Building 1D lanthanide chains and non-symmetrical [Ln₂] “triple-decker” clusters using salen-type ligands: magnetic cooling and relaxation phenomena

Abstract

A solvothermal reaction between Ln(NO)·6HO (Ln: Gd, Tb and Dy), 2-hydroxy-1-naphthaldehyde, 2-OH-naphth, and ethylenediamine, en, in MeOH in the presence of a base, NEt, led to the formation of the 1D coordination polymers [Ln(L)(MeO)(MeOH)]·MeOH (Ln = Gd (1·MeOH), Tb(2), Dy (3·MeOH); HL = 1,1'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol), the Schiff-base ligand derived from the condensation of 2-OH-naphth and en), while a similar reaction in an excess of NaN yielded 1D coordination polymers [Ln(L)(N)(MeO)(MeOH)] (Ln = Gd (4), Tb (5), Dy (6)). Finally, upon replacing ethylenediamine with o-phenylenediamine, o-phen, we managed to isolate the discrete dimers [Dy(L')(MeOH)]·2MeOH (7·2MeOH) and [Gd(L')(MeOH)]·2MeOH (8·2MeOH) (HL' = 1,1'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis (naphthalen-2-ol), the Schiff-base ligand from the condensation of 2-OH-naphth and o-phen). Polymers 1-3 describe one-dimensional chains, containing alternating seven- and eight-coordinate Ln metal centers, polymers 4-6 contain eight-coordinate lanthanide ions, while in both 7 and 8 the two Ln centers are eight- and seven-coordinate, adopting square antiprismatic and "piano-stool" geometry, respectively. The magnetocaloric properties of the three Gd analogues were determined from magnetic measurements, yielding the magnetic entropy change -ΔS = 21.8, 23.0 and 16.0 J kg K at T = 3.0 K on demagnetization of 7 T to 0, for 1, 4 and 8, respectively. The study of the magnetic properties also revealed that all three Dy analogues (3, 6 and 7) display out-of-phase signals, therefore suggesting slow magnetic relaxation, while such behaviour was not established in the Tb analogues.

Three Giant Lanthanide Clusters Ln37 (Ln = Gd, Tb, and Eu) Featuring A Double-Cage Structure

“…Because of the isotropy of Gd 3+ ion and the high magnetic density of the high-nuclearity metal cluster, the magnetocaloric effect of compound 1 was studied. As shown in Figure c,d, the magnetic entropy change (Δ S m ) is 38.7 J·kg –1 ·K –1 at 2 K for Δ H = 7 T by using the Maxwell equation of Δ S m(Δ H ) = ∫[∂ M ( T , H )/∂ T ] H d H . The experimental value is smaller than the calculated value of 45 J·kg –1 ·K –1 for 37 uncorrelated Gd 3+ ions ( S = 7/2) based on the equation −Δ S m = nR ln­(2 S + 1) (where R is the gas constant, and S is the spin state), which may have resulted from the anti-ferromagnetic interaction.…”

Tuning slow magnetic relaxation behaviour in a {Dy2}-based one-dimensional chain via crystal field perturbation

“…8 Aer that, numerous Ln-based SMM materials including discrete Ln x (x $ 1) coordination clusters, chainlike, two dimensional and three dimensional coordination compounds have been prepared and investigated in detail. [9][10][11] Aiming at enhancing the performance of Ln-based SMM materials, many effective efforts have been dedicated by researchers in the past decades. [12][13][14][15] It is noteworthy that netuning the symmetry of ligand eld and/or the orientations of single-ion easy axes of lanthanide ions have been viewed as general and satisfactory approaches to increase the single-ion anisotropy of Ln(III) ions and further improve the values of U eff and T B of SMM materials.…”

Four rare structurally characterized hetero-pentanuclear [Zn4Ln] bis(salamo)-type complexes: syntheses, crystal structures and spectroscopic properties

“…Salen-type ligands and their analogues are very versatile chelating ligands in inorganic and organometallic chemistry. 1 Their complexes have considerable intrinsic value due to their wide applications in electrochemistry, 2 building supramolecular structures, 3 catalysis fields, 4 magnetism, 5 biological fields 6 and so forth.…”