Spectroscopy of structurally disordered hydrated iron fluoridotitanate in the regions of vibrational and electronic excitations

Gerasimova, Yu. V.; Aleksandrovsky, A. S.; Laptash, N. M.; Gerasimov, M. A.; Krylov, A. S.; et al./ Spectrochimica Acta Part A-molecular And Biomolecular Spectroscopy/ https://doi.org/10.1016/j.saa.2021.120244

Raman and optical absorption spectra of disordered hydrated iron fluoridotitanate (HITF) single crystal were studied. Temperature transformations of the Raman spectra indicate independent ordering processes of the [TiF6]2− and [Fe(H2O)6]2+ complexes below the structural phase transition. The absorption spectrum in the near-infrared and visible ranges includes transitions from the high spin ground state 5T2 of Fe2+ ion to the excited 5E state and a set of excited triplets. Analysis by Tanabe-Sugano method gives crystal field Dq = 490 cm−1 and Racah parameters B = 340 cm−1 and C = 1904 cm−1. Considerable decrease of B parameter as compared to the free ion value indicates a decrease of interelectron repulsion in the disordered neighborhood of Fe2+ ions.