Hypervalent Iodine with Linear Chain at High Pressure

Iodine is an element of fascinating chemical complexity, and numerous hypervalent iodine compounds reveal vital value of applications in organic synthesis. Investigation of the synthesis and application of new type of hypervalent iodine compound has extremely significant meaning. Here, the formation of CsI(n) (n > 1) compounds is predicted up to 200 GPa using an effective algorithm. The current results show that CsI(3) with space group of Pm-3n is thermodynamically stable under high pressure. Hypervalence phenomenon of iodine atoms in Pm-3n CsI(3) with endless linear chain type structure appears under high pressure, which is in sharp contrast to the conventional understanding. Our study further reveals that Pm-3n CsI(3) is a metallic phase with several energy bands crossing Fermi-surface, and the pressure creates a peculiar reverse electron donation from iodine to cesium. The electron-phonon coupling calculations have proposed superconductive potential of the metallic Pm-3n CsI(3) at 10 GPa which is much lower than that of CsI (180 GPa). Our findings represent a significant step toward the understanding of the behavior of iodine compounds at extreme conditions.