Bis-phenoxido and bis-acetato bridged heteronuclear {(CoDyIII)-Dy-III} single molecule magnets with two slow relaxation branches

Two bis-mu-phenoxido-bis-mu-acetato heterobimetallic {(CoDyIII)-Dy-III} complexes 1 and 2, formulated as [Co-III-(DyL)-L-III(mu-OAc)(2)(NO3)(2)] derived from the comparable hexadentate Schiff bases N,N'-ethylenebis(3-ethoxysalicylaldimine) and N,N'-ethylenebis(3-methoxysalicylaldimine) were synthesized and X-ray structure analysis confirms their nearly identical structures. These are the first examples of bis(mu-phenoxido)-bis(mu-carboxylato) {(CoDyIII)-Dy-III} systems. The AC susceptibility measurements show that both complexes exhibit a field-induced slow magnetic relaxation with two relaxation branches. While the high-frequency process spans the usual range of the relaxation time for analogous single molecule magnets (tau(0) similar to 10(-7) s), the low-frequency branch is as slow as tau similar to 0.1 s at T = 1.9 K and B = 0.2 T.