Visible and near-infrared emitting heterotrimetallic lanthanide–aluminum–sodium 12-metallacrown-4 compounds: discrete monomers and dimers

Abstract

The luminescence properties of two types of heterotrimetallic aluminum–lanthanide–sodium 12-metallacrown-4 compounds are presented here, LnNa(ben)₄[12-MC_{Al(III)N(shi)}-4] (LnAl₄Na) and {LnNa[12-MC_{Al(III)N(shi)}-4]}₂(iph)₄ (Ln₂Al₈Na₂), where Ln = Gd^III, Tb^III, Er^III, and Yb^III, MC is metallacrown, ben⁻ is benzoate, shi³⁻ is salicylhydroximate, and iph²⁻ is isophthalate. The aluminum–lanthanide–sodium metallacrowns formed with benzoate are discrete monomers while, upon replacement of the benzoate with the dicarboxylate isophthalate, two individual metallacrowns can be joined to form a dimer. In the solid state, the terbium version of each structure type displays emission in the visible region, and the erbium and ytterbium complexes emit in the near-infrared. The luminescence lifetimes (τ_obs) and quantum yields have been collected under ligand excitation (Q^L_Ln) for both LnAl₄Na monomers and Ln₂Al₈Na₂ dimers. Several of these values tend to be shorter (luminescence lifetimes) and smaller (quantum yields) than the corresponding values recorded for the structurally similar gallium–lanthanide monomer and dimer 12-MC-4 molecules. However, the quantum yield value recorded for the visible emitting Tb₂Al₈Na₂ dimer, 43.9%, is the highest value observed in the solid state to date for a Tb^III based metallacrown.