Electron-deficient multicenter bonding in pnictogens and chalcogens: mechanism of formation

Abstract

Phase change materials (PCMs), which bear a strong relationship with pnictogens (group V or 15) and chalcogens (group VI or 16), are mostly chalcogens related to A^IVB^VI and A^V₂B^VI₃ families. The exceptional properties and technological applications of PCMs have sparked interest in the nature of the unconventional chemical bonding present in the crystalline phases of PCMs, which has been reported as resonant, hypervalent, electron-rich multicenter, three-center-four-electron, and metavalent bonding along the last seventy years. This unconventional bond is also expected to occur at high pressure in most pnictogens, chalcogens, and A^IVB^VI and A^V₂B^VI₃ compounds that are not PCMs at room pressure. These compounds are characterized at room pressure by a mixture of primary covalent ppσ-bonds and secondary bonds in which the lone electron pairs (LEPs) are involved. In this work, we provide evidence of the existence of an unconventional bonding (similar to that of PCMs) in the highpressure phases of pnictogens and chalcogens using theoretical simulations. We also unravel the mechanism of its formation and how it depends on the type of LEP present in secondary bonds. Moreover, we show that the unconventional bond of PCMs is the electron-deficient multicenter bond. This comprehensive understanding of chemical bonding in pnictogens and chalcogens, which can be extrapolated to advanced materials, such as PCMs, will play a crucial role in explaining the structure and properties of advanced materials as well as in enhancing their applications.