Cu(II)-Dy(III) and Co(III)-Dy(III) based single molecule magnets with multiple slow magnetic relaxation processes in the Cu(II)-Dy(III) complex.

Two dinuclear Schiff-base complexes [Cu(II)Dy(III)] and [Co(III)Dy(III)] have been synthesized and structurally characterized. The AC susceptibility measurements taken at BDC = 0.2 T show a slow magnetic relaxation typical for single-molecule magnets. Unusual is the presence of three relaxation branches in [Cu(II)Dy(III)]; the slowest (low-frequency) process possesses the barrier to spin reversal of U/kB = 2.8 K and an extrapolated relaxation time as slow as τ0 = 0.11 s. The intermediate-frequency process is typical for SMM of this class with U/kB = 122 K and τ0 = 9.9 × 10(-7) s; an onset of the high-frequency process is evidenced and this is the fastest. In contrast, the [Co(III)Dy(III)] complex free of exchange coupling exhibits only a single relaxation path with SMM parameters U/kB = 113 K and τ0 = 7.0 × 10(-9) s.