Magnetic Nature of the Cr^III–Ln^III Interactions in [Cr^III₂Ln^III₃] Clusters with Slow Magnetic Relaxation

Abstract

Two 3d‐4f hetero‐metal pentanuclear complexes with the formula {[CrIII 2LnIII 3L10(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 μ 3‐OH bridges. Also reported with this series is the diamagnetic CrIII–YIII analogue (3). Fortunately, we successfully prepared AlIII–LnIII analogues with the formula {[AlIII 2LnIII 3L10(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 [CrIII 2TbIII 3] (1), [CrIII 2DyIII 3] (2), and [AlIII 2DyIII 3] (5), which are derived from the single‐ion behavior of LnIII ions and/or the CrIII–LnIII ferromagnetic interactions.

Mechanism of magnetisation relaxation in {MIII2DyIII2} (M = Cr, Mn, Fe, Al) “Butterfly” complexes: how important are the transition metal ions here?

“…The transverse components for both the complexes are found to be larger for Dy1, and the effect on the measured χT values for both compounds, and in particular for the {Cr 2 Dy 2 } one, is a substantial decrease in the value expected considering the summation of the Y and Al analogues with the deleted 4f/3d contributions respectively. This at first sight surprising reduction in the χT value has also been observed for a recently reported {Cr 2 Dy 3 } system41 where this was attributed to the changes in the anisotropies of the Dy( iii ) ions. It should also be noted that the magnetisation plots for the {Cr 2 Y 2 } compound indicate that the contribution of the coupled Cr( iii ) ions is far from isotropic in nature.…”

Magnetic materials based on heterometallic CrII/III–LnIII complexes

“…In order to understand the nature of the Cr III –Ln III magnetic interaction the authors prepared an analogous Al III –Ln III derivative 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 ( 48a ), Dy ( 48b )]. 159 Predominant ferromagnetic interactions were found to prevail between Cr III and Ln III ions. AC magnetic susceptibility confirmed SMM behavior for [Cr III 2 Tb III 3 ] ( 12a ), [Cr III 2 Dy III 3 ] ( 12b ), and [Al III 2 Dy III 3 ] ( 48b ) without expected maxima until 1.8 K , mainly due to fast QTM.…”

“…Zhao and co-workers reported trigonal bipyramidal {Cr 2 159 Predominant ferromagnetic interactions were found to prevail between Cr III and Ln III ions. AC magnetic susceptibility confirmed SMM behav- [Cr 4 (hdpta) 2 (OH) 4 ] complex ligands.…”

SMM Behaviour of the Butterfly {CrIII2DyIII2} Pivalate Complex and Magneto‐structurally Correlated Relaxation Thermal Barrier

“…Compared to other 3d-4f SMMs systems, Cr(III) ones are much less explored, with some Cr(III)-Ln(III) fluoride bridged examples and several alkoxo or hydroxo bridged ones. [7,9,10,[12][13][14][15][16] Among the latter, the butterfly complexes {Cr III 2 Ln III 2 }, in which the lanthanide occupies the body position and the Cr(III) ions the wing one, are among the best studied. [7][8][9][10][11]17] All of them are built up with amino-alcohol ligands (AA) and carboxylates or acetylacetonates (acac) as auxiliary ligands (L), resulting in the butterfly core of the type {Cr III 2 Ln III 2 (AA) 2 (OR) 2 } (R =À CH 3 , H).…”

“…Thus, to better understand the magnetic interactions between 3 d and 4 f metal ions and the effect on the SMM behaviour, preparation of simple complexes with a small number of 3 d and 4 f ions is desirable to search for possible magneto‐structural correlations. Compared to other 3 d –4 f SMMs systems, Cr(III) ones are much less explored, with some Cr(III)‐Ln(III) fluoride bridged examples and several alkoxo or hydroxo bridged ones [7,9,10,12–16] …”