Sławomir But

Spectroscopic studies of Eu(III) and Nd(III) complexes with several polyoxometalates

Abstract The results of studies related to synthesis and spectroscopic properties of polyoxometalates (POM) and their europium(III) and neodymium(III) complexes (Ln/POM) are presented. A series of lanthanide(III) sandwiched Ln(POM) 2 , Ln 2 POM or encapsulated within the cavity of the POM complexes, synthesized for these studies, were verified based on the results of thermogravimetric analysis and infrared spectroscopy. Absorption of Nd(III) and luminescence (excitation and emission) spectra of Eu(III) as well as results of Eu(III) ion lifetime measurements were used for characterization of the complexes. The Eu(III) luminescence lifetimes, measured both for solid and aqueous solutions, indicate that the sandwiched complexes Eu(POM) 2 have no water of hydration, whereas the complexes Eu 2 POM have four or six water molecules, and europium-encrypted derivatives three or four H 2 Os in the Eu(III) inner coordination sphere.

A new spectrophotometric method for the determination and simultaneous determination of tungsten and molybdenum in polyoxometalates and their Ln(III) complexes

Abstract A new spectrophotometric method is proposed for the determination of tungsten and molybdenum in polyoxometalates (POM) and their lanthanide(III) complexes (Ln/POM), using disodium-1,2-dihydroxybenzene-3,5-disulfate (Tiron), used as colorimetric reagent. Mo(VI) and W(VI) in solutions of polyoxotungstates and polyoxomolybdates can be determined from calibration graphs obtained by recording absorbancies in the wavelength range 352–500 nm for molybdenum and 352–400 nm for tungsten, where Beer’s law is obeyed. This method can be also applied for the simultaneous determination of these elements in polyoxotungstomolybdates without previous chemical separation. The procedure is based on the recording of absorption spectra using values of absorbancies at two points on the spectrum. The content of Mo and W can be determined using an appropriate mathematical equation and molar absorptivity coefficients for each of two determined Mo and W ions at two points with the absorption spectrum. Calibration graphs for 2–10 (also to 40) μg/ml of Mo(VI) and 4–20 (also to 80) μg/ml of W(VI) were established by measuring the absorbance at 400 nm for molybdenum and at 352 nm for tungsten, respectively. Limiting concentrations of several interfering ions [P(V), V(V), Si(IV), As(III), Eu(III), Gd(III)] were evaluated. The standard error for measurements of all samples studied (POMs and their Ln(III) sandwiched and encrypted complexes) is

EPR study of sandwiched gadolinium(III) complexes with polyoxometalates

Abstract The gadolinium-sandwiched complexes with polyoxometalates: [GdW 10 O 36 ] 9− , [Gd(SiW 11 O 39 )] 13− and [Gd(SiW 11− x Mo x O 39 ) 2 ] 13− (where x =2, 5, 8) have been chosen for electron paramagnetic resonance (EPR) study. The EPR spectra obtained for the ‘pure’ Gd(III) compounds (not doped) markedly differ from the U-spectrum characteristic for Gd(III) in glasses. This report shows how some of the spectroscopic properties of lanthanide(III) complexes can be studied with EPR through examples of Gd 3+ ion interactions with polyoxometalates. Analysis of EPR spectra obtained at X- (9.4 GHz) and Q- (35 GHz) bands provide estimates of zero-field splitting (ZFS) parameter D , a linewidth of the central line and effective g -factors for particular EPR lines. An interesting pattern showing a linear dependence of the D -value on the content of number x of Mo atoms, in the [Gd(SiW 11− x Mo x O 39 ) 2 ] 13− structure, was obtained and an attempt to explain it was made.

Simultaneous determination of molybdenum(VI) and tungsten(VI) and its application in elemental analysis of polyoxometalates.

Spectrophotometric determination of molybdenum(VI) and tungsten(VI) with application of Artificial Neural Networks is proposed and it was applied for elemental analysis of solid polyoxometalates. Better results in comparison with previously those achieved by previous published method were demonstrated. MALDI-TOF Mass Spectrometry was tested for possible determination of molecular weight of polyoxometalates utilizing different matrices. Phenomena observed during desorption-ionisation processes are discussed. LDI-TOF MS was found to be suitable for the determination of Mo:W ratio in polyoxometalates as a rapid screening method to follow synthetic procedure.

Chemometric and statistical analysis of polyoxometalate interaction with lanthanide(III) ions

Application of CAT (computer-assisted target factor analysis) for quality assessment and quality control in spectroscopy is demonstrated. As a working example, interaction of polyoxometalates (POM) with neodymium in aqueous solutions is followed by UV-Vis spectroscopy. CAT is combined with Monte Carlo and resampling techniques (i.e. threshold bootstrap methods) in order to capture the complete distribution of suitable interpretations of the systems under study. Decisions during the evaluation process are based on statistical criteria conditional on the empirical distributions obtained from CAT. Single component spectra of the Nd-POM solution species are extracted and species concentrations in the experimental samples are obtained together with their respective confidence limits.

Synthesis and Spectroscopic Studies of Chosen Heteropolytungstates and Their Ln(III) Complexes

The heteropolytungstates [(Na)P5W30O110]4− (I), [(Na)Sb9W21O86]18− (II) and [(Na)As4W40O140]27− (III) and the monovacant Keggin structure of the general formula [XW11−xMoxO39]n− (X-Si, P; n = 7 for P and 8 for Si) (IV) as well as their europium(III) complexes were studied. The structures of I–IV as well as the europium(III) encrypted [(Eu)P5W30O110]12− (VI), [(Eu)Sb9W21O86]16− (VII), [(Eu)As4W40O140]25− (VIII) and sandwiched [Eu(XW11−xMoxO39)2]n− (n =11 for P and n = 13 for Si) (V) complexes were synthesized and spectroscopically characterized. The complexes were studied using UV-Vis absorption and luminescence, as well as the laser-induced europium ion luminescence spectroscopy. Absorption spectra of Nd(III) were used to characterize the complexes formed. Excitation and emission spectra of Eu(III) were obtained for solid complexes and their solutions. The relative luminescence intensities of the Eu(III) ion, expressed as the ratio of the two strongest lines at 594 nm and 615 nm, η = I615/I594, which is sensitive to the environment of the primary coordination sphere about the Eu(III) ion, was calculated. In the case of the sandwiched [Eu(XW11−xMoxO39)2]n− complexes a linear dependence of the luminescence quantum yield of Eu(III) ion, φ, (calculated using [Ru(bpy)3]Cl2 as a standard) on the content of Mo (number of atoms, x) in the [Eu(XW11−xMoxO39)2]n− structure was observed.

Spectroscopic studies of Ln(III) complexes with polyoxometalates in solids, and aqueous and non-aqueous solutions

Chosen polyoxometalate (POM) anions and their lanthanide(III) complexes, LnPOM, have been synthesized and spectroscopically characterized in solid state, aqueous and non-aqueous solutions. POMs, such as Keggins, Dawsons and Andersons type, Na9EuW10O36, compositions that function as inorganic cryptands ([(Na)P5W30O110]14−-Preyssler anion, and [(Na)As4W40O140]27−), containing inorganic (Na

Electron Paramagnetic Resonance study of chosen gadolinium(III) sandwiched- and encapsulated-polyoxometalate complexes

Abstract The gadolinium(III) complexes with polyoxometalates were studied using X-band Electron Paramagnetic Resonance (EPR) spectroscopy. We selected the following sandwiched complexes: Gd(SiW 11 O 39 ) 2 13− [ I ], GdW 10 O 36 9− [ II ], Gd(P 2 W 17 O 61 ) 2 17− [ III ], and encrypted [GdSb 9 W 17 O 86 ] 16− [ IV ], [GdP 5 W 30 O 110 ] 12− [ V ]. The EPR spectra obtained for the compounds I – III and IV – V differ markedly from the U-spectrum characteristic for Gd(III) in glasses. The values of the zero-field splitting parameter D for both kind of complexes studied have been estimated. Taking into account the spin-hamiltonian calculations, the existence of Gd(III) ion in two different surroundings, in a strong crystal field of rhombic symmetry and in a weak crystal field, is observed. The differences observed between the case I – III and IV – V seems to be related to a various coordination of the Gd(III) ion and its hydration degree. Our study shows a relation between the presence of particular g -values of the spectral lines and the number of the inner-sphere water molecules as well as the type of the Gd(III) complex (sandwiched and/or encrypted) in solid.

Spectroscopic studies of the lanthanide(III) ions with pyridine carboxylic acid N-oxide ligands and in mixed ligand complexes

A series of Ln(III) complexes with pyridine carboxylic acid-N-oxides (L) Ln-L, and mixed ligand complexes of Ln-L plus bipyridine (bipy) or 1,10-phenanthroline (O-phen) (X) Ln-L-X have been studied. These complexes were characterized in solution using Nd(III) absorption in the spectral range of the 4I9/2 → 4G5/2 transition corresponding to the hypersensitive band, and in the solid state with the use of IR and Eu(III) luminescence spectroscopy. In solutions a series of Nd(III) complexes and mixed ligand complexes has been examined and the formation of binary LnL and LnL2 complexes and mixed ligand LnL2X complexes evidenced. Solid complexes of Eu(III) with nicotinic acid N-oxide and ternary with nicotinic acid N-oxide plus phen were studied with the use of Eu(III) luminescence lifetime measurements and IR spectroscopy, proving the formation of binary [Eu(nicN-oxide)3(H2O)2].2H2O and ternary [Eu(nicN-oxide)3phen].H2O complexes.

Photoluminescence and electrochemiluminescence studies of chosen rare earths systems

Abstract Eu(III) complexes with chosen Keggin polyoxomatalates, POM, containing organic counter cations (tetrabutylammonium, tetrabutylphosphonium, triphenylethylphosphonium), were synthesized, and their photophysical properties were studied. The synthesized complexes had the general formula of X n H 5- n [EuSiW 11 O 39 ], formulated based on the results of elemental and thermogravimetric analysis and FTIR spectroscopy. The photophysical properties of the obtained compounds were investigated using photoluminescence and electrochemiluminescence, ECL, methods in solutions and solids. The most intense luminescence of Eu(III) was observed for the complexes with tetrabutylammonium cations. After the addition of phenanthroline to the X n H 5- n [EuSiW 11 O 39 ] solutions, a large increase in the Eu(III) luminescence intensity and a lengthening of its luminescence lifetime were observed as a result of the formation of ternary complexes. Attempts to apply ECL as a method of light emission by generating species capable of forming excited states in Ln/POMs, i.e., Tb(III) and Eu(III) in the Na 9 EuW 10 O 36 and Na 9 TbW 10 O 36 complexes, were made. The influence of the POM complexes on the ECL was also tested using the Tb/EDDHA (EDDA=ethylenediamine di(o-hydroxyphenylacetic acid)) complex, which is effective in generating ECL.