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

Abstract

The coordinative properties of 12-crown-4 (12c4) with Sm 2+ , Eu 2+ , and Yb 2+ have been examined using nonaqueous and inert atmosphere conditions and led to the isolation of five complexes: Ln( 12c4)(THF) 2 I 2 (Ln = Sm 1, Eu 2), [Ln(12c4) 2 (CH 3 CN)][Ph 4 B] 2 (Ln = Sm 3, Eu 4), and [Yb(12c4) 2 ][Ph 4 B] 2 (5). Most complexes were prepared via the salt metathesis of LnI 2 with tetrabutylammonium tetraphenylborate ([TBA][Ph 4 B]) 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 (CH 3 CN)] 2+ complex cations, where two 12c4 molecules are not sufficiently large to coordinatively saturate these larger cations without further ligation, while the smaller Yb 2+ cation is fully encapsulated in two 12c4 molecules (5). Solution UV−vis−NIR studies show that when 12c4 is added to acetonitrile solutions of LnI 2 , 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.