Solvent Modification of the Structures and Magnetic Properties of a Series of Dysprosium(III) Single-Molecule Magnets.

Solvent effects on the structures and magnetic properties of single-molecule magnets (SMMs) have been of great interest for modification of the SMMs using chemical modulation. By systematically varying the reaction solvents (MeOH, ethanol, n -propanol, and n -butanol), we have successfully synthesized a series of Dy ^III -H ₄ daps complexes (H ₄ daps = N ', N ‴-[(1 E ,1' E )-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene)]bis(2-hydroxybenzohydrazide), including two binuclear compounds, [Dy ₂ (H ₂ daps) ₂ (MeOH) ₄ (H ₂ O) ₂ ](CF ₃ SO ₃ ) ₂ ·0.5MeOH ( 1 _MeOH ) and [Dy ₂ (H ₂ daps) ₃ (EtOH) ₂ ]·2EtOH·Et ₂ O ( 2 _EtOH ), and two mononuclear compounds, [Dy(H ₄ daps) ₂ ](CF ₃ SO ₃ ) ₃ · n -PrOH ( 3 _PrOH ) and [Dy(H ₄ daps)(CF ₃ SO ₃ ) ₃ ( n -BuOH)]·0.5Et ₂ O ( 4 _BuOH ). Using different solvents, the ligand-to-metal ratios can be adjusted from 1:1 in 1 _MeOH and 4 _BuOH to 3:2 in 2 _EtOH and 2:1 in 3 _PrOH . Through the solvent crossover experiments, the role of the solvents and the conditions to form these complexes were carefully studied. The size of the different alcohols, their coordination ability to the Dy ^III center, and the solubility of the complexes in these alcohols might affect the assembly process and lead to modification of the structures and magnetic properties of these Dy ^III -H ₄ daps complexes. Magnetic studies revealed that these four complexes all exhibit slow magnetic relaxation under a zero or an applied direct-current field, with an energy barrier of about 100 K for the binuclear compound 1 _MeOH . In combination with theoretical calculations, the magnetic-structure relationship of these four compounds has been analyzed. This work demonstrates the crucial role of different solvent molecules in the fine-tuning of the structures and magnetic performances of different lanthanide complexes.