Pressure‐Induced Polymerization and Electrical Conductivity of a Polyiodide

Abstract

We report the high-pressure structural characterization of an organic polyiodide salt in which ap rogressive addition of iodine to triiodide groups occurs.C ompression leads to the initial formation of discrete heptaiodide units, followed by polymerization to a3Danionic network. Although the structural changes appear to be continuous,t he insulating salt becomes as emiconducting polymer above1 0GPa.T he features of the pre-reactive state and the polymerized state are revealed by analysis of the computed electron and energy densities.T he unusually high electrical conductivity can be explained with the formation of new bonds.Polyiodides (PIs) in crystal form were discovered about 200 years ago. [1] Their structural diversity,which is due to the bonding flexibility of iodine,r emains the subject of continuous interest. [2][3][4] Nowadays,v arious PIs are known, ranging from I 3 À to I 29 3À ,with the general formula I nÀ 2 m+n and n up to 4. Their building blocks consist of I 3 À as adonor and I 2 as an acceptor forming ac harge transfer (CT) complex. CT complexes can interact further to form extended structures with various topologies,u pt oc ubic networks.A st he aggregation of iodine units is somewhat unpredictable,t he design of PIs is not easy.Moreover,the classification of higher units is,thus far,pragmatically based on the distance between iodine atoms,but universal criteria are still lacking.Different theoretical approaches to study bonds in PIs exist, for example,calculations of the potential energy surface and bond order, [5] energy decomposition analysis (EDA), [6] analysis of the electron density and its Laplacian at bond critical points (BCP), [7] theelectron localization function, and the one-electron potential. [8] Furthermore,t he energy den-

Tribochemistry, Mechanical Alloying, Mechanochemistry: What is in a Name?

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Attractive and repulsive forces in a crystal of [Rb(18-crown-6)][SbCl6] under high pressure

“…One can anticipate a clear structural response of the [Rb(18-crown-6)] + system to such extreme conditions, with the simple parameter of )] + center separation as a function of the applied pressure. Pressure, traditionally less widely used due to technical/ experimental challenges, has become a powerful tool for tuning the properties of different crystals (Woodall et al, 2016;Pore ˛ba et al, 2019). Unlike temperature, which typically leads to smaller changes, pressure can significantly modify interatomic and intermolecular interactions in crystals, and even alter their structure, acting as a key thermodynamic variable.…”

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

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