Structures and optical properties of cyclic-ether complexes of europium/ytterbium made via a redox approach

To obtain cyclic-ether complexes of europium/ytterbium with generally less preferable cyclic ethers (i.e., those with large/small ring openings, cage-type cryptands, and N-containing crown ethers), a novel redox approach is used. Accordingly, 24-crown-8 (24c8), benzo-15-crown-5 (benzo-15c5), N-phenylaza-15-crown-5 (pac), [2.2.2]cryptand (c222), and kryptofix21 (k21) are made to react with europium and ytterbium metal nanoparticles, 2-4 nm in size. Europium and ytterbium are selected as both lanthanides are flexible in their oxidation state (II/III), and cover a typical range of cation radii (r(Eu$^{2+}$): 139 pm to r(Yb$^{3+}$): 113 pm) in the 4f-row (radii for CN = 8). As a result, [Yb(24c8)]$_4$[AlCl$_4$]$_8$THF (1), [Eu(benzo-15c5)$_2$]I$_2$ (2), [Yb(benzo-15c5)$_2$]I$_2$ (3), [BMIm][Eu$_4$Cl$_4$(pac)$_4$][AlCl$_4$]$_5$ (4), [{Yb(pac)}$_2$(mu-Cl)2][AlCl$_4$]$_2$ (5), [EuCl(c222)][AlCl$_4$] (6), [EuI(c222)]I (7), [{Yb(c222)}$_2$(mu-Cl)]$_2$[AlCl$_4$]$_6$1.5THF (8), [BMIm][Yb(c222)]I$_3$ (9), [Eu(k21)$_2$]I$_2$naph (10), and [BMIm][{Yb(k21)}$_2$mu-Cl)$_3$]I$_2$ (11) are obtained as new compounds. The title compounds show various coordination scenarios with mono- to tetranuclear building units. ... mehrAll are luminescent with a narrow-line blue emission of 4 and the strong second harmonic generation (SHG) effect of 6 being specifically interesting. As the redox approach used here leads to the coordination of the lanthanide cations with all applied cyclic ethers - although exhibiting less preferred size and/or coordinative binding with the lanthanide cation - it may present a novel synthesis strategy to generally prepare new metal complexes with cyclic ethers with interesting optical, magnetic or catalytic properties.