Date/Time
Date(s) - 13/01/2022
1:30 pm - 2:30 pm

Title: Expanding the Range of Oxidation States inMolecular Complexes of the Rare-Earth and Actinide Metals 

Date: Thursday, January 13, 2022

Time: 1:30-2:30 pm

Zoom link available from chemgrad@mcmaster.ca 

Host: Nick Hoffman 

Abstract: The discovery that crystallographically-characterizable molecularcomplexes of the rare-earth metals (Sc, Y, lanthanides) in the formal +2oxidation state were isolable for metals beyond Eu, Yb, Sm, Tm, Dy, and Nd intris(silyl-cyclopentadienyl) complexes such as (Cp’₃Ln)^1?and (Cp”₃Ln)^1?, where Cp’ = C₅H₄SiMe₃and Cp” = C₅H₃(SiMe₃)₂, has initiatedan extensive search for other ligand systems and coordination environments thatwill stabilize low oxidation state ions.  This effort has been stimulatedby the structural, spectroscopic, and magnetic results that indicate thatreduction of precursors containing 4fⁿ lanthanide +3 ions can form4fⁿ5d¹ lanthanide +2 ions rather than the traditional 4fⁿ⁺¹products.  These discoveries have also led to An(II) complexes (An =actinide metal) with 5fⁿ6d¹ and 6d² electronconfigurations.  The initial synthetic studies suggested that a trigonaltris(silyl-cyclopentadienyl) coordination environment was crucial for isolatingthe new oxidation states, but results with a variety of ligands includingamides, aryloxides, and polyalkylcyclopentadienyl ligands indicate that theseoxidation states are more generally accessible.  The diversity of ligandsystems that support +2 oxidation states for the rare-earth and actinide metalswill be presented and an evaluation of the factors that allow access to theseoxidation states will be described.  This appears to involve a variety ofsubtle factors including speed of crystallization.  Some unusual physicalproperties of these new complexes will also be discussed.