Magnetic Nature of the Cr-Ln Interactions in [CrLn] Clusters with Slow Magnetic Relaxation.

Two 3-4 hetero-metal pentanuclear complexes with the formula {[CrLnL(OH)(HO)]EtNH} [Ln=Tb (), Dy (); HL=pivalic acid, EtN=triethylamine] have been produced. The metal core of each cluster is made up of a trigonal bipyramid with three Ln ions (plane) and two Cr ions (above and below) held together by six -OH bridges. Also reported with this series is the diamagnetic Cr-Y analogue (). Fortunately, we successfully prepared Al-Ln analogues with the formula {[AlLnL(OH)(HO)]EtNH⋅HO} [Ln=Tb (), Dy ()], containing diamagnetic Al ions, which can be used to evaluate the Cr-Ln magnetic nature through a diamagnetic substitution method. Subsequently, static (dc) magnetic susceptibility studies reveal dominant ferromagnetic interactions between Cr and Ln ions. Dynamic (ac) magnetic susceptibility studies show frequency-dependent out-of-phase ('') signals for [CrTb] (), [CrDy] (), and [AlDy] (), which are derived from the single-ion behavior of Ln ions and/or the Cr-Ln ferromagnetic interactions.