Electron exchange for hydrated ions in the α-NiSO 4 · 6H 20 lattice—Electron paramagnetic resonance study of transition-metal ions in ZnSeO 4 · 6H 2O

Abstract

The magnetothermodynamic measurements of Giauque et al. showed that the Ni 2+ in α-NiSO 4 · 6H 2O could be fit very well by an axial spin Hamiltonian. We have studied the EPR of Ni 2+, Co 2− and Cue+ in both this lattice and in the isostructural lattices of NiSeO 4 · 6H 2O and ZnSeO 4 · 6H 2O. In both of the nickel lattices exchange effects are very important, but the diamagnetic zinc lattice can be used as a reference, and this paper reports the EPR of these ions in ZnSeO 4 · 6H 2O. The axial spin Hamiltoniar is a result of the hydrogen bonding of the M(H 2O) 6 2+ complex. Two axial H 2O grou ps have three hydrogen bonds vs only two for the other four waters. This results in a tetragonal crystal field with decreased negative charge along the fourfold axis, and we find that the spin-Hamiltonian axis is very nearly along the axis formed by the unique waters. For Ni(H 2O) 6 2+ we obtain g ‖ = 2.219, g ⊥ = 2.238 with D = +4.20 cm −. For Co(H 2O)) 6 2+ and Cu(H 2O) 6 2+ we obtain g ‖ = 5.975, g ⊥ = 3.45, A ‖ = 77.0 gauss, A ⊥ = 20 gauss and g ‖ = 2.42 95, g ⊥ = 2.0965, A ‖ = 115.6 gauss, A ⊥ = 9.5 gauss, respectively. Some variationo. in the orientation of the principal axes were also determined for the three ion;. A short discussion is also giN en for the effects of electron exchange on these ions in α-NiSO 4 · 6H 2O.