Crystal polarised spectra of pentachloromanganese(III) ion

Abstract

Crystal polarised spectra of Mn^III ions doped in [Et₄N]₂InCl₅ and of [bipH₂]MnCl₅(bipH₂= bipyridinium ion) have been recorded. From band polarisations and energy shifts it is concluded that the d–d transitions occur at < 20 kk (1 kk = 1000 cm^–1) and that the absorption present at ca. 24 kk is due to a charge transfer transition. For the doped species an assignment in C_4v symmetry, with ⁵B₁ < ⁵A₁ < ⁵B₂ < ⁵E, is possible, whilst for [bipH₂]-MnCl₅ an assignment in C_2v symmetry seems to explain the polarisations better with ⁵A₂ < ⁵A₁(d_z²) < ⁵B₁ < ⁵B₂ < ⁵A₁(d_x²–y²), i.e. with x- and y-axes lying between the equatorial ligands and not along them. Simple point-charge crystal field calculations, with radial parameter ratios of 1–2, give satisfactory agreement with the observed spectra, while angular overlap calculations give much poorer agreement.