Kenneth T. McGregor

Single crystal EPR studies of the Cu2Cl84− ions in the complex tris(ethylenediamine)cobalt(III) di‐μ‐chloro‐bis[trichlorocuprate(II)] dichloride dihydrate

Single crystal electron paramagnetic resonance studies have been carried out on the exchange‐coupled pairs of copper(II) ions contained in the title compound. EPR measurements were made at X‐, K‐, and Q‐band microwave frequencies at selected temperatures in the range 2–77 °K. The angular variation of the Q‐band spectra taken at 4.2 and 77 °K were used to diagnonalize the appropriate spin Hamiltonian. The Zeeman interaction and the zero‐field interactions were found to have different principal coordinate systems. Although the dipolar interaction dominates the zero field splitting, a small but finite contribution from the anisotropic exchange interaction is present. The temperature dependence of the spectrum indicates that an interdimer exchange interaction is also present. The interdimer interaction causes the fine structure of the triplet excitations to be averaged into a single resonance line at 77 °K. The temperature of coalescence of the fine structure is 17 °K. Although the fine structure is resolved ...

Magnetic susceptibility and electron paramagnetic resonance studies on bis(2,2′-bipyridyl)thioureacopper(II) perchlorate

Single-crystal, polycrystalline, and frozen solution e.p.r. spectra of bis(2,2′-bipyridyl)thioureacopper(II) perchlorate are reported. The low temperature (1·6–67·7 K) magnetic susceptibility of a polycrystalline sample of the complex is also reported. The intermolecular exchange interaction was found to be extremely small (ca. –0·02 cm–1) which allowed the observation of magnetically non-equivalent sites. The molecular parameters determined (gz= 2·020 ± 0·005, gx= 2·168 ± 0·005, and gy=2·141 ± 0·005 and K ≃ 0·64) indicate a predominantly d3z2–r2 ground state but with significant mixing of excited states and with substantial delocalization of the unpaired spin density.

The magnetic properties of the dimeric vanadium(III) complexes tetra-μ-carboxylatobis[π-cyclopentadienylvanadium(III)] for R = methyl, phenyl and furanyl groups

Abstract Magnetic susceptibilities have been measured in the temperature range 113–370 K for the dimeric compounds tetra-μ-carboxylatobis[π-cylopentadienylvanadium(III)] for R = methyl, phenyl and furanyl groups. The S = 1 vanadium(III) ions are exchange coupled with coupling constants of −227, −197, and −185 cm−1, respectively. The corresponding biquadratic coupling constants are 17, 34, and 36.5 cm−1, respectively. The EPR spectra also reflect the exchange coupling.

Simulation of the Electron Paramagnetic Resonance Spectrum of the Triplet Ground State Dimer Di-μ-(Pyridine N-Oxide)Bis[Bisnitrato(Pyridine N-Oxide)Copper(II)]

Abstract The EPR spectrum of the triplet ground state dimer di-μ-(pyridine N-oxide)bis[bisnitrato(pyridine N-oxide)copper(II)] has been reported recently1. Of the very few triplet ground state copper(II) dimers with resolved metal hyperfine structure2,3, the EPR spectrum of this complex is most complete. Previously, the analysis of the spectra of triplet ground state copper(II) complexes, in order to extract magnetic parameters, has been made using the equations reported by Wasserman et al.4 The best magnetic parameters should be obtained from a simulation of the experimental spectrum. We wish to report here the computer simulation of the EPR spectrum of a powdered sample of [Cu(II) (PYO)2 (NO3)2]2.

Simulation of the Half-Field Resonance of the EPR Spectrum of Tetra-μ-benzoatobis [π-cyclopentadienylvanadium(III)]

Abstract The preparation of tetra-μ-benzoatobis[π-cyclopentadienylvanadium-(III)] was recently reported along with other complexes belonging to the general class [π-C5H5V(OOCR)2]. Based on the reduced magnetic moment of the complex and its mass spectrum, a dimeric structure was postulated. The dimeric structure is strongly supported by recent x-ray investigations2,3 of very similar carboxylate systems. The epr spectrum of the complex was recently reported;4 however, owing to obscuring features (vida post) of the spectrum, the pertinent Spin Hamiltonian parameters were not determined. We report here the simulation of a portion of the epr spectrum from which the magnetic parameters were obtained.

The EPR Spectrum of Di-μ-(pyridine N-oxide) bis [bisnitrato(pyridine N-oxide)copper(II)] in the Corresponding Zinc(II) Crystal

Abstract It has been shown1–3 that the exchange interactions in the dimeric4 complex di-μ-(pyridine N-oxide) bis [bisnitrato(pyridine N-oxide) copper(II)], [Cu(pyO)2]2 lead to a triplet ground state for the copper(II) pairs. The triplet state epr spectrum has been observed1,3,5,6 for a powdered sample of the complex coprecipitated with the corresponding zinc(II) complex, and the computer simulation of this spectrum has been carried out by two different groups3,5,6. As is often the case when dealing with spectra of powdered samples, there exist ambiguities with the spectrum of [Cu(pyO)2-(NO3)2]2 since all of the resonances were not observed, and consequently, the interpretation and values of the parameters remain in question. It was felt that examination of the epr spectra of single crystal samples should permit a rigorous analysis of this problem.

Chloro-bridged triplet ground-state copper(II) dimer

Magnetic susceptibility measurements on the dimer di-µ-chloro-bis[chloro(dimethylglyoxime)copper(II)] indicate a triplet ground state with a singlet–triplet splitting of 6·3 cm–1.