A family of acetato-diphenoxo triply bridged dimetallic ZnIILnIII complexes: SMM behavior and luminescent properties

Abstract

Eleven dimetallic Zn^II–Ln^III complexes of the general formula [Zn(µ-L)(µ-OAc)Ln(NO₃)₂]·CH₃CN (Ln^III = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7), Ho (8), Er (9), Tm (10), Yb (11)) have been prepared in a one-pot reaction from the compartmental ligand N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H₂L). In all these complexes, the Zn^II ions occupy the internal N₂O₂ site whereas the Ln^III ions show preference for the O₄ external site. Both metallic ions are bridged by an acetate bridge, giving rise to triple mixed diphenoxido/acetate bridged Zn^IILn^III compounds. The Nd, Dy, Er and Yb complexes exhibit field induced single-ion magnet (SIM) behaviour, with U_eff values ranging from 14.12 to 41.55 K. The Er complex shows two relaxation processes, but only the second relaxation process with an energy barrier of 21.0 K has been characterized. The chromophoric L²⁻ ligand is able to act as an “antenna” group, sensitizing the near-infrared (NIR) Nd^III and Yb^III-based luminescence in complexes 2 and 11 and therefore, both compounds can be considered as magneto-luminescent materials. In addition, the Sm^III, Eu^III and Tb^III derivatives exhibit characteristic emissions in the visible region.