Harriswangler, CharleneFreire-García, AntíaArgibay-Otero, SarayRodríguez-Rodríguez, AuroraRodríguez Seijo, José ManuelEsteban-Gómez, DavidVázquez-López , Ezequiel M.Platas-Iglesias, Carlos2025-12-032025-12-032025-04-15Harriswangler, C., Freire-Garcia, A., Argibay-Otero, S., Rodriguez-Rodriguez, A., Rodriguez, J. M., Esteban-Gomez, D., ... & Platas-Iglesias, C. (2025). Structural effects of the Pb2+ 6s2 lone pair activity: Eccentricity. Coordination Chemistry Reviews, 529, 216434. https://doi.org/10.1016/j.ccr.2025.2164340010-8545https://hdl.handle.net/2183/46601This is the author accepted manuscript of an article published in Coordination Chemistry Reviews. The final published version is available at https://doi.org/10.1016/j.ccr.2025.216434. © 2025 Elsevier. Licensed under CC BY-NC-ND.[Abstract] The stereochemical activity of the 6s2 lone pair has profound consequences on the coordination chemistry of metal ions like Tl+, Pb2+ and Bi3+. The coordination chemistry of Pb2+ is very likely the most extensively investigated among the metal ions with [Xe]4f145d106s2 electronic configuration, allowing for a detailed analysis of the factors that affect the stereochemical activity of the 6s2 lone pair. In this review, the X-ray structures of a wide variety of Pb2+ 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 Pb2+ 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.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/LeadLone pairHolodirectedHemidirectedEccentricityjournal articleembargoed access10.1016/j.ccr.2025.216434