Novel stable ytterbium acetylacetonate–quinaldinate complexes as single-molecule magnets and surprisingly efficient luminophores

Abstract

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q⁻) ligand, namely 1D-polymeric [Yb(acac)₂(Q)]_n (1, acac⁻ is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)₂(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb³⁺. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C–H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q⁻ thereby decreasing the energy of coordinating C–O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.