Self-assembled octanuclear [Ni5Ln3] (Ln = Dy, Tb and Ho) complexes: synthesis, coordination induced ligand hydrolysis, structure and magnetism

The variable coordination behavior of 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}-6-methoxyphenol (H2L) and its hydrolyzed derivative with NiCl2·6H2O and LnIII nitrate salts leads to the formation of a series of coordination aggregates featuring an octanuclear core structure of [Ni5Ln3]. Reactions at room temperature in a MeOH-CHCl3 medium with NEt3 resulted in isostructural heterometallic complexes [Ni5Ln3(L)4(μ-OH)2(μ3-OH)6(o-val)2(H2O)6]NO3·7H2O (where Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3); o-val = o-vanillin). Each complex exhibits an octanuclear fused partial hexacubane topology, constructed from phenolate-based ligand anions, incorporating five 3d and three 4f ions. Direct current magnetic susceptibility measurements revealed an increase at low temperatures for 4-MUcomplexes 1 and 2, suggesting ferromagnetic interactions, while complex 3 predominantly exhibits antiferromagnetic exchange interactions. AC magnetic susceptibility measurements did not indicate any slow relaxation properties in the magnetization. CASSCF calculations for complex 1 show that all three Dy3+ centers have anisotropic axes; however, the relative orientation of these magnetic axes diminishes the likelihood of the molecule behaving as a single-molecule magnet (SMM), a conclusion further supported by POLY_ANISO calculations.