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. 2023 May 21;24(10):9061.
doi: 10.3390/ijms24109061.

Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet

Julio Corredoira-Vázquez  1   2 , Paula Oreiro-Martínez  1 , Daniel Nieto-Pastoriza  1 , Ana M García-Deibe  1 , Jesús Sanmartín-Matalobos  1   3 , Matilde Fondo  1
Affiliations

Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet

Julio Corredoira-Vázquez et al. Int J Mol Sci. .

Abstract

The reactivity of the new flexible potentially pentadentate N3O2 aminophenol ligand H4Lr (2,2'-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H4Lr with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy4(H2Lr)3(Cl)4(μ3-O)(EtOH)2(H2O)2]·2EtOH·H2O (1·2EtOH·H2O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy5(H2Lr)2(H2.5Lr)2(NO3)4(µ3-O2)2]·2H2O (2·2H2O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho2(H2Lr)(H3Lr)(NO3)2(H2O)2](NO3)} 2.5H2O (3·2.5H2O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy4 and Ho2 complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H2O is a single molecule magnet, with an Ueff barrier of 61.2 K (43.2 cm-1). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.

Keywords: N3O2 aminophenol; SMM; lanthanoid; peroxide ligand.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthetic route for the isolation of H4Lr and its metal complexes.
Figure 1
Figure 1
Ellipsoids diagram (50% probability) for [Dy4(H2Lr)3(Cl)4(μ3-O)(EtOH)2(H2O)2] (1). Only metal ions and their cores are labeled, for clarity.
Figure 2
Figure 2
Mononuclear blocks that are present in 1: (a) schematic representation of neutral 1.1 and 1.3 blocks; (b) schematic representation of the monoanionic 1.2 block. The bending of the ligand is not shown in the figure, only its coordination mode, to facilitate the understanding of the structure.
Figure 3
Figure 3
Dy4 core environment for 1, showing only the oxygen bridges. The intermolecular distances between bridged Dy atoms are also shown.
Figure 4
Figure 4
Coordination modes of the pentadentate aminophenol ligand in 1.
Figure 5
Figure 5
Ellipsoids diagram (50% probability) for [Dy5(H2L)2(H2.5L)2(NO3)4(µ3-O2)2]. Only metal ions and their cores of the asymmetric unit are labeled, for clarity.
Figure 6
Figure 6
Balls and sticks representation for a dinuclear block [Dy2(H2Lr)(H2.5Lr)(NO3)2(µ2-O2)]1.5−. Only the metal ions and their coordination spheres are represented as balls for the shake of clarity.
Figure 7
Figure 7
(Left) Ball diagram showing the bridges between the Dy3+ centres. The µ3-κ2:κ2:κ2 bond for the peroxide donors between Dy1, Dy2, and Dy3 is shown, with distances d(Dy1···Dy2) = 4.2636(6) Å; d(Dy1···Dy3) = 3.6317(4) Å and d(Dy2···Dy3) = 3.5923(4) Å. (Right) Coordination mode for the aminophenol in 2. The flexion of the ligand is not represented for the shake of clarity.
Figure 8
Figure 8
Ellipsoids diagram (50% probability) for the cation [Ho2(H2Lr)(H3Lr)(NO3)2(H2O)2]+ in 3. Only metal ions and their cores are labeled, for clarity.
Figure 9
Figure 9
Schematic representation of the blocks [Ho(H3Lr)(NO3)(H2O)]+ (3.1, R = H, n = 1) and [Ho(H2Lr)(NO3)(H2O)] (3.2, R does not exist, n = 0). The flexion of the ligand is not represented for the shake of clarity.
Figure 10
Figure 10
χMT vs. T for: (a) 1·5H2O; (b) 2·2H2O; (c) 3·2.5H2O. Insets: M/NµB vs. H at 2 K.
Figure 11
Figure 11
Frequency dependence of χ″M for 2·2H2O in a zero dc field at different temperatures.
Figure 12
Figure 12
Dependence of τ with temperature plot for 2·2H2O in zero field. The solid line accounts for the best fit, considering Orbach plus QTM relaxation processes.
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