Influence of the coordination environment on slow magnetic relaxation and photoluminescence behavior in two mononuclear dysprosium(III) based single molecule magnets

The reaction of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H(4)daps] with Dy(NO3)(3)center dot 5H(2)O led to the formation of two new Dy(III) based complexes with formulae [Dy(H(4)daps)(H2O)(3)(NO3)] (NO3)(2) (H2O) (1) and [Dy(H(3)daps)(H2O)(2)(NO3)] (NO3) (MeOH) (2). Complexes 1 and 2 were characterized by crystal structure determination, magnetic measurements and photoluminescence studies. In comparison with complex 1, complex 2 shows a slight difference of local symmetry around the Dy(III) center which is attributed to deprotonation of the ligand and also to different binding modes of the peripheral NO3- anion. AC magnetic susceptibility measurements reveal that both complexes exhibit single-molecule magnet (SMM) behavior, with the thermal energy barrier of 1 being higher than that of 2 (U-eff = 32.7 K for 1 and 23.8 K for 2). Our investigation discloses that small differences in the coordination environment around the metal centre played an important role in the difference in relaxation dynamics of the complexes. Solid state photoluminescence studies showed their photoluminescence behaviour with quantum yields of 0.98 and 1.44%.