Electron paramagnetic resonance study of manganese (II) in near tetrahedral dihalogenobis(triphenylphosphine oxide)zinc

Abstract

E.p.r. single crystal studies of manganese-doped ZnCl₂(OPPh₃)₂, supported by crystal space group analysis, show that the needle direction of the crystal is also a principal axis of D and g. However there are two sets of equivalent manganese ions in the unit cell and their principal axes are related by reflection in the planes ac and bc which contain the needle direction; the structure appears to be identical with that of CuCl₂(OPPh₃)₂. The zero-field splitting terms are of the same order as g β B so exact computer diagonalisation of the energy matrix and least squares fitting of the experimental data were used to determine g values and second and fourth order terms in the spin operators. Forbidden lines (ΔM_I=± 1, ± 2) were only observed when the field was not along a principal axis; their intensities, which were at some orientations greater than the normally allowed transitions, and their separations, were reproduced very well by computation. From the mean hyperfine spacings of different electron spin transitions, D was shown to be positive while temperature variation showed ΔD/ΔT to be more negative than for Mn²⁺ in the ferroelectric LiNbO₃. The single crystal data have permitted an accurate assignment of the powder spectrum, reported earlier, and its variation with temperature. Preliminary studies on a single crystal of manganese-doped ZnI₂(OPPh₃)₂ confirm the very high value of D of about 1 cm^–1 reported earlier from a powder study.