posted on 2024-02-10, 18:03authored byHannah
B. Wineinger, Benjamin Scheibe, Jacob P. Brannon, Todd N. Poe, Brian M. Rotermund, Joseph M. Sperling, Thomas E. Albrecht-Schönzart
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.