A spectroscopic study of Eu(III)/Eu(II) and Sm(III)/Sm(II) solutions in acetonitrile obtained by controlled-potential reduction

✍ Scribed by J.M. Dyke; N.S. Hush

• Publisher: Elsevier Science
• Year: 1972
• Weight: 556 KB
• Volume: 36
• Category: Article
• ISSN: 0022-0728
• DOI: 10.1016/s0022-0728(72)80256-0

✦ Synopsis

Introduction

Cokal and Wise 1, in interpreting their polarographic and coulometric studies on a number of rare earth ions in acetonitrile 2'3 suggested that successive appearance and disappearance of colours in solutions containing a rare earth in both its divalent and trivalent oxidation states which they had reported may be associated with mixedvalence complex formation. As optical intervalence transfer bands 4'5 have not been recorded for rare earth complexes, it was decided to investigate this suggestion in detail.

Three lanthanides, samarium, europium and ytterbium, were studied by Cokal and Wise 1. They report for europium that on reduction of europium(III) to europium(II) in acetonitrile a yellow-green colouration was produced, the intensity of which was at least approximately proportional to the europium(II) present. Ytterbium(III) and samarium(III) both showed colours on reduction (brilliant yellow and dark brown, respectively), the intensity of which reached a maximum when approximately one-half of the trivalent rare earth ion had been reduced, and decreased as the reduction to the dipositive state was completed.

In order to be able to identify any possible intervalence interaction absorption it is necessary to know the optical spectra of the trivalent lanthanide and the divalent lanthanide under conditions which are as close as possible to the experimental conditions of ref. 1. Because of the weak interaction of theforbitals with the environment and the sharp and fairly weak transitions, identification of the optical spectrum of a trivalent lanthanide is relatively straightforward 6. Divalent lanthanide spectra, however, are more difficult to interpret 6. The intense, broad absorption bands observed for divalent samarium and europium can be attributed to excitations of the type f"~f"-ld. In these ions, although the 4forbitals are relatively unaffected by the crystal field, the 5d orbitals will be subject to a greater environmental influence and, as a result, the positions and number of bands observed for samarium(II) and europium(II) will be expected to depend more markedly on the nature and geometrical arrangement of the co-ordinating ligands in the inner co-ordination shell.