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

Abstract

The variable coordination behavior of 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}-6-methoxyphenol (H₂L) and its hydrolyzed congener towards NiCl₂·6H₂O and Ln^III nitrate salts provides a family of coordination aggregates containing an [Ni₅Ln₃] octanuclear core structure. Room temperature reactions in MeOH−CHCl₃ medium and in the presence of NEt₃ yielded isostructural [Ni₅Ln₃(L)₄(μ-OH)₂(μ₃-OH)₆(o-val)₂(H₂O)₆]NO₃·7H₂O (Ln = Dy³⁺ (1), Tb³⁺ (2), and Ho³⁺ (3); o-val = o-vanillin) heterometallic complexes. All the three complexes hold an octanuclear fused partial hexacubane topology from the utilization of phenolate-based ligand anions, clipping five 3d and three 4f ions. Direct current magnetic susceptibility measurements showed an upsurge at low temperature for complexes 1 and 2, indicative of ferromagnetic interactions, while antiferromagnetic exchange interaction predominates for complex 3. AC magnetic susceptibility measurements were not able to show any slow relaxation property to the magnetization. CASSCF calculations for complex 1 indicate that all three Dy³⁺ centres have anisotropic axes but the relative orientation of the magnetic axes reduces the probability of this molecule to behave like an SMM which is further established by the POLY_ANISO calculations.