High-Spin Iron(II) as a Semitransparent Partner for Tuning Europium(III) Luminescence in Heterodimetallic d-f Complexes

Publisher Website
Google Scholar
Abstract
The segmental ligand 2-{6-(N,N-diethylcarbamoyl)pyridin-2-yl}-1,1′-dimethyl-5,5′-methylene-2′-(6-methylpyridine-2-yl)bis[1H-benzimidazole] (L3) reacts with a stoichiometric mixture of LnIII (Ln=La, Eu, Gd) and MII (M=Zn, Fe) in acetonitrile to produce selectively the heterodimetallic triple-stranded helicates (HHH)-[LnM(L3)3]5+. In these complexes, MII is pseudooctahedrally coordinated by the three wrapped bidentate binding units, thus forming a noncovalent tripod which organizes the three unsymmetrical tridentate segments to give ninefold coordination to LnIII. The introduction of a methyl group at the 6 position of the terminal pyridine in L3 sterically reduces the complexing ability of the bidentate segment for MII. Spectroscopic (ESI-MS, UV/Vis/NIR, NMR), magnetic and electrochemical measurements show that 1) the head-to-head-to-head triple helical complexes (HHH)-[LnM(L3)3]5+ are quantitatively formed in solution only for ligand concentrations larger than 0.01 M, 2) FeII adopts a pure high-spin electronic configuration in (HHH)-[LnFe(L3)3]5+, and 3) the FeII/FeIII oxidation process is prevented by steric constraints. Detailed photophysical studies of (HHH)-[EuZn(L3)3]5+ confirm that the pseudotricapped trigonal-prismatic lanthanide coordination site is not affected by the methyl groups bound to the terminal pyridine, thus leading to significant Eu-centered emission upon UV irradiation. In (HHH)-[EuFe(L3)3]5+, a resonant intramolecular Eu→FeIIhs energy transfer partially quenches the Eu-centered luminescence; however, the residual red emission demonstrates that high-spin iron(II) is compatible with the sensitization of EuIII in heterodimetallic d–f complexes. The influence of the electronic configuration of FeII on the efficiency of EuIII→FeII energy-transfer processes is discussed together with its consequence for the design of optically active spin-crossover supramolecular devices.

This publication has 89 references indexed in Scilit: