Visualizing lone pairs in compounds containing heavier congeners of the carbon and nitrogen group elements

Abstract

In this mini-review, I discuss some recent work on the stereochemistry and bonding of lone pairs of electrons in divalent compounds of the heavier carbon group elements (Sn^II , Pb^II) and in trivalent compounds of the heavier nitrogen group elements (Bi^III). Recently developed methods that permit the real-space visualization of bonding patterns on the basis of density functional calculations of electronic structure, reveal details of the nature of s electron lone pairs in compounds of the heavier main group elements — their stereochemistry and their inertness (or lack thereof). An examination of tetragonalP4/nmm SnO, α-PbO and BiOF, and cubic$Fm\bar 3m$PbS provides a segue into perovskite phases of technological significance, including ferroelectric PbTiO₃ and antiferroelectric/piezoelectric PbZrO₃, in both of which the lone pairs on Pb atoms play a pivotal rôle.