Single molecule magnet behavior and luminescence of {Ln₄} and {LnZn} complexes

A series of tetranuclear coordination clusters [Ln₄L₂(HL)₂(μ₃-OH)₂(NO₃)₂](NO₃)₂ [Ln = Dy (1·3CH₃CN·5H₂O), Gd (2·4CH₃CN·5H₂O), H₂L = 6,6′-dimethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis-(nitrilomethylidyne)] diphenol] and dinuclear complexes [LnZnL(NO₃)₃(H₂O)]·2CH₃CN [Ln = Dy (3), Er (4), Yb (5), Lu (6)] were prepared and characterized. Static magnetic measurements revealed the presence of ferromagnetic interactions between the Dy(iii) ions and weak antiferromagnetic couplings between the Gd(iii) ions in 1 and 2. Dynamic magnetic studies showed that complexes 1 and 3 exhibit slow magnetic relaxation under a zero static field as expected for single molecule magnet (SMM) behavior, whereas complex 4 is a field-induced SMM. Clear hysteresis loops were observed for 1 and 3 at 2 K, verifying their SMM behavior. Luminescence investigations demonstrated that complexes 1 and 2 show ligand-based emission and can act as luminescence thermometers below 100 K, whereas complexes 3 and 5 display the characteristic emission of lanthanide ions. From the high-resolution emission spectra of 3 and 5, the energy gaps between the ground state and excited states of Dy(iii) and Yb(iii) ions were determined.