Absorption and magnetic circular dichroism spectra of Cs₂ZrBr₆: Os⁴⁺

The optical absorption and magnetic circular dichroism spectra of Re4+in the cubic hosts, Cs2ZrCl6, Cs2NaYCl6, and Cs2ZrBr6

“…Thus from known cases [18] one can estimate that t~g-+eg d-d transitions will be at least an order of magnitude less intense than the spectra in figures 2-7. The second point has recently been emphasized by Bird et al [19] and is clearly borne out by our earlier studies [4][5][6][7][8]. Again, in the present paper we find that the changes which occur in going from ReC16 ~-to ReB% 2-are explicable on a charge-transfer basis but are not in a d-d picture.…”

“…While some such transitions are likely present in this region, we believe our observed spectra (figures 2-7) are due entirely to ligand-to-metal charge-transfer transitions, except possibly for some of the very weak features. The arguments for this point of view have already been presented previously [4][5][6][7][8] and will not be repeated in detail here. The two main points are, first, the much lower intensity expected for the d-d transitions which are thus obscured by the observed chargetransfer spectra and, second, the behaviour of the bands as a function of ligand spin-orbit coupling constant.…”

“…The Os 4+ spectrum is more complex because many more states arise from a given charge-transfer excitation. However, it is clear that the spectrum can be cleanly divided into a low energy region (< 18 000 cm -1) of exclusively d-d transitions, and a high energy region ( > 18 000 cm -1) which is dominated by ligand-to-metal charge-transfer transitions [6][7][8]. Although many d-d transitions undoubtedly occur in the high energy region, they are expected to be substantially weaker than even the forbidden charge-transfer transitions, and there appears [6][7][8] to be no basis for assigning any important features of the observed spectra to d-d transitions despite previous assertions to the contrary [9].…”

“…However, it is clear that the spectrum can be cleanly divided into a low energy region (< 18 000 cm -1) of exclusively d-d transitions, and a high energy region ( > 18 000 cm -1) which is dominated by ligand-to-metal charge-transfer transitions [6][7][8]. Although many d-d transitions undoubtedly occur in the high energy region, they are expected to be substantially weaker than even the forbidden charge-transfer transitions, and there appears [6][7][8] to be no basis for assigning any important features of the observed spectra to d-d transitions despite previous assertions to the contrary [9]. The Os a+ charge-transfer spectra have been interpreted [6][7][8] on the basis of the Jorgensen j-j coupling model [10], and comparisons with Ir a+ spectra and especially comparisons between OsC162- [7] and OsBrn 2- [8] seem to provide convincing evidence for the soundness of such an interpretation.…”

“…spectra of Ir 4+ [1][2][3][4][5] and Os 4+ [6][7][8] in a variety of hosts at low temperature and as a function of temperature. Charge-transfer spectra are easier to interpret for Ir 4+ in view of its tag 5 octahedral ground-state configuration.…”