Magnetic Nature of the Cr(III)–Ln(III) Interactions in [Cr(III) (2)Ln(III) (3)] Clusters with Slow Magnetic Relaxation

Two 3d‐4f hetero‐metal pentanuclear complexes with the formula {[Cr(III) (2)Ln(III) (3)L(10)(OH)(6)(H(2)O)(2)]Et(3)NH} [Ln=Tb (1), Dy (2); HL=pivalic acid, Et(3)N=triethylamine] have been produced. The metal core of each cluster is made up of a trigonal bipyramid with three Ln(III) ions (plane) and two Cr(III) ions (above and below) held together by six μ (3)‐OH bridges. Also reported with this series is the diamagnetic Cr(III)–Y(III) analogue (3). Fortunately, we successfully prepared Al(III)–Ln(III) analogues with the formula {[Al(III) (2)Ln(III) (3)L(10)(OH)(6)(H(2)O)(2)]Et(3)NH⋅H(2)O} [Ln=Tb (4), Dy (5)], containing diamagnetic Al(III) ions, which can be used to evaluate the Cr(III)–Ln(III) magnetic nature through a diamagnetic substitution method. Subsequently, static (dc) magnetic susceptibility studies reveal dominant ferromagnetic interactions between Cr(III) and Ln(III) ions. Dynamic (ac) magnetic susceptibility studies show frequency‐dependent out‐of‐phase (χ′′) signals for [Cr(III) (2)Tb(III) (3)] (1), [Cr(III) (2)Dy(III) (3)] (2), and [Al(III) (2)Dy(III) (3)] (5), which are derived from the single‐ion behavior of Ln(III) ions and/or the Cr(III)–Ln(III) ferromagnetic interactions.