Hydroxido supported and differently networked octanuclear Ni6Ln2 [Ln = GdIII and DyIII] complexes: structural variation, magnetic properties and theoretical insights

Abstract

The design and synthesis of a Schiff base H₂L, (2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol), bearing an ONOO donor set has been explored for its reactivity pattern with LnCl₃·6H₂O (Ln = Gd^III and Dy^III) and Ni(CH₃CO₂)₂·4H₂O in the presence of NEt₃ for molecular aggregation. Coordination driven spontaneous self-assembly reactions provide [Gd₂Ni₆L₄(μ₃-OH)₆(μ-OH)₂(CH₃CO₂)₂(μ-H₂O)₂(H₂O)₃(MeOH)]·8H₂O (1) having a ‘butterfly-shaped’ core and [Dy₂Ni₆L₄(μ₃-OH)₄(μ-Cl)₂Cl₄(H₂O)₂(MeOH)₂]·2MeOH·4H₂O (2) with a ‘candy-shaped’ core. Fusion of six partial cubane units led to a mineral-like core in 1, developed around the central Ni₂(OH)₂ moiety, whereas in the case of 2, four such partial cubanes collapsed on Dy₂(OH)₂. Direct-current (dc) magnetic susceptibility measurements revealed that predominant ferromagnetic interactions lead to a high-spin S = 13 ground state for 1. Complex 2 exhibits slow relaxation of magnetization under an applied small dc field with an energy barrier to reorientation of the magnetization, U_eff = 19.3 K. The static and dynamic magnetic data are analysed and corroborated by density functional theory (DFT) and detailed CASSCF based calculations.