)

An E.P.R. study of Mn²⁺ in single crystals of LiKC₄H₄O₆. H₂O (LPT) was carried out from ～300 K to 77 K and four magnetically differently oriented but symmetry related triclinic complexes of Mn²⁺ were observed. Spin hamiltonian parameters were obtained at ～ 300 K. The E.P.R. results suggest that LPT is not only isomorphous but also isostructural to LiNH₄C₄H₄O₆ . H₂O (LAT). In LPT no structural phase transition could be detected in the temperature range 300 K to 77 K. The observed small magnitude of the low symmetry effect is attributed to the small contribution of fourth order crystal field terms relative to that of the second order crystal field terms, to the zero-field splittings of the ⁶ S ground state of Mn²⁺. A temperature dependent anomalous behaviour is observed in the low field region of the E.P.R. spectrum for B//[010] and its neighbourhood.     

Synthesis and Antitumor,Antioxidant Effects Studies of N-Ethylpiperazine Substitute Thiourea Ligands and Their Copper(II) Complexes

A series of N-ethylpiperazine substitute thioureas [C₆N₂H₁₃NHCSNHR], where R = -C₃H₅ (L ₁ ), -C₁₀H₇ (L ₂ ), and -C₇H₇ (L ₃ ), and their copper (II) complexes have been synthesized. These ligands and complexes have been characterized by elemental analyses, IR, ¹H and ¹³C-NMR spectra, UV-Vis, magnetic susceptibility, thermogravimetrical analyses, and MALDI-TOF MS. In vitro antitumor activity of ligands and their complexes has been screened toward several tumor cell lines. The effects on these complexes of the growth of L1210 and MCF7 were studied comparatively with that of free ligands. Antioxidant and radical scavenging activities of synthesized compounds were determined by various in vitro assays including 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radicals (ABTS+), and ferrous ion (Fe²⁺) chelating activities. Moreover, these activities were compared to synthetic and standard antioxidant trolox. The results showed that the synthesized compounds had effective antioxidant power.     

The oxidation of H2CO on a copper(110) surface

The oxidation of H₂C¹⁶O by adsorbed ¹⁸O was studied on an Cu(110) sample by temperature programmed reaction spectroscopy. Formaldehyde exchanged its oxygen with surface ¹⁸O upon adsorption to yield H₂C¹⁸O_(a) and ¹⁶O_(a). Formaldehyde was also oxidized by surface ¹⁶O and ¹⁸O atoms to H₂COO which subsequently released one of the hydrogen atoms to form HCOO. The evolution of H₂ from the Cu(110) surface was desorption limited, and the low pre-exponential factor for the recombination of the surface hydrogen atoms suggested stringent requirement on the trajectories of the colliding partners. The formate was very stable and dissociated at elevated temperatures to simultaneously yield H₂ and CO₂. The surface concentration of ¹⁸O exerted a pronounced affect on the activity of the oxidation of formaldehyde on Cu(110).     

Structures and stabilities of endo- and exohedral Si20H20 derivatives: X@Si20H20 and XSi20H20, X = H + , H,N, P,C − , and Si −

Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si₂₀H₂₀ and XSi₂₀H₂₀, (X = H⁺, H, N, P, C^?, and Si^?) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si₂₀H₂₁ ⁺ shows that the proton cannot be positioned in the Si₂₀H₂₀ centre, but prefers attach to Si₂₀H₂₀ exohedrally with C_2v symmetry. Most investigated I_h endohedral complexes X@Si₂₀H₂₀ (X = H, N, P, C^?, and Si^?) are local minima, except for ²N@Si₂₀H₂₀, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi₂₀H₂₀ (X = H, N, P, C^?, and Si^?) have C_2v or C_s local minima, and most of them are more stable than their endohedral isomers with the exception of C_2v ⁴PSi₂₀H₂₀ and ⁴Si^?Si₂₀H₂₀.     

Experimental and Theoretical Study of Hydrogen Atom Abstraction from C2H6 and C4H10 by Zirconium Oxide Clusters Anions

使用配有团簇产生和化学反应源的飞行时间质谱装置,研究了锆氧阴离子团簇Zr_xOy^-与乙烷和丁烷的反应. 在反应中发现了Zr₂O₅H^-和Zr₃O₇H^-产物. 用密度泛函理论研究了乙烷在Zr₂O₅^-上的反应通道,发现乙烷脱氢反应可以发生,从而证明观察到的产物是源于脱氢反应. 该工作揭示了锆氧负离子团簇与烷烃反应中的新通道.     

Optical,structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound

ABSTRACT

The new organic-inorganic compound [C₂H₅NH₃]₂ZnCl₄ has been grown by the slow evaporation at room temperature. The zero-dimensional (0-D) structure for this compound was determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group Pna2₁ and consists of ethylammonium cations [C₂H₅NH₃]⁺ and [ZnCl₄]^2? tetrahedra anions. That is interconnected by means of hydrogen bonding contacts N-H···Cl. The molecular geometry and vibrational frequencies of [ZnCl₄]^2? and [C₂H₅NH₃]⁺ in the ground state was calculated using density functional method (B3LYP) with 6–31G(d) and 6–311G (d,p) basis set. The optimized geometric bond lengths and bond angles, obtained by using B3LYP/6–311G (d,p), show the best agreement with the experimental data. The optical absorbance was measured in order to deduce the absorption coefficient α, optical band gap E_g. The optical band gap is determined by extrapolating the plotted graph of (αhυ)^1/2 vs. (hυ). The large value of indirect optical band gap energy indicates the insulating nature of this material. Moreover, the extinction coefficient, refractive index and the dielectric permittivity of [C₂H₅NH₃]₂ZnCl₄ compound were calculated and the results are discussed. The evolution of the dielectric loss as a function of frequency revealed a distribution of relaxation times, probably ascribed to the reorientational dynamics of alkyl chains in this compound, and then analyzed with the Cole–Cole formalism.     

The effect of the hydrogen fluoride chain on the aromaticity of C6H6 in the C6H6···(HF)1–4 complexes

The effect of the hydrogen fluoride chain ((HF)_n) on the aromaticity and π character of C–C bonds of C₆H₆ in the C₆H₆···(HF)_n (n = 1–4) complexes were investigated using density functional theory employing RM05 functional. It was found that the binding energy between C₆H₆ and different (HF)_n chains showed a maximum at n = 3 (C₆H₆···(HF)₃). Also, the π–hydrogen interaction (πHI) and the bifurcated fluorine interaction (BFI) increased and decreased the π character of the C–C bond of C₆H₆, respectively. In addition, the change of aromaticity of the C₆H₆ due to the interaction with the HF chains was also studied using three different aspects such as aromatic fluctuation index (FLU), average two centre index (ATI) and proton nuclear magnetic resonance (HNMR) spectrum. The most change in the aromaticity happens when the C₆H₆ interacts with (HF)₃ chain. The variation of aromaticity with the binding energy and the summation of two-body terms were investigated and very good linear correlations were observed.     

A pyrolysis study on C4–C8 symmetric ethers

Pyrolysis of diethyl (C₄), di-n-propyl (C₆), di-isopropyl (C₆) and di-n-butyl (C₈) ethers were studied in a jet-stirred reactor between 720 and 1140 K, at 10 atm with an initial ether mole fraction of 0.1%. Major common pyrolysis products were observed to be CO, CH₄, H₂, and C₂H₄. All ethers produced the n/2 alcohol and olefin as products of molecular reaction to a small extent. Under pyrolysis conditions at 10 atm, hydrogen abstraction reactions by H atoms and CH₃ radicals were found to be important. Acetylene and benzene were formed for all ethers when T > 1000 K. A kinetic mechanism is used to represent these results. This study shows that there is need of systematic studies in determining site specific rate constants of important fuel related reactions of ethers.