| Fe2+/Fe3+: Couple, an Ideal Redox for Topochemical Reactions Olivier Mentre1; 1UCCS, Villeneuve d'Ascq, France; PAPER: 315/Chemistry/Keynote (Oral) SCHEDULED: 14:25/Thu. 24 Oct. 2019/Aphrodite A (100/Gr. F) ABSTRACT: The possibility to modify inorganic oxides at moderate temperatures, under kinetic rather than thermodynamic control leads to metastable structural rearrangements with novel electronic partitions and original properties. In most cases, the abundant literature reports modifications of the anionic sub-array dealing with anionic vacancies, interstitials or anionic exchanges. However, intercalation or morerare exsolution cases show exotic cationic modifications towards original intercalated/depleted phases. The Fe<sup>2+</sup>/Fe<sup>3+</sup> redox properties stand ideally for easy in-lab reactions. For instance, the controlled oxidation of the 2D-ising ferromagnetic BaFe<sup>2+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>2</sub> into Fe-depleted BaFe<sub>2</sub>/3+2-x(PO<sub>4</sub>)<sub>2</sub> (x<0.66) leads to a series of intermediate phases with full vacancy/Fe ordering and to nanometric Fe<sub>2</sub>)O<sub>3</sub>) [1]. On the opposite, playing redox chemistry in 2D-oxides such as the multiferroic, YbFe<sub>2.5</sub>+2O<sub>4</sub> and Yb<sub>2</sub>Fe<sub>2.66</sub>+3O<sub>7</sub>, the metal content is maintained but re-organized during reduction/oxidation very similarly to the hexagonal YMn<sup>3+</sup>O<sub>3</sub> system [2,3]. Generally, all transformed compounds require complex crystal-chemistry features with occurrence of supercells, modulated structures, and/or disordered intergrowths. The possibility to tune, in a controlled way, various pristine frameworks opens a wide field of investigation for tailor-made crystallographic architectures within the field of giant anion/cation-labile systems. References: [1] I.Blazquez Alcover. et al., Crystal Growth and Design, 15(2015) 4237-4247. [2] S. Nicoud et al., JACS, 139 (2017),17031-17043. [3] H. Kabbour et al., Inorg. Chem, 56(2017), 8547-8553. |
