Macrocycle supported dimetallic lanthanide complexes with slow magnetic relaxation in Dy2 analogues

Six dimetallic lanthanide complexes, [Ln(2)(L')(acac)(4)] (1(Dy)-3(Gd)) (Ln = Dy (1(Dy)), Tb (2(Tb)) and Gd (3(Gd))) and [Ln(2)(L')(tfac)(4)] (4(Dy)-6(Gd)) (Ln = Dy (4(Dy)), Tb (5(Tb)) and Gd (6(Gd))) (H2L' = 1,9-dichloro-3,7,11,15-tetraaza-1,9 (1,3)-dibenzenacyclohexadecaphane-2,10-diene-1,9-diol), have been synthesized by the reaction of lanthanide nitrates with the HL ligand in the presence of acetylacetonate (acac) (or trifluoroacetylacetonate (tfac) and triethylamine (HL = 4-chloro-2,6-bis(-((3-((3-(dimethylamino)propyl)amino)propyl)imino) methyl)phenol). Ln-Assisted modification of the Schiff base HL occurred and led to the formation of a new macrocyclic ligand (H2L'). X-ray crystallographic analysis revealed that the Ln(III) ions of complexes 1(Dy)-6(Gd) are all eight-coordinated in a square antiprismatic geometry with D-4d local symmetry. Magnetic measurements of these complexes revealed that 1(Dy) and 4(Dy) show single-molecule magnet behaviour with energy barriers of 66.7 and 79.0 K, respectively, under a zero direct magnetic field. The orientations of the magnetic axes and crystal field parameters were obtained from theoretical calculations and an electrostatic model. The magneto-structural correlations of SMMs 1(Dy) and 4(Dy) are further discussed in detail.