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IrF₈ Molecular Crystal under High Pressure

Lin, Jianyan, Zhao, Ziyuan, Liu, Chunyu, Zhang, Jing, Du, Xin, Yang, Guochun, Ma, Yanming
Journal of the American Chemical Society 2019 v.141 no.13 pp. 5409-5414
energy, fluorides, oxidation, physical phases, stoichiometry
An important goal in chemistry is to prepare F-rich transition metal fluorides due to the high oxidation states and potential applications such as oxidating and fluorinating agents. Thus far, the highest F stoichiometry in the neutral transition metal fluorides is 7. Here, we identify a hitherto unknown IrF₈ compound through first-principles swarm-intelligence structure search calculations under high pressure. The three identified IrF₈ phases exhibit typical molecular crystal characters, showing +8 oxidation state in Ir. The spatial symmetry of the basic building block in the three IrF₈ phases gradually increases with pressure (e.g., dodecahedron → square antiprism → quasicube). The pressure-induced faster increase of Ir 5d orbital energy level with respect to F 2p provides a strong charge transfer driving force from Ir 5d to F 2p, facilitating the formation of F-rich compounds. More interestingly, the predicted electron affinities of the three predicted IrF₈ phases are comparable/larger than that of PtF₆, the strongest oxidation agent in the third row transition metal hexafluorides. The built high-pressure phase diagram of Ir–F binary compounds provides useful information for experimental synthesis.