摘要:

Stark hole-burning spectroscopy is used to investigate the effective dipole moment change of cresylviolet perchlorate (CVP) in various glass and polymer hosts such as ethanol:methanol (EM), polyvinyl alcohol (PVA), poly (2-hydroxyethyl) methacrylate (PHEMA), polyvinylbutyral (PVB), and formamide. The strong correlation between effective dipole moment change of the guest molecule and the holeburning efficiencies of the host matrices illustrates the sensitivity of the dipole moment change as a direct measure of guest-host interactions. Hole-burning is found to be more efficient as the dipole induced reaction field increases. This relationship is discussed in terms of the unusual hole-burning mechanism suggested for this molecule. The effective dipole moment change of cresylviolet perchlorate ranges from 0.14 to 0.59 Debye.

ISSN:0038-7010    

DOI:10.1080/00387019909349972

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Proton-ligand dissociation and metal-ligand stability constants of 3-(p-Tolylsulphonamido)rhodanine (TSR) with some transition metal ions were calculated potentiometrically in 0.1 M KC1 and 20% (v/v) ethanol-water mixture. The order of stability constants was found to be: Th4+>UO2+2>Gd3+>Ce3+>La3+>Mn2+<Co2+<Ni2+<Cu2+>Zn2+The dissociation constantspKHof TSR and the stability constantslog Kof their complexes were determined at different temperatures (303, 308 and 318 K). The corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavourable. The formation of the metal complexes have been found to be spontaneous, exothermic or endothermic (depend on the metal) and entropically favourable. The stoichiometries of these complexes were determined spectrophotometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.

ISSN:0038-7010    

DOI:10.1080/00387019909349973

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The 12-coordinated hexakis(nitrato)europate(III) ion displays a luminescence spectrum compatible with Th, symmetry, with essentially a single emission line at 16 873 cm−1arising from the5D0→7F1transition. At low temperature (4.2 - 170 K), the lifetime of the5D0level amounts to 10.9 ms and then sharply decreases because of vibrational de-excitation processes (Ea= 2 250 ± 1 490 cm−1). The forbidden5D0→7F0transition displays an extensive pattern of Stokes and anti Stokes vibrational components and its energy reflects a nephelauxetic parameter for the nitrite ions δO(NO2) equal to -14.4, slightly larger than the one associated to the nitrate ion in [Eu(NO3)6]3-. The ligand excitation spectrum contains several bands displaying extensive vibrational structure mostly due to the δ(NO2) vibrational mode.

ISSN:0038-7010    

DOI:10.1080/00387019909349974

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An IR-spectral study of sulphato- and chloro complexes of palladium (II) with 2-aminopyridine and aniline, respectively, is reported. The results obtained confirm the bidentate co-ordination of both 2-aminopyridine and SO4group in the case of sulphato-2-aminopyridine-palladium (II) leading to polynuclear structure of the complex in solution. The comparative investigation of sulphato-dianiline-palladium (II) suggests that the self-dependent ability of the SO42-ion for bridging co-ordination can stabilize chain-like complexes of palladium (II) only in the solid state.

ISSN:0038-7010    

DOI:10.1080/00387019909349975

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The fluorescence characteristics of the Schiff bases 2-(3-pyridylmethyliminornethyl)phenol (1), 2-(2 pyridyliminomethyl)phenol (2), N.N-bis(salicylidene)-2,3-pyridinediamine (3), N,N'-bis(salicylidene)-2,6-pyridinediamine (4) and 2-(2-amino-4-methoxymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (5) were studied in various solvents at different pH values. Corresponding quantum efficiencies were determined. Compound 1, which showed a tendency towards tautomeric mterconversion to ketoamine in polar protic solvents, was not fluorescent at pH < 8. The fluorescence of other compounds was very sensitive to solvent polarity and the pH of the medium. Compounds 2-4, preferably present as enolimines in all solvents, were not fluorescent in non-polar and moderately polar solvents, whereas weak emission was observed in polar solvents, like methanol, dimethylformamide and dioxane/water 1/1 (0.001 <Q< 0.072). A significant increase in Stokes shifts and in quantum efficiencies was noted as a result of increasing polarity of dioxane/water mixtures, indicating specific interactions with polar water molecules. The emission was promoted at acidic pH values where a pyridinium cation was formed (0.061 <Q< 0.519, in dioxane/water 1/1 at pH 3.4). Compound 5, which was a tautomeric mixture of enoiimine and cyclic diamine in all solvents, was fluorescent in polar as well as in non-polar media. The quantum efficiency varied dependent on the solvent and pH (0.023 <Q< 0.435). The cyclic diamine, i. e. the more rigid structure was supposed to be responsible for the fluorescence in non-polar and aprotic solvents as well as at neutral, and weakly basic pH values.

ISSN:0038-7010    

DOI:10.1080/00387019909349976

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0038-7010    

DOI:10.1080/00387019909349961

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor