Gerald F. Kokoszka

Electron Paramagnetic Resonance Spectra of Zinc‐Doped Copper Acetate Monohydrate

The electron paramagnetic resonance of the copper—zinc pairs in zinc‐doped copper acetate monohydrate has been observed at 77°K by using an X‐band EPR spectrometer. Single crystals containing less than 1% zinc ions were grown from a slightly acidic aqueous solution containing about 75% copper acetate and 25% zinc acetate.The experimental results could be fit to the spin Hamiltonian: H=gzβHzSz+gxβHxSx+gyβHySy+AzSzIz+AxSxIx+AySyIy. The values Az=0.0147±0.006 cm−1, Ax<0.0018 cm−1, and Ay<0.0023 cm−1 were measured for the doublet‐state cupric ions. The g values were found to be: gz=2.344±0.005, gx=2.052±0.007, and gy=2.082±0.007.These results are consistent with the model proposed by Slichter, in which he has shown that the components of the hyperfine tensor should be twice as large for a doublet species as compared to the corresponding triplet species when the exchange integral J is much larger than the components of the hyperfine tensor.Since the microsymmetry at the cupric ion site is no higher than C2v, t...

Magnetic and Optical Spectra of Two Dimeric Copper Chloride Pyridine‐N‐Oxide Complexes

The electron paramagnetic resonance spectra and the optical absorption spectra of dichlorobispyridine‐N‐oxide copper(II) [(C5H5NO)2CuCl3] and dichloromonoaquopyridine‐N‐oxide copper(II) [C5H5NOCuCl·H2O] have been observed at room temperature. The magnetic resonance studies were carried out at both X‐band and K‐band frequencies. The observed spectra could be fit to an S=1 spin Hamiltonian. The direction of the maximum zero‐field splitting did not correspond to the principal z axis of the g tensor. For (C5H5NO)2CuCl2 the angle between these two directions was about 23° and for C5H5NOCuCl·H2O the angle was about 27°. A study of the intensity of the EPR signal as a function of temperature indicated that the triplet state was about 550 cm−1 above the single ground state for (C5H5NO)2CuCl2 and about 885 cm−1 above the singlet state for the other complex. The optical spectra of both examples revealed two bands in the 8000‐to−15 000‐cm−1 region and a higher energy transition at about 22 000 cm−1.

Magnetic properties of some binuclear copper(II) complexes

Abstract The magnetic susceptibility of three binuclear copper compounds, dichloromonoaquo-(pyridine-N-oxide)copper(II), [Cu(pno)Cl 2 ], dichlorobis(pyridine-N-oxide)copper(II), [Cu(pno) 2 Cl 2 ], and copper monochloroacetate 2·5 hydrate, [Cu(ClAc) 2 ], has been measured as a function of temperature. The exchange integral, J , has been determined to be 943, 770 and 292 cm −1 for Cu(pno)Cl 2 , Cu(pno) 2 Cl 2 and Cu(ClAc) 2 , respectively. These values are compared to the J values determined by electron paramagnetic resonance on the same three compounds. A brief discussion of the accuracy of these values is presented. In addition, for two of the compounds, Cu(ClAc) 2 and Cu(pno)Cl 2 , a better fit of the data was possible by assuming the presence of a small amount of monomeric complex in the samples. This was verified by additional EPR measurements.

Electron Paramagnetic Resonance Spectra of Two Zinc‐Doped and Nickel‐Doped Copper Chloride Pyridine‐N‐Oxide Complexes

The electron paramagnetic resonance spectra of zinc‐doped dichlorobispyridine‐N‐oxide copper(II) [(C5H5NO)2Cu(Zn)Cl2] and zinc‐doped dichloromonoaquopyridine‐N‐oxide copper(II) [C5H5NOCu(Zn)Cl2·H2O] have been observed at liquid‐nitrogen temperature. The data could be fit to the usual S=½ spin Hamiltonian. The g values obtained in this study for the copper—zinc pairs agree with the g values obtained for the copper—copper pairs in the pure material to within experimental uncertainty. Copper hyperfine splittings and chlorine superhyperfine splittings were also observed. The magnetic parameters for (C5H5NO)2Cu(Zn)Cl2 are gz=2.323, gx=2.056, gy=2.080, Az=129×10−4 cm−1, Ax=Ay<10×10−4 cm−1, A′=25×10−4 cm−1, and B′=7×10−4 cm−1, while for C5H5NOCu(Zn)Cl2·H2O gz=2.306, gx=2.056, gy=2.083, Az=139×10−4 cm−1, and Ax=Ay<10×10−4 cm−1 obtain. An analysis of the data with a simple LCAO MO approach suggests relatively strong metal—ligand bonds.The data obtained from the study of nickel‐doped (C5H5NO)2CuCl2 could be fit to ...

Magnetic and Optical Spectra of Copper Monochloroacetate 2.5 Hydrate

The electron paramagnetic resonance spectra of copper monochloroacetate 2.5 hydrate, Cu(O2CCH2Cl)2·2.5H2O, [Cu(ClAc)2], and zinc‐doped Cu(ClAc)2 have been observed at both K‐band and X‐band frequencies. The EPR spectrum of the pure material was characteristic of a species with a spin of one, while the spectrum from zinc‐doped Cu(ClAc)2 revealed an additional spectrum due to a species with a spin of ½. The g values for both the copper—copper pairs and the copper—zinc pairs were identical with values gz=2.38 and gx=gy=2.07. The hyperfine coupling constant for the copper—copper pairs was about 84×10−4 cm−1, while in the copper—zinc spectrum it was about 158×10−4 cm−1. These results are consistent with the assumption of a weakly coupled interaction. The temperature variation of the doubly integrated intensity of the derivative spectrum indicated that the triplet state lies some 230 cm−1 above the singlet ground state. In the optical absorption spectrum of Cu(ClAc)2 three bands were observed. A very intense ba...

Dynamic Jahn–Teller Effects and Magnetic Anisotropies in Aqueous Solutions and Water–Ethanol Glasses of Copper(II) Solvates and Complexes with 2,2′‐Dipyridine

Dynamic Jahn–Teller effects have been recognized previously in solids which contain copper(II) ions in octahedral environments. In solutions, dynamic Jahn–Teller effects have now been observed in the EPR spectrum of the tris(2,2′‐dipyridine) copper(II) complex. This is shown by the small temperature coefficient of the apparent tumbling correlation time, τc, which is associated with anisotropy contributions to the EPR linewidth and by the insensitivity of τc to variations of the solvent viscosity. In partially substituted complexes, such as the tetraaquo (2,2′‐dipyridine) copper(II) species which has also been studied here, the dynamic Jahn–Teller effects are inhibited due to the inhomogeneous nature of the first coordination sphere. The possible importance of dynamic Jahn–Teller effects in homogeneous solvates of copper(II) is discussed. Evidence is presented to show that addition of ethanol to aqueous solutions of copper(II) nitrate results in the formation of inhomogeneous species.