Powder ESR Spectra Research Articles

The coordination chemistry of 2-imidazolidinone

A number of complexes having the general formula M(EU) n(anion) 2 is described, in which M 2+ = Mg, Mn, Co, Ni, Cu, Zn and Cd, Eu stands for 2-imidaziolidinone (also called, N, N′-ethyleneurea), n varies from 1 to 7, and the anions are ClO 4 −, BF 4 −,NO 3 −, NCS −, Br − and Cl −. The compounds have been analysed and characterized by chemical analyses, infrared spectra, ligand-field spectra, X-ray powder diagrams and ESR spectra. In compounds with 6 or 7 ligands per metal ion, the metal ions are found to be octahedrally coordinated by six EU ligands. A seventh ligand is sometimes held in the crystal lattice. In compounds with less than six ligands per metal ion, the geometry around the metal ion is tetrahedral or distorted octahedral, depending upon the particular combination of M and anion. The position of the CO stretching frequency in the infrared, which is unusually taken as a measure for the coordination site of amides, appears to be not indicative for the present ligand. The origin seems to be intense mixing of the amide vibrations, making that both the cation and the anion (coordinating respectively with the CO and NH groups) influence these vibrations in opposite directions. All spectral data agree with oxygen coordinated imidazolidinone ligands, this is usually observed with this type of ligands in combination with first-row transition metal ions, although bridging ligands with one CO and NH as coordinating site may also occur.

ESR study of a bromine-containing radical in γ-irradiated bromomalonamide

Both powder and single-crystal ESR spectra of two paramagnetic species formed by γ-irradiation of bromomalonamide at 77°K have been obtained. One radical shows a large bromine hyperfine interaction plus a small proton interaction and the g, A(81Br) and e2qQ(81Br) tensors have been determined from an analysis of the spectra of the deuterated form. The data have been interpreted as favoring the structure · CHBrCONH2 for this species. The second fragment has been identified as CONH2, but ESR parameters are not reported since it has been studied previously. Neither species is stable at room temperature in the host crystal.

An ESR study of the · CHICONH 2 radical in γ-irradiated single crystals of iodoacetamide

Powder and single-crystal ESR spectra of iodoacetamide, γ-irradiated and observed at 77 K, have been analyzed. Hyperfine interaction with one iodine and one hydrogen nucleus is observed and the A( 127I), A(H), g, and e 2qQ( 127 I) tensors have been found. These data indicate that the radical species is the π-electron radical ·CHICONH 2, and are consistent with a planar or nearly planar structure. The g and A( 127 I ) tensors are axial, or nearly so. The odd-electron spin densities in the iodine 5 s and 5 p orbitals are larger than found for the halogens in the analogous fluoroand chloro-radicals but are comparable with the values found for bromine in ·CHBrCONH 2.

Jahn—teller distortions in copper(II) complexes as determined from ESR powder spectra

Cations Cu(ligand) 2+ 6 doped in lattices of non-cubic Zn(ligand) 6(anion) 2 are shown to have ESR powder spectra, corresponding with two types of cations, distorted octahedral and regular octahedral. Upon lowering of the temperature the number of distorted molecules increases. Despite of the non-cubic symmetry the results are essentially similar to single crystal observations and investigations on cubic lattices.

On the powder ESR and ENDOR spectra of flavoprotein radicals

The flavoprotein radicals exhibit so-called powder ESR spectra, which are mainly characterized by the anisotropic hyperfine tensors of the two strongly coupled nitrogens. Spectra simulations have been attempted. The powder electron-nuclear double resonance (ENDOR) spectra mainly consist of the signals due to the CH 2(8) group and the matrix protons. The degree of protonation of the radicals is inferable from the hyperfine coupling to this methyl group. The principal values for the hyperfine interaction with CH 3(8) could be studied by taking advantage of the anisotropy of the powder ESR spectrum. The results suggest a planar configuration of the neutral and anionic radicals within flavoproteins.

The Powder ESR Spectra of Some Bis(amino acidato)copper(II) Complexes

Abstract Copper(II) complexes with some natural amino acids were prepared, and their powder ESR spectra were measured. The pattern types of the ESR spectra of these Cu(II) complexes with amino acids were classified into four types, and by the pattern type, the cis- or trans-isomer was estimated.

An ESR Study of Some Substituted Pyridine N-Oxide Copper(II) Complexes

Abstract The ESR (methanol solution, frozen solution, powder, and single crystal) spectra of [CuL4](ClO4)2, where L=pyridine N-oxide, α-picoline N-oxide, β-picoline N-oxide, γ-picoline N-oxide, and 2,6-lutidine N-oxide, and of [CuL6](ClO4)2, where L=pyridine N-oxide and γ-picoline N-oxide, have been obtained. The preparation of hexa(γ-picoline N-oxide) copper(II) perchlorate is reported. The solution and frozen solution spectra indicate a very similar bonding in all the complexes, with moderately ionic metal-oxygen. The powder spectra reveal all the tetrakis complexes to be axially symmetric; though tetra(γ-picoline N-oxide) copper(II) perchlorate shows a reversal of the usual order of the g-values. This is explained in terms of the packing interactions within the crystal structure, rather than metal-ligand interaction. All the single crystal spectra are characteristic of axially symmetric complexes. Hexa(pyridine N-oxide)copper(II) perchlorate gives an isotropic ESR spectrum, but this does not seem to be due to exchange interaction. Hexa(γ-picoline N-oxide)copper(II) perchlorate gives an axial ESR spectrum with a considerable tetragonal misalignment.

Zero-Phonon Transition and Fine Structure in the Phosphorescence of Fe3+ Ions in Ordered and Disordered LiAl5O8

Phosphorescence and excitation spectra have been measured in Fe3+-doped ordered and disordered LiAl5O8. A good fit with the Tanabe-Sugano diagram for a high spin d5 configuration with B=644 cm−1 and C=2960 cm−1 has been obtained. From the calculated 10 Dq value of 8000 cm−1 and a comparison with the excitation spectra of Fe3+ in β-NaAlO2 it has been shown that the spectra are due to Fe3+ ions in tetrahedral interstices. A sharp zero-phonon transition has been observed in the low-temperature phosphorescence and excitation spectra of the ordered phase of LiAl5O8 and its occurrence was found to be correlated with an anomalously small Stokes shift of 500 cm−1. X-ray powder diffraction, phosphorescence, and ESR spectra show that there exist only two phases of LiAl5O8, an ordered and a disordered phase. Evidence is given that the previously postulated metastable phase is a phase with incomplete ordering.

Electron Resonance Powder Spectra for Systems with S > 12

A qualitative interpretation, ignoring nuclear hyperfine effects, of the line shapes and positions of all the lines occurring in the ESR powder spectra for S = 32, 52 systems with rhombic environments is presented. The formulation of the problem assumes the zero-field tensor is dominant in determining the angular dependence of oriented crystal spectra. In favorable cases, g factors and zero-field splitting parameters can be determined, and results from powder spectra are compared with spin-Hamiltonian parameters obtained from a single crystal study of Cr3+: (NH4)2[In(H2O)Cl5].

ESR Study of VOF53− Ion

Spin-Hamiltonian parameters for the VOF53− ion were determined from solution, frozen glass, powder, and single-crystal ESR spectra. The most important finding is the presence of superhyperfine splittings due to the equatorial and axial fluorine ligands; the strongest interaction is found to result from the in-plane π bonding between the 3dxy orbital of vanadium and the 2py orbitals of fluorine. Bonding in the complex ion has been discussed in terms of LCAO MO theory.

ESR and Optical Spectrum of Potassium Perchromate

The ESR powder spectra of both pure K3CrO8 and of K3NbO8, containing small amounts of K3CrO8, have been obtained. The spectra have yielded the values: g∥=1.9434, g‖=1.9848, for the two spin Hamiltonian parameters of chromium in the +5 oxidation state. It has been shown that the g factors can only be explained by assuming the ground state to be B1(dxy). Further, the optical spectrum of K3CrO8 in 30% H2O2 has been obtained and the single observed band at 20 000 cm—1, has been assigned to the B1→E transition. Both the ESR and the optical spectra indicate a strong degree of covalent character in the bond between the chromium atom and the peroxide ions.