TlF and PbO under High Pressure: Unexpected Persistence of the Stereochemically Active Electron Pair

Even under a pressure of 46 GPa, the low-symmetry lone-pair structures of isoelectronic TlF and PbO (see picture for β-PbO), classic examples of systems with a stereochemically active lone pair, resist transformation into the corresponding high-symmetry NaCl and CsCl structures. Ab initio calculations allowed a simple bonding picture for lone-pair structures involving inert-pair elements to be developed.