Rhombus-Shaped Tetranuclear [Ln₄] Complexes [Ln = Dy(III) and Ho(III)]: Synthesis, Structure, and SMM Behavior

Abstract

The reaction of a new hexadentate Schiff base hydrazide ligand (LH3) with rare earth(III) chloride salts in the presence of triethylamine as the base afforded two planar tetranuclear neutral complexes: [{(LH)2Dy4}(μ2-O)4](H2O)8·2CH3OH·8H2O (1) and [{(LH)2Ho4}(μ2-O)4](H2O)8·6CH3OH·4H2O (2). These neutral complexes possess a structure in which all of the lanthanide ions and the donor atoms of the ligand remain in a perfect plane. Each doubly deprotonated ligand holds two Ln(III) ions in its two distinct chelating coordination pockets to form [LH(Ln)2](4+) units. Two such units are connected by four [μ2-O](2-) ligands to form a planar tetranuclear assembly with an Ln(III)4 core that possesses a rhombus-shaped structure. Detailed static and dynamic magnetic analysis of 1 and 2 revealed single-molecule magnet (SMM) behavior for complex 1. A peculiar feature of the χM" versus temperature curve is that two peaks that are frequency-dependent are revealed, indicating the occurrence of two relaxation processes that lead to two energy barriers (16.8 and 54.2 K) and time constants (τ0 = 1.4 × 10(-6) s, τ0 = 7.2 × 10(-7) s). This was related to the presence of two distinct geometrical sites for Dy(III) in complex 1.

Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties

“…In this context, polynuclear lanthanide complexes where the nuclearity is 5 or 10 are quite sparse. Our interest in such systems has emanated from our recent forays in this field in which we have been able, by utilizing hydrazone Schiff base ligands, to assemble tetra‐,4a, b hexa‐4c and octanuclear4d complexes. The latter possessed a new cyclooctadiene‐type of conformation 4d.…”

Hydrazone-Based Lanthanide Single-Molecule Magnets

“…A new rhombus-shaped Dy 4 complex [21] was separated by Chandrasekhar's group using ligand H 3 L 14 in Fig. 5.21, which can be considered as the modification of picolinohydrazone ligand H 2 L 10 by hydroxymethyl group.…”

[5×1 + 1×1] Hexanuclear Lanthanide(III) Cocrystal Complexes: Syntheses, Structures, and Magnetic Properties

“…Most recently, Liu and co‐workers has reported molecular magnet behavior of cocrystal containing a tetranuclear metallocage and mononuclear Dy III ‐radical complex . As a matter of fact, there has been a ever‐present interest in the field of lanthanide coordination chemistry due to their promising applications for the development of catalysts and photoluminescent and molecular magnetic materials. Also, multifunctional sensors based on lanthanide complexes have received much attention due to their unique luminescence properties arising from the 4f electrons of Ln(III) ions, large Stokes shift, long lifetimes and sharp emission property .…”