Formation of twelve-fold iodine coordination at high pressure

High pressure can modify the chemical properties of the elements, giving rise to exotic bonding. Here the authors report the prediction of a nitrogen-rich iodine nitride compound IN6 where the iodine atom has an unusual twelve-fold coordination, stable above 100 GPa. Halogen compounds have been studied widely due to their unique hypercoordinated and hypervalent features. Generally, in halogen compounds, the maximal coordination number of halogens is smaller than eight. Here, based on the particle swarm optimization method and first-principles calculations, we report an exotically icosahedral cage-like hypercoordinated IN6 compound composed of N-6 rings and an unusual iodine-nitrogen covalent bond network. To the best of our knowledge, this is the first halogen compound showing twelve-fold coordination of halogen. High pressure and the presence of N-6 rings reduce the energy level of the 5d orbitals of iodine, making them part of the valence orbital. Highly symmetrical covalent bonding networks contribute to the formation of twelve-fold iodine hypercoordination. Moreover, our theoretical analysis suggests that a halogen element with a lower atomic number has a weaker propensity for valence expansion in halogen nitrides.

Automated summary

In this study, the authors report the prediction of a nitrogen-rich iodine nitride compound (IN6) with an unusual twelve-fold coordination of the iodine atom under high pressure. They discovered the existence of a hypercoordinated IN6 compound composed of N-6 rings and an unusual iodine-nitrogen covalent bond network using particle swarm optimization method and first-principles calculations. The formation of twelve-fold iodine hypercoordination is facilitated by the presence of high pressure and N-6 rings. The findings also suggest that halogen elements with lower atomic numbers have weaker valence expansion propensity in halogen nitrides.