Structures and magnetic properties of two series of Schiff base binuclear lanthanide complexes

Abstract

Until now, although there are many examples of studying the magnetic properties of Schiff base binuclear lanthanide complexes, the relationship between the structure and magnetic properties of the complexes still is worth further investigation in order to improve the magnetic properties of Schiff base lanthanide complexes. In this work, we successfully obtained two series of binuclear Ln complexes by in situ reaction of 4‐diethylaminosalicylaldehyde, benzoic hydrazide and different lanthanide salts at 80°C under solvothermal conditions, namely, [Ln2(L)3(NO3)3]·CH3CN·CH3OH·H2O [Ln = Dy (1), Ho (2), Gd (3) L = deprotonated 4‐diethylamino salicylaldehyde benzoylhydrazine], [Ln2(L)4(CH3COO)]CH3COO·CH3CN [Ln = Dy (4), Ho (5), Gd (6)]. The complex 1 contains three Schiff base ligands L, two Dy (III) ions, and three NO3−. The ligand H1L is formed by in situ Schiff base reaction with 4‐diethylaminosalicylaldehyde and benzoic hydrazide with the participation of Ln (NO3)3. When replacing Ln (NO3)3 with Ln (OAc)3, obtained three μ2‐OAc bridged binuclear Ln (III) complexes. The magnetic study showed that complex 4 exhibits field‐induced single‐molecule magnet (SMM) behavior while complex 1 does not show any SMMs behavior. In addition, we have studied the magnetocaloric effect of complexes 3 and 6, their maximum −ΔSm values are 21.37 J kg−1 K−1 and 15.32 J kg−1 K−1, respectively, under ΔH = 7 T and T = 2 K.

Effect of coordinated anions on ferromagnetically coupled Dy2 zero-field single-molecule magnets

“…2,15–19 The higher the number of lanthanide ions, the less likely it is to have the same axis orientation; therefore, the SMMs containing only two lanthanide( iii ) ions are attracting more and more attention. 20–42 If a lanthanide( iii ) dinuclear SMM exhibits ferromagnetic interaction, the magnetic axis orientation of the two lanthanide( iii ) ions can be consistent, but this is a great challenging task; the reason is that the 4f electrons of different lanthanide( iii ) ions are not prone to magnetic exchange; even when the magnetic exchange occurs, it is usually a weak antiferromagnetic coupling. Notably, the ferromagnetic coupling between cations in lanthanide( iii ) SMMs may suppress the quantum tunnelling effect, which facilitates the presentation of SMM behavior in the zero field.…”

Synthesis, Structure, and Magnetic Properties of Homometallic Mono-, Penta-, and Hexanuclear Dysprosium Complexes

“…To this end, efforts are devoted to explore flexible multidentate ligands to assemble versatile metal complexes with different nuclearities by a small variation in reaction conditions, including the use of metal salts with different anions or the change of the acidity/basicity, and so on. Schiff base ligands have been extensively studied and made great progress to construct metal complexes. − These ligands have not only suitable flexible coordination pockets involving C–C/C–N bond rotation, which allows a flexible coordination response and provides diverse coordination geometries for metal centers, but also the versatile binding to the metal ions depending upon the reaction conditions. Due to these interesting properties, we have been exploring the Schiff base ligands with some progress. − In this text, the Schiff base ligand, H 2 L (phenol, 2,2′-[(4,5-dimethyl-1,2-phenylene)­bis­(nitrilomethylidyne)]­bis­[6-methoxy-]), which can provide versatile coordination modes for metal ions depending on its different types of donors, is used to successfully construct three homometallic Dy­(III)-based complexes with mono-, penta-, and hexanuclearity as ([Dy­(HL) 2 ]­(NO 3 )·2H 2 O ( Dy 1 ), [Dy 5 (L) 4 (CH 3 CO 2 ) 6 ]­(CH 3 CO 2 )·6MeOH·H 2 O ( Dy 5 ) and [Dy 6 (L) 2 (L 1 ) 2 ( u 3 -OH) 4 (CF 3 SO 3 ) 6 (EtOH) 4 ]·2EtOH ( Dy 6 )) (H 2 L 1 = (2-(hydroxymethyl)-6-methoxyphenol)).…”

A heptanuclear {Dy2Cu5} complex as a single-molecule magnet

“…Slow magnetic relaxation (SMR) has often been observed among SB-based mononuclear, dinuclear and polynuclear complexes. 5–10 Many of them are field-induced single-ion magnets (SIMs) and single-molecule magnets (SMMs).…”