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

Abstract

Six dimetallic lanthanide complexes, [Ln₂(L′)(acac)₄] (1_Dy–3_Gd) (Ln = Dy (1_Dy), Tb (2_Tb) and Gd (3_Gd)) and [Ln₂(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.