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1. Enhanced Fe-Centered Redox Flexibility in Fe–Ti Heterobimetallic Complexes

   https://doi.org/10.1021/acs.inorgchem.9b00442  

   Moore, James T.; Chatterjee, Sudipta; Tarrago, Maxime; Clouston, Laura J.; Sproules, Stephen; Bill, Eckhard; Bernales, Varinia; Gagliardi, Laura; Ye, Shengfa; Lancaster, Kyle M.; et al (April 2019, Inorganic Chemistry)
2. Fe-Ti vs. Fe-Fe charge transfers: A comprehensive review and its applications in minerals and glasses

   https://doi.org/10.2138/am-2025-9835  

   Vigier, Maxence; Evans, Helen; Rossman, George R; Jobic, Stéphane; Fritsch, Emmanuel (August 2025, American Mineralogist)

   Tomascak, P; Nestola, F (Ed.)

   Abstract Iron-titanium (Fe-Ti) charge transfer is mentioned in numerous articles as the source of the coloration of many natural minerals and some man-made materials, but no global review of this phenomenon has been provided so far. Iron and titanium are ubiquitous in nature and are often found in the same material as Fe2+ and Fe3+, and Ti4+ (more rarely Ti3+). When Fe and Ti ions are in close geometric proximity in an oxide or (alumino)silicate structure, charge transfer can occur between the two ions, even though their concentration might be below 100 ppm. This results in a variety of absorption features that contributes to the color of minerals. Adebate remains on the exact nature of Fe/Ti electronic transition, i.e. Fe2+ + Ti4+ → Fe3+ + Ti3+ or the reverse, but solving this issue is not within the scope of the present work. Ascertaining a metal-metal charge transfer is often not straightforward. This review compiles existing knowledge on Fe-Ti charge transfer in both crystalline and amorphous materials and identifies several key characteristics in more than 40 different materials. A charge transfer is associated with broad, intense, optical absorption bands that decrease in intensity at elevated temperatures. It is also strongly pleochroic in non-isotropic materials. Until now, Fe-Ti charge transfer transitions have been primarily described in the 2.25 to 3.1 eV range, corresponding to yellow to orange to brown colors, with notable exceptions such as blue sapphire or kyanite, and green andalusite. This review suggests that Fe-Ti charge transfer can occur across the entire visible spectrum, and the position of the absorption band correlates with the Fe-Ti nteratomic distance. This correlation highlights the presence of multiple crystallographic sites for both Fe and Ti in many oxides, leading to multiple Fe-Ti bands within these materials (e.g. sapphire, ilmenite, pseudobrookite). Finally, the use of metal-metal distances is suggested to differentiate this heteronuclear Fe-Ti charge transfer from the common homonuclear charge transfer Fe2+-Fe3+. 

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3. Revelation of Fe(V)/Fe(IV) Involvement in the Fe(VI)–ABTS System: Kinetic Modeling and Product Analysis

   https://doi.org/10.1021/acs.est.0c07792  

   Luo, Cong; Sadhasivan, Manasa; Kim, Juhee; Sharma, Virender K.; Huang, Ching-Hua (March 2021, Environmental Science & Technology)

   null (Ed.)
4. Synthetic Metallodithiolato Ligands as Pendant Bases in [Fe ^I Fe ^I ], [Fe ^I [Fe(NO)] ^II ], and [(μ-H)Fe ^II Fe ^II ] Complexes

   https://doi.org/10.1021/acs.inorgchem.9b03409  

   Kariyawasam Pathirana, Kavindu Dilshan; Ghosh, Pokhraj; Hsieh, Chung-H.; Elrod, Lindy Chase; Bhuvanesh, Nattamai; Darensbourg, Donald J.; Darensbourg, Marcetta Y. (March 2020, Inorganic Chemistry)

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5. Fine structure transitions with spectral features in Fe V and Fe VI

   https://doi.org/10.1016/j.adt.2024.101700  

   Nahar, Sultana N (February 2025, Atomic Data and Nuclear Data Tables)

   This work is part of the groundwork for iron opacity calculations for solar modeling. A B S T R A C T An extensive set of E1 transitions with spectral features for Fe V obtained using relativistic Breit–Pauli R-matrix (BPRM) method is presented. The results correspond to a larger amount of atomic data and of higher accuracy in comparison to the earlier R-matrix results. We report 1,712,655 transitions among 4300 fine structure levels with 𝑗 ≤ 10, 2𝑆 + 1 = 5, 3, 1, 𝐿 ≤ 10, of even and odd parities of n ≤ 10 and 𝑙 ≤ 9. The close coupling wavefunction expansion of Fe V includes ground and 18 excited levels of the core ion Fe VI. The theoretical spectroscopy of the fine structure levels for unique identifications was carried out using an algorithm based on quantum defect theory and angular algebra. The completeness of the calculated data sets is verified for all possible bound levels belonging to the relevant 𝐿𝑆 terms. The energies are in very good agreement with measured values within a few percent for most levels. Comparison of transition parameters and lifetimes also indicate general agreement with others. The present data processed for spectral features that show the detectability of Fe V is well within range of James Webb Space Telescope and other observatories. The present results for Fe VI, obtained from relativistic atomic structure calculations in Breit–Pauli approximation using code SUPERSTRUCTURE, include allowed E1 and forbidden E2, M1, E3, M2 transitions, 506,512 in total among 1021 energy levels, bound and continuum. Calculations show much larger number of bound levels of configurations of 3𝑠23𝑝53𝑑4 than those listed at NIST compilation table. The calculations included an optimized set of 9 configurations with orbitals going up to 4f. Comparison of energies, oscillator strengths, lifetimes with available values show good agreement although some large differences are also noted. In contrast to Fe V, the spectral features of Fe VI show three regions of strong lines in the soft-xray to ultraviolet wavelengths. 

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