A Rare Earth Metallocene Containing a 2{,}2′-azopyridyl Radical Anion

Title: 

A rare earth metallocene containing a 2{,}2′-azopyridyl radical anion

Year of Publication:

2021

Authors:

IV, FDelano, Castellanos, E, McCracken, J, Demir, S

Journal:

Chem. Sci.

Abstract:

Introducing spin onto organic ligands that are coordinated to rare earth metal ions allows direct exchange with metal spin centres. This is particularly relevant for the deeply buried 4f-orbitals of the lanthanide ions that can give rise to unparalleled magnetic properties. For efficacy of exchange coupling{,} the donor atoms of the radical ligand require high-spin density. Such molecules are extremely rare owing to their reactive nature that renders isolation and purification difficult. Here{,} we demonstrate that a 2{,}2′-azopyridyl (abpy) radical (S = 1/2) bound to the rare earth metal yttrium can be realized. This molecule represents the first rare earth metal complex containing an abpy radical and is unambigously characterized by X-ray crystallography{,} NMR{,} UV-Vis-NIR{,} and IR spectroscopy. In addition{,} the most stable isotope 89Y with a natural abundance of 100% and a nuclear spin of ½ allows an in-depth analysis of the yttrium–radical complex via EPR and HYSCORE spectroscopy. Further insight into the electronic ground state of the radical azobispyridine-coordinated metal complex was realized through unrestricted DFT calculations{,} which suggests that the unpaired spin density of the SOMO is heavily localized on the azo and pyridyl nitrogen atoms. The experimental results are supported by NBO calculations and give a comprehensive picture of the spin density of the azopyridyl ancillary ligand. This unexplored azopyridyl radical anion in heavy element chemistry bears crucial implications for the design of molecule-based magnets particularly comprising anisotropic lanthanide ions.

URL:

http://dx.doi.org/10.1039/D1SC04285H