Molecular Architecture and Single-Molecule Magnet behavior Control by Playing with Lanthanide Ionic Radii and Bulkiness Ancillary Ligands.

Abstract

A library of three dinuclear complexes [Yb(hfac)₃(L)]₂⋅3(CH₂Cl₂) (1)⋅3(CH₂Cl₂), [Dy₂(hfac)₆(L)₃]⋅3(CHCl₃) (4)⋅3(CHCl₃), [Yb(tta)₃(L)]₂ (6), four dinuclear enantiomers [Ln(facam)₃(L)]₂⋅CH₂Cl₂ Ln=Dy ((-)7⋅CH₂Cl₂, (+)7⋅CH₂Cl₂) and Yb ((-)8⋅CH₂Cl₂, (+)8⋅CH₂Cl₂), two tetranuclear complexes [Ln₂(hfac)₆(L)]₂⋅(CH₂Cl₂)_n (Ln=Yb, n =1 (2)⋅CH₂Cl₂; Ln=Dy, n=0 (3)) and two pentanuclear complexes [Dy₅(hfac)₁₅(L)₃]⋅2(C₂H₄Cl₂) (5)⋅2(C₂H₄Cl₂) and [Nd₅(hfac)₁₅(L)₃]⋅2(CH₂Cl₂) (10)⋅2(CH₂Cl₂) (1,1,1,5,5,5-hexafluoroacetylacetonate (hfac^-), 2-tenoyltrifluoroacetylacetonate (tta^-), 3-(trifluoro-acetyl-(+/-)-camphorate (facam^-) and L=[4'-(4'''-pyridyl-N-oxide)-1,2':6'1''-bis-(pyrazolyl)pyridine] ligand) were isolated and characterized by single crystal X-ray diffraction. The final molecular architectures could be controlled by playing with the ionic radii of Yb(III), Dy(III) and Nd(III) ions and steric hindrance of the β-diketonate. Natural circular dichroism (NCD) highlighted no exciton CD couplet for chiral compounds. All the compounds involving Nd(III) in both O9 and N3O6, Dy(III) in O9 and Yb(III) in both O8 and N3O6 coordination sphere present field-induced SMM while Dy(III) in O8 environment displays SMM behavior in zero applied dc field. The relaxation of the magnetization occurs mainly through a Raman process with contribution of QTM in zero field and Direct process under applied field. The relaxation time of the magnetization increases with the enhancement of the steric hindrance of the ancillary β-diketonate ligands.