Structure and assembly studies of two planar Dy(iii) single molecule magnets with double relaxations

Abstract

A systematic understanding of the assembly mechanism of single-molecule magnets (SMMs) is of great significance for the directional synthesis of Dy(III) SMMs as well as improving SMM performance. Herein, we present the interesting formation mechanisms of two new single molecule magnets [Dy₄(μ₃-OH)₂(L¹)₄(L′)₂]·5CH₃CN (1, HL′ = 5-bromo-2-hydroxybenzaldehyde) and [Dy₆(μ₃-OH)₂(L²)₂(HL²)₂(H₂L²)₂Cl₂(EtOH)₂]Cl₂·4MeOH·2CH₃CN·4H₂O (2) featuring planar Dy₄ and Dy₆ skeletons fused from two- and four edge-sharing triangular Dy₃ units, respectively, which were obtained from the reactions of N,N′-bis(5-bromo-2-hydroxybenzylidene)-2-dimethylpropane-1,3-diamine (H₂L¹) with Dy(NO)₃·6H₂O and 2-[(5-bromo-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol (H₄L²) with DyCl₃·6H₂O, respectively. Another eye-catching feature is that both 1 and 2 are zero-field SMMs with rarely reported double relaxations. The third interesting feature is that the intermediates formed in the reaction courses of 1 and 2 were tracked using time-dependent high resolution electrospray ionization mass spectrometry (HRESI-MS), which helped to propose a step-by-step assembly mechanism of (H₂L¹ + Dy → Dy(L¹) → Dy₂(L¹)₂ → Dy₂(L¹)₃ → Dy₃(L¹)₃ → Dy₄(L¹)₃ → Dy₄(L¹)₄ → Dy₄(L¹)₄(L′)₂) for 1 and (H₄L² + Dy → Dy₂(L²) → Dy₂(L²)₃ → Dy₃(L²)₄ → Dy₆(L²)₆) for 2.