Amending the anisotropy barrier and luminescence behavior of heterometallic trinuclear linear [MII-LnIII-MII] (LnIII=Gd, Tb, Dy; MII=Mg/Zn) complexes by change from divalent paramagnetic to diamagnetic metal ions

Abstract

The sequential reaction of a multisite coordinating compartmental ligand [2-(2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino)-2-methylpropane-1,3-diol] (LH4) with appropriate lanthanide salts followed by the addition of [Mg(NO3)2]·6 H2O or [Zn(NO3)2]·6 H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg2Ln]3+ (Ln=Dy, Gd, and Tb) and [Zn2Ln]3+ (Ln=Dy, Gd, and Tb) cores. The formation of these complexes is demonstrated by X-ray crystallography as well as ESI-MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. The comprehensive studies discussed involve the synthesis, structure, magnetism, and photophysical properties on this family of trinuclear [Mg2Ln]3+ and [Zn2Ln]3+ heterometallic complexes. [Mg2Dy]3+ and [Zn2Dy]3+ show slow relaxation of the magnetization below 12 K under zero applied direct current (dc) field, but without reaching a neat maximum, which is due to the overlapping with a faster quantum tunneling relaxation mediated through dipole-dipole and hyperfine interactions. Under a small applied dc field of 1000 Oe, the quantum tunneling is almost suppressed and temperature and frequency dependent peaks are observed, thus confirming the single-molecule magnet behavior of complexes [Mg2Dy]3+ and [Zn2Dy]3+.