484 / 2019-03-18 15:08:44

Exploration of new oxidation states at high pressures

Oxidation state,Transition metal fluoride,High pressure,Structural prediction

全体主题 > High Pressure Physics and Materials Science

Oxidation state, a key concept in chemistry, reflects the chemical state of elements in compounds and their electron gain and loss during chemical reaction. Therefore, it is closely related to the physical and chemical properties of the compounds. Considering the diverse d electron configurations of transition metal elements, much effort has been made to explore their potential oxidation states. Here, we mainly focus on two elements (e.g. gold (Au) and iridium (Ir)). The strong relativistic effect makes Au have positive or negative oxidation states in its compounds, exhibiting intriguing physical and chemical properties. Till thus far, Ir shows the highest achieved oxidation state (+9) among all the known elements, through the full use of its nine valence electrons in chemical reaction.
With the aid of the first-principles swarm-intelligence structural search calculations, we identify new oxidation states of Au not accessible at ambient pressure. In more detail, Au can obtain more than one electron from Li atoms in Li-Au compounds, acting as 6p element [1]. The highest positive oxidation state of +6 is achieved in AuF6 molecular crystal [2]. Moreover, the unprecedented mixed-valence states (i.e. +3 and +5) of Au has been disclosed in AuO2 [3]. Our study provides a useful strategy for achieving new oxidation states of gold.
The preparation of F-rich transition metal fluorides is of great interest from both fundamental and applicable standpoints. Pressure-induced IrF8 not only breaks the boundary of the F-rich stoichiometry of transition metal fluorides but also becomes the first bulk solid containing the +8 oxidation state in Ir. More interestingly, the oxidizing power of three identified IrF8 phase is close to or probably exceeds PtF6 from the standpoint of the calculated electron affinities [4].
[1] Yang, G.; Wang, Y.; Peng, F.; Bergara,A.; Ma, Y.J. Am. Chem. Soc.2016, 138, 4046-4052.
[2] Lin, J.; Zhang, S.; Guan, W.; Yang, G.;Ma, Y.J. Am. Chem. Soc.2018, 140, 9545-9550.
[3] Tang,M.; Zhang,Y.; Li,S.; Wu,X.;Jia,Y.; Yang, G. ChemPhysChem2018, 19, 2989-2994.
[4] Lin, J.; Zhao, Z.; Liu, C.; Zhang, J.; Du, X.; Yang, G.; Ma, Y. J. Am. Chem. Soc.2019, 141, DOI: 10.1021/jacs.9b00069.