Compounds with stereochemically inert lone pairs

The classical view of the lone pair is that, after mixing of the s and p orbitals on the heavy metal cation, the lone pair occupies an inert orbital in the ligand sphere [6]. This pair of electrons is considered chemically inert but stereochemi-cally active [7]. However, this implies that the lone pair would always and in any (chemical) environment be stereochemically active, which is not the case. For example, TIF [8] adopts a structure, which can be considered as a NaCl type of structure which is distorted by a stereochemically active lone pair on thallium. In contrast TlCl [9] and TlBr [10] adopt the undistorted CsCl type of structure at ambient temperature, and at lower temperatures the (again undistorted) NaCl type of structure. The structure of PbO [11] is clearly characterized by the stereochemically active lone pair. In all the other 1 1 compounds of lead with... 

The purpose of this chapter is to address the role of heavy oxoanions containing a chemically inert, but stereochemically active, lone-pair of electrons on the structures of purely inorganic actinide compounds. This work is not intended to be a comprehensive survey of all compounds that fall into this class, but rather its goal is to highlight key compounds with atypical structures where the influence of the lone-pair of electrons can be ascertained, if only in part. 

There are substantial variations on the eoordination numbers and geometries for actinide compounds containing a chemically inert, but stereochemically active, lone-pair of eleetrons. These oxoanions are to varying degrees oxidizing in nature and therefore it is expeeted that the penta- and hexavalent oxidation state will be found for the early actinides. This predietion is bom out with iodate (a... 

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