Structural effects of the Pb2+ 6s2 lone pair activity: Eccentricity
Charlene Harriswangler, Antía Freire-García, Saray Argibay‐Otero, Aurora Rodríguez‐Rodríguez, J. Molina Rodriguez, David Esteban‐Gómez, E.M. Vázquez-López, Carlos Platas‐Iglesias
Abstract
The stereochemical activity of the 6s 2 lone pair has profound consequences on the coordination chemistry of metal ions like Tl + , Pb 2+ and Bi 3+ . The coordination chemistry of Pb 2+ is very likely the most extensively investigated among the metal ions with [Xe]4f 14 5d 10 6s 2 electronic configuration, allowing for a detailed analysis of the factors that affect the stereochemical activity of the 6s 2 lone pair. In this review, the X-ray structures of a wide variety of Pb 2+ complexes were analyzed by approximating their coordination environments to a prolate spheroid. The eccentricity (ε) of the spheroid provides a straightforward measure of the stereochemical activity of the Pb 2+ lone pair. Holodirected structures are characterized by a rather spherical distribution of the donor atoms around the metal ion, leading to values of ε < 0.05. The stereochemical activity of the lone pair may result in either moderately hemidirected structures, with ε values in the range 0.05–0.15, or strongly hemidirected structures, when ε > 0.15. Hemidirected structures are favored by low coordination numbers and the presence of negatively charged donor atoms. In this work not only have many representative complexes been analyzed to provide a classification of these systems according to their eccentricity, but also a simple tool is provided for coordination chemists, through which they can easily classify their complexes as holodirected or hemidirected. The analysis of numerous X-ray structures of Pb 2+ complexes using eccentricity measurements, provides a straightforward quantification of the stereochemical activity of the 6s 2 lone pair. • The X-ray crystal structures of Pb 2+ complexes show that the 6s 2 lone pair displays varying degrees of stereochemical activity. • The Pb 2+ coordination environment can be described as a spheroid with eccentricity ε. • Holodirected structures are characterized by ε < 0.05. • Lone pair stereochemical activity results in moderate (0.05 < ε < 0.15) and strongly (ε > 0.15) hemidirected structures.