Hypervalent Iodine with Linear Chain at High Pressure

Shubo Wei, Jianyun Wang, Shiyu Deng, Shoutao Zhang, Quan Li
<span title="2015-09-24">2015</span> <i title="Springer Nature"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/tnqhc2x2aneavcd3gx5h7mswhm" style="color: black;">Scientific Reports</a> </i> &nbsp;
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.
more &raquo; ... rvalence 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. Iodine compounds have always been the subject of extensive studies because of their significant properties such as conduction characteristic 1,2 , optical property 3 , catalytic performance 4,5 and medical application 6 , etc. For instance, cesium iodide (CsI) is one of the simplest and most representative ionic solids, and extensive theoretical and experimental studies have been carried out 7-15 . CsI exhibits variety of interesting phenomena such as pressure involved metallization and superconductivity under high pressure 12-14 . In addition, organic molecules bearing hypervalent iodine moieties have been transformed from laboratory curiosities to useful and routinely employed reagents in organic synthesis [16] [17] [18] [19] [20] [21] . Comparing with the relatively and easily synthesized organic complexity, the synthesis of inorganic hypervalent iodine compounds with attractive properties and its corresponding structures have been a long-standing puzzle. For I 3 − ion, its linear geometric structure was determined for the first time in 1935 by Mooney, who carried out X-ray analysis on ammonium triiodide 22 . The I 3 − anion belongs to the type of compounds known as hypervalent, which violate the Lewis octet rule 23 . Due to the representative hypervalence property of I 3 − ion, it is of great consideration for further study of CsI n (n > 1) compounds to explore the possibility of forming hypervalent CsI n with interesting properties or structures. Previous experimental works show that crystal CsI 3 and CsI 4 can be synthesized at ambient pressure 24-27 . Subsequently, experimental XRD measurement proposed that the crystal information of CsI 3 and CsI 4 were orthorhombic Pmnb and monoclinic P2 1 /a symmetry, respectively 28-30 . W. Zhang et al. did an excellent work for Na x Cl y system by combining theoretical predictions and diamond anvil cell experiments 31 . They reported that Na 3 Cl, Na 2 Cl, Na 3 Cl 2 , NaCl 3 and NaCl 7 are theoretically stable and have unusual bonding and electronic properties at high pressure 31 . Na-Cl and Cs-I system are clearly analogous as typical ionic solids and they may adopt the same structures. Currently, the synthesis or the full high-pressure structural information of CsI n are still far from being clear and established. These structural uncertainties have impeded in-depth understanding and further exploration of phenomena of CsI n might under compression. Here, we present systematic structure searches to establish the thermodynamically stable structures of CsI n (n = 2 − 5) up to 200 GPa using the developed CALYPSO (Crystal structure AnaLYsis by Particle
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