Exploring the Slow Relaxation of the Magnetization in Co^III‐Decorated {Dy^III₂} Units

Abstract

We have prepared and structurally characterized a new member of the butterfly-like {Co(III) 2 Dy(III) 2 } single-molecule magnets (SMMs) through further Co(III) decoration, with the formula [Co(III) 4 Dy(III) 2 (OH)2 (teaH)2 (tea)2 (Piv)6 ] (teaH3 =triethanolamine; Piv=trimethylacetate or pivalate). Direct current (DC) susceptibility and magnetization measurements were performed allowing the extraction of possible crystal-field parameters. A simple electrostatic modeling shows reasonable agreement with experimental data. Alternating current (AC) susceptibility measurements under a zero DC field and under small applied fields were performed at different frequencies (i.e., 10-1500 Hz) and at low temperatures (i.e., 2-10 K). Multiple magnetization relaxation pathways are observed. Comparison with previously reported {Co(III) 2 Dy(III) 2 } complex measurements allows an overall discussion about the origin of the dynamic behavior and its relationship with crystal-field split ground multiplet sublevels.

Synthesis, Crystal Structures, Magnetic Properties, and Fluorescence of Two Heptanuclear CoIII4LnIII3 Compounds (Ln = GdIII, DyIII): Multiple Relaxation Dynamics in the DyIII Analogue

“…In weakly exchange coupled Dy III containing compounds, slow relaxation of magnetization arises not only due to intrinsic magnetic anisotropy of the Dy III centers but also due to ligand field effects associated with the coordination geometry. [16a], Again, the presence of diamagnetic Co III ions in 2 can potentially influence the magnetic behavior that, in turn, increases the effective energy barrier as observed in previously reported Co III Dy III systems. [27c] In case of the 9‐coordinated Dy1/Dy1D centers having DyO 9 coordination environment, the oxide oxygen atom O11/O11D is closest (2.298 Å) to Dy1/Dy1D while for the 8‐coordinated Dy2 center with DyO 8 coordination environment, alkoxo oxygen atom O5 is closest (2.272 Å) to Dy2 among other ligand atoms.…”

“…A number of compounds containing both Co III and Dy III have been reported previously (Table S7) . In terms of nuclearity, those systems include Co III Dy III ,[27h], Co III 2 Dy III , Co III 2 Dy III 2 , Co III 4 Dy III 2 ,[42a] Co III Dy III 3 ,[44l] Co III 3 Dy III 3 [44m] and Co III 2 Dy III 4 . [33a, o], However, no compound of nuclearity Co III 4 Dy III 3 (or Co III 4 Ln III 3 , Ln = Ce–Yb) was reported previously.…”

“…As listed in Table S7 and S8, the double‐relaxation channels in most cases are not well resolved in zero‐dc field[44f], [44g], [44k], [46a], [46c], [46e], [46h] and also even under an applied dc field. [27h], [42a], [44d] Only in very few cases, the two processes are well resolved in zero‐dc field. [44h], [46b] Clearly, compound 2 is among some few examples where the two channels are well resolved in zero‐dc field and the U eff values of both channels could be determined.…”

Single Molecule Magnet Features in the Butterfly [CoIII2LnIII2] Pivalate Family with Alcohol‐Amine Ligands

“…The SMM behaviour of 2-Dy was deeply analysed in previous reports. [22,26] Now we are adding the ab-initio computation additional information that correctly supports the AC data. This complex shows two well resolved relaxation processes under zero appplied DC field.…”

“…[20] Most of these examples correspond to complexes bearing the same structural motif: [Co 2 III Ln 2 III À (μ 3 À (OR)) 2 ] butterfly arrangement, where À OR belongs to alcohol-amine type ligands. [18,[21][22][23][24][25][26][27][28][29] The SMM behaviour of this particular family of complexes have been recently reviewed by some of us. [30] In this context, we have previously reported the only example of this type of {Co III 2 Ln III 2 } compounds where several Ln(III) ions has been explored in order to analyse the influence of the Ln(III) over magnetic behaviour.…”