Structures and Lone Pair Cations

Lone pair cations exhibit external pairs of electrons which do not participate in the bonds but can influence dramatically the geometry of the structures (52). This is the case of cations like Bi(III), Pb(II) or T1(I) whose 6s2 lone pairs have been shown to present an important stereochemical activity. Such cations which can be found in the rock salt type layers are capable of influencing the oxygen framework and may consequently affect the superconducting properties of the layered cuprates. 

The oxide Tl0 5Pb0 5Sr2CaCu207, prepared for the first time by Subramanian et al. (34) was investigated by electron microscopy (35). 

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