Effect of Noble Metals on Luminescence and Single-Molecule Magnet Behavior in the Cyanido-Bridged Ln-Ag and Ln-Au (Ln = Dy, Yb, Er) Complexes.

Abstract

Self-assembly of lanthanide(III) complexes of 2,2':6',2″-terpyridine (terpy) with dicyanidoargentate(I) and dicyanidoaurate(I) anions in water results in the formation of six isostructural dinuclear systems [LnIII(terpy)(H2O)(NO3)2][MI(CN)2] (LnIII/MI = Dy/Ag, 1; Dy/Au, 2; Yb/Ag, 3; Yb/Au, 4; Er/Ag, 5; Er/Au, 6). They form three-dimensional supramolecular networks based on dinuclear molecules linked by hydrogen bonds, π-π interactions, and argentophilic (Ag···Ag) or aurophilic (Au···Au) interactions. All of the assemblies show complex solid-state strong UV and weak vis-NIR absorption due to overlapping contributions from 2,2':6',2″-terpyridine, dicyanidoargentate(I), dicyanidoaurate(I), and lanthanide(III) ions. Moreover, they exhibit excitation-wavelength-dependent multicolor photoluminescence ranging from bright white to blue via yellow, green, and cyan colors due to variable contributions from the dicyanidometalate and ligand. Assemblies 3-6 show NIR emission originating from YbIII and ErIII metal centers. Furthermore, compounds 1-6 and their magnetically diluted samples are magnetic-field-induced single-molecule magnets with energy barriers of up to 35 K. The effect of noble metal substitution on the magnetic properties of particular lanthanide ions is described. The influence on the thermal anisotropic energy barrier, which relates to the strength of the magnetic anisotropy, depends on the type of lanthanide used. The Ag-to-Au substitution enhances the anisotropy of the prolate YbIII ion and decreases it for the oblate DyIII ion. It also modifies the strength of dipolar interactions affecting the slow magnetic relaxation processes.