Systematic study of luminescent properties of new lanthanide complexes using crown ethers as ligand

This is a report on the synthesis, characterization and spectroscopic study of 24 lanthanide-crown ether coordination compounds, where Eu(III), Tb(III) and Gd(III) were complexes to 12-crown-4 (12C4), 15-crown-5 (15C5), 1,10-phenanthroline (phen) and 2,2′-dipyridyl (dipy). The compounds were synthesized in an ethanol/acetone solution at room temperature and analyzed using CHN elemental analysis and infrared, absorption and emission spectroscopies. The polarizability that the ligand exerts on the emission process was verified and found remarkable. The Eu-15C5-phen complex showed the highest quantum efficiency (71.6%) because of its low non-radiative rate and highest polarizability with reference to the ligands system.     

Thermodynamic study of mixtures containing oxygenated compounds

Excess volumes, V^E, isentropic compressibility deviations, Δκ_S, and excess enthalpies, H^E, of 1-butanol or 2-butanol with tetrahydrofuran have been determined at the temperatures 283.15 K, 298.15 K and 313.15 K, for 2-butanol H^E are also given at 290.15 K and 305.15 K. A brief discussion of the results is given in terms of molecular interactions.     

Thermodynamic properties of aqueous non-electrolyte mixtures. Alkanols + + water systems.

The molar excess enthalpies, H^E, at 298.15 K, and the liquid-liquid equilibrium, LLE, of aqueous mixtures of alkanols have been measured.The results are interpreted qualitatively in terms of intercomponent molecular interactions and hydrophobic stabilization of the water structure by the alkanol molecules. The results obtained indicate that the geometry, the number of alkyl groups in the aliphatic chain and the relative position of the functional group -OH have an important action on these two effects.     

Sublimation Study of Six 5-Substituted-1,10-Phenanthrolines by Knudsen Effusion Mass Loss and Solution Calorimetry

The vapor pressures of six solid 5-X-1,10-phenanthrolines (where X = Cl, CH₃, CN, OCH₃, NH₂, NO₂) were determined in suitable temperature ranges by Knudsen Effusion Mass Loss (KEML). From the temperature dependencies of vapor pressure, the molar sublimation enthalpies, Δ_cr^gH_m⁰(⟨T⟩), were calculated at the corresponding average ⟨T⟩ of the explored temperature ranges. Since to the best of our knowledge no thermochemical data seem to be available in the literature regarding these compounds, the Δ_cr^gH_m⁰(⟨T⟩) values obtained by KEML experiments were adjusted to 298.15 K using a well known empirical procedure reported in the literature. The standard (p⁰ = 0.1 MPa) molar sublimation enthalpies, Δ_cr^gH_m⁰(298.15 K), were compared with those determined using a recently proposed solution calorimetry approach, which was validated using a remarkable amount of thermochemical data of molecular compounds. For this purpose, solution enthalpies at infinite dilution of the studied 5-chloro and 5-methylphenantrolines in benzene were measured at 298.15 K. Good agreement was found between the values derived by the two different approaches, and final mean values of Δ_cr^gH_m⁰(298.15 K) were recommended. Finally, the standard molar entropies and Gibbs energies of sublimation were also derived at T = 298.15 K. The volatilities of the six compounds were found to vary over a range of three orders of magnitude in the explored temperature range. The large difference in volatility was analyzed in the light of enthalpies and entropies of sublimation. The latter was tentatively put in relation to the rotational contribution of the substituent group on the phenanthroline unit.     

Enthalpies of formation and isomerization of aromatic hydrocarbons and ethers by G3(MP2)//B3LYP calculations

A computational method for estimation of the gas‐phase enthalpies of formation of aromatic hydrocarbons and ethers has been developed. The method is based on high‐level G3(MP2)//B3LYP calculations, atomization reactions, and structure‐dependent correction terms. By this method, enthalpies of formation Δ_fH_m°(g, 298.15 K) of 86 aromatic compounds were evaluated. The calculated enthalpies of formation raise questions of the reliability of several experimental enthalpies of formation reported in the literature. As an application of the computational enthalpies of formation, reaction enthalpies for several types of isomerization reactions of aromatic compounds were calculated. In cases in which experimental reaction enthalpies were available for comparison, the agreement between the computational and experimental data proved to be excellent. Copyright © 2008 John Wiley & Sons, Ltd.     

Enthalpies of formation of olefinic ethers by G3(MP2)//B3LYP calculations

The gas‐phase enthalpies of formation at 298.15 K of a number of acyclic and cyclic olefinic ethers (mainly α,β‐unsaturated ethers), together with those of a few cyclic mono‐ and dienes, have been estimated by G3(MP2)//B3LYP calculations. In most cases, the computational and experimental data (if available) are in good mutual agreement. Whenever significant deviations between the experimental and computational data were found, the experimental enthalpies of formation arise from a single data source, and it appears that small experimental errors are embedded therein. A marked error was found in the experimental enthalpy of formation of 2‐chloroethyl ethyl ether, used in this work as a reagent for estimation of the enthalpy of formation of 2‐chloroethyl vinyl ether by an isodesmic reaction. Moreover, significant errors were also found in the literature values for the computational (B3LYP/6‐311G**) enthalpies of formation of several Me‐substituted derivatives of methyl vinyl ether. The present computational method, besides providing acceptable enthalpies of formation for unsaturated ethers, was also found to give accurate Δ_fH(g) values for cyclic mono‐ and dienes. Thus, the G3(MP2)//B3LYP computational method proved to be a valuable tool for investigating the energetics of olefinic ethers and hydrocarbons. Copyright © 2008 John Wiley & Sons, Ltd.     

Entropy Effects in Intermolecular Associations of Crown-Ethers and Cyclodextrins with Amino Acids in Aqueous and in Non-Aqueous Media

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation.     

On the preferential solvation of drugs and PAHs in binary solvent mixtures

The preferential solvation parameters, i.e., the differences between the local and bulk mole fractions of the solvents in solutions of certain drugs and polycyclic aromatic hydrocarbons (PAHs) are derived from their solubilities in binary solvent mixtures by means of the inverse Kirkwood-Buff integral (IKBI) and the quasi-lattice quasi-chemical (QLQC) methods. The solutes include caffeine, niflumic acid, diazepam, benzocaine, phenacetin, paracetamol, nalidixic acid, anthracene, and tr-stilbene and both aqueous and non-aqueous mixtures are considered. The findings are rationalized in terms of the interactions between the solute and solvents and the solvent components among themselves.     

Spectral properties of 1,3,4-oxadiazole derivatives in binary solvent mixtures

The influence of nonspecific intermolecular interactions on the fluorescence band shift of 1,3,4-oxadiazole derivatives has been investigated in the binary solvents hexane-ethanol, toluene-ethanol, toluene-acetonitrile, and carbontetrachloride-2-propanol. The dependences obtained have been analyzed in terms of preferential solvation. It has been shown that the maximum solvation energy for slightly polar compounds occurs in toluene-ethanol, toluene-acetonitrile, and carbontetrachloride-2-propanol. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 177–181, March–April, 2008.     

Kinetic sonication effects in light of molecular dynamics simulation of the reaction medium

Molecular dynamics (MD) simulation of the structure of ethyl acetate solutions in two water–ethanol mixtures was performed at 280 and 330 K. The MD simulations revealed that ethyl acetate was preferentially solvated by ethanol, water being mainly located in the next solvation layer. With increasing temperature ethanol was gradually replaced by water in the first solvation shell. These findings explain the decrease in the rate of ester hydrolysis with increasing molar ratio of ethanol in the solution as the reaction rate was linearly dependent on the relative ethanol content in the first solvation shell of the ester. Predominance of ethanol results in decreased polarity and water activity in the shell and accordingly in a decreased reaction rate. Based on the results of the MD simulations, the principal conclusion of this work is that ultrasound enhances the kinetic energy (the effective temperature) of species in the solution and, in this way, evokes shifts in the solvation equilibria thus affecting the reaction rate. It appears that ultrasound does not completely break down the solvent shells or clusters in the solution as previously believed. Phenomena of thermo-solvatochromism and reaction rate levelling by ultrasound in binary solvents are described.     

Spectral Investigations of Solvatochromism and Preferential Solvation on 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone

Solvatochromic and preferential solvation of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra of DHDMAQ in different solvents show the intra molecular charge transfer band in the region 400–550nm. The observed blue shift with solvent polarity indicates the delocalisation of the excited state, owing to reduction in quasiaromaticity of the chelate rings formed by intra molecular hydrogen bonds, due to electrostatic or hydrogen bonding interaction. This is also confirmed by the observed low oscillator strength and the transition dipole moment. The observed quantum yield of DHDMAQ in different solvents is due to the inter molecular hydrogen bond in the excited state in addition to the intra molecular hydrogen bond. It also reveals from the low oscillator strength, which indicates that the radiative decay is low. Excited state dipole moment of DHDMAQ is calculated by solvatochromic data and it shows a lower value than ground state dipole moment. The preferential solvation parameter shows that in dimethyl formamide (DMF) + ethanol mixture, the DHDMAQ is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF + dichloromethane mixture DHDMAQ is preferentially solvated by DMF.     

Kinetics of the thermal decomposition reaction of diethylketone cyclic triperoxide in acetone–toluene and acetone–1‐propanol binary solvent mixtures

The thermal decomposition reaction of diethylketone triperoxide (DEKT) ca. 0.02 M was studied in binary mixtures of acetone–toluene and acetone–1‐propanol at 150 °C. Products of DEKT thermolysis in solution, detected by GC analysis, were diethylketone, bibenzyl and butane. The reactions were explored by GC at different solvent compositions and in each case the reactions followed a pseudo first order kinetic law, up to at least 90% peroxide conversion. The rate coefficient value of the reaction is affected by the solvent properties, showing an increase in the k_obs values with increases in the polarity of the solvent mixture in acetone–toluene systems. Changes in the rate coefficient values are probably caused by the presence of the apolar toluene solvent, which dominates the preferential solvation around the DEKT molecule through non‐specific interactions. In acetone–1‐propanol mixtures the solvation effect is slightly dominated by the specific interactions between the 1‐propanol and a polar intermediate specie represented by the biradical, initially formed. The rate coefficient value increases ca. 6% in the mixture with 0.1 mole fraction of 1‐propanol in comparison with the value in pure acetone; but no more changes in rate coefficient values are observed when the amount of the alcohol increases. The critical state of the reaction (intermediate biradical) is preferentially solvated by the 1‐propanol instead of acetone, but in mixtures of different composition, it is not possible to detect any effect on the reactivity for homolytic rupture of the O? O bond. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational and orientational relaxation of thiocyanate ion in crown ether complexes

The IR absorption and Raman spectra of the following complex compounds based on thiocyanates and crown ethers have been studied: KSCN-18-crown-6, KSCN-dibenzo-18-crown-6, NaSCN-dibenzo-18-crown-6, and NaSCN-benzo-15-crown-5. The shape of the contour of the spectral line corresponding to the stretching vibration ₁(CN) of the thiocyanate ion in the indicated compounds in the temperature interval involving solid and liquid phases have been investigated for the first time. The reorientation parameters and molecular-relaxation characteristics of the thiocyanate ion in the crown compounds have been calculated. It is found that an increase in temperature leads to gradual freeing of cations and to the properties of crown compounds becoming identical to those of pure salt melts.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 23–27, January–February, 2005.     

Solution calorimetry of organic nonelectrolytes as a tool for investigation of intermolecular interactions

The paper is mainly the review and generalization of the previous publications of the authors. It demonstrates that solution calorimetry method gives the opportunities of more detailed understanding of various aspects of intermolecular interactions in solution. We are assured that prerequisite to such an understanding is the successive analysis of various solute–solvent systems from the simplest ones which include alkanes as a solute or as a solvent to the most complex systems with solvent self‐association via hydrogen bonding. Particular findings discussed in this paper are (i) an inconspicuous contribution of electrostatic solute–solvent interaction to the solvation enthalpy and, accordingly, the dominating contribution of dispersion interactions for nonspecifically solvated solutes; (ii) new, very general method for the extraction of specific interaction enthalpy from the enthalpy of solvation; (iii) new method of determination of self‐association enthalpies for the solvents associated via hydrogen bonding; (iv) new method for determination of cooperative hydrogen bonding enthalpies of proton acceptors with associated species of alcohols; (v) the unique method of experimental determination of the hydrophobic effect enthalpy. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental and computational thermochemistry of three nitrogen-containing heterocycles: 2-benzimidazolinone, 2-benzoxazolinone and 3-indazolinone

The standard molar enthalpies of combustion, sublimation, and formation of three nitrogen-containing heterocycles, namely, 2-benzimidazolinone, 2-benzoxazolinone and 3-indazolinone were determined calorimetrically. The standard (p°?=?0.1?MPa) molar enthalpies of formation in the gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at T?=?298.15?K, measured by static bomb combustion calorimetry and from the standard molar enthalpies of sublimation at T?=?298.15?K, measured by Calvet microcalorimetry. Møller–Plesset calculations at the MP2 level and density functional calculations with the B3LYP functional and extended basis sets were also performed to determine the energetically preferred tautomeric form of the molecules. The results were qualitatively independent of the calculational level, where in general the DFT calculations were in better agreement with experiment than those from MP2. The gas and solid phase enthalpic differences between imines and amides, wherein –CH=N- is contrasted with –CONH-, have been studied and roughly constant values have been found.     

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.     

Dielectric relaxation study of dipropylsulfoxide/water mixtures

The complex dielectric spectra of dipropylsulfoxide (DPSO)/water mixtures in the whole concentration range have been measured as a function of frequency between 100 MHz and 20 GHz at four temperatures between 298.15 K and 328.15 K. The dielectric parameters, static dielectric constant (ε_s), relaxation time (τ) and relaxation strength (Δε) have been obtained by the least squares fit method. The relaxation in these mixtures can be described by two Debye functions, whereas for pure DPSO Cole-Davidson type is valid. The relaxation times of the mixtures show a maximum at about x(DPSO) ≈ 0.3. In the concentration range where a maximum appears, the interaction of DPSO with water is presumably the result of hydrogen bonding between water and the sulfonyl group of the sulfoxide molecule. The concentration and temperature dependent excess dielectric constant and effective Kirkwood correlation factor of the binary mixtures have been determined. The excess permittivity is found to be negative for all concentrations.     

Polymer thermophoresis in solvents and solvent mixtures

The thermophoresis of homopolymer chains dissolved in a pure non-electrolyte solvent or solvent mixture is theoretically examined. Thermophoresis is related to the temperature-dependent pressure gradient in the solvent layer surrounding the monomer units (mers). The gradient is produced by small changes in the solvent or solvent mixture density due to the mer-solvent interaction. The London-van der Waals interaction was considered as the main reason of the excess pressure around mers. The resulting expression for the thermophoretic mobility (TM) contains the Hamaker constant for mer-solvent interaction, as well as solvent thermodynamic parameters, including the cubic thermal expansion coefficients of the solvents and the temperature coefficient of the solvent partition factor (for the solvent mixture). This expression is used to calculate the interaction constants for polystyrene and poly(methyl methacrylate) in several organic solvents and binary solvent mixtures using thermophoretic data obtained from thermal field-flow fractionation. The calculated constants are compared with values in the literature and found to follow the same order among the different solvents and to be of the same order of value although several times larger. Furthermore, the model explains weak polymer thermophoresis in water compared with less polar solvents, which correlates also with monomer size. The concentration dependence of polystyrene TM in solvent mixtures also provides a satisfactory explanation by the proposed theory using a concept of secondary diffusiophoresis due to secondary temperature-induced solvent concentration gradient. The method for the evaluation of the diffusiophoresis contribution is proposed.     

Saccharin: a combined experimental and computational thermochemical investigation of a sweetener and sulfonamide

The standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous phase at a temperature of 298.15?K have been experimentally determined for saccharin and for benzenesulfonamide. These compounds were also studied theoretically using density functional theory, the B3LYP functional and extended basis sets.