Counter anions influence the relaxation dynamics of phenoxy-bridged Dy single molecule magnets.

The syntheses, structures and magnetic properties of a series of dimeric dysprosium(iii) complexes [Dy2L2(CH3OH)(H2O)]·2X·solvent {X = Cl (1), NO3 (2), ClO4 (3)} and [Dy2L2(CH3OH)2]·2X·solvent {X = CF3SO3 (4)}, formed from the 1 : 1 reactions of the H2L ligand with the corresponding dysprosium salts, are reported. Structural and magnetic studies reveal that counter anions on the periphery play a significant role in determining the dynamic magnetic relaxation process of these complexes. The coordination geometries of the Dy(1)(iii) centers are eight-coordinate triangular dodecahedra in 1-4. All compounds exhibit single-molecule magnet (SMM) behavior under a zero dc field and optimal applied dc field except 3, which displays only slow relaxation of magnetization. A comparison of the magnetic properties and structural parameters of the four compounds shows that the short Dy-Ophen distances and the large Ophen-Dy-Ophen angles create an axial ligand field in which dysprosium(iii) complexes exhibit magnetic anisotropy and SMM properties.