Andrzej Szyczewski

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.

An EPR study of γ-irradiated single crystals of cholesta-4, 6-diene-3-one

Abstract Cholesta-4, 6-diene-3-one single crystals irradiated with γ-rays at room temperature have been investigated by electron spin resonance. EPR spectra at room temperature exhibit a characteristics triplet which splits into two doublets. The main triplet has been interpreted as being caused by the addition of a hydrogen atom to the 7-position of the molecule, leaving an unpaired electron in the 2p2 orbital of the carbon atoms in position 6 and 4. The hyperfine spectrum is generated by interaction of the unpaired electron with two equivalent α-protons in position 4 and 6 and with tow non-equivalent β-protons in position 7. The principal values of the hydrogen hyperfine tensors are determined together with the g tensor of this radical.

Spectral analysis in ultraweak emissions of chemi- and electrochemiluminescence systems

Investigation of ultraweak emissions in the processes of chemiluminescence, CL, and electrochemiluminesce, ECL, requires special techniques of their recording and spectral analysis. From among the hitherto proposed methods of detection of the emission spectra of these processes, that of the cut-off filter was most sensitive. The usefulness of this method in interpretation of the CL and ECL systems of the quantum yields in the range 1×10−9−1×10−11 containing ions and complexes of Eu(III), Tb(III) and Dy(III) was shown. Exceptional character of the emission bands of lanthanide ions, being a result of the f-f electron transitions and in particular their low FWHM, permitted the application of the cut-off filter method to their analysis. The results obtained for CL and ECL on the basis of analysis of ultraweak emission proved to be successful in analytical applications. The systems containing Eu(III) ions hydrated or complexed with organic ligands enabled inferring changes in the coordination sphere of the ions.

Radiation damage in androst-4-en-3,17-dione molecules: an ESR study of free radicals in single crystals

Abstract Electron spin resonance spectroscopy has been used to investigate γ-radiation damage of androst-4-en-3,17-dione molecules in single crystals. The spectra found are attributed to hydrogen abstraction radicals. It is possible to assign a definite structure to the specimen by analyzing the orientational variation of the spectra. The unpaired electron of the radical is delocalized in the 2 p z -orbitals of the C(6), C(4) and O(3) atoms giving rise to a hyperfine spectrum from interaction with two equivalent α-protons in positions 4 and 6 and with two non-equivalent β-protons attached to C(7). The theoretical splittings and the spin density distribution of the unpaired electron are calculated by the INDO method.

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.

EPR study of selected gadolinium complexes : β-diketonates and polycarboxylates

Abstract The gadolinium chelates with: acetylacetone—Gd(acac)3 · 3H2O, thenoyltrifluoroacetone—Gd(TTA)3 · 2H2O, benzoylacetone—Gd(BAC)3 · 2H2O, ethylenediaminetetraacetate Gd(EDTA) and diglycolate Gd(DGA)3 have been chosen for EPR study (X band). The EPR spectra of these complexes were obtained in the form of badly separated signals and thus were difficult to interpret. In order to improve the spectra resolution a computer analysis based on Fourier transform was applied. This analysis permitted a considerable increase in resolution of the spectra and revealed the fine structure of Gd3+ ion in the condensed phase.

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.

An ENDOR study of the radicals in a γ-irradiated single crystal of 17α,21-dihydroxyprogesterone

Abstract Single crystals of 17α,21-dihydroxyprogesterone were γ-irradiated at 295 K and studied using X-band ESR and ENDOR. Two types of radical were observed and a structure was assigned to the specimen by analysing the orientational variation of the spectra. The first radical is formed by abstraction of the hydrogen atom from the C(6) carbon while the unpaired electron is delocalized onto the system O(3) C(3) C(4) C(5) C(6). The second radical is formed by attachment of the hydrogen atom to the oxygen O(3) of the carbonyl group, and delocalization of the unpaired electron onto the atoms C(3), C(4) and C(5). The effect of substitution of hydroxyl groups on the hyperfine splitting tensor has been also analysed.

Internal Dynamics of Norethisterone by NMR, IINS and QC Methods

The low-temperature inelastic incoherent neutron scattering spectrum of norethisterone was compared with that calculated by the density functional theory method. The quantum chemical calculations permitted proposing the assignment of the vibrational modes. In particular, the dynamics of the methyl group substituted at C(13) of the steroid skeleton was analysed on the basis of the neutron scattering spectra and temperature dependence of the spin-lattice relaxation time (1H NMR).

Proton relaxation studies of 17α hydroxy- and 21 hydroxy-progesterones by1H NMR

Proton spin-lattice relaxation timesT1 in 17α hydroxy- and 21 hydroxy-progesterones have been performed in the temperature range from 100 to 400 K at the frequencies of 30 and 90 MHz. The dynamic processes involving the methyl group reorientation about the threefold symmetry axis of the C−C bond are separated, and their activation parameters are determined.