J. Pietrzak

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.

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.

An ESR study of the stable radical in a γ-irradiated single crystal of 17α-dydroxy-progesterone

Abstract Electron spin resonance spectroscopy was used to investigate γ-radiation damage of 17α-hydroxy-progesterone molecules in a single crystal. Two types of radicals with different rates of recombination were observed and a definite structure was assigned 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 C(3) atoms, giving rise to a hyperfine spectrum by interaction with two equivalent α-protons in positions 4 and 6 and with two non-equivalent β-protons attached to C(7). The hyperfine coupling tensors are reported, together with the g tensor of the radical. The presence of additional intermolecular interactions caused by hydrogen bonding between O(3) and HO(17) of two molecules does not change the type of radical (which is the same as the stable radical in a γ-irradiated single crystal of progesterone) but does increase the hyperfine coupling anisotropy.

EPR study of free-radical structure and conformation in pyridoxine hydrochloride single crystal

Abstract Numerical analysis of experimental EPR spectra of γ-irradiated single crystals of pyridoxine hydrochloride (vitamin B 6 ) allowed determination of the structure of the radical formed. Six hyperfine couplings were distinguished. The geometrical model of the radical was found to be in good agreement with the geometry expected from the crystal structure. Semi-empirical INDO and CNDO calculations were performed.

EPR and electron nuclear double beam resonance of free radicals formed in γ-irradiated single crystals of sulphamethoxazole

Abstract The hyperfine structure of free radicals generated by γ-irradiation of sulphamethoxazole single crystals has been observed. The principal values and direction cosines of the g and hyperfine tensors were determined from EPR spectral analysis. The free radicals were found to be produced by abstraction of a hydrogen atom from the methyl group of the sulphamethoxazole molecule, and the delocalization of an unpaired electron was found to be restricted only to the isoxazole ring of this molecule.

Magnetic Susceptibility in a Low-Dimensional Synthetic Metal TCPF-P

The principal components of the magnetic susceptibility tensor and magnetic anisotropy of the low-dimensional organoiron complex TCPF-P single crystal were measured from 1.9 to 290 K. The analysis of its magnetic properties is based on its molecular structure and magnetic susceptibility. The Neel and Weiss temperatures were found to be essentially dependent on the orientation of the single crystal. The latter is assumed to be the result of coexistence of the interaction among the localised electrons and conduction electrons under the preserved spatial separateness.

Single crystal ESR study of bis(N-benzylpyridoxaldiminato) copper(II)

Abstract Single crystals of bis(N-benzylpyridozaldiminato) Cu(II) were studied by ESR in three perpendicula planes at 300 K and 9.4 GHz. Only one exchange—narrowed line was observed for the two magnetically inequivalent copper ions in the monoclinic symmetry lattice with space group P2 1 a and elementary cell parameters a = 9.561(9), b = 16.605(8), c = 17.561(2) A and β = 104(1°) . Each ligand is bidentate via the phenolic oxygen and the imino nitrogen atoms, leading to tetrahedrally distorted square planar environment around the copper atom. The ESR linewidth remained Lorentzian for all orientations considered. The components of the g xx = 2.043(4), g yy = 2.064(4), g zz = 2.259(4) . The linewidth anisotropy was analyzed in terms of dipole-dipole interactions, magnetic inequivalence of molecules and hyperfine interactions.

Polymerization of 1,3,5‐trithiane in the solid state initiated by UV‐irradiation. II. Investigation of the initiation process

The influence of the irradiation and polymerization atmosphere on polymer yield was observed. It was shown that in the initiation process oxygen presence is necessary. ESR studies of UV-and γ-irradiated 1,3,5-trithiane were done. The influence of the irradiation atmosphere on generated radicals and the influence of UV-action on radicals formed by γ-irradiation was also investigated. The possible initiation mechanism of cationic polymerization of 1,3,5-trithiane is discussed. A comparison of the 1,3,5-trithiane is polymerizations initiated chemically and by UV- or γ-irradiation is also given.