An optical investigation into the 3d¹and 3d²transition-metal halides and oxyhalides, compounds near to delocalisation

Electronic structure of the spin-12quantum magnet TiOCl

“…With this alignment the relative separation between Ti 3d and the ligand p states still appears ≈ 0.5 eV too small. The value of 2 eV for the correlation gap as determined from optical spectroscopy 23,24 is in reasonable agreement with our photoemission data and the LDA+U calculations (not seen here, as the figure displays only the occupied DOS).…”

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

“…On the contrary, the spectrum of the catalyst differs from that of TiCl3 in the visible range, where the absorption bands are less intense and broader. In this respect, it should be noticed that for TiCl3 the assignment of the absorption bands in the 12500-14000 cm -1 region (Jahn-Teller split d-d transitions of Ti 3+ sites in a distorted 6-fold geometry) and higher than 30000 cm -1 (fully allowed charge transfer p-d transitions) is firmly established; [30,40,41] whereas the nature of the couple of bands at around 19000 and 27000 cm -1 , having an intensity intermediate between that of localized d-d transitions and that of charge-transfer transitions, was a matter of discussion in the specialized literature. Absorption bands in this energy regions are characteristic of many 3d 1 and 3d 2 transition metal-halides, and often overlap to produce relatively unstructured absorption responsible for a prevalence of black materials.…”

“…The most common interpretation is that they are due to inter-site hopping transitions of the type 2(3d 1 ) → 3d 0 +3d 2 , involving couples of Ti sites bridged by chlorine ligands. [40,41] The much lower intensity of these bands in the UV-Vis spectrum of the catalyst might be an indication that they are mainly due to localized (intra-site) more than inter-site d-d transitions. This implies that, although bridged by chlorine ligands (as revealed by the charge-transfer band higher than 30000 cm -1 ), the reduced Ti sites in the catalyst do not "communicate" each others.…”

Symmetry disquisition on theTiOXphase diagram(X=Br,Cl)Fausti1, Lummen2, Angelescu3 et al. 2007Phys. Rev. B274271View full textAdd to dashboardCite

“…3,4 The attention originally devoted to the layered quasi-two-dimensional 3d 1 antiferromagnets arose from considering them as the electron analog to the high-T c cuprates. 5 Only recently TiOX emerged in a totally new light, namely, as a one-dimensional antiferromagnet and as the second example of an inorganic spin-Peierls compound ͑the first being CuGeO 3 ͒. 6,7 The TiO bilayers constituting the TiOX lattice are candidates for various exotic electronic configurations, such as orbital ordered, 3 spin-Peierls, 6 and resonating-valence-bond states.…”