Solvent triggered structural diversity of triple-stranded helicates: single molecular magnets

Abstract

Multiple-stranded helicates are of interest in respect of their simplicity in geometry and significance in biology and materials. Bis-β-diketones have shown their advantage in terms of structure and geometry in the construction of multiple-stranded helicates, but further studies on their properties are limited due to their poor crystallization. In this study, solvents are found to play a decisive role in the crystallization of triple-stranded helicates. [Dy₂(BTB)₃(H₂O)₄] is used as a precursor to solvent-dependently crystallize three complexes [Dy₂(BTB)₃(CH₃OH)₄]·3CH₃OH (1), [Dy₂(BTB)₃(DME)₂] (2) and [Dy₂(BTB)₃(DOA)(H₂O)₂]·4.5DOA (3) (BTB = 3,3′-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl), where the key structural motif of the triple-stranded helicate, [Dy₂(BTB)₃], is retained. Four methanol molecules are found to ligate to Dy³⁺ ions in 1, while each Dy³⁺ ion is chelated by one DME molecule in 2. Interestingly, it is observed that 1,4-dioxane as a bridge ligates to two adjacent Dy³⁺ ions, giving rise to the formation of a 1D chain structure. Magnetic measurement shows that 1 and 2 display slow magnetic relaxation under zero dc field, while single molecular magnet behavior is obtained for 3 under an applied dc field of 2000 Oe.