Magnetic Nature of the CrIII-LnIII Interactions in [CrIII2LnIII3] Clusters with Slow Magnetic Relaxation

Two 3d-4f hetero-metal pentanuclear complexes with the formula {[CrIII2LnIII3L10(OH)6(H2O)2]Et3NH} [Ln=Tb (1), Dy (2); HL=pivalic acid, Et3N=triethylamine] have been produced. The metal core of each cluster is made up of a trigonal bipyramid with three LnIII ions (plane) and two CrIII ions (above and below) held together by six μ3-OH bridges. Also reported with this series is the diamagnetic CrIII-YIII analogue (3). Fortunately, we successfully prepared AlIII-LnIII analogues with the formula {[AlIII2LnIII3L10(OH)6(H2O)2]Et3NH⋅H2O} [Ln=Tb (4), Dy (5)], containing diamagnetic AlIII ions, which can be used to evaluate the CrIII-LnIII magnetic nature through a diamagnetic substitution method. Subsequently, static (dc) magnetic susceptibility studies reveal dominant ferromagnetic interactions between CrIII and LnIII ions. Dynamic (ac) magnetic susceptibility studies show frequency-dependent out-of-phase (χ'') signals for [CrIII2TbIII3] (1), [CrIII2DyIII3] (2), and [AlIII2DyIII3] (5), which are derived from the single-ion behavior of LnIII ions and/or the CrIII-LnIII ferromagnetic interactions.