Ligand substitution effect on single-molecule magnet behavior in dinuclear dysprosium complexes with radical functionalized phenol as bridging ligands.

Reaction of Dy(hfac)(3)·2H(2)O (hfac = hexafluoroacetyl acetonate) with 2-(2-hydroxyphenyl)nitronyl nitroxide (NITPhOH) and 2-(5-bromo-2-hydroxyphenyl)nitronyl nitroxide (NIT5BrPhOH) yielded [Dy(2)(hfac)(4)(NITPhO)(2)] 1 and [Dy(2)(hfac)(4)(NIT5BrPhO)(2)] 2, respectively. These compounds are phenoxo-O bridged binuclear complexes with the radical unit of a ligand coordinated to a single Dy. The Ln centers exhibit a heptacoordinated environment. Despite having very similar structures, these compounds exhibit distinct magnetic behaviors. Compound 1 shows slow relaxation of its magnetization indicating single-molecule magnet behavior, while no frequency-dependent out-of-phase signals were found for complex 2. This difference is likely to result from electronic effects induced by halogen substitution.