Homodinuclear lanthanide {Ln₂} (Ln = Gd, Tb, Dy, Eu) complexes prepared from an o-vanillin based ligand: luminescence and single-molecule magnetism behavior

Abstract

Four dinuclear lanthanide complexes [Gd2 (H2L)2 (µ-piv)2 (piv)2]·2CHCl3 (1), [Tb2 (H2L)2 (µ-piv)2 (piv)2]·2CHCl3 (2), [Dy2 (H2L)2 (µ-piv)2 (piv)2]·2CHCl3 (3) and [Eu2 (H2L)2 (µ-piv)2 (piv)2]·2CHCl3 (4) were synthesized by the reaction of appropriate Ln(III) chloride salts and a multidentate ligand, 2,2'-(2-hydroxy-3-methoxy-5-methylbenzylazanediyl)diethanol (H3L) in the presence of pivalic acid. 1-4 are neutral and are held by two monoanionic, [H2L](-) ligands. The two lanthanide ions are doubly bridged to each other via two phenolate oxygen atoms. Both the lanthanide ions are nine coordinated and possess a distorted capped square antiprism geometry. Photophysical studies reveal that Tb(3+) (2) and Dy(3+) (3) complexes display strong ligand-sensitized lanthanide-characteristic emission. The Tb(3+) complex (2) shows a very high overall quantum yield of 76.2% with a lifetime of 1.752 ms. Magnetic studies reveal single-molecule magnet behavior for 3 which shows in its ac susceptibility studies a two-step slow relaxation yielding two effective relaxation energy barriers of ΔE = 8.96 K and 35.51 K.

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

“…Besides, the emergence of a broad band at around 468 nm could be ascribed to ligand‐based emission. The split pattern observed in the Dy III based band centered at around 569 nm ( 4 F 9/2 → 6 H 13/2 transition) into two components, one at 562 nm and the other at 576 nm, is attributable to the presence of two crystallographically inequivalent Dy III centers in 2 because the 4 F 9/2 → 6 H 13/2 transition in Dy III based systems is highly sensitive to Dy III geometry . Again, the emission band at 506 nm ( 4 F 9/2 → 6 H 15/2 transition) is significantly overlapped with the ligand based emission band.…”

“…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.…”

Hydrazone‐Ligand‐Based Homodinuclear Lanthanide Complexes: Synthesis, Structure, and Magnetism

“…From a chemist's point of view, a fascinating aspect is the handle the ligand design has in modulating the nuclearity of homonuclear complexes. Thus, we have recently shown the utility of an o ‐vanillin‐based ligand, 2,2′‐(2‐hydroxy‐3‐methoxy‐5‐methylbenzylazanediyl)diethanol (H 3 L), in the assembly of homometallic dinuclear Ln 2 complexes, with the Dy III analogue showing SMM properties with two relaxation time constants …”

Fine‐Tuning Ligand Fields with Schiff‐Base Ligands in Dy2 Compounds

“…It has been noted that organic ligands play a vital role in the synthesis of discrete SMMs as well as in the modulation of SMM properties . Schiff‐base ligands possessing rich O,N‐based multichelating sites have been widely used in the synthesis of many lanthanide‐based coordination compounds . In such compounds, the ligand systems formed by reactions between o ‐vanillin and acylhydrazine derivatives are a particularly good choice because the phenoxo atoms of the o ‐vanillin can be deprotonated to act as a bridge between metal ions to produce a superexchange pathway .…”