Coordination Chemistry and Spectroscopic Properties of Eu(II), Sm(II), and Yb(II) with 12-Crown‑4

• Published in: Crystal growth & design 2024-02, Vol.24 (4), p.1544-1550
• Main Authors: Wineinger, Hannah B., Scheibe, Benjamin, Brannon, Jacob P., Poe, Todd N., Rotermund, Brian M., Sperling, Joseph M., Albrecht-Schönzart, Thomas E.
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.3c00878

The coordinative properties of 12-crown-4 (12c4) with Sm2+, Eu2+, and Yb2+ have been examined using nonaqueous and inert atmosphere conditions and led to the isolation of five complexes: Ln­(12c4)­(THF)2I2 (Ln = Sm 1, Eu 2), [Ln­(12c4)2(CH3CN)]­[Ph4B]2 (Ln = Sm 3, Eu 4), and [Yb­(12c4)2]­[Ph4B]2 (5). Most complexes were prepared via the salt metathesis of LnI2 with tetrabutylammonium tetraphenylborate ([TBA]­[Ph4B]) and 12-crown-4 in acetonitrile, while some were crystallized from THF. The half-sandwich compounds 1 and 2 crystallize with trans iodide orientation and exhibit mixed d–f and f–f and d–f photoluminescence when excited with 546 and 365 nm light, respectively. The full sandwich compounds 3 and 4 feature [Ln­(12c4)2(CH3CN)]2+ complex cations, where two 12c4 molecules are not sufficiently large to coordinatively saturate these larger cations without further ligation, while the smaller Yb2+ cation is fully encapsulated in two 12c4 molecules (5). Solution UV–vis–NIR studies show that when 12c4 is added to acetonitrile solutions of LnI2, the f–d transitions shift to higher energies, suggesting destabilization of the lower lying d orbitals and increased stability of the divalent state by complexation to 12c4 in solution.