End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N₃O₂] Ligand: Synthesis, Structure, and Magnetism

Abstract

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln-(DAPMBH)(N 3 )C 2 H 5 OH]C 2 H 5 OH} n where H 2 DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)a new pentadentate pyridine-base [N 3 O 2 ] ligand and Ln = Dy (1), Y 0.930 Dy 0.070 (2), Er (3), Y 0.923 Er 0.077 (4), and Gd (5). Xray diffraction analysis of 1−5 show that the central lanthanide atoms are eight-coordinated with the N 5 O 3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N 3 − bridges connecting the metal centers into infinite chain. The [LnN 5 O 3 ] coordination polyhedron can be regarded as a distorted dodecahedron (D 2d). AC magnetic measurements revealed that compounds 1−4 show field-induced single-molecule magnet behavior, with estimated energy barriers U eff ≈ 47−17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln 3+ ions mediated by the end-to-end azide bridging groups (J ≈ −0.015 cm −1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln 3+ ions.

An Azido‐Bridged Dysprosium Chain Complex Showing Zero‐field Slow Magnetic Relaxation

“…The room‐temperature χ M T value of 14.11 cm 3 mol −1 K is consistent with an isolated Dy 3+ center ( 6 H 15/2 , S =5/2, L =5, J =15/2, and g =4/3) with the expected χ M T value of 14.17 cm 3 mol −1 K. Upon decreasing the temperature, the χ M T value remains almost constant down to 70 K, below which it decreases to 10.52 cm 3 mol −1 K at 2 K, which is mainly attributed to the depopulation of m J sublevels and/or large magnetic anisotropy. The overall curve of the data is very similar to other mononuclear Dy 3+ SIMs and chain complexes [23,25,28] . In contrast, the χ M T curve of {Dy(DClQ) 3 (H 2 O) 2 } gradually descends upon cooling reaching a minimum of 12.6 cm 3 mol −1 K at 9.5 K and then increases upon further cooling to a maximum of 13.8 cm 3 mol −1 K at 2 K (Figure S6), which should be attributed to the presence of ferromagnetic coupling between the discrete Dy 3+ ions via strong hydrogen bonds and intermolecular π⋅⋅⋅π interaction.…”

“…In the DyN 4 O 4 polyhedron of 1 , the Dy−O bond lengths are 2.344 and 2.374 Å, while the Dy−N bond distances are 2.542 and 2.374 Å. These bond distances are within the typically observed range for Dy complexes [21–24] . In addition, the average Dy−N bond distance (2.458 Å) in 1 is significantly short than the bond distance (2.524 Å) in {Dy(DClQ) 3 (H 2 O) 2 }.…”

“…To date, most reported discrete clusters or extended networks are transition metals based molecular magnetic materials. In stark contrast, azido‐bridged lanthanides complexes remain relatively rare, not to mention azido‐bridged lanthanides coordination polymer (Table S1, ESI) [22,23,24] . Recently, Yagubskii and co‐workers reported the first 1D pure azido‐bridged lanthanide chain complex via building block approach [21] .…”

A Series of Novel Pentagonal-Bipyramidal Erbium(III) Complexes with Acyclic Chelating N3O2 Schiff-Base Ligands: Synthesis, Structure, and Magnetism

“…Most of the complexes described in this work, in particular, the neutral complexes, 1-4, were obtained using the pentadentate ligand with the [N 3 O 2 ]-binding node, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H 2 DAPMBH], that was synthesized by us via a ketonehydrazine condensation reaction between 1 equivalent of 2,6-diacetylpyridine and 2 equivalents of 4-methoxybenzoylhydrazine, in 96% ethanol [56]. We found that the interaction of anhydrous ErCl 3 with H 2 DAPMBH in absolute C 2 H 5 OH in the presence of 2 equivalents of the deprotonating agent, Et 3 N, leads to the formation and precipitation of pure neutral complex, [Er(DAPMBH)Cl(C 2 H 5 OH)] (1), practically insoluble in absolute ethanol with a very high yield.…”

“…Ligands [H 2 DAPMBH] and [H 4 DAPS] were synthesized according to the published procedures [40,43,56].…”